[davidl]

I have found a pretty good price on some AA NiMH with solder taps at http://www.batteryspace.com/index.as...ROD&ProdID=222
So the question is, How do they go together? Do I solder tab to tab or put a wire through the holes in the tabs? Or I could solder tab to tab for those in a straight line and put wires in the holes to make turns. What is the usual practice?

 

[Syzygies]

I have a pile of similar AAA cells. The main disadvantage of a custom battery pack is that if you give your amp to someone else, they'll be stumped what to do when the pack finally fails. The main advantage is that you can squeeze more cells in a given space. So start with your available space, and work the geometry back from there.

I've taken apart various battery packs, and 9V cells. There's no one way to do this, you just hook them up in series somehow. Using wire minimizes possible solder heat damage to the cells themselves, because you can then solder the tabs away from contact with the cells.

Again, work the geometry back from your available space, and let this force your hand on how you wire them.

 

[Icy006]

I used AAA NiMHs with tabs, and arranged them in rows next to each other. Bent the tabs so they lined up with the adjacent battery's tabs, and soldered them together. With 3 rows, I bent the end tabs up to connect the rows together in series. Viola, high voltage 700mAh pack in a small space. Beats the heck out of my 170mAh 9V batteries.

It's true that heat can damage cells, so I tried to do this in a fairly touch-and-go manner. Bending the tabs such that they stayed together sufficiently was a pain...I used tape to hold cells together and still while soldering the tabs up.

Worked out great - 18 cells (6X3) wrapped up in gaf tape fits perfectly in my Hammond. I can throw up some pics of the tabs soldered together later if you like.

p.s. I did this with the 20-pack from batteryspace shown in your link

 

[mono]

Having bought batteries from batterspace.com previously, I would advise one to question their mAH ratings and instead choose a known quality battery like PowerEx or Sanyo (includes GE, Panasonic, et al. brands). Sanyo being the major value player out there and easy to find locally.

Granted, tabless means you need a holder, but for replacement purposes if you're gonna use standard sized batteries anyway it would be desirable to have the holder too?

Syzygies has a good point about giving the amp to someone else. One idea there is to make sure the amp works with at least fairly efficient, sub -200Ohm cans @ 9V, then on the custom battery pack just use a 9V snap-on connector and allow enough space in battery area for at least a generic 9V replacement battery to be swapped in.

 

[davidl]

I started with what I thought was a very narrow technical question. And you guys have correctly pointed out the assumptions and choices behind it.

I can't vouch for this company's batteries. I'll put one across a precision resistor and check the run time. I couldn't find cheap name brands with solder taps.

I've just "finished" my first Pimeta and hooked it up to an 18V battery charger (the $3 radio shack one) to see if it works. It does!

I also built the Chu Moy crossfeed. Do I want it built into this amp or into a future home amp or as a separate component to interface with anything?

Rather than pick an enclosure and get batteries to fit, I'm going to mock it up with a board and a couple of pieces of aluminum for the front and back and figure out how big it really is. Then I'll select an enclosure.

If I pass this on in the future I can configure away from the custom battery pack at that point.

I'm going to set it up so the battery pack can charge in place. Do I want it to be able to run on a PSU or just charge and run from batteries. All these choices are the frustration and the fun, I guess.

Dave

 

[Icy006]

There are different approaches. Personally I'd be bothered running my amp off unregulated DC from some random wall-wart, and I'm not up to building a STEPS quite yet so I'm using a battery with enough run-time to get me through the most usage-intensive day. There will be a DC jack - but this hooks up only to the trickle charger circuit to charge the battery overnight (power to amp disabled when charging).

It's mild enough that an extra day overnight charge left on accidentally won't destroy the battery, and strong enough to bring a full charge for the next day's use. This way I have the best sound quality, I won't be tempted to lug the wall-wart on the go, and it fits my usage patterns without downtime.

I just found out that Tangent put up a new power supply design called the TREAD. Very small and simple, and it can function as just a regulator off a random DC wall-wart. This would also make a great option, with or without batteries.

 

[Syzygies]

Quote:

Originally Posted by Icy006 There will be a DC jack - but this hooks up only to the trickle charger circuit to charge the battery overnight (power to amp disabled when charging). It's mild enough that an extra day overnight charge left on accidentally won't destroy the battery, and strong enough to bring a full charge for the next day's use. This way I have the best sound quality, I won't be tempted to lug the wall-wart on the go, and it fits my usage patterns without downtime.

This is word for word my strategy too. I use twelve 1000 mAh AAA cells, and a normally closed switching DC jack that cuts off the amp when power is inserted.

 

[Vadi]

I put 4 AA cells in a vice. Then 4 on top of 4 against a wall.

 

[Vadi]

After the soldering I glued them together too (I used thermal adhesive compound from Arctic Silver). So yes, I could've skipped the vice part.

 

[mono]

On some packs I've made in the past I found it easier to secure the cells together before any soldering, so i'd have exact-length solder connections and along with that, those connections help to preserve the shape of the pack rather than the opposite.

Batteryspace.com and other places have some shrink-fit tubing for packs. I dont' claim it's necessarily the best solution for containment but it does produce a pack that looks similar to what people are accustomed to as manufacturer-made packs before they started getting more proprietary with custom cartridge-like plastic shells.