Re: volts/rpm

Hi,

A good (and accurate) way to measure armature resistance is to chuck
up the motor in a drill press (use low RPMs) and measure the DC open-
circuit voltage on the motor leads.

Then comes the important part. Make sure the motor is secured in a
vise. Switch your meter to DC Amps and place it across the motor
leads. Measure the short-circuit current.

Take the voltage reading from part (1) and divide it by the current
reading from part (2). Ohm's Law now gives you an accurate
calculation of the motor's armature resistance.

What can screw up the readings is part (2). If you notice the drill
press motor labor and drop RPMs, or worse yet, the test motor gets
loose from the vise and spins, be prepared to extract your meter from
the nearest wall where it will be imbedded. Your readings will not be
accurate then (or ever again with that meter).

I speak from hard-won and expensive experience.

Mariss

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> ccs@M... wrote:

> miniscule, but the IR drop is not always so low. You can measure
> armature resistance, but it is tricky because the brushes don't give
> very good contacts when not moving.

> Jon