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View Full Version : Acceptable voltage differance for connecting packs in series


Rugar
12-23-2005, 01:10 AM
I have 2 packs of TP3S2P 4200PL I connect in series for my Fliton Extra. These packs have 7 cycles on them, and have been within .02v of each other every time after charging with my two Astro 109's. Today I got two TP205 balancers, and after charging them with the balancers the packs show a difference of .04v. How much voltage difference between packs is acceptable before hooking them together in series? How about hooking them in parallel first to even the voltage out before hooking them in series? What about storing them hooked in parallel so they stay at the same voltage?
Help from you battery guru's would be appreciated.

Jim McPherson
12-23-2005, 01:46 AM
I have 2 packs of TP3S2P 4200PL I connect in series for my Fliton Extra. These packs have 7 cycles on them, and have been within .02v of each other every time after charging with my two Astro 109's. Today I got two TP205 balancers, and after charging them with the balancers the packs show a difference of .04v. How much voltage difference between packs is acceptable before hooking them together in series? How about hooking them in parallel first to even the voltage out before hooking them in series? What about storing them hooked in parallel so they stay at the same voltage?
Help from you battery guru's would be appreciated.

What are you using to measure your voltage? Are you sure it is accurate down to 0.01 volts?
Keep in mind that the volt difference between the packs is the sum of the differences in the cells. 3 cells summed together are 0.04 volts off of another 3 cells summed together. This means the actual difference between the cells is very low (could be only 1/100th a volt).
I'd say that as long as the 2 packs are within .1 volt of each other (assuming 3 cells per pack) then you'd be good to go. Just don't run them till they are completely discharged.
Small volt differences tend to be a self medicating type of problem. The higher voltage pack discharges faster thus equaling itself out. Don't try this with large voltage differences though.
Putting the packs in parallel is a bad idea and could lead to problems. You'd be trying to fast charge a cell in the last .1 volts of its charge cycle. This could damage the cell.

-Jim

Rugar
12-23-2005, 01:56 AM
I'm measuring voltage with a Astro Flight Watt Meter and with a Multi-Meter. Each meter shows a difference of .04v of each other, but each meter shows the exact same voltage difference between the two packs.

Rugar
12-23-2005, 06:42 PM
Putting the packs in parallel is a bad idea and could lead to problems. You'd be trying to fast charge a cell in the last .1 volts of its charge cycle. This could damage the cell.

-Jim

I seem to be getting conflicting information on this from other forums. Seems others do this without a problem to equal out the packs. Ive also read that I could charge them in parallel and leave them connected that way to keep the packs equal until ready for use, then hook them together as a series pack for discharge.

RD Blakeslee
12-23-2005, 06:55 PM
http://www.rcgroups.com/forums/showthread.php?t=170524
http://www.rcgroups.com/forums/showthread.php?t=360273

Rugar
12-23-2005, 07:41 PM
http://www.rcgroups.com/forums/showthread.php?t=170524
http://www.rcgroups.com/forums/showthread.php?t=360273

Thanks for the links RD
Its always important for the readers to be able to take in as much information as possible to determine the right and wrong way to do things for themselves. But this is only possible if members will post their opinions so we have different information to sort through.

Jim McPherson
12-23-2005, 08:37 PM
I'm sorry, I probably was not clear. I don't suggest trying to equalize packs of 2 different voltages by putting them in parallel. However, keeping them that way after charging, running them, and chargeing them in parallel is just fine.

-Jim

RD Blakeslee
12-24-2005, 04:15 AM
http://www.rcgroups.com/forums/showthread.php?t=455934