Re: [CAD_CAM_EDM_DRO] Volt and amp ratings for surplus steppers

On Tuesday 30 May 2006 01:42 am, rexarino wrote:

> Newbie questions, and apologies for asking basic stuff. I did a
> search of old messages, but apparently didn't use the right search terms.
>
> I have a number of steppers from printers and other sources.

Yeah, me too, a whole box of 'em. That's what got me started on getting
interested in this stuff to begin with. :-)

> Some are obviously too small for CNC use, but others might work. However,
> I'm confused by the stated volt and amp ratings painted on them. Size
> doesn't seem to relate directly to their volt-amp ratings.
> Do large, weak steppers exist, possibly from older designs?

Yes.

> Does the volt and amp rating state a maximum for each winding, or the
> total unit, or a stall current, or...?

Good question.

> Can a 3 volt stepper be operated at higher voltages (and consequently
> higher current) as it seems from the posts I've read?

A higher current won't happen right off when you apply a higher voltage,
that's the nature of inductance, that there's a lag time involved. In fact
that lag happens when you apply any voltage, and the whole point of using a
higher voltage is to get the current up to the level you want quicker. And
then you cut the voltage off. That's what chopper drives are all about.
Otherwise if you just applied a higher voltage and then let the current
continue to rise you'd burn the motor out.

> How does one identify the capabilities of a surplus stepper?

Good question. At least some of what you have appears to be marked, from
what you're saying.

One page that I remembered that might be helpful was done by Roman Black, who
described a way of measuring stepper motor torque in a fairly simple DIY
setup. I don't have a URL handy or I'd post it, but perhaps that will give
you enough info to find it or perhaps somebody else has the URL handy for it.

Electrically, if you have marked specs great, otherwise maybe a part number
works, but I suspect that a lot of what's out there is special made for a
given mfr. and you may not find much. The physical size of the motor should
help some, and measurement of resistance, and the configuration of the
windings (how many wires, etc.).

I'd also be interested in seeing any other replies you get. :-)

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