Re: [CAD_CAM_EDM_DRO] Re: determining stepper motor current

Hi Mariss;

That probally should read "is a terrific and good way to read motor
currents if the meter has a true RMS converter". Depending on the
meter, the waveform and the converter the results can be either very
good or very bad. The quality of the readings will very widely
depending on the conversion method and the quality of the converter.

I learned of these issue when working with a engineer on some old tube
based circuitry (yes tubes). The equipment had very interesting heater
controls, that absolutely required an True RMS converting multimeter be
used whenever the element current was adjusted.

Dave


Mariss Freimanis wrote:

>RichD,
>
>Actually a battery powered multimeter set to DC Amps at very low
>speeds (< 1 step per sec) or AC Amps at higher speeds (>240 full
>steps per sec) is a terrific and very accurate way to measure step
>motor phase current directly. Mind that the current will be Amps RMS
>for the AC setting.
>
>Mariss
>
>
>--- In CAD_CAM_EDM_DRO@yahoogroups.com, RichD <cmsteam@s...> wrote:
>
>
>>Alan,
>>Meter??
>>I hope you know that you can't use an ampmeter to measure motor
>>
>>
>current.
>
>
>>It's chopping at ~20kHz.
>>The best way is to calculate based on the sense resistor value as
>>
>>
>given
>
>
>>before and set the VRef pot accordingly to needs.
>>I don't understand the 1.2 vs 3.4 diff unless your ohmeter is ??? or
>>the diff is that the higher reading is across a center tapped coil.
>>RichD
>>
>>
>>alanhunt2001 wrote:
>>
>>
>>>Hi Rich
>>>Thanks for your help - will try upping the peak current.
>>>Although the label says 1.2ohm, each coil actually measures 3.2ohm
>>>so I think this will give about 2watts? But my meter shows that
>>>
>>>
>I'm
>
>
>>>sending 0.2A (is this the average current through coils??) at 32v.
>>>
>>>so 0.2A x 3.2ohm =.64v and 0.13watt I think its a question of
>>>using either peak current or average current in the equation.
>>>
>>>I wish I had measured vref on the old board before removing all
>>>components from it and as the board contained a multitude of
>>>components for changing vref through software I can'nt even
>>>reconstruct the schematic easily!!
>>>
>>>Thanks again
>>>Alan
>>>
>>>
>
>
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