Re: [CAD_CAM_EDM_DRO] Motor current measurement

Thanks,

It is the fluctuating nature of the current at the output that was
concerning me. I do have an old, simple scope - I haven't used it in years
so I guess I'll just have to get it out and dust it off and try to remember
where the on-switch is!

The driver boards I'm playing with are the 'modular' design ones by (Hans?)
which have a screw pot to adjust the current. I have them coupled up to some
4volt 1.1amp motors and I'm feeding them with 36volts. I set the sense
current up to what I think should be 1amp output and everything works OK but
neither the motors or the L298s get even remotely warm. I know this is a
good thing but it made me wonder whether I am actually getting the 1amp
output and whether the motors should be giving me more 'push'.
I was a bit wary of just disconnecting one motor lead and putting a
multimeter in series in casied the chip..

Best wishes,
Ian
--

Ian W. Wright
Sheffield, UK


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----- Original Message -----
From: "Jon Elson" <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Friday, November 22, 2002 6:38 AM
Subject: 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
>
>
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