Re: Driving unmarked steppers

This was part of the old thread on mystery motors.

go back to the thread on this and check the message index on the web
to the right of reply.

--- In CAD_CAM_EDM_DRO@y..., "Les Watts" <leswatts@r...> wrote:
> You can measure very low resistances using the four wire
> kelvin method and one meter.
>
> Two wires are hooked to a good approximation of a current source.
The
> constant current will be forced through the unknown device even with
> variations in the resistance of connections and wires to the source.
>
> A separate two wires are hooked to the unknown device
> to a high impedance voltmeter. Almost no current flows due
> to that high impedance so again it will measure accurately
> despite contact and wire resistance to it.
>
> So you force a current and measure a voltage. Resistance
> is simply V/I.
>
> One might ask "what is a good current source" ? Well a good
> lab supply can do that but so can a norton equivalent... a battery
and a
> resistor.
>
> You can easily measure sub milliohms with such a setup.
> I used this in production with a/d cards in a computer for
> a polymer thick film car side mirror heater I developed.
> I measured the resistance of silver conductive ink.
>
> Tell me what you want to measure and if you have a meter
> and I can be more specific about how to make the current source
> approximation.
>
> All you need is junk parts really.
>
> Les
> Leslie Watts
> L M Watts Furniture
> Tiger, Georgia USA
> http://www.rabun.net/~leswatts/wattsfurniturewp.html
> ----- Original Message -----
> From: "Hugh Currin" <currinh@O...>
> To: <CAD_CAM_EDM_DRO@y...>
> Sent: Friday, February 15, 2002 6:01 PM
> Subject: [CAD_CAM_EDM_DRO] Re: Driving unmarked steppers
>
>
> > Paul, et al:
> >
> > I know little of this so maybe Mariss or others with some
electrical
> > background can straighten me out. But not to keep my foot out of
my
> mouth, I
> > think you can get better information on low resistances by using
two
> meters,
> > one mearsuring voltage and another measuring current. With these
two data
> > points ohms law will give the resistance. It is my undertanding
that ohm
> > meters are not too good at low resistances, at least
quantitatively.
> >
> > FWIW. :-)
> >
> > Hugh Currin
> > Klamath Falls, OR
> >
> > On Friday 15 February 2002 02:04 pm, you wrote:
> > >
> > > This is a really useful bit of info -And yes, I do have some
other
> unknown
> > > motors of the newer square design. 4 wire size 23, about 75mm
(3") long.
> > > Comparing the numbers with some data sheets, the wattages tally
pretty
> > > closely. All I need to do now is to find a good milliohm
meter.....
> > > A visit to the local store and ask for a demo on real world
components
> is
> > > in order.....
> > >