Re: [CAD_CAM_EDM_DRO] Re: determining stepper motor current

If the motors are squealing, you can have an electrical noise problem.
If they are hissing, I believe that's normal. My router/mill was
squealing really bad. I wound up building a little 555 based oscillator
to use instead of the built-in oscillator on the L297. That quietened
it down to the aforementioned hissing. I used pots for R1 and R2, and
tweaked them until it was quiet.

The problem stems from noise being picked up in the current limiting
circuit. The current limiter winds up locking onto a harmonic of the
20khz. That's why it is audible, and the motor output isn't as high as
it could be.

Regards,
JJ

On Friday, December 12, 2003, at 05:14 AM, alanhunt2001 wrote:

> Rich,
> The meter I mean is the one on the DC power supply and not on the
> motor side of the L298. I was thinking if this would be the average
> current through the motor rather then the peak/chopped current.
>
> But thinking about it furthur, I suppose it will only show that
> total supplied power (less 5v power) through L298/motor is 6.4watts
> (32v x .2A)
> I have upped the current a little, my x axis is still stalling and
> all the motors are intermittently making lots of whistleing and
> whinning noise which they did not do with the old controller.
> Motors do not appear to be giving off any heat so will gradually
> increase vref.
>
> Alan
>
> --- 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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