Electric Imp Testing Log
April 18, 2003 -Friday
It's the batteries, stupid! : SIADIS was giving me the answer, but I did not know/understand how to read it yet. The program was showing me pack voltage of around 26 volts. I thought that this was because the inverter could only read pack voltage after the high power contacts had closed. I knew that when I went over and read the pack voltage with the multimeter, it would read 385 volts. I was wrong. The inverter can read the pack voltage with the main contacts open.
The SIADIS program is a powerful program that allows you to change a number of control parameters of the inverters. Since the error message had to do with low voltage, I went into the SIADIS program and changed parameter # 420 Vbat_UnderVolt. It was set to 50 Volts. I changed it to 10. With this setting, I could get the front motor to spin, but not the rear motor. I began to have a horrible suspicion: Was the pack voltage actually dropping to 20 Volts?
I set up the multimeter so that I could read it as I turned on an inverter. Sure enough, the voltage flashed from 380 volt to 20 volts as the capacitors attempted to charge. The obscure religious message: 'Prech. Time > 3s' began to make more sense as the error message 'Precharge time greater than 3 seconds'. As soon as I switched off the inverter, the voltage began to return to 380.
The next step was going through the battery pack to discover the bad batteries. This would be a nightmare if we had to reach each of the battery's terminals in place. This is where the individual battery sensing wires paid for all the effort we expended to install them.
Switch on the inverter. The capacitors try and charge, the voltage drops. At the battery wire sensor box, I quickly check 20 battery voltages. I switch off and on the inverter to reload the batteries and then measure another 20 batteries. Whenever I find a cell that seems a little low, I test it with the same method. If the battery is bad, it will go to a large negative voltage. The battery not only does not add any power, it actually acts as a resistor. Immediately after being under load, they read as low but a minute later, some read as nominal 2.14!
Battery #: 123, 132, 135, 136, 156, 164, 171, 174, and 023. I find eight bad batteries The crew is not amused. It takes all day to swap out the bad batteries.
19, 2003, Saturday - Small Steps.
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