2X2 9V NiMH Power Supply -- Comments?
Jul 30, 2002 at 8:11 PM Thread Starter Post #1 of 2


Feb 1, 2002
My plan is to make my META42 totally portable, instead of using external battery pack, I'm thinking of squeezing some rechargeables into my Hammond enclosure (www.alliedelec.com, 806-3628).

My requirements for the PS:
1. Fit inside enclosure
2. Minimum maintenance
3. Cheap!
4. 12V+
5. Reasonable mAH capacity

After some research online, i think grouping 2X2 9V NiMH is my solution.

1. If I remove their battery shell, re-wrap and re-wire em', I think they'll fit (2X9V will fit, haven't actually try 4X9V yet).
2. I plan to seal the batteries in the enclosure, use a 3PDT toggle switch to switch between Series(for normal operation) & Parallel (for charging).
3. 8.4V NiMH $4.00/pc, and since I already have a charger, I don't have to spend money building/buying another.
4. 2X9V(8.4) in series is 16.8V, should be enough for META42 running with AD8620.
5. 160mAHx2 = 320mAH. Well, i think 160mAH is alright too, if i can only fit 2x9V.

However, I have some concern,
1. Will the charger be able to charge 4 x 8.4V NiMH parallel at the same time? I am charging a 8.4V and a 7.2V in parallel right now, I think it's overchaging the 7.2V though, as soon as i get more of those 8.4V, It should be alright. I presumed the charger will stop automatically!
2. 3PDT toggle switch takes up too much space in the enclosure. I was thinking of using relays to control the swithes(SW1,2,3. see picture attached), but i don't know how

I thought about other solutions too, like 3.6V Li-Ions or 1.2V NiMH. I found some cheap cells at allectronics.com. But the problems are the charger and size of the cells, I will need to build/buy a new charger. Furthermore, the enclosure will not fit enough cells to make it to 12V+. Not to mention the Li-Ion might explode if I didn't charge it right!

I know there are many people out there with the same problem, how do you guys deal with it? What's your solution to your portable Amp PS needs? Some thread in Head-Fi & Headwize suggested using 16x1.2V NiMH! I'd rather build a Li-Polymer charger for this battery.
Jul 30, 2002 at 8:25 PM Post #2 of 2
When I do get around to building my META42, I'm planning to put in 10 AA NiMH cells for 12V, or 15V using alkalines.

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