Mustang ZEVA BMS Error Experiments 7/15/2017 In suggested order. 1. Motor current cutback ------------------------ Measure the following at full throttle vs. cutback level, from 0 to 10 in 1 integer steps: Solo: - BMS error state - BMS error reason -- note cutback level vs. time, then look at BMS log afterwards - Max battery current -- ditto - Spot check with old BMS Requires passenger: - Max motor current - use clamp-on ammeter - 0-30 MPH acceleration time -- use stopwatch, or perferrably iPhone movie so curves can be drawn - 0-60 MPH acceleration time -- ditto - Then disconnect variable cutback resistor and measure added resistance vs. cutback level. Then compare to 5 kOhm potbox and plot theoretical max battery current vs. measured. - Then determine if there is a cutback scenario that will work short term. If so, then add a fixed series resistor to the potbox and switch the cutback relay control back to BEW W30 and add the additional cutback required to get the drivers attention and protect the batteries but not become unsafe. Estimated values are 5 kOhm always to limit the motor controller to 500 amps, and 10 kOhm more switched in with BEW to limit to 250 amps, similar to what was done with the Curtis setup except that was speed limit not torque limit, and I am actually not sure what resistor I used for cutback, but I could go look, I think I can still find the resistor, but I didn't save the old documentation. Let's save versions going forward, putting old drawings in an old folder. 2. Battery current cutback -------------------------- - Learn how to change max battery current setting on motor controller and then do similar tests where battery current is reduced and then check for BMS error. This may be a better mid term solution, providing more torque at lower speeds. The same method could also be used to lower motor current from above than adding a series resistor. 3. Cable routing ---------------- - Look for RS485 cables close to power cables and move them apart and see if the problem goes away or gets better. For example the two oversized extension cords on each side of the top front battery rack could be moved or shortened. 4. Twist motor cables --------------------- - Twist motor cables, then see if problem goes away or gets better. 5. Aluminum shielding --------------------- - Shield motor cables, with heavy duty aluminum foil taped to the radiator box to provide grounding - Shield BMS -- ditto - Shield LV looms -- ditto - Shield motor -- ditto, but don't block air flow 6. Move BMS to cab ------------------ Actually this is another form of shielding, by using the car body. Use old BMS if it works similar to new BMS. Requires fabricating a ~10' extension harness with: HV+ -- be careful for safety HV- -- ditto GND 12B: W15, goes to 2 places BOKn: W16 BEW, SOC and BTP not necessary for short term experiment -- yellow light, fuel gage and battery temp gage respectively. 7. Filtering ------------ - Obtain oscilloscope with FFT or spectrum analyzer and probe incoming low voltage lines to the BMS. - If noise found, add noise suppressors tuned to the correct frequencies coming through and see if the problem goes away -- it may be 15.6 kHz or a much higher harmonic. - Also solve the yellow status light coming on and the green status light going off during drive at the same time, applying filters to the status PCA. 8. Steel or mu metal shielding ------------------------------ - With the scope or SA, create varying loop antennas and sniff for radiated frequencies. - If lower than 1 MHz frequencies found, which is likely, try steel near the source, mu metal near the BMS, or both.