Jay Summet via EV wrote:
As I rotate the shaft by hand, the ohm meter goes negative (I assume due
to current/voltage being generated by the motion.)
Correct. There is always a little residual magnetism in the field, so
moving the motor will generate a voltage. This messes up any readings
you try to make with an ohmmeter.
My high/low resistance were 0.5 and 0.2 ohms
As others have noted, the true resistance is so low that you can't
measure it with a normal ohmmeter.
The best test is to actually run the motor on a 12v battery. The motor
needs about 30 amps to run, regardless of voltage (it just runs faster
at higher voltages). Even 6v is enough, but 12v is easier to get.
Use a set of jumper cables to connect the armature and field in series
to a 12v car battery. There will be a spark when you touch the last
connection, so don't make it on the motor's terminals (the arc can
damage the threads).
After the initial spark, the motor should start running. Because it's a
series motor, the starting current is high, but falls quickly as it
comes up to speed. You can't overspeed it on 12v or less.
If you reverse the field or armature connections (but not both), the
motor will run backwards.
If the brushes are set to neutral position, it runs the same speed
forwards and backwards. If the brushes are advanced, "forward" will be a
little faster than reverse.
The motor should run smoothly, with no hesitations or clicking noises.
If there is a problem with the motor, they can be repaired for a lot
less than a new motor. There are still some old-timer motor repair shops
that know how.
Hope this helps!
(I had a lot of 0.3 and 0.2's flashing back and
forth, so the average was probably around 0.25 ohms).
Then disconnected the motor controller leads from the motor.
Next, take a reading from each motor terminal to the motor housing. A
new motor that is brush dust free, should read about 20 megohms or as a
open circuit. I do this every time with a new motor or when the motor is
clean.
I cheated a little bit here. I just checked resistance between the motor
+ and - leads (The motor +/- was disconnected from the controller, but
the wires connecting the two fields was still in place, so essentially
all 4 motor terminals were in series.)
I tried resistance readings from both the + and - to the truck chassis,
the metal case of the motor, and the front shaft of the motor. All
readings were no connection (sometimes starting at 35 M ohms and quickly
going up to 0L)
Question: Because neither the +/- terminal had any measurable connection
to the chassis of the truck or the motor, am I safe in assuming all 4
terminals don't need to be disconnected and measured independently?
--
Teaching children to program goes against the grain of modern education.
Just imagine the chaos if they learned to think logically, plan, create,
implement, test, and execute!
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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