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 A123 voltage drop

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Cody
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PostSubject: A123 voltage drop   Wed Apr 25, 2012 9:47 am

What kind of voltage drop are you guys seeing during matches?
I cycled a pack and one of the cells voltage went to .666v while the others were 3.2
With the dropped cell and the HV jumper on the scorpion XL I wasn't getting any power to the esc and rx
I got the pack back to full charge and everything back to normal but it just leaves me worried of the voltage dropping below 16v
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Evan Steeves
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PostSubject: Re: A123 voltage drop   Wed Apr 25, 2012 11:25 am

if you have a rebellious cell in your pack i would check if it has a different internal resistance compared to the other cells also if wired in nimh style series i have found that draw across cells changes when there is a long line of cells in series. what is the battery configuration and how is it wired, is it using bars or wire strips or steel ribbon. also does the oddball cell reside in the furthest away position from the positive and negative wires, if not it may just need to be replaced with a new cell.
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Cody
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PostSubject: Re: A123 voltage drop   Wed Apr 25, 2012 12:47 pm

It's 5s (cluster configuration i guess) with battery bars, the cell with low voltage was the connected to the positive lead
I ment to check the resistance but I got sidetracked
I'll have to see what the pack has done sitting over night, it charged to about 2000mah and balanced to within .02 volts before the charger timed out
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PostSubject: Re: A123 voltage drop   Wed Apr 25, 2012 1:05 pm

Sounds like you could have a dud cell if it repeats its shenanigans again Sad
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Cody
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PostSubject: Re: A123 voltage drop   Wed Apr 25, 2012 4:29 pm

I had full intentions of replacing it then decided to see what a charge did
I even had the soldering iron warmed up haha

I'm just nervous that even with a good pack that the pack falls below 16 volts after voltage drop and the drive esc cuts out especially since I think we're pushing it with the 26650 capacity already
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Cody
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PostSubject: Re: A123 voltage drop   Wed Apr 25, 2012 5:54 pm

All 5 cells measured 32.5x k-ohms
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Alex P. HASD Bots
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PostSubject: Re: A123 voltage drop   Wed Apr 25, 2012 9:33 pm

u may already know this but make sure all your connection wires from each cell are the exact same length, if not current will be drawn at different rates creating quite the problem
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Cody
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PostSubject: Re: A123 voltage drop   Wed Apr 25, 2012 11:25 pm

We used battery bars So that shouldn't be a problem
Do the positive and negative leads matter?

Do any of you gus balance your A123 or just have any idea of pack voltage after a match?
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Alex P. HASD Bots
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PostSubject: Re: A123 voltage drop   Thu Apr 26, 2012 7:52 pm

with balancing each point of connection basically becomes numbered (not sure which is which) but if you do not have those numbers corresponding to the write balance port there is a possibility that the charger is not reading your battery to what it should be, in turn giving u problems my team encountered this problem this year, but i don't know what they did to fix it because i was usually off working on another part of the bot. and our usual cell voltage after a match we usually saw our 6s pack to drop to about 3.2 volts per cell or around 19.2 volts total, starting out the cells usually had 3.6 volts per cell or around 21.6 volts
alex shared this site but it may help you balance, it did for us
http://scriptasylum.com/rc_speed/lipo.html
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Cody
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PostSubject: Re: A123 voltage drop   Thu Apr 26, 2012 11:10 pm

Thats the website I found on google when my friend and I put the balancing leads on
Heres a random picture of the pack from a week or two ago

Cant really see much though
Voltage by multimeter matches the charger so the leads are fine

I'm gonna get the pack taped up and do some runs on it and see how it does
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Alex P. HASD Bots
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PostSubject: Re: A123 voltage drop   Fri Apr 27, 2012 6:56 am

thatd be your best bet and hopefully you got extra batteries, and just in case have a fire exstinguisher on hand What a Face
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