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Re: (ET) E20 lacking power



You didn't mention if the armature resistors were warm or hot - probably because they weren't, in which case never mind..

On the current measurement - use the shunt already in tractor- grab the power meter leads with a DVM set on 200mV scale . That should be accurate enough. The schematic I have shows the main shunt being 20" of #6 AWG @ .4ohms/1000 ft = 667microhms, so your DVM will read 667 microV / Amp - or 0.1V at 150A which I think is full scale on the panel meter. The 200mV scale on the DVM will work up to 300A. This calculation may be off depending on the exact wire stranding the shunt wire is made of. The archives has some numbers on this.... And here it is:

doing a search in the list archives for "shunt wire resistance", the 5th result is from Tom Coate
Date: Tue, 04 Jun 2002

Click on that link and the answer is there:
"According to my wire table, standard annealed copper wire, 6 AWG, has a resistance of 0.3951 ohms per 1000 feet at 68 degrees F. So... the 20 inch length in the tractor should have a nominal resistance of 0.0006585 ohms. I don't know if they count on some resistance from the terminals on top of that. In any event, it's not a lot! So good connections make a huge difference."

so I think my numbers are about right..

On the motor shunt getting hot - others have reported bad connections to that shunt. You may want to clean them up.

Also poor motor performance and large currents is usually associated with a weak (or missing) field. You may want to hook up the voltmeter across the field terminals and check that it's 36V when in cruise mode - actually I guess anything below the field weakening setting should be 36V?.


SteveS
E20