When I calculated a resistor to use on my Elec Trak mower control board I first tested the minimum pull in voltage of my contactor. My 300Amp GE contactor had a coil voltage of 42 volts but would pull in at 12Vdc using a variable bench supply. I measured the coil resistance then used V= Vsytem*R/(R +Rcoil) I didn't want my coil voltage to fall below 24V and I assumed that my system voltage could sag to 32V on heavy current draw (it's a 36V system). Sometimes a contactor that hasn't been used for awhile has a much higher pull in voltage until you cycle it several times, so I would also break it in. Also, don't forget a snubber across your coil to protect other components from voltage transients when power to the coil is removed (switch opened). You can see the mower at http://www.austinev.org/evalbum/405.html
Rod "First, what do you have for a precharge resistor? I used a light bulb, but a physical resistor will of course work, too." I used a 60W "vibration resistant" light bulb (intended for garage door openers). Seems to work great. "Second, what voltage do you see across the controller's B+ and B- terminals? When the first contactor is closed, this voltage should rise as the controller's capacitors charge thru the precharge resistor." That seems to be happening correctly. Final Voltage is around 120V, which is also the pack resting voltage. "Third, have you checked to see what DC voltage or current will pull in your AC relay? Perhaps the resistor you have in series with the coil is too large, so the coil current doesn't rise high enough to pull it in. " This sounds like the problem, as I feared. Nice to eliminate any other possibilities, though. It's going to be really difficult to get to those (although not impossible). I don't remember the exact values, but it seemed to be a little below what you used (since I have a lower voltage pack), and almost matched the coil resistance. Would it hurt to use a "fair radio" style charger to apply different voltages to the coil or would I see false readings due to the ripple? That's about all I have at the moment that could do that. Of course I could always "cheat" and just use a manual switch, which would be triggered after the voltage comes up. That would also give an additional shutoff control in the passenger cabin. I like the automatic operation, though. Thanks. IMPORTANT - THIS MESSAGE (INCLUDING ANY ATTACHMENTS) IS INTENDED ONLY FOR THE USE OF THE INDIVIDUAL OR ENTITY TO WHICH IT IS ADDRESSED, AND MAY CONTAIN INFORMATION THAT IS PRIVILEGED, CONFIDENTIAL AND EXEMPT FROM DISCLOSURE UNDER APPLICABLE LAW. IF YOU ARE NOT THE INTENDED RECIPIENT, YOU SHOULD DELETE THIS MESSAGE IMMEDIATELY AND YOU ARE HEREBY NOTIFIED THAT ANY READING, DISSEMINATION, DISTRIBUTION OR COPYING OF THIS MESSAGE, OR THE TAKING OF ANY ACTION BASED ON IT IS STRICTLY PROHIBITED. THANK YOU.
