Sep 08, 2006, 11:25 AM ... Joined Dec 2005 149 Posts Question Question on P connecting lipos Two batteries, same voltage and cell count (3S) but differing capacities, say 700 and 800mah. Can they be connected with an adapter into a 3S2P without worries of different capacity, or does the capacity have to match as well. I am guessing they have to match but am hoping I am wrong.
 Sep 08, 2006, 11:42 AM Southern Pride Haralson County GA. USA Joined Oct 2004 34,852 Posts This will start another great debate but no they do not have to be the same capacity. They need to be very close to the same voltage and it is best to connect them in paralel while they are mostly discharged and charge them in parallel. It is also best if they have approximatley the same C rating and past history. Charles
 Sep 08, 2006, 01:16 PM Registered User Joined Jan 2002 6,591 Posts My experiments and experience supports Charles'. After you've gained some experience, you may find you can be a little less conservative, but I would advise you to get the experience first. Your example of 700 and 800-sized packs is fortuitous. The smaller the packs, the easier it is to contain collateral damage if there's an accident. - RD
 Sep 08, 2006, 03:29 PM ... Joined Dec 2005 149 Posts I will be charging them separately with a balancing charger so the voltages should be fine. I was just wondering how the depletion of the stored energy would balance out. If current flow is the same in all parts of a circuit, I was thinking the lesser capacity battery would drain low well before the larger capacity battery causing its cells to drop in voltage sooner. I am probably missing a basic principle somewhere. It has been a while.
 Sep 08, 2006, 03:39 PM Deletedfor proving Nauga wrong Joined Mar 2005 15,855 Posts I find it easier to hit the same voltage by charging the two packs. Since the LiPo charger automaticly stops at the same voltage every time... (+/- less than .02 v) I then connect - to - and put a resistor between + leads... and verify my self-ranging DVM indicates 0V across the resistor. (that indicates less than 1 milivolt differential...) If you take the step of doing the differential voltage check across a resistor.. you won't have a problem paralleling packs of the same cell count. (3S, 4S... Parallel count doesn't matter) Once they are paralleled... if thats your primary use of the packs... keep them paralleled. one charge ballance pack A... next charge ballance pack B... or parallel the taps plugs too (using the resistor trick) and you can ballance both packs at once. ************* Smaller pack may indicate a lower voltage under load than the larger pack... but that will reduce the current draw on the smaller pack... You'll find that as soon as the load is off, both packs have the same voltage. Internal resistance of the cells will take care of keeping one pack from draining before the other. (also with them paralleled... the high pack would charge the low pack until they hit the same voltage. This is why parallelling cells works)
Sep 08, 2006, 03:41 PM
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