# Trickle Chargers



## tomb

There have been several posts lately about trickle chargers for battery-powered amps, and how to design/build them. Here are some building photos of trickle chargers for a couple of PIMETA's. The chargers are based on the LM317, with 2x9V, powered with a linear regulated 24VDC 500ma walwart (Jameco). The batteries are not pictured, but I'm using some 250mah, 8.4V "9V" batteries I got on e-bay. I will leave the calculations to others. The walwart is linear-regulated only to ensure good sound if the amp is operated under wall power. You will need higher voltage if you use 9.6V "9V" batteries.

 The idea started with __redruM and this thread a little over a year ago:
http://www6.head-fi.org/forums/showthread.php?t=110663

 One of the most recent detailed discussions was started by ozshadow here:
http://www6.head-fi.org/forums/showthread.php?t=185796

 __redruM essentially drew from Tangent's design for a charger in the PPA. Since then, what's shown in the schematic below is used in the PINT and the Mini3. The schematic and layout shown in the photos is as follows:





  

 Parts List:
 1 - LM317T, TO-92 case
 2 - 1N4001 Diodes
 1 - 100 ohm 1/8 watt resistor
 Protoboard, jumper lead wire

 Also added were two Radio Shack 9V battery leads (higher quality versions), and an isolated, 2.1mm walwart socket.

 Parts and jumpers placed on protoboard and taped - ready for soldering:

  

 Bottom view of leads:

  

 Finished board after dremeling from protoboard and a little shaping:

  

 Adding the leads and the walwart socket:

  

 A pair of finished charger circuits, clear heat shrink, and leads, ready to go:

  

 Chargers next to a couple of PIMETA's in progress:

  

 Many thanks to Tangent and __redruM for their comments and ideas in various threads.


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## ozshadow

Whats the M+- by the way ?


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## dhp

Quote:


  Originally Posted by *ozshadow* 
_Whats the M+- by the way ?_

 

they were just the pads on the PINT board that you used for putting 2 9Vs in series, but it's simple enough to do ptp


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## joostoo

Have you used it yet? I think you have the pinout wrong, the pinouyt for the to-92 version is different from the to-220 one.

 Check the datasheet: http://cache.national.com/ds/LM/LM317L.pdf


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## tomb

Quote:


 Originally Posted by *joostoo*
_Have you used it yet? I think you have the pinout wrong, the pinouyt for the to-92 version is different from the to-220 one.

 Check the datasheet: http://cache.national.com/ds/LM/LM317L.pdf_

 

 LOL! That's pretty wild. Two LM317's with completely opposite pinouts. The one I used is here:
http://www.mouser.com/index.cfm?hand...oductid=218612

 The Fairchild data sheet shows the pinouts here:

  

 Yes, I have hooked it up, and it seems to work fine.


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## joostoo

Quote:


  Originally Posted by *tomb* 
_LOL! That's pretty wild. Two LM317's with completely opposite pinouts. The one I used is here:
http://www.mouser.com/index.cfm?hand...oductid=218612

 The Fairchild data sheet shows the pinouts here:





 Yes, I have hooked it up, and it seems to work fine._

 

LOL wow, that is wierd. I assumed the pinout is kind of "universal", like with 780x's.


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## tomb

Yes, like I said - it checks out. I didn't know the pinout in the beginning, anyway - had to look it up from the Mouser catalog pages, and this is what it gave.

 I just measured it again to be sure - there's 12.6mA in the battery circuit. That almost perfectly matches __redruM's original number in the first post (12.5mA).

 That TO-92 pinout could really mess somebody up. You would think they'd be consistent from mfr to mfr - at least with the pinout.


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## Matez

Sorry for OT but where to buy this black and silver thing which holds the protobord? What is the english name for it?


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## Teerawit

Quote:


  Originally Posted by *Matez* 
_Sorry for OT but where to buy this black and silver thing which holds the protobord? What is the english name for it?_

 

"Helping hands" is the common name. Panavise is a brand that makes some, and this name is also used to refer to the vise device.


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## mono

Quote:


  Originally Posted by *joostoo* 
_Have you used it yet? I think you have the pinout wrong, the pinouyt for the to-92 version is different from the to-220 one.

 Check the datasheet: http://cache.national.com/ds/LM/LM317L.pdf_

 

I might be looking at that cockeyed but it sure looks the same to me.


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## tangent

Quote:


  Originally Posted by *ozshadow* 
_Whats the M+- by the way ?_

 

'M' stands for "midpoint", the place where the two batteries are tied together.

  Quote:


  Originally Posted by *joostoo* 
_the pinouyt for the to-92 version is different from the to-220 one._

 

No, it only looks that way at a casual glance because TO-92 pinouts are often given from the bottom of the package, whereas TO-220s are given from the front or top.


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## tomb

Quote:


  Originally Posted by *Tangent* 
_No, it only looks that way at a casual glance because TO-92 pinouts are often given from the bottom of the package, whereas TO-220s are given from the front or top._

 

Well, that explains the discrepancy. Thanks. BTW, I may go back and strap on a 50ohm resistor. Your most recent recommendation for 75ohms total is probably a better match for these high-mah batteries.

  Quote:


  Originally Posted by *matez* 
_Sorry for OT but where to buy this black and silver thing which holds the protobord? What is the english name for it?_

 

Teerawit is correct - Helping Hands, $2.49 at Harbor Freight.


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## NeilR

If you have a switched wall supply, you may want to consider putting a 3rd diode between w+ and the reg. Otherwise, with the PSU switched off, the battery will "power" the wall supply output via the regulator (it "leaks" back through the reg). If the PSU has an LED it will light it up. If it is a Tread or Steps, with the specified 10-20ma drain on the LED, it will drain the batteries fairly quickly.


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## peterpan188

One question about charging batties.

 Batteries have different voltage rating, 9.6V, 1.5V, and whatever out there. How does that affect the charging circuit?

 Does different types, NiMH, NiCD or LiIon matter?

 Thanks,
 Peter


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## tangent

Quote:


  Originally Posted by *peterpan188* 
_Batteries have different voltage rating, 9.6V, 1.5V, and whatever out there. How does that affect the charging circuit?_

 

The charger has to have a higher output voltage than the battery being charged. Any in-depth discussion of a particular charger will discuss this. For example, this section in the PINT docs, which covers the wall voltage issues for the charger discussed here.

  Quote:


 Does different types, NiMH, NiCD or LiIon matter? 
 

Yes. The circuit discussed here only works for NiMH and NiCd. Lithium chemistries are an entirely different beast. Do a search...it's been discussed here several times before, with at least one circuit being developed.


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## mik000000

Sorry to revive the thread...
 I am using a bank of 12 AA batts (2000ma) for my pimeta. According to the formula in the pint docs, my resister value should be 6R.
 Is this correct?


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## NeilR

That's right.... 1.25/6 = 208ma.

 You need to watch the power dissipation, though. That resistor will run very hot, dissipating a full 1/4 watt. I suspect you'll be pushing the envelope of the trickle charger design on that board/size/space, etc.


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## mik000000

thanks NEILR. 
 would i be better to aim for .05c with a 10-12R resistor instead? trickle is only to top up batts anyway. shoudl be sufficient as long as batts are not too discharged?


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## NeilR

That is your primary charger, unless you are pulling the batteries and charging them elsewhere? if your primary, you really want to get as close to 0.1C as you can.

 I'm just trying to say you want the biggest, meanest, toughest 1206 part you can find and you want to keep an eye on it when you first fire it up. I'm curious how it works out for you because I've thought about these issues surrounding AA's but haven't tried it myself.

 I took a quick look at Mouser for 1/4W 1206. They have very limited values. Your job will be to hunt down an acceptable value, I guess. Ideally you would want a 1/2W part to be a littel conservative.


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## mik000000

will be mainly desk powered, and occasionally battery. yes, circuit will be primary charger. I am putting pimeta, tread, charger circuit and 12 AA into hammond 1455k1601. is v/tight and will be difficult to remove batts to charge elsewhere. was planning 1/4" jack, but may have to revert to 3.5 for lack of room. I already will be going to parts place tomorrow to find shorter 470uf caps in order to fit..lol. 

 also what is and why 1206 type resistor? local parts store carries many values in 2-5w square ceramic pkg. i think is wirewound, but not sure. did not think it was critical item, and these are vv/cheap


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## star882

Quote:


  Originally Posted by *tomb* 
_There have been several posts lately about trickle chargers for battery-powered amps, and how to design/build them. Here are some building photos of trickle chargers for a couple of PIMETA's. The chargers are based on the LM317, with 2x9V, powered with a linear regulated 24VDC 500ma walwart (Jameco). The batteries are not pictured, but I'm using some 250mah, 8.4V "9V" batteries I got on e-bay. I will leave the calculations to others. The walwart is linear-regulated only to ensure good sound if the amp is operated under wall power. You will need higher voltage if you use 9.6V "9V" batteries.

 The idea started with __redruM and this thread a little over a year ago:
http://www6.head-fi.org/forums/showthread.php?t=110663

 One of the most recent detailed discussions was started by ozshadow here:
http://www6.head-fi.org/forums/showthread.php?t=185796

 __redruM essentially drew from Tangent's design for a charger in the PPA. Since then, what's shown in the schematic below is used in the PINT and the Mini3. The schematic and layout shown in the photos is as follows:






_

 

If the power supply is regulated, you can just use a resistor. Put it across D2 (omiting the regulator circuit) and calculate the value to make a slightly lower than design rate when fully charged. This way, it will charge faster when less than full charge (which you will want) and slow down as it charges up (also desirable). In some cases, if the regulated supply voltage is very close to the full battery voltage plus the diode drop, it can be designed to charge fast when discharged and essentially stop when charged. However, that generally doesn't work all that well with Ni-based batteries. Pb and Li-based batteries, however, work very well with that and in fact, that's the recommended way to charge them.


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## tomb

Quote:


  Originally Posted by *star882* 
_If the power supply is regulated, you can just use a resistor. Put it across D2 (omiting the regulator circuit) and calculate the value to make a slightly lower than design rate when fully charged. This way, it will charge faster when less than full charge (which you will want) and slow down as it charges up (also desirable). In some cases, if the regulated supply voltage is very close to the full battery voltage plus the diode drop, it can be designed to charge fast when discharged and essentially stop when charged. However, that generally doesn't work all that well with Ni-based batteries. Pb and Li-based batteries, however, work very well with that and in fact, that's the recommended way to charge them._

 

All true, but charging faster is _not_ what was wanted in this design. The idea was to use the amp indefinitely while connected to the wall power supply _without a performance hit._ Thus, the reason for a regulated circuit to trickle the batteries at a constant, trivial demand.


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## NeilR

Quote:


  Originally Posted by *mik000000* 
_will be mainly desk powered, and occasionally battery. yes, circuit will be primary charger. I am putting pimeta, tread, charger circuit and 12 AA into hammond 1455k1601. is v/tight and will be difficult to remove batts to charge elsewhere. was planning 1/4" jack, but may have to revert to 3.5 for lack of room. I already will be going to parts place tomorrow to find shorter 470uf caps in order to fit..lol. 

 also what is and why 1206 type resistor? local parts store carries many values in 2-5w square ceramic pkg. i think is wirewound, but not sure. did not think it was critical item, and these are vv/cheap_

 

Don't pay any attention to me, I'm clueless 
	

	
	
		
		

		
		
	


	




 For some reason I thought you were working with a Pint and in that case the onboard parts are surface mounted. If you have the space, pick up a 1 watt resistor and you'll be fine. A 2-5W would be fine but probably overkill.

 If it were me, I would go to a bigger case before I used a 1/8" minipin instead of a 1/4". The more I use minipins the more I hate em


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## tomb

*PIMETA Pairs*
 Pics of the completed amps with the trickle chargers. The walwart used is a linear-regulated 24VDC @ 500mA, Jameco #174861 at $13.15. I can detect a subtle, slight loss in bass when using the walwart vs. pure batteries (fully charged, of course). So, it may not be up to the standard of the old Elpac (certainly not a TREAD), but it sure is convenient.

  

  
 470uF Nichicon UPW (10x16mm shorty's)
 Double stacked BUF634, single on Gnd, Class A bias trannies
 AD8066/AD8065 in one, AD8620/AD8610 in the other
 Batteries are 8.4V, 250mah from the Shoreline Market on Ebay.
 Hammond 1455J1201 cases

 P.S. Many thanks to Tangent and __redruM!


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## gtp

I dunno if this is a dumb question or not, so please bear with me.

 Is it possible to set things up with a wallwart/circuit so I charge the batteries but do not power the amp? In other words, the amp _always_ runs on batteries, whether a wallwart is plugged in or not. However, when a wallwart is plugged in, it charges the batteries (which may or may not be powering the amp at the time). This way I wouldn't need a linear regulated wallwart but could still charge the batteries. Further, the amp would always sound the same, not better with or without the wallwart.

 Big Thanks,
 GTP


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## NeilR

Not a dumb question at all. The problem is that you are sending a constant current to the battery. Lets say your amp draws 50ma and your charger is set up to deliver 20ma (0.1C to 9V batteries). If you charge and play at the same time, you have 20ma coming in and 50ma going out; you are losing ground 
	

	
	
		
		

		
		
	


	




 If you are fast charging a battery and the amp draws very little current, you might get away with it. The way I visualize it, the PSU would essentiually be powering the amp anyway and any noise from the PSU would flow into the amp.



  Quote:


  Originally Posted by *gtp* 
_I dunno if this is a dumb question or not, so please bear with me.

 Is it possible to set things up with a wallwart/circuit so I charge the batteries but do not power the amp? In other words, the amp always runs on batteries, whether a wallwart is plugged in or not. However, when a wallwart is plugged in, it charges the batteries (which may or may not be powering the amp at the time). This way I wouldn't need a linear regulated wallwart but could still charge the batteries. Further, the amp would always sound the same, not better with or without the wallwart.

 Big Thanks,
 GTP_


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## tomb

Having a little more time on these amps now, I would have to say that I can tell no difference - walwart vs. batteries. Some of it may have to do with the power caps getting broken in. They are definitely smoother now. The Jameco linear-regulated walwart is only $13 and change, so the cost-benefit ratio is much better than with the old, expensive Elpac.

 As far as charging only, that is essentially what Tangent recommended in the first thread. As you say, it would only require the cheapest of walwarts. The simplest method would be to use a switched plug - so that if the walwart was plugged into the amp, the batteries would be out of the amp circuit. However, that would not accomplish exactly what you describe, but it would be pretty easy to do and is actually the more common method.

 Edit: I take it back. Listening to my Senn's, there is a difference: more bass, but not as open on batteries; less bass, but much livelier on walwart. I guess that would correspond to more current/less voltage on batteries, but more voltage/dirty current on walwart. These differences go completely unnoticed with KSC75's or PortaPro's.

 I am building some TREAD walwarts - I'll post back on how they do when finished.


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## Alcaudon

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_*[size=medium]PIMETA Pairs[/size]*
 Pics of the completed amps with the trickle chargers. The walwart used is a linear-regulated 24VDC @ 500mA, Jameco #174861 at $13.15. I can detect a subtle, slight loss in bass when using the walwart vs. pure batteries (fully charged, of course). So, it may not be up to the standard of the old Elpac (certainly not a TREAD), but it sure is convenient.








 470uF Nichicon UPW (10x16mm shorty's)
 Double stacked BUF634, single on Gnd, Class A bias trannies
 AD8066/AD8065 in one, AD8620/AD8610 in the other
 Batteries are 8.4V, 250mah from the Shoreline Market on Ebay.
 Hammond 1455J1201 cases

 P.S. Many thanks to Tangent and __redruM!_

 


 Wow!!! Very nice work!!!! Where did you get those knobs??? They look great!!


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## tomb

Thank you for the nice comments!

 Those knobs are a two for $2.95 Radio Shack standard. 
	

	
	
		
		

		
		
	


	




 They've upgraded them since the pic on their website:
Silver Tone Knurled Knob

 BTW, addressing that post above yours, a TREAD walwart loses no quality compared to the batteries.


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## Alcaudon

Just one more question tomb....

 All I need to charge a couple of Ni-MH/Ni-Cd 9V batteries is just that simple circuit above and a wallwart of 24V and 500mA???? Nothing else to take care of??? 

 I mean, I don't mind reducing battery life, I'm planning to build a small portable amp (something similar to a47) and I was planning just to take out the batteries and recharge them when necessesary (I want the amp as small as possible), but it might be worth a little more space on the board if I could just recharge them inside.

 Thanks!!!!!!!!


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## tomb

Quote:


  Originally Posted by *Alcaudon* /img/forum/go_quote.gif 
_Just one more question tomb....

 All I need to charge a couple of Ni-MH/Ni-Cd 9V batteries is just that simple circuit above and a wallwart of 24V and 500mA???? Nothing else to take care of??? 

 I mean, I don't mind reducing battery life, I'm planning to build a small portable amp (something similar to a47) and I was planning just to take out the batteries and recharge them when necessesary (I want the amp as small as possible), but it might be worth a little more space on the board if I could just recharge them inside.

 Thanks!!!!!!!!_

 

It won't reduce the battery life at all if you disconnect the charger after about 24hrs. It's been awhile since I looked at the calcs in this thread, but I think - 250mah/12ma =~21hrs. That small of a current you can probably leave connected semi-continuously. Not that you would do that, but it's not going to hurt if you forget for a day or two.

 About the walwart - it's gotta be DC, and the batteries can't be more than the 8.4V variety - a 24V walwart is somewhat close at that rating (with 2X batteries, of course). If you used the 9.6V batteries that are available places, it won't cut it. Of course, the paragraph above assumes 250mah batteries. Those are pretty easy to get by a number of e-bay sellers. (I think the Thomas and MAHA's are way too expensive.)

 Jameco has a very nice 24VDC at 500ma linear, regulated walwart for about $13. It gives pretty good sound when connected to a PIMETA - the bass is a tad "squishy" compared to a full-blown TREAD or batteries alone. If you're using Grado's, you may not even notice that deficiency (no offense). 
	

	
	
		
		

		
			





 I can't predict for your amp, though - the 500ma is a typical size walwart for headphone amps. The charger itself, as noted above, only uses 12ma. Adding double buffers and biasing probably brings a PIMETA up to 150-200ma, but maybe not that much. Your A47 will be less than that.

 Please let me recommend a PIMETA. Tangent's design is genius in its simplicity. If you are contemplating something more than a CMoy, but less than a PPA/M3, the PIMETA is it. It is far superior to an A47 and can be built very cheaply.


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## Alcaudon

Thanks for your answer tomb!!!!!!


  Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Jameco has a very nice 24VDC at 500ma linear, regulated walwart for about $13. It gives pretty good sound when connected to a PIMETA - the bass is a tad "squishy" compared to a full-blown TREAD or batteries alone. If you're using Grado's, you may not even notice that deficiency (no offense). 
	

	
	
		
		

		
		
	


	


_

 

I've found a pretty cheap wallwart at a local store that I think will do. Anyway I don't plan to listen to the amp while plugged, it's just to recharge batteries. And, yes, I will probably use it with a pair of sr-60, 
	

	
	
		
		

		
		
	


	




. But I'm making the amp for portable use, so it will be permanetly connected to my k81 (since I bought them my other cans look at them with jealousy from the bottom of my shelf 
	

	
	
		
		

		
		
	


	




 )

  Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Please let me recommend a PIMETA. Tangent's design is genius in its simplicity. If you are contemplating something more than a CMoy, but less than a PPA/M3, the PIMETA is it. It is far superior to an A47 and can be built very cheaply._

 

Don't worry!!!!! a PIMETA is on the list, and so a PPA and a SOHA and probably a Millet and................. 
	

	
	
		
		

		
		
	


	



 I'm just new to diy (just a couple of cmoys) but I'm enjoying it much and it's going to be a long lasting hobby, I just want to start from the basics and learn as much as I can.


 Thanks again!!!!!!


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## mminutel

I hate to ask this but can anyone give me a full picture of all of the wires spread out so I can tell exactly where they all go. I think I know what is going on but not positive.


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## tomb

I am sorry it's not clear to you right now. I guess I should've photographed the entire assembly with the wires connected. If you refer to this photo:




 1. The battery connectors are wired together - red wire from one is soldered to the black wire of the other one (melt some heat shrink on the joint). This leaves you with two 9V connectors with {one black lead<->connector1<->redblackjoint<->connector2<->red lead}.

_EDIT: See the photos post below. The above is not really true - I used all of Tangent's prepared pads. The middle "+" and "-" pads provide the series connection between the battery sockets. However, either method is equivalent._

 2. The black wire on the DC plug socket is the walwart/Tread negative lead. It bypasses the trickle charger completely and connects to the PIMETA board in the (-) position _*with the black lead of the battery connector assembly.*_

 3. The red lead of the battery connector assembly is connected to the bottom terminal of the trickle charger perf board.

 4. A short purple wire is connected from the positive terminal of the DC socket to the input of the trickle perf board. A longer purple wire (almost the same length as the black DC socket wire) is connected to the amp power output of the trickle charger: the middle position. This wire becomes the (+) power connection to the PIMETA board.

 If no voltage is flowing from the DC socket, the battery (+) is routed through the single diode into the purple wire at the middle of the trickle perf board, and into the PIMETA.

 If the DC power is connected (must be at a higher voltage than the two batteries), then battery voltage is blocked, except for the small trickle current provided by the VREG (LM317 - TO-92).

 Of course, the PIMETA switch must be thrown before the circuit is complete to the amp. The trickle charger, however, will continue to flow current to the batteries as long as the DC source is connected.

 Somewhere along the way in the discussion of the trickle charger, a 3rd diode was deleted. This diode used to be where the wire jumper is on the bottom right of the perf board. What this means is that if you connect a TREAD or other such source that has its own LED, and you do not plug it into the wall source, the batteries will drain backward through the walwart/TREAD's LED. It's not much of a hassle, but there are some people who keep their power plugged into a power strip and flip the switch on the whole thing.

 I hope that helps. I'm not in a position to take my PIMETA's apart, photograph, and post them right now - maybe later on.


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## mminutel

Alright, so you will have 3 wires running into the Pimeta instead of the normal 2 right? you still hook it up as a single supply and not a dual? I am pretty sure I understand. I don't want you to take them apart cause I know that is a pain I was just wondering if anyone already had a picture. Thanks a lot.


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## tomb

Yes - the batteries are treated together as a single supply. Because of the charger, the only wire that is paralleled is the negative lead of the DC socket and the negative lead from the battery string. Even then, they are soldered together into the same position on the board: (-). The only other wire soldered to the board is the purple wire from the mid-position on the charger: (+). _EDIT: I actually used the extra pads - see the photos post below._

 Tangent has provided the intermediate battery connections (M's) for convenience. However, adding the trickle charger is a little bit confusing compared to the original design. Soldering the battery leads together in the middle lets you think of the assembly as one battery only, simplifying the rest of the issues with connections.

 At least, that's the way I chose to do it. 
	

	
	
		
		

		
		
	


	




 EDIT: Reviewed my notes, extra length was not an issue.


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## velo1

Hello,

 I'm new to DIY so please bear with me. I built a Pimeta powered with 2 Tenergy 9v rechargables. Info with them says they are rated at 9 v, 250 mAh 
http://www.all-battery.com/index.asp...ROD&ProdID=523
 I built the trickle charger as described by Tomb and bought the suggested Wall Wart (linear-regulated 24VDC @ 500mA). The amp runs fine using the Wall Wart and sounds great with the batteries. But, I only get about 2 hours on the batteries after charging for 24 hours or more (listening with Grado 60's at low volume). Is that normal for this amp or is the battery voltage too high for the 24V power supply such that I do not get a full charge? Or, did I wire something up incorrectly (Voltages at various points on the board are "correct", approx 9V). Thanks!


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## tomb

Quote:


  Originally Posted by *velo1* /img/forum/go_quote.gif 
_Hello,

 I'm new to DIY so please bear with me. I built a Pimeta powered with 2 Tenergy 9v rechargables. Info with them says they are rated at 9 v, 250 mAh 
http://www.all-battery.com/index.asp...ROD&ProdID=523
 I built the trickle charger as described by Tomb and bought the suggested Wall Wart (linear-regulated 24VDC @ 500mA). The amp runs fine using the Wall Wart and sounds great with the batteries. But, I only get about 2 hours on the batteries after charging for 24 hours or more (listening with Grado 60's at low volume). Is that normal for this amp or is the battery voltage too high for the 24V power supply such that I do not get a full charge? Or, did I wire something up incorrectly (Voltages at various points on the board are "correct", approx 9V). Thanks!_

 

The Tenergy's are exactly what I use and I get 4-5 hrs use. That's with double buf's and the Tangent transistor-option for biasing into Class A. With the trickle charge of about 12ma, the charge should take 20-21hrs. The walwart, as described, actually puts out about 23.9V.

 If this is your result with the batteries brand new, they may need exercising. It takes 3 or 4 charge cycles for the batteries to attain full charge capability.

 If that's not it, you might look at wiring, or any additional component that could be drawing much higher current out of the batteries. For instance, a high-powered LED could draw 20-30ma, which is significant at this level of power draw. Or, if for some reason you have an opamp or buffer oscillating, that could be drawing more power. My results are typically with KSC75's, and the Grado's will draw more current, perhaps, but the Class A biasing should negate this difference, I would think.

 Anyway, those are the things I'd check - maybe someone else can think of other possibilities. I'm hopeful that perhaps your batteries are just not broken in, yet.


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## velo1

Thanks for your reply Tomb! I've got the double buffs, but not the Class A bias. The batteries are brand new. Also, right now the OP amps I am using are TI OPA2132P and OPA132U. I'll install the AD 8620/8610 combo as soon as I get another Brown Dog adaptor and see if that makes a difference. Thanks again.


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## tomb

A number of people have been asking me about the exact connections to the board from the batteries, trickle charger, and power jack. So, I did some research and took a closer look at how I did my PIMETAs. As it turns out, I didn't connect the two battery sockets in series, but used all of Tangent's pads, instead. That's the same thing, really - and it makes no difference which you do - either connect negative to positive between the two battery sockets, or use the second set of pads on the PIMETA board.

 In either event, here are some prepared photos that completely document the connections. I trust that they will be self-explanatory. If not, please post and I'll try to elaborate further. Thank you for your interest!


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## joneeboi

I've been trying to figure this out for days, but I'm going to leave the head-scratching for later days and just ask.

 In the equation R = 1.25/(Battery capacity in mAh/10), where is this 1.25V coming from? Is this across the LM317? The schematic suggests two 9V batteries and 250mAh capacity. I am running on one 9V (rated at 7.2V) and 150mAh.

 I have within reach a few wallwarts: 19VDC, 3.42A; 12VDC, 2000mA; 14.4VDC, 1000mA. I'm not sure the 14.4V one works, but suppose I were to use the 12V one, what would the resistor value be? I tried it setting R = 47 ohm and using the 12V wallwart, but I got this huge humming noise which completely sapped the bass (the humming was annoying too 
	

	
	
		
		

		
		
	


	




 ).

 Would I use the same equation, R = 1.25V/0.015A = 83 ohm, for the charger? Or is 1.25V a different value?


----------



## tomb

Quote:


  Originally Posted by *joneeboi* /img/forum/go_quote.gif 
_I've been trying to figure this out for days, but I'm going to leave the head-scratching for later days and just ask.

 In the equation R = 1.25/(Battery capacity in mAh/10), where is this 1.25V coming from? Is this across the LM317? The schematic suggests two 9V batteries and 250mAh capacity. I am running on one 9V (rated at 7.2V) and 150mAh.

 I have within reach a few wallwarts: 19VDC, 3.42A; 12VDC, 2000mA; 14.4VDC, 1000mA. I'm not sure the 14.4V one works, but suppose I were to use the 12V one, what would the resistor value be? I tried it setting R = 47 ohm and using the 12V wallwart, but I got this huge humming noise which completely sapped the bass (the humming was annoying too 
	

	
	
		
		

		
		
	


	




 ).

 Would I use the same equation, R = 1.25V/0.015A = 83 ohm, for the charger? Or is 1.25V a different value?_

 

1.25V is the voltage that the LM317 regulator maintains between pin ADJUST and pin OUT. Place a resistor between those pins and it sets the leaving current from the regulator.

 Quoting Tangent from another thread:
  Quote:


  Originally Posted by *tangent* 
_The formula is R=1.25/I, where I is the charge current, which should be one tenth the mAh number for a trickle charger, but in mA units. So for 170 mAh, you get R=1.25/0.017, R=74. The next common value up from that is 75, which is what I recommend in the PINT schematic._

 

His reference to charge current as 1/10 the battery's mah rating is a general rule-of-thumb recommendation for trickle-charging batteries (equates to 10hrs, actually). So for your 150mah, you'd probably want 15ma.

 R=1.25/15 = 83.3 ohms. Anything from 75 to 100ohms is probably fine.

 Quoting Tangent again from his PPA battery board article:
  Quote:


  Originally Posted by *tangent* 
_The key to picking the power supply voltage is to look at all the voltage drops in the charge path. Figure that each cell will require about 1.55V across it at peak during fast charging. Then add in all the diode drops along the charge path and the 1.25V across R2. Whatever is left between this and the power supply voltage is dropped across the regulator. Depending on the output current, an LDO will require about 1V across it to maintain regulation. A standard regulator requires 2 to 3V across it at minimum._

 

In your case, 7.2V is 6 cells. So 6 * 1.55V = 9.3V. You have about 3V across the LM317 and the 1.25V across the charge current resistor, so 9.3V + 3V + 1.25V = 13.55VDC. Consequently, your 14.4VDC and 19VDC walwarts will work, no problem. This is a very conservative estimate, but your 12VDC walwart is probably not close enough to be useful.


----------



## mono

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_...so 9.3V + 3V + 1.25V = 13.55VDC. Consequently, your 14.4VDC and 19VDC walwarts will work, no problem. This is a very conservative estimate, but your 12VDC walwart is probably not close enough to be useful._

 

I suspect the humming heard is due to it being unregulated, and as such it may be unsuited to charging while simultaneously listening, but with it's 2A current rating may be floating high enough to charge the cells (something a multimeter could check).


----------



## mminutel

Ha! I just thought of this. I have a couple of 270mAh batteries so I would need a charger above 540ma? I never think of this stuff when I go to buy things.


----------



## kklee

Assuming that the batteries are in series, the current won't be affected. However, you will need a higher voltage. I ended up using a 24V wall wart for 2x9V.


----------



## mminutel

Ah Thank You! I was scared there for a second. Mine is 24V 400mA.


----------



## joneeboi

Right. So with the help of tomb and mono I was able to successfully put together the circuit and all is well. All except that there still isn't any bass when I plug it in and listen. I tried first with some Zune buds just to make sure it would work, but then they started to get really warm. Taking them out, I switched to my KSC75s and that is when I discovered the lack of bass. I know tomb mentioned this in an earlier post, but is there any sort of solution? Get a wall wart closer to the projected voltage (I am using 19V and need 13.3)? Add another battery in series?


----------



## tomb

Quote:


  Originally Posted by *joneeboi* /img/forum/go_quote.gif 
_Right. So with the help of tomb and mono I was able to successfully put together the circuit and all is well. All except that there still isn't any bass when I plug it in and listen. I tried first with some Zune buds just to make sure it would work, but then they started to get really warm. Taking them out, I switched to my KSC75s and that is when I discovered the lack of bass. I know tomb mentioned this in an earlier post, but is there any sort of solution? Get a wall wart closer to the projected voltage (I am using 19V and need 13.3)? Add another battery in series?_

 

That wouldn't cause the problem. No bass can be caused by a number of things, none of which have to do anything with the charger.

 Before we go off-topic with this thread on a subject other than the trickle charger - you might post a separate thread for your problem. You might ask - "PIMETA - No Bass?" or something like that.

 You'll get more help that way, anyway. I promise I'll try to help.


----------



## trains are bad

I have a 12v sealed lead acid battery of the kind that power PowerWheels or emergency lighting in buildings. Can I just use a wall wart at 15v, and hook it, up, trust the current regulation in the wall wart to limit the current, and leave it hooked up for a 'long time'? Car batteries are constantly under like 15v from the alternator, right?


----------



## tomb

Quote:


  Originally Posted by *trains are bad* /img/forum/go_quote.gif 
_I have a 12v sealed lead acid battery of the kind that power PowerWheels or emergency lighting in buildings. Can I just use a wall wart at 15v, and hook it, up, trust the current regulation in the wall wart to limit the current, and leave it hooked up for a 'long time'? Car batteries are constantly under like 15v from the alternator, right?_

 

There is no current regulation in a walwart to trust. It'll supply as much current as physically possible until the battery is destroyed or until it's charged enough that the current flow starts to drop. At which point, the voltage will climb on the now lightly loaded, unregulated walwart until it damages the battery again.


----------



## mono

Quote:


  Originally Posted by *trains are bad* /img/forum/go_quote.gif 
_I have a 12v sealed lead acid battery of the kind that power PowerWheels or emergency lighting in buildings. Can I just use a wall wart at 15v, and hook it, up, trust the current regulation in the wall wart to limit the current, and leave it hooked up for a 'long time'? Car batteries are constantly under like 15v from the alternator, right?_

 

What exactly is "wall wart at 15V"? Linear, switching or unregulated? The important part of running this unregulated with it's only inherant voltage:current foldback limits is what it's peak VA and unreglated regulation range is. In other words how high the voltage really gets and what current rate results at end of normal charging cycle, and how long you'd really want or need to leave it charging. Occasional, slight overcharging may not degrade the battery lifespan enough to matter but it should not be persistently overcharging itself.

 Some devices do use a basic unregulated wart to charge SLA cells, I've a all-in-one jump-starter/tire-inflator/flashlight thingamajig that charges it's *12V* 12Ah battery with an unregulated 12V/500mA wart and it doesn't seem to have harmed it much, it still has reasonable runtime after 3 years but I don't ever leave it plugged in to charge for more than a day at a time. Incidentally I don't recommend one of those all-in-ones for inflating tires, it's so asthmatic it might only get a beach ball inflated before you got tired of waiting.

 To get good charge the voltage depends on temp but generally around room temp it is about 2.3V per cell so a 6 cell *12V* battery is around 13.8V. Anything beyond this that the charger provides, and can maintain current while delivering, would just be an ever increasing charge rate which is not a problem in itself unless your wart were quite large, the rate is low enough but once the cell becomes fully charged the problem is this higher voltage causes electrolysis. 

 To avoid that you want to either unplug the battery when it is done charging - that point determined through measurements of voltage, or select a charging system that limits the fully charged voltage from the wart to a "float" voltage level, which for typical SLA batteries is a a range but the upper part would be your concern, a peak barely above 14.0V. It never hurts to have battery manufacturer datasheet to compare to their recommendations.

 If you wanted to be really cheap to get the job done you could try putting a resistor in series on the positive charger lead, such that it drops the current down to a negligable level once the battery is fully charged (again determined through measurements, but maybe somewhere in the dozens-of-ohms value resistor would suffice depending on exactly what this charger wart is, maybe a few hundreds of ohms). 

 Naturally the sky is the limit for how elaborate you could do it instead, the more conservative answer is of course to develop some circuit based around a charger IC.

 Now I have to ask, why are you using a large (compared to most battery packs) SLA battery? It is not going to sound any better than running straight from a typical linear regulated wall wart unless you had some circuit that was particularly susceptible to noise.


----------



## trains are bad

Capacity.
 Portability (well, transportability).
 I got it for free.
 I use it for lots of other stuff, like field charging my RC batteries, emergency jumping my toyota, camping.

 I have been just taking it home now and again to charge it on my dad's automotive charger, but I'm getting tired of that.


----------



## mono

If you really want to try a wall wart I suggest either the resistor in series or choosing a lower capacity wart like 12V & no more than 500mA, or really both of these if not a regulator (maybe an LDO) to limit voltage to 14V. If your peak voltage with present wart isn't much higher you could try a series of diodes to drop the voltage down a tad instead, 14.0V isn't really a target you can aim slightly lower but just a tad over 13.8 should be a minimum unless it is very warm then drop the voltage a few tenths of a volt.


----------



## _atari_

Hi,

 I have tried this solution - and designed a PCB for this. If you are interested check this thread.


----------



## Avro_Arrow

I thought I would revive this tread with a trickle charger I use.
  It has both current limit and voltage limit.
  The schematic is from the LM317 data sheet so I don't mind sharing.
  Components were chosen from what I had in my "junk box".
  The Eagle file is available by request.


----------



## MrTom

Wow - brilliant. As if by magic I had just finished a conversation with a friend about making a portable amp and how he'd go about charging the batteries without removing them... HeadFi, you've done it again!


----------



## i_djoel2000

can we use LM317LZ instead of LM317T?
   
  if we can, what's the difference with the LM317? or are they practically the same?


----------



## cobaltmute

The T version is in a TO-220 package, the LZ version is in a TO-92 package.  Big difference in the amount of heat they can dissipate.
   
  If your charging current is low, you can use the LZ version.


----------



## i_djoel2000

Quote: 





cobaltmute said:


> The T version is in a TO-220 package, the LZ version is in a TO-92 package.  Big difference in the amount of heat they can dissipate.
> 
> If your charging current is low, you can use the LZ version.


 


  my charger specs are 15V, 500mA. is the LZ gonna be sufficient?


----------



## i_djoel2000

hi again.. say i want to add an LED indicator to indicate whenever the charger is charging the battery. where should i place it?


----------



## overdream

i_djoel2000 said:


> hi again.. say i want to add an LED indicator to indicate whenever the charger is charging the battery. where should i place it?




Anyone ?


----------



## Avro_Arrow

connect the resistor and LED at the power input jack.


----------



## i_djoel2000

how do i calculate the charging current rate? i'd like to set them to 25-30mA/hour. i'm using LM317T TO-220 style


----------



## Fred_fred2004

Use this formula
  1.25/R = I
   
  cheers
  FRED


----------



## i_djoel2000

Quote: 





fred_fred2004 said:


> Use this formula
> 1.25/R = I
> 
> cheers
> FRED


 

 thanks Fred!
   
  in that case, the default configuration in the first page gives you 12.5mA charging current, correct?


----------



## i_djoel2000

i just made my charger, but it doesn't work, the amp won't turn on even though the battery is connected. i don't know what's the problem, and i'm pretty confident i followed the circuit correctly. both diode work well when i checked them with my multimeter. no idea about the LM317 though, but i assume it works decently as well since i've never used it at all until this moment. resistor is 1/4W 60.2 ohm
   
  here are some pictures:


  red wire is connected to battery, blue to amp (+) pole, black to (-) pole battery, and white to amp (-) pole
   
  anybody can point what i did wrong here?


----------



## Avro_Arrow

Is your power jack shorted?


----------



## i_djoel2000

Quote: 





avro_arrow said:


> Is your power jack shorted?


 


  the lower pin is positive, upper and right pins are negative. i checked with my multimeter and there is no short between the lower pin to upper or right pin
   
  i checked the charger last night and i still couldn't find what the problem is..


----------



## Fred_fred2004

Just trace out the positive path using your multimeter, start at the DC socket and work through the circuit at some point you will find it stops and theres the hole 
   
  cheers
  FRED


----------



## i_djoel2000

Quote: 





fred_fred2004 said:


> Just trace out the positive path using your multimeter, start at the DC socket and work through the circuit at some point you will find it stops and theres the hole
> 
> cheers
> FRED


 

 i just did..
   
  should we have impedance reading across the diode? because i just traced the connection from dc socket, and stopped at the diode connected to LM317 because i didn't get any reading across the multimeter
   
  i checked the diode using multimeter too, and they check out


----------



## Fred_fred2004

Are you saying there is no positive voltage at the junction of the diode and the lm317 ?


----------



## i_djoel2000

Quote: 





fred_fred2004 said:


> Are you saying there is no positive voltage at the junction of the diode and the lm317 ?


 

 i connect the black rod to + dc socket pin, and then work my way down using the red one throughout the positive path and then it stopped at the junction between diode 1 and diode 2
   
  sorry if my previous comment misled you..


----------



## Mullet

I'm using this charging circuit for my PPA-S project. I'm having an issue though. I've hooked up everything correctly and get ~18v by connecting two 9v batteries in series. When I plug in my 24v 500mA Jameco wallwart my two Tenergy 250mA 9v batteries eventually get pretty damn hot. They also have started to disform. Any idea what can be going on here? I've used the standard parts including 75ohm resistor.


----------



## MisterX

How much current is your circuit putting into the batteries?
 Should be somewhere around 16mA....
 (disconnect the positive lead from the first battery, set the meter to read amps, connect the meter between the first battery and the charge circuit, power up the circuit, what's the meter read?)


----------



## wakibaki

From the numbers, you are running 24VDC into a battery with about ~16.5V depending on state of charge. So you're dropping 7.5V across 75 ohms, which is 100mA, far too much to trickle charge a 250mAh battery. You need ~330 ohms to get the current below 20mA, (less than C/10).

w


----------



## Mullet

I'm a bit confused in terms of your math and reading about the circuit on this thread. Based on the given formula, I was under the impression that 75 ohm resistor would be fine because 1.25/75 would come out to 16mA, which would come out to around 16 hours to charge the batteries. I haven't read anywhere about being aware of a voltage drop. Just that you want to have a supply that has more voltage than the batteries in series. Maybe I'm missing something.
  
 With regard to measuring the current, my MM doesn't read Amperage. Instead, could I use any value resistor and measure the voltage across that? I have nothing that is super low other than a 1 ohm resistor that measures 1.2 ohms. I do have a few 1k ohm resistors. Would those work better?


----------



## wakibaki

Sorry, should have read the thread, I didn't realise there was regulation in there.

Measure the voltage across the resistor (75R) and make sure you have 1.25V.

w


----------



## Mullet

Nope don't have 1.25v. I ended up with what looked like 2.5mA when I did V/R. This was between + in from the wallwart and on + on the first battery terminal with the batteries disconnected and power on. Then I turned power off and got nothing. I'm assuming this circuit allows charging with the power off. I connected the batteries and did the same measurement and blew something. Can't tell what it was, but I saw and smelled magic smoke. Looking at the schematic and at the data sheet I think I might have wired up something wrong. The data sheet for this version of the LM317 says that pin 1 is Adjust. Pin 2 is Vin and Pin 3 is Vout. On Tangent's schematic Pin 2 is Vout and Pin 3 is Vin. I'm using the part in his BOM. I wired things up based on the schematic, not based on the parts pin out. Anyways, time to reorder some new parts and start from scratch.


----------



## tangent

> Originally Posted by *Mullet* /img/forum/go_quote.gif
> 
> This was between + in from the wallwart and on + on the first battery terminal with the batteries disconnected and power on.


 
  
 1.25V is expected between ADJ and OUT, not IN and OUT. The voltage drop between IN and OUT varies depending on the battery voltage, even if all else is fixed.
  


> The data sheet for this version of the LM317 says that pin 1 is Adjust. Pin 2 is Vin and Pin 3 is Vout.


 
  
 I'm not aware of any standard way to number the pins on 3-pin parts. Packages with so few pins typically have their pins function-labeled, rather than numbered.
  
 In data sheets, such parts are usually drawn as 2D parallel projections, with no standard orientation, which makes it easy to mentally flip things around so you get the pin order backwards.
  
 This is especially easy to do when popping back and forth between data sheets for TO-220 and TO-92 versions of the LM317, since some manufacturer data sheets draw TO-92 from the bottom view. When I see that characteristic D-shaped outline, I initially see it as from the top, probably because I'm used to seeing these parts from the top side of the board. (I made that mistake yet again while composing this message, thus the edit!)
  


> The data sheet for this version of the LM317


 
  
 What version is that? Please give manufacturer and package type, at least.
  


> On Tangent's schematic


 
  
 Which one is that?
  
 The only current schematic on my site that I'm aware of with an LM317 based trickle charger is the PIMETA v2 schematic, which doesn't have numbered LM317 pins.
  


> in his BOM


 
  
 Again, which one? I have many parts lists on my site.


----------



## Mullet

Tangent,
  
 My apologies for not offering enough information with regard to schematics, etc. The schematic I was using is from the PINT amp, since I have one that I'm building (and having major DC offset issues with, but that's for another thread). Since the design has been deprecated it's no longer on Tangent's current site. You can find it using the waybackmachine. Here's a link...
  
 http://web.archive.org/web/20060709073018/http://tangentsoft.net/audio/pint/misc/sch-1.3.pdf
  
 I used the parts list from the PINT pages as well...
  
 http://web.archive.org/web/20060709072626/http://tangentsoft.net/audio/pint/plists.html
  
 511-LM317LZ is the part I used for the LM317. The pin out is pretty easy to identify. Here is the datasheet...
 http://www.st.com/web/en/resource/technical/document/datasheet/CD00000469.pdf
   
Is this the correct part to use with the PINT even? I could go with something like this instead, which looks to have an easier pin out to deal with...

 http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/LM317LZ/?qs=sGAEpiMZZMtUqDgmOWBjgMYFDKwfkxOWk1Et%252bC0eWgo%3d
  
 Thanks,
 Mullet


----------



## tangent

The LM317 symbol I used on that schematic came straight out of the gschem parts library. I have no idea why its creator numbered the pins that way. I can't fix the PINT schematic in the Wayback Machine short of asking them to remove the content, which seems like an overreach to me.
  
 Why did you dig the PINT out of the Wayback Machine anyway? Why not build something that has a large, satisfied user base instead?


----------



## Mullet

I chose to build the PINT because I had the opportunity to pick up a board on the FS forums. I scored at PPA-S as well, which is what I'm using the trickle charger for.


----------



## doors666

I am trying to use the charger from o2. I am  using a single battery and will be using dc input, say a 15v walwart, this is to drive a cmoy based on ne5532.  Attached is the circuit I am trying to simulate. I had a few questions about this.
  
 1. How do I simulate a battery. What would be the approximate resistance and capacitance of a 9v rechargeable battery.
  
 2. is it safe to switch on the amp while its charging. Can the amp be used safely while its charging.
  
 3. If I use about 20mA current to charge, how much total current will be needed from the regulator. How much if I am using the amp while charging. I guess ne5532 uses Iq 20ma + 80ma max for output and 20 ma for charging, so total 120ma. Sounds good? 7812 driven from 15v supply at 120mA wont need a heatsink right? Is there a smaller cheap regulator I can use for this. SMD is also fine.


----------



## tangent

doors666 said:


> 1. How do I simulate a battery.


 
  
 Normally with a voltage source, same as with your 15V input supply.
  
 That will only simulate a perfect battery, which has no ESR and a flat voltage vs time curve.
  
 There is nothing in SPICE that simulates the chemistry of a real battery. You can try to approximate various aspects of the battery, such as by adding 2-3 Ω in series on the positive terminal of the voltage source, being the ESR of a "9V" NiMH battery.
  


> What would be the approximate resistance and capacitance of a 9v rechargeable battery.


 
  
 The ESR, as I said, is about 2-3 Ω.
  
 Capacitance? While there certainly is some capacitance in a battery, it's not especially useful to try and model it, at least as far as battery charging goes.
  
 If you're trying to model a NiMH battery using nothing but passive components, don't bother. A battery is an active nonlinear device.
  


> 2. is it safe to switch on the amp while its charging. Can the amp be used safely while its charging.


 
  
 Yes.
  
 The LM317 based chargers are nicer in this regard, in that they help lower the total supply impedance when they are active. In this O2 design, the 330 Ω resistor effectively causes the wall supply to not contribute to the power performance of the downstream circuit, since the source impedance of the battery is a couple of orders of magnitude lower.
  


> 3. If I use about 20mA current to charge, how much total current will be needed from the regulator. How much if I am using the amp while charging. I guess ne5532 uses Iq 20ma + 80ma max for output and 20 ma for charging, so total 120ma. Sounds good? 7812 driven from 15v supply at 120mA wont need a heatsink right?


 
  
 You're going about that calculation the wrong way.
  
 Again, because of the 330 Ω between the regulator and the battery — and the load! — ~99% of the current needed by the load will come from the battery, not from the wall supply. If you're using a 20 mA trickle charge and the load is drawing 40 mA, that means > 39 mA will come from the battery, and less than 1 mA from the wall supply.
  
 The solution is not to increase the charge current, because that will endanger the battery, since there is no intelligent cut-off circuit. Correct solutions include:
  

Accept that you cannot run such a load continuously without running the battery down. If you only use the circuit for a few hours a day, it will have time to recover overnight, if you leave it plugged in most of the time.
Switch to one of the LM317 based chargers, which form a true constant-current source with near-zero output impedance, so they take the load while the wall supply is plugged in, not the battery.


----------



## doors666

tangent said:


> Normally with a voltage source, same as with your 15V input supply.
> 
> That will only simulate a perfect battery, which has no ESR and a flat voltage vs time curve.
> 
> ...


 
  
 I was asking about the battery as a load while charging it, not as a source. Just to test the circuit in ltspice.
  
 I guess i gotta live with option 1. I think 2 would require me to disconnect the batteries when they are charged or it might damage the batteries or would need some detection mechanism and  cutoff for batteries.


----------



## tangent

doors666 said:


> I was asking about the battery as a load while charging it, not as a source.


 
  
 I know.  That's why I remarked that there is nothing in SPICE to simulate the chemistry of a battery, whether charging or discharging.
  
 If you just want a load for the charger, you can use Ohm's Law to calculate an approximately correct resistor, or you could insert a current sink.  Neither will really tell you that much about whether the circuit works, though. Doing that is kind of like in algebra where you find that you've made a pointless substitution and end up proving that 4=4. True, but not actually interesting.
  
 The electrical version of that is where you have a current source on one side and a current sink on the other, and learn that current in equals current out. That is, you'll just end up proving Kirchhoff's Current Law.
  


> 2 would require me to disconnect the batteries when they are charged or it might damage the batteries or would need some detection mechanism and  cutoff for batteries.


 
  
 Where did you get that idea?
  
 An LM317 trickle charger is no more dangerous to the battery than the circuit you're already looking at, provided that you configure it as a true trickle charger, which is defined as one having a charge current of C/10 or lower, yet not so low that it can't keep up with the battery's self-discharge rate.
  
 For a 250 mAh "9V" NiMH battery, that means 25 mA or lower, which you get with a current setting resistor of 50 Ω or higher in an LM317 trickle charger. (R=V/I, R=1.25/0.025, R=50.)
  
 These principles apply just as well to the circuit you're looking at now, except that the charge current varies as the battery voltage increases. I guess one could argue that this makes it "safer" because it can cause less damage if you leave it sitting there, but that assumes that long hours of sitting on _any_ trickle charger are good for a battery. That is not the case.


----------



## doors666

I checked the output resistance of the 7812, its listed at around 15 milliohms while the tenergy 9v rechargeable is listed at max 1200 milliohms.
  
http://www.synthdiy.com/files/2006/LM7812.pdf
  
http://www.all-battery.com/datasheet/10001_datasheet.pdf
  
 It doesn't look like the resistor is in the path when using a dc source as well as a battery with the amp switched on. Only the battery charging current goes through it. From 7812 to the amp, it goes through D4. From battery to the amp, it goes through D2. Resistor is in the path only for charging the battery from 7812.
  
 Had a doubt about CCS, how will CCS help in running the amp while the amp is in use. If I set the ccs to 20ma, it doesnt have enough to power both the battery and the amp. If I set it to say 150ma, it will cause issues with the battery if the amp is not running.


----------



## tangent

Ah, I didn't see that dangling wire as a bypass path.


----------



## tangent

By the way, it's not difficult to modify the PIMETA v2 LM317 trickle charger to let the wall supply run the amp when on wall power, bypassing the battery:
  
  
  

 Unlike the one you show, the LM317 isn't regulating the wall power supply, so you'll want to use a reasonably clean wall supply if you go this route.


----------



## jrabbit

I can not see the pic at all!! Are there anyway to recover it? PLease help im really interested at this.
  
 Thanks,
 Jill


----------



## tomb

jrabbit said:


> I can not see the pic at all!! Are there anyway to recover it? PLease help im really interested at this.
> 
> Thanks,
> Jill


 
  
 I've replaced most of the photos in my posts.  I'm sorry to say that I lost the original _redruM schematics.  This post about Trickle Chargers occurred before the infamous Head-Fi hack several years ago.  Links and photo locations were lost for all posts that were before that date.  Anyway, there should be plenty there to make sense for everyone, now.


----------



## NiHaoMike

tangent said:


> By the way, it's not difficult to modify the PIMETA v2 LM317 trickle charger to let the wall supply run the amp when on wall power, bypassing the battery:
> 
> 
> 
> ...


 

 What about put the diode between the output of the LM317 and the circuit output? That point will be 1.25V above the battery voltage with the charger connected.


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## tangent

I'm not sure exactly what you mean, so why don't you draw it?
  
 Then, before posting it, consider carefully what the voltages will be under the various conditions. I suspect you'll find that there is a path with your idea that causes problems.


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## NiHaoMike

With the charger connected, the 317's output will be 1.25v above the adj pin which is connected to the batteries, so the diode will conduct it to the output. The other diode from the batteries to the output will be reverse biased and have no effect. Only way you'll get problems is if the load draws too much current for the 317 to handle.
  
 Without the charger connected, that point will be slightly lower than the battery voltage when the load is drawing current, maybe 100mV or so worst case. That's not enough to cause any problems, since it takes another diode drop to make current flow through any parasitic diodes in the 317. If you're really worried about it, use two series diodes (will also reduce the load voltage difference with and without the charger connected) or use a Schottky from battery to output.


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