On 4/14/2020 4:51 PM, Peri Hartman via EV wrote:
Nominally 240. But it really can be anything and I can convert it to
what I need.
Peri
>>>>>>>> Cells <<<<<
You can get about one third of the specific energy (~8000 W/kg) from
ordinary A123 26650 cordless tool cells.
You can get over 20,000 W/kg from A123 F1 cells, but the cost will
take your breath away.
John Metric sells some very high-performance drag racing cells that
might work for you.
>>>>>>>>>>>> BMS <<<<<<<<<
At first look, it seems extremely simple to build your own BMS.
Measure the cell voltage, switch on a by-pass resistor, turn off
the charger, turn off the controller, blink a few LEDs. Piece of cake,
right?
It is, in practice, a _very_ hard thing to build. It has to be 100%
reliable in _all_ respects, or you will absolutely get a fire. Guaranteed.
It has to withstand very large, very broad spectrum, magnetic
fields. The EMI and RFI issues are enormous. Then, you have to deal with
the high voltages, and figure out how to deal safely (and reliably) with
those large voltages.
When it fails, (it will fail at some point,) it must warn that it
has failed, and fail in a manner that does not cause the pack to become
unbalanced or cause some safety issue.
It also has to deal with battery faults like an open cell, a
reversed cell, over voltage, etc. in a safe and predictable manner that
warns the user in every instance, and shut down the charger or
controller in a safe manner.
Processors, like Arduinos, fail in unpredictable ways when subjected
to the large magnetic fields, the huge broad spectrum RFI and huge EMI
that the inverter and the charger subjects the battery to.
_Huge_ undertaking. You will ruin several packs trying to work out
the bugs.
Bill D.
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