Quote:
Originally Posted by DJBecker
You can over-rev a typical EV motor with modest voltage. Perhaps with 24V if there is no load. Certainly with 48V.
The motor voltage limit is a combination of insulation breakdown, especially over time+heat+voltage, and commutator/brush arcing.
In particular, think about current multiplication and what happens with the freewheel current.
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True. However, dc motors are essentially no different from a generator. . as the rpm increases, the back emf from the motor begins to balance the forward voltage from the battery supply. when they're equal, the motor can't speed up any faster (unless you're doing something like going down a really steep hill, in which case it could actually charge your batteries.)
i think the fact that you're actually hitting the motor with full voltage spikes, instead of a steady voltage, counteracts this though.
Quote:
Originally Posted by DJBecker
There isn't a reasonable way to do a low pass filter. The currents are too large, and the load varies too much. You would end up with something that is inefficient or huge, likely both.
In particular, think about current multiplication and what happens with the freewheel current.
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it could certainly be done with a low pass filter. the variable load isn't an issue, you would just size it for a fifty percent duty cyle. any other speed would require less work from the capacitor filter bank. On the other hand, you're right that it would end up being quite large. not enormous though. i'll see if i can set up a pspice simulation of this and stick the results on here. for worst-case scenario i'll model the motor as a constant current of 1000 amps in series with 1/5 ohm to make it show up as 200 volts to the outside components.