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Can you wire Lipo packs in series?

Old 08-17-2006, 03:20 AM
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Epowerreg
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Default Can you wire Lipo packs in series?

What would happen if you wired 2 -7.4v lipo packs in series? and could you charge them as an 14.8 v pack?
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Old 08-17-2006, 04:01 AM
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Twmaster
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yes.
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Old 08-17-2006, 06:20 AM
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dimadee
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I believe you would first need to ensure that both packs are individually balanced.
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Old 08-17-2006, 07:03 AM
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Vamooska
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Very much so..balancing is a must for that type procedure. Please also try to pick the same brand of packs. That is iffy at best. If you don't...here is what can happen. Good manufacturers will match cells for a pack. By that I mean they will compare internal resistance and discharge characteristics of all cells and match them with others as close to the same parameters as possible to assemble a pack. If you haphazardly throw cells together, chances are you will get a pack that has inherently different structures of cells and will hardly if ever, balance. When a pack is out of balance, the charging cycle can very easily lead to overcharged cells.....not good.
My advice is this. If you have a 3 cell pack and one cell puffs, make it a 2 cell pack. Go down in cell count and not up. That goes for parallel and series.
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Old 02-18-2007, 10:13 AM
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jjjsellers
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Yes but here is the thing...current WILL ALWAYS be exactly equal in series batteries, and parallel loads on equally charged identical battries with be equal except for minor random differences between theoretically identical battereis.


So what you say? Well Lithium BURNS very easily because it is a light element...AND these battries tend to get HOT if force current through them when they are completely discharged or over charged...bad news....at the very least you ruin the battery for most types and at the most you have an explosion for conflageration on your hands.

So...you MUST have balanced charger for series batteries which will charge each indepentantly in identical ways. That takes care of the series part of the problem.

Now the second part can be a bit more touchy since not all supposedly identical batteries are actually identical, so they might have slightly different discharge characteristics...which doesn't matter much until you get to the end of the charge at which time...again...you either ruin the battery or have an hot event.

This leads to a set of rules.

1) Most chargers do no anticipate batteries in parallel, and because you must use blanced charger to charge individual cells, you don't want them in parallel when you are charging. So charge each series set with a blanced charger designed for the set...each set SEPERATELY until COMPLETELY CHARGED at which time the charger will tell you things ar charged.

2) Use ONLY Identical sets of series batteries and CHARGE EACH SET SEPERATELY AND COMPLETELY using the SAME blanced charger to make the charging conditions as identical as possible.

3) THEN AND ONLY THEN connect them in parallel, ONLY WHEN IDENTICALLY CHARGED WITHOUT DISCHARGING ANY SET AT ALL...also it is a good idea to charge all sets without a great deal of seperation in time so that charge condition of sets don't change over time.

4) DON'T RUN THE BATTERIES COMPLETELY DOWN, but take care to use them so that you know there is some charge left...a significant drop in current availability or votage is a good sign you had better stop using the batteries IMMEDIATELY...until completely recharged again by the above safety procedures.
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Old 02-18-2007, 10:37 AM
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slipstick
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Originally Posted by Epowerreg View Post
What would happen if you wired 2 -7.4v lipo packs in series? and could you charge them as an 14.8 v pack?
Yes of course. That's all a 4S (14.8V) pack is, 4 cells wired in series.

But you'd be a fool to try it with anything other than 2 IDENTICAL packs.

Steve
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Old 02-24-2007, 06:20 PM
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Tram
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Yeh, you can, as the others have said wire them in series, however, like slipstick said, you would want to make sure it is 2 like packs.. I wouldn't wire a TP 3S 2100 and a CSRC 3S 2100 in series and feel comfortable with it..

Jeff
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