Short Circuited: 10 Sanyo 2700 Pack.

[rizky_p]

i have 10 sanyo 2700 made into pack soldered in series, apparently after several uses under high load the heat generated slowly weaken the wrapping and eventually created a short(casing to casing short) . It was only happened about 10-15 second before i ripped everything appart and cool the cells down. Man it was really hot, the cables literaly melt away and smokes are everywhere. It was probably about 100watts(?) of energy dump in a fraction of time . Never had that experience before, now i assembled the pack and put a double sided tape so every cells now has 1mm of cleareance to others and should be much safer compares to my previous setup. Only one loose its wrapping so i throw it away and uses the rest. I am not sure what is the condition of the batteries. Should i dump all of them?

thanks.

 

[SilverFox]

Hello Risky p,

Welcome to the world of RC racing...

The RC people usually are trying to propel a vehicle or airplane, but the end results is that the batteries get hot.

You have probably lost some cycle life, but if they still hold voltage under load, and have over 80% of their initial capacity, they should still be good.

Tom

 

[rizky_p]

Thanks Tom...:wave:

 

[wptski]

Tom:

Didn't we conclude that a cell wrapper melts at >160F?

 

[SilverFox]

Hello Bill,

That sounds about right to me...

Tom

 

[rizky_p]

170F/71C?? no wonder the cells were untouchable. It was definately that hot..

The pack now sags to 10.45v under 2.3A of load(10 cells series). According to your(SilverFox's) AA Shootouts Sanyo shouldnt drop this low. This is a bad sign right? :mecry:

 

[SilverFox]

Hello Risky p,

That would not be too bad for 9 cells...

Tom

 

[Handlobraesing]

Fully charge the pack, wait about 3 days and measure the voltage. If there are cells with low voltage that stands out, mark them. Wait a few more days, then measure again. If the pattern still holds, the marked cells are likely plagued with not being able to hold charge.

Also measure the of each cell under load. The ones that exhibits low voltage that stands out is damaged.

The wrapping on the Sanyo 2700/Duracell 2650 is paper thin and incredibly fragile. You'll damage the wrapper along the top and bottom rims after a few use even if you use them with care. They're in a great constraint to make the whole thing fit into AA size.

 

[rizky_p]

Hello Risky p,

That would not be too bad for 9 cells...

Tom

no it is a 10 cells pack not 9 cells...



@Handlobraesing: thanks i'll try that.

 

[SilverFox]

Hello Risky p,

I am sorry if I wasn't obvious enough...

My point was that your pack is behaving like a 9 cell pack. If it is a 10 cell pack, it would seem that you may have a bad cell.

Tom

 

[rizky_p]

Hello Risky p,

I am sorry if I wasn't obvious enough...

My point was that your pack is behaving like a 9 cell pack. If it is a 10 cell pack, it would seem that you may have a bad cell.

Tom

No problem SIlverFox, i think i will have to single out a bad cells if not all and replace it. Better be more carefull next time