Michael A. Radtke wrote:
I think that I am only concerned with detecting the motor coasting with the controller off.
That can be pretty easy. Measure the armature voltage of your motor versus RPM. Figure out what voltage corresponds to what RPM with no field current.
It will probably be something like 500 RPM per volt. Let's say you want to know when it is under 1000 RPM; then you need to detect an armature voltage under 2v.
The relay trick I mentioned won't be sensitive enough to do this. Instead, I'd use an optocoupler. Its infrared LED will turn on above 1v. Put a resistor in series to the armature, chosen so the LED current at maximum motor voltage is about half the LEDs maximum current rating. Put a trimpot across the LED, and you can adjust the exact voltage.
I think that Lee's circuit will do that, but I think that the sensing relay won't energize unless the motor has been spun up to a high enough speed under power. There may be a range where the relay never energized but there still was enough speed to cause damage: such as coasting.
That's true. The relay is cheap and easy, but not very sensitive. The opto circuit is more sensitive and repeatable. It just takes more parts.
Both ideas make me think that I could use a high voltage transistor connected as a current source across the armature to drive an opto-isolator. The circuit would be self powered by the armature voltage and result in an isolated binary signal to the microprocessor to represent the motor's state.
That can work, too. Just be aware that the armature voltage is incredibly noisy, and can have monstrous spikes. It would be a tough job for a transistor.
Another choice is to ignore the problem and let common sense prevail.
That's fine if you are the only driver. But, are you sure your wife or a friend will *never* drive your EV? I have had cases where someone got in an EV, pressed the clutch, and revved up the motor "to see how it sounds". Well, it will hit about 10,000 RPM in about 1 second. It sounds like "whine... BANG!"
-- Anyone can make the simple complicated. Creativity is making the complicated simple. -- Charles Mingus -- Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm _______________________________________________ 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)
