Quote:
Originally Posted by P-hack
I'm not entirely convinced that the thing monitoring the pack needs to be entirely isolated from the pack. Are you assuming the 12v converter is isolated (also expensive if so)? From what I gather the system needs to be isolated from the frame most importantly, so the frame doesn't act like a big antenna/ground loop, but if the controller and monitoring and charging (and lights and etc) are also referenced to the pack with no reference to frame, excepting for shielding, then no big deal.
So if your cheap non-isolating 12v converter is referenced to pack ground, and you make sure everything that depends on it does not reference frame, then the whole thing can "float". Which is probably something you should do with a non-isolated 12v converter anyway.
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My 12V converters are indeed isolated from the car's 12V side. Isolated up to ridiculous voltages, according to the datasheet. Verified by my multimeter. Arduino boards must be isolated from each other when measuring voltages at different parts of a series string battery pack as voltage potential [obviously] increases from cell to cell, all they way up to pack voltage at the end. Each board is isolated from the car's 12V system, NOT isolated from the pack. I repeat: each board is not isolated from the cells they are monitoring (how would you measure pack voltage if they were?), which is why isolating boards from the car and from each other (via optos and DC-DC converters) is necessary.