[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.

 

[ozshadow]

Whats the M+- by the way ?

 

[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

 

[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

 

[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.

 

[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.

 

[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.

 

[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]

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.

 

[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.

 

[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.

 

[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.

 

[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.

 

[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

 

[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.