Parallel Battery Packs

by Spork99 on Thu Aug 11, 2011 9:41 am

I haven't seen this mentioned, but isn't it possible to power the Minty boost with multiple series connected pairs of 1.5V batteries with the pairs connected in parallel? The voltage output would be 3V with the current draw distributed evenly over the pairs of batteries.

-Spork
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Re: Parallel Battery Packs

by adafruit_support_bill on Thu Aug 11, 2011 9:57 am

with the current draw distributed evenly over the pairs of batteries.

That's the problem. Unless the cells are carefully matched, the current draw will not be even. It is generally bad practice to parallel cells.
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Re: Parallel Battery Packs

by Syn7 on Fri Feb 08, 2013 9:32 pm

So If I use two 2 x AA banks parallel with diodes on the positive leads to prevent them from affecting eachother is that still bad? I did read the battery tutorial and all the FAQ's. In the FAQ it says refer to bat tutorial for the answer but it never really said why. Any info or links would be much appreciated. I thought that by using 4 x AA's with a 3v output would double my amphours. Seemed like a good idea and I even found a tutorial that showed me the diodes idea and kinda sorta explained why but not really :P So I come here to double check because I trust you guys and I see I am wrong. I can accept that, I'm just curious as to why. What are the benefits and disadvantages?

Thanx for your time.

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Re: Parallel Battery Packs

by adafruit_support_bill on Sat Feb 09, 2013 6:41 am

The protection diodes do work, but at a cost of some voltage drop over the diode (and power loss proportional to the drop). With a 3v battery pack and a 0.7v drop using a typical silicon diode, the loss can exceed 20%. With a Schottky diode it will be about 1/2 that.
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Re: Parallel Battery Packs

by Syn7 on Sat Feb 09, 2013 1:35 pm

would that be 20% added on to the 20% or so that is already lost from battery to device in a 2xAA bank?
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Re: Parallel Battery Packs

by adafruit_support_bill on Sat Feb 09, 2013 2:04 pm

Yes. And since you would only be delivering about 2.3v to the MintyBoost, it would have to work harder which would reduce the boost efficiency even more. :(
If you want more capacity, you would be better using C cells. Another alternative is 4xAA NiMH rechargeable cells in series (4.8v). Or a 3.7v LiPo cell.
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Re: Parallel Battery Packs

by Syn7 on Sat Feb 09, 2013 2:09 pm

Sweet. Thanx. I think I'll just go with two AA's for now then later I'll make a LiPo solar charger for it and switch it over then. Again, thanx for the info.
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