kiev wrote:He did mention that one side measured 9 Ohms for part of the undamaged length and estimated two in series would be about 20 Ohms. The gauge of the wire and number of turns seems consistent with the measurement.
But If it were 240 Ohms, then the power load would be 540 W for about 0.6 seconds to charge the MCU cap.
Yes I saw that part of the resistor measured 9 ohms, but I'm not sure I would automatically assume it was "undamaged". There could potentially have been shorted turns in that half which caused the rest of the resistor overheat as the "normal" high resistance part would take the brunt of the dissipation.
Also 240 is ambiguous - it could be a two prefix + multiplier code for 24 ohms, but its more common for low value large power resistors to use a full value with the tolerance letter in place of the decimal point, which would make it 240 ohms.
If the point of it is to pre-charge the capacitors, 5400 watts for 60ms seems awfully quick not just for stress on the resistor but for the capacitors! 540 watts for 0.6 seconds seems much more reasonable for a "soft start" circuit, especially when you factor in contactor switching times. Most power supply soft start circuits have a charge time of approx one second.
It may well be 24 ohms after all, but if it is, I wonder if it's a part just waiting to fail due to excessive inrush current though a device that should be avoiding just such an inrush...
it really would be great if someone with a wrecked pack could measure this resistor to be sure, but I know that's unlikely to happen.