Is it a good idea to make 1 4s1p battery from 2 2s batteries? - RC Groups
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Sep 13, 2006, 04:57 AM
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Is it a good idea to make 1 4s1p battery from 2 2s batteries?

This might be a dumb question but I'm somewhat new so please don't be too harsh.
I have 2 new identically rated 2 cell lipos(Apex MK3 1350mah, 15C) that I bought for a plane that I was planning on getting.
Well, plans changed and I ended up with a different plane that won't really fly with 2 cell lipos(I think the plane, actually wing is designed to balance with 3 cell 2100 or bigger batteries).
so instead, I was wondering if it is a good idea to create a patch cable to connect the 2 2 cells in serial, i.e, + of batt1 to + of new connector, - of batt1 to + of batt2 , - of batt2 to - of new connector. That should make it a 4s1p lipo right?
Am I asking for trouble or is that a somewhat common thing to do? Any advice/comments would be greatly appreciated. Thanks
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Sep 13, 2006, 06:42 AM
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Right. It is common, in case the packs are equal, I mean their age, cycles, of course the type as well.
You have to fully charge both separately for the first time. When both are full, You can connect them in parallel to 2s2p for couple of hours (Avoid short circuit!! in parallel means - to - and + to +), to let voltages perfectly equalize. Then it is possible to connect them (also permanently) and treat them as 4s pack, including charge as 4s, but You would better use balancer with integrated charge guard (like LBA6) or balancing charger.
You have to avoid deep discharge, but it takes place with any Lipo pack - but in case the packs are not absolutely equal, this becomes much more important.
Using device like "CellSaver" - external LVC monitoring every cell voltage during flight, and charging with balancing charger like FMA Cellpro, makes Your 4s pack safe and reliable even if not matched.
Last edited by coro; Sep 13, 2006 at 06:47 AM. Reason: added "Avoid short circuit!!"
Sep 13, 2006, 11:00 AM
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Hi, thanks for your response and the tips. The batteries should be fairly equal since they're both brand new and haven't been used.
I will connect them parallel first to equalize but I will probably not connect them permanently since I might use them as 2 cells later on.
Sep 13, 2006, 07:56 PM
just look at it smokin'
z-matrix's Avatar
if i were you i whould disassemlbe the packs so i could solder 2 terminals(1 from 1st pack, 1 from 2nd pack), and put another balancer plug on the new pack, (2 power cords will be not needed), then put heat shrink tubes on the pack where needed.

2s1p = > 4s1p

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