Re: [CAD_CAM_EDM_DRO] Motor current measurement

Alan Marconett KM6VV wrote:

>Hi Ian,
>
>A current probe for a 'scope will do the job. Or put small value
>resistors in series with the leads, and 'scope across them.
>
>Alan KM6VV
>
>
>"Ian W. Wright" wrote:
>
>
>>Hi,
>>
>>This may seem like a daft question but how does one measure the current
>>going to a stepper motor when setting up a driver board (L297/298
>>combination)?
>>
>>

The L298 is a full-bridge driver, if I recall. You don't have any
grounded lead to use in
that case, so it becomes a fully floating measurement. A DVM can be
used pretty easily
for that, although some DVMs are very sensitive to pulse-like signals
and may give
inaccurate or wildly fluctuating readings. The current sense resistor
is from the junction of the
lower transistors to ground, so one end of it is grounded. That is the
best point to measure,
BUT, you have to measure the peaks, not the average. That generally
requires a scope.
What you will see is short bursts of motor current between longer
periods of no current.
When the transistors are on, you see the motor current. When the
transistors are off, you
see no current.

Jon