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Originally Posted by mechman600
I have very limited electronics knowledge, so coming up with a device for each cell that trips the charger when the first one hits 3.6V will be a challenge, but this is what I will do.
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I used celllog8m devices. They're made for R/C stuff, but they'll monitor the voltage of 8 cells at once. They can be setup to send an alarm signal for high voltage. With my BMS, this signal was sent to an arduino (brain) and the arduino then cut power to the charger.
Quote:
Now another charging question. Let's use the Kelly 72V/10A charger that I used to own as an example. It had a constant max voltage of 88.2V, and on 25 cells that is an average of slightly more than 3.5VPC. I imagine that once 88.2V is reached, most cells will be right around 3.5VPC but a few will be lower (lets say 3.4V) and few will be higher (lets say 3.7V).
Once the charger holds 88.2V for, say, 10 minutes and is pulling back the current more and more until it decides to switch to float (82.8V), what will the voltage do on the higher voltage, weaker cells? Will they stay at 3.7V or will they continue to increase past 4.0-4.5V (because they are full) while the stronger cells catch up, eventually causing a disaster?
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EDITED:
The answer is no. Once your charger hits the constant voltage phase, the high/weak cells voltage WILL continue to increase very quickly. But, since the charger is monitoring voltage, it should also decrease amperage very quickly to compensate. This is why the manual way I talked about above works out.
The real disaster happens when you hit 3.6V and you're still in constant current mode. That voltage will just start shooting up and that cell will start heating up until something bad happens.