Al, Big fuses take over a minute to open at rated current. Early DC builders worried about that and used a undersize fuse. The problem is the fuse self-heats and may make the internal element brittle and it may crack from vibrations. Do it like wiring a house, maximum current +80% so you would use a 250 amp fuse rated at 300 volts DC or more with an interrupting capability >10,000 Amps. Your motor controller being AC will limit current and if a phase fails it will take out the 250 Amp fuse and the motor will not just got to 100%. Wire sizes should be based on 250 amps as well. David Kerzel Modular EV Power LLC
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Al Sent: Thursday, February 07, 2013 11:18 PM To: Electric Vehicle Discussion List Subject: [EVDL] Fuse sizing I am looking for advice on fuse sizing for a semiconductor type fuse for a 70kW AC drive system. Worst case pack voltage under max load would be ~300vdc so max current would be ~233A. I notice that DC systems use fuse ratings well below the theoretical max current. For instance, when using a Zilla 1000A controller they recommend a 500A fuse. I know that typically a series DC motor/contoller combo hits max current only briefly when accelerating, but an AC system is more of a constant torque (constant current?) arrangement. It seems to be a bit of a guessing game. You don't want to go too high as you may sustain more damage before the fuse opens. On the other hand, if you go too low you could get unexpected fuse openings. So, am I looking at using a 200A or 175A or even a 150A fuse? Thanks, Al _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
