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Old 11-17-2009, 09:35 PM   #2585 (permalink)
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Originally Posted by williamson View Post
Who's going to overspeed in one second, in gear? So I think this would save a speed sensor!
I was talking about overspeed with a fellow EVer and he brought up a scenario I hadn't thought of. If some part of the gear train fails (like a weak homemade coupler, or some shaft that is not designed for the torque of a electric motor), it'll likely happen quickly at high amps. Before you know it, that motor could be screaming fast. Only a smart controller would be able to save it (with maybe some drpm/dt limit or something).

Additionally, there's always the case of coasting downhill. There was a guy on the EVDL who shared his pictures of a D&D motor that he blew up. Started at the top of a hill, forgot he was in 1st gear, and around 35 mph the thing blew up... An audible alarm or flashing light could guard from such a $1500 incident (perhaps controlled by the controller too).

Just something to think about. Having said all that, my overspeed hack broke a while ago. I had rigged the shift light on my tach to open a relay to open the main contactor at the specified rpm, but then my tach broke. Now I just make sure to shift at certain speeds...
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