Series Tieing Lithium Ions PROBLEM HELP

wess.vic

Feb 5, 2015
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I was tying two 3.7v 4000mah li-on battery cells together. I first checked the voltages from each and they both had 3.89 volts. I then connected them in series soldered to the protection circuit. Checked the voltage at the load end of the PCB got no voltage what so ever. tested at the input side no voltage. Tested common and each input leg got 3.89 volt as I expected. I never had this problem before with lithium ion batterys and cant figure out whats happening. The load voltage should be around 7.4-7.5v. Please help it would be appreciated Thanks, Victor
 

davenn

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Sep 5, 2009
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so did you get ~ 7.4 V directly across the batteries when in series ? ( without being connected to the protection circuit or anything else)

is the protection circuit designed for 7.4V or 3.9V ?
 

wess.vic

Feb 5, 2015
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PCB is designed for 7.4v and no I couldn't get anything before connecting to the pcb. 0volts
 

ChosunOne

Jun 20, 2010
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Well, this does seem kind of obvious, but somebody's gotta say it: When you connected the cells together in series, did you connect positive to positive or negative to negative; (instead of [+] to [-])? So that the two potentials oppose each other and cancel each other out? 'Cause I can't see any other way you're reading 3.89V on each cell and 0.0V on the combination.
 

davenn

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Well, this does seem kind of obvious, but somebody's gotta say it: When you connected the cells together in series, did you connect positive to positive or negative to negative; (instead of [+] to [-])? So that the two potentials oppose each other and cancel each other out? 'Cause I can't see any other way you're reading 3.89V on each cell and 0.0V on the combination.

yup exactly
sounds like a miswiring problem to me too
 

wess.vic

Feb 5, 2015
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I wired leads on then put a nice piecece of heat shrink wrap around them. I might have put the wire for my positive lead on the negative and that's whats screwing up my wiring. Because if my leads are right yes I do have positive to negative. I'll take a reading again with my meter and check the polarity. Thanks
 
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