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Old 03-21-2017, 12:00 AM   #3067 (permalink)
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Originally Posted by MPaulHolmes View Post
thingstodo, I never posted anything much about the BMS. A microcontroller powered by the 12v system supply monitoring 'n' battery voltages. It monitors the 'n' batteries by receiving the voltages from little attiny25 microcontrollers that are powered by each cell. They send the voltage by a sort of morse code across optocouplers. The attinys are only powered when their cell circuit is enabled, so if the 12v power is off, there's zero draw from the cells. One neat trick was, for each attiny25 to measure its cell's voltage, it would just measure a 1.25v reference on the A/D channel. Then, from that you can infer the cell's voltage. For example, if you read 1023, that would mean the cell's voltage was 1.25v. But if you read 512, that would mean the cell's voltage was 2.5v, etc...
Too bad you didn't post earlier on the BMS. I need something simple, no balancing ..

.. I like no power used when not enabled .. I like opto's so the differential voltage is not a big deal ... the cell voltage measurement sounds interesting. It would be interesting to see if the resolution could be boosted in the 2.75 - 3.00 V area without messing up any of your other advantages. mV resolution on the low end would help when I am bottom balancing batteries

.. having the 12V power the ATtiny's sounds like a hundreds of volts isolation isolated supply with a small current output ... another of your magic circuits?

An ATTiny that I can epoxy to the plastic case of .. whatever I use - NiCd, NiMH, LiPolymer. Flexibility, tied to a product that is easy to source. Not the latest battery management IC that is sampling .. sometime ... and I won't get unless I buy 1000's. Running code I just *MAY* understand. That's what Open Source is about!

Sorry about that .. sometimes I get carried away
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MPaulHolmes (03-23-2017)