Problems with parallel lipo's

[Chuck E Cheese]

i was hopeing that someone could help me with a few problems i am having with wireing lipo packs in parallel. i am not new to FE or electronics so i understand the theory good. here are the set-up's and 2 problems i am having:

1) this is a 2s boat, NEU 1512 1d, cc 240, 2 x 2s-5000mah 30c in parallel. one of the packs (the same one every time) uses aprox 200 mah more than the other. i use a y made out of 12 guage wire with 5.5mm connectors to put the packs in parallel. WHY IS ONE PACK USING MORE?

2) neu 1515 1y, cc240, 2 x 4s-5000mah 30c in parallel. this is the same as above only on this boat one of the batteries was fully charged and the other was 3000mah used. i use 10 guage with 5.5mm.

i was wondering if it could be that there is too much solder on one side of the connectors or is that something that would not make a difference? the wire legnths are the same on both packs and i am getting solid continuity. i guess the next thing i should check is flipping the Y connector and see if the pack that is low changes. i havent paid any attention to that yet.

if anyone has had a similar problem or can shed some light on what is going on please help me... thanks

[rockwerks]

It can be many reasons. but yes a bad solder joint is a very highly likely culprit.

[Chuck E Cheese]

it is not a bad connection, just has solder that soaked the wire about 3/4 inch up from the connector.

[rockwerks]

it is not a bad connection, just has solder that soaked the wire about 3/4 inch up from the connector.

That would make it a bad solder joint, higher resistance possible

[Himalaya]

1) Pack IR(internal resistance) did that.

Any chemical battery naturally differ from cell to cell, even within a same batch. During discharge the lower IR pack will provide more current flow, thus more charge is used.

So the more-charge-used pack is better than the other, for less IR.


2) Don't do that. Direct parallel two packs with different remaining charge level hurts them.

The fully charge 4S pack is 4.2x4=16.8V, the 3/5 used pack is usually 3.75x4= 15V. A current flow as high as (16.8-15)/2*IR will accur at the moment they are paralleled together, one pack charging the other. Say the IR is 10mΩ, the current could be 80A. Remember how much max charge current is allowed on your pack's back label?