Jeremy Green wrote:
I was never able to get much of a reading on the resistance to the frame
of the motor. There wasn't enough conductivity for my multimeter to get
much of a read.
High resistances are typically measured with a "megger" -- a special
ohmmeter to measure resistances way up in the megohms. Rather than the
usual 9v battery in most meters, a "megger" has a high voltage power
supply, to get enough current to flow in the meghohm resistance so it
can be measured.
You can "make do" with an ordinary meter as well. You can use your EV's
pack voltage as a convenient high voltage source. Set your multimeter to
a voltage scale suitable for measuring your pack voltage. Connect the
pack, the meter, and the unknown resistance (like your motor's armature
to frame) in series.
Most meters have an input resistance of 10 megohms. Check your manual,
or measure its resistance with another meter. So, what you are doing is
applying a high voltage across the unknown resistance through a 10
meghohm resistor, and measuring the voltage across this 10 meghom
resistor. Ohm's law will thus tell you the current, and from that
current, you can deduce the unknown resistance.
For example, suppose you have a 120vdc pack, and a 10 meghom meter. The
meter reads 10 volts. Therefore the current I = V /R = 10v / 10megohms =
1 microamp. The other 110v must be across the unknown resistance. With 1
microamp flowing, its resistance must therefore be R = V / I = 110v / 1
microamp = 110 megohms.
--
I am funding five battery startups, and there are probably 50 out there.
[But] that is a very tough problem. It may not be solvable in any sort
of economic way. -- Bill Gates
--
Lee A. Hart. Christmas is coming! See my electronic Christmas tree at
http://www.sunrise-ev.com/projects.htm#christmastree
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