Hmmm Precharge circuit the saga of reviving the 0V liFePO4's continues.

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terramir
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Joined: Monday, July 21, 2008 - 18:09
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Hmmm Precharge circuit the saga of reviving the 0V liFePO4's continues.

All batteries are now measured out of 2750 cells this is the tally about 2000 0V cells about 150 cells with less than .2 Volts about 230 cells between .3 and .4 about about 60 cells between .4 and .5 about 40 between .5 and .9and about 25 between 1.0 and 1.99 and about 60+ over 2V plus 25 that are holding a charge from the first batch which I didn't write down what their original charge was, that varied from .2 to 3.2 and a bunch of 0V and as well 123 leaking cells.
Everything that was logged above .5V is charged and they all seem to be holding a charge for various lengths of time, (between 2 days and 10 so far).
Now for the 0V cells I have something special in mind, while I will put them on the charger circuit I found eventually I would like to precharge them with 107mA (closest to 100mA vaild resistor value with a 5V source) until they reach 3.3V then I want the charge to turn off automatically, so I then can put them in the regular charger design to fill them. Manually doing this is risky because I can't watch these cells 24/7 So I thought this little circuit up I would like your comments:
voltage cutoff circuit.jpg
My thinking here was the current through Q1 will flow at about a 100mA rate due to the current limiting resistor until the voltage of the cell rises to 3.31V when the voltage in the cell has risen to 3.31V it will supply .7V through the voltage divider to Q2 which will then open and light the LED and so to say short the base current that would keep q1 open.
Now what do those guys among you that understand electronics think will this circuit work and will it do what I think it will. Namely turn off the charge to the cell until it drops down to a level below 3.3V which won't be long and well it will go back and forward and the led will blink for a while. Then after a while the cell will have absorbed so much current that it will hold the level of 3.3V for a while and the blinking will slow.
Am I missing something?
terramir

garygid
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Joined: Friday, December 19, 2008 - 23:25
Points: 441
Re: Hmmm Precharge circuit the saga of reviving the 0V ...

The base to emitter voltage of Q2?

Cheers, Gary
XM-5000Li, wired for cell voltage measuring and logging.

terramir
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Last seen: 4 years 5 months ago
Joined: Monday, July 21, 2008 - 18:09
Points: 33
Re: Hmmm Precharge circuit the saga of reviving the 0V ...

The base to emitter voltage of Q2?

yeah I see that's where I got trapped I posted this circuit in an electronics forum as well and I see that I have to add the diode voltage drop as well I keep thinking of transistors like little relays thinking the base emmiter voltage has virtually nothing to do with the collector emmiter voltage and current. I got a valve mentality stuck in my brain. turns out it would work with modified resistor values but it seems like the current would not stop so it wouldn't turn off q1 :( I asked in the other place gonna ask here too if I add a resistor to the base of q1 would that cause the current to the battery to be shut down if q2 "turns on" cause then the resistor would drop to remaining current if Q2 was turned on at least that was my thinking. still need help though
terramir

garygid
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Last seen: 12 years 2 months ago
Joined: Friday, December 19, 2008 - 23:25
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Re: Hmmm Precharge circuit the saga of reviving the 0V ...

With R4 about 560 ohms, it would probably work. The "charging" current (near 100 ma at the start) would gradually drop to around 30 ma before it is "turned off". The LED gradually gets brighter. This does not have a very exact shutoff voltage, but it should "work".

Cheers, Gary
XM-5000Li, wired for cell voltage measuring and logging.

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