Re: [CAD_CAM_EDM_DRO] Re: testing with multi-meter

On Sun, 20 Apr 2003 22:31:26 -0000, you wrote:

>"andrewyslee" <andrewlee@s...> wrote:
>> Is it safe to connect a multimeter to the phase A/phase B of the
>> motor cables, set to measure current/voltage. If it is what would I
>> expect to read?
>
>Digital multimeter max. Amp is only 200mA.
>
>Set to read DC Volt and connected to 1 phase. Reading was 0.000 when
>power off. The moment driver is powered on the Reading changed to 1
>(meaning no reading I think) What does this mean?

Depends on the meter, might have meant 1 volt, if so, then the phase
was grounded. If the range is set to the bulk supply voltage, (if the
DMM is not autoranging), then you can't overload the meter with that
measurement. I assume that this motor is bipolar: In which case,
unless the motor is turned off, the other end of the winding should be
about a volt less than the bulk supply voltage.

Much depends on the mode of the controller. When measuring current,
and you don't have a large enough current scale, you can take a 0.1
ohm, 10 watt resistor (available at Radioshack or Tandy, I think),
place it in series with the motor lead, then measure the voltage
across that resistor. It will be 0.1 volt/amp of current. (subject
to the resistor accuracy and meter accuracy, of course.)

There's a bunch of other modes, but they depend on controller and type
of motor.

Rest position (not turned off) should lock the motor in place with all
the phases showing either connect or disconnect. One trick to do is
to take a bipolar LED (one that's red and green for different
polarities will do), place a 3.9 K ohm resistor in series with it,
then wire that across the motor terminals for each phase.

Not only is it pretty, but the changing colors will indicate if the
motor is stepping, and will show you where the phases are in
relationship to each one. If you have a unipolar motor, then use a
resistor of the same value in series with a red (or green, or
whatever) LED. Cathode to driver, and anode through resistor to
supply voltage. That will also monitor the phases....

If I build stuff, I tend to put this kind of "warm fuzzy" feature
in...

Harvey

>
>Andrew