Thanks Lee and Roland. I think that I am only concerned with detecting the motor coasting with the controller off. I already have an interlock with the throttle and the reversing switch done with my microprocessor software. I was considering blocking the switch while the motor was spinning as well. Detecting the spin in some simple way was the goal.
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. Roland suggests current sensing which implies a current path. I think that there is no current path unless the reversing switch is already switched, and I was hoping to block that until the motor stops or at least is quite slow. 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. What I don't know is about how much voltage to expect from the armature vs. speed based on residual field magnetism. Another choice is to ignore the problem and let common sense prevail. I wouldn't put my manual transmission car in reverse while travelling forward. To do so would probably cost as much as switching my ElectraVan into reverse under the same circumstances. Thanks for your suggestions, Mike ------------------------ Original Message ------------------------ Date: Fri, 12 Apr 2013 12:43:30 -0600 From: "Roland Wiench" <[email protected]> To: "Electric Vehicle Discussion List" <[email protected]> Subject: Re: [EVDL] Reversing Contactors Yet Again Not simple. My first controller was a Cable Form controller normally design for industrial vehicles that did not have a mechanical reverse gear. It use 600 amp reversing contactors with a surge rating of 2000 amps. There are mechanical interlocks, electrical interlocks and a control relays that also have mechanical and electrical interlocks. This reversing circuit could switch on the dynamic braking which also activates plug braking which disconnect the armature circuit and shorts it out. This circuit was never use in my EV because it had a transmission. There was three modes of dynamic braking that can be adjusted. Violent, Standard and Soft. The violent mode shatter the motor coupler when I accelerated and than stop the motor. So it was recommended to choose the soft mode and come to a complete stop. Not only the two contactors were switch out, but there was a free wheeling diode for each contactor which was switch out. A current sensor circuit was install in series on the wire that came from the field of the motor to the free wheeling diode. This current sensor circuit is like a current relay which you can get in open frame or in a factory assembly package that has adjustments to limit the amount of current to a low level where it then will activate the other contactor. This current sensor circuit is available from any electrical supply company. Roland ----- Original Message ----- From: "Michael A. Radtke" <[email protected]> To: "Electric Vehicle Discussion List" <[email protected]> Sent: Friday, April 12, 2013 10:48 AM Subject: Re: [EVDL] Reversing Contactors Yet Again > Hello, > > So, it's a good plan to block the reverse switching while the motor is > still spinning. Any suggestions for a simple way to detect that? > > Thanks, > Mike > _______________________________________________ > 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) _______________________________________________ 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)
