Mark Grasser wrote: > I seem to remember one of the hottest points being the brushes themselves. > I am going to drill and tap about ΒΌ" deep for 4-40 screw on the wire end > of the brush. Concerns would be these: are the brushes a god point to > read temperature? Am I in danger of splitting the brush during this > process? > Will the screw threads hold up? Would I be smarter attempting to epoxy > the thermistor to the brush instead? Oh, What temperatures should I > expect?
Convention appears to be to epoxy a thermocouple into the brush for monitoring brush temperatures. The positive brushes tend to run hotter, so if you only monitor one, make it a positive one. Jim Husted noted that there are downsides to attaching a temperature sensor to the brush, including the possibility of the sensor wiring becoming connected to the traction power, the sensor wiring interfering with free movement of the brush (e.g. most thermocouple wire is relatively stiff solid core), and that you have to redo the sensor when you replace the brushes. He suggested the mounting the sensor to the brush holder might be a reasonable compromise. Below are a couple of relevant posts from those more knowledgeable than I on this subject. Cheers, Roger. > -----Original Message----- > From: Otmar [mailto:otli...@evcl.com] > Sent: July-24-05 5:54 PM > To: e...@listproc.sjsu.edu > Subject: Re: Thermocouple position, was: Re: 120v 6.7" ADC? > > At 9:17 PM +1000 7/14/05, James Massey wrote: > >Hi Otmar and all > > > >At 10:37 AM 12/07/05 -0700, Otmar wrote: > >>I was taught by the engineers at ADC to drill a half inch deep hole > >>in the positive brush and put the thermocouple in there. > > > >Any ideas as to why the positive brush? > > > >Is it just an ADC in-house convention, or is there a technical reason for > it? > > > >I can theorise no reason for the positive brush to get hotter than > >the negative, unless the electron flow into the brush heats it more > >than the electron flow out of the negative one. > > > >Any theories? > > Sorry for the delay, I've been out of town and am just getting to > hundreds of EV list messages. > > > I was told the positive brush gets hotter. I can only theorize that > it has to do with electron flow. > > -- > -Otmar- > -----Original Message----- > From: owner...@listproc.sjsu.edu [mailto:owner...@listproc.sjsu.edu] On > Behalf Of Jeff Major > Sent: June-19-07 10:42 AM > To: e...@listproc.sjsu.edu > Subject: Re: Max motor temperatures and temp sender install > > > Hi Mark, Richard, > > Class H insulation is 180 degree C. Meaning at 180C, > insulation will last 10,000 hours(or half life of > 10,000). It depends where the thermal sensor is > located in the motor. Cannot be in the armature, that > is hard to do because it rotates. So, I'm guessing, > it is in the field coil. Now it depends on the motor > design, but the ones I worked with years ago, would, > on the one hour temp rise test, have the armature > reach rated temp first. So there would be a > differential between the arm and field coil temps. > The temp sensor would be selected to that field coil > temp which related to arm temp limit. So the > assumption would be that when your temp sensor trips, > the hottest part of the motor is at limit. > > Having a 120C temp would indicate that you should back > off or end the trip soon, probably not stop at the > side of the road and wait for the motor to cool down. > You might also add forced air cooling if you find the > temp light coming on often. > > As for motor temperature in general, at the end of > thermal rating tests I used to run, it was not > uncommon to have the outside of the motor frame at > 100C. As for the brushes, we used to install > thermocouples in the brush by carefully drilling a > hole in the top of the brush, insulating the TC with > epoxy and then insterting the TC into the epoxy filled > hole. On short time based thermal runs, like 5 or 10 > minutes or shorter, the brush would be the limiting > temperature for the motor. This was allowed to reach > 200 degree C as the internal brush temperature where > no insulation is present. The outside of the brush > would be lower where the pigtails and springs are. > > So, for a field coil temp limit, 120 to 140C sounds > good to me. On the brush, I'd say 180C, hopefully > that would be just peaks on the brush, like at the top > of a hill, and the average would be 40 or 50 lower. > > My experience was back in the good old days, so I > don't really know how they design those new motors. > Hope that helps. > > Jeff _______________________________________________ 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)
