Quote:
Originally Posted by Heady
What voltage did you use on the wall-wart? 9V? Another question is, did you solder the cells together?
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For the one I pictured, An unregulated wall-wart will need to be at least 7V & 100mA, more-or-less, substitution of higher VA wart will mean quicker charging. TYpical 9V DC wart would work for charging alone but would be too dirty a source for running the amp. You'd need to consider the rate any given wart charges, such that if the rate is too high to be a trickle charge when finished, you disconnect it to prevent overcharge. It's no different that charging any other pack with an unregulated charger, the charger's voltage drops (or rises within limits) to that of the pack and the VA spec of the transformer determines the current.
For a linear supply I just fine-tuned it to the peaked voltage of the charged pack. NiMH cells have a final vDrop at the end but that just results in a trickle at that point... depending on the cell's resistance. Substituting your own charger can require measurements if you want to get that last few % charge or want to leave it unattended (as with any charging scenario).
I did solder the cells. I got a great deal on those cells and bought 3 dozen (this was over a year ago, the source (
Electronic Goldmine) doesn't have them anymore and my supply has just about ran out), point being that I first did some test-runs with soldering them because I'd often heard (and maybe even repeated myself) than one shouldn't solder directly do them. Charging those Prismatics is very easy because they are very near the same length of a AA cell, I have some I charge in a AA quickcharger. Holders are a different story, there may be some out there somewhere but last time I looked I didn't see any. Then again, I could not have gotten 6 cells in a H65 if they were in a typically designed holder.
I can't tell you if the seals in those cells (Sanyo TH-900FS) are more heat-resistant than other types or if batter seal technology itself is better than it used to be, OR if I just have a good quick technique. Either way, my first tests with other packs still work fine- no leakage nor significant capacity decreases so at least these particular cells do not appear to have been compromised in any way by soldering. I have a 100% success rate soldering these particular cells.
When I soldered, i first took very fine sandpaper, not ultra-fine, maybe 400-600 grit, and hazed the area I'd solder. Then I put them in the refridgerator to cool them down and had solder station and short lengths of wire ready. Finally a quick solder with medium power (30-40W) iron, maybe 2 seconds contact. Finally I wrap packs together. I was using heat-shrink meant for packs but I ran out of that and just used very heavy duty packing tape on that pictured pack, with a tiny drop of super-glue between each cell to hold them together prior to wrapping. It is an ugly way of doing it, but in function it has worked great for several projects.
The remaining issue I found was what I briefly mentioned previously, that eventually the cells will have worn out as all do, at which point I'll put a snap-on type 9V connector on it so it can run from same type of pack, regular NiMH *9V*, or alkaline. Note also that the Serpac H65 I used was the open-compartment type (still has the battery hatch), you could probably cut away the compartment on the 9V H65 model but why? There
WAS a lot of cutting and filing involved, trimming of the PCB and case studs, it is certainly not just a "drop-in" pack that will fit without alterations of the PCB & case. IMO it was worth it.
