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From: hr(bob) hofmann on 8 Aug 2007 02:26
I just scrapped the two motors out of an old Epson printer. Markings
on one are EM-289, 940906B, the second is marked EM-293, 940903B Each
motor has 4 wires going to the motor. From the feel of the rotors,
these may be stepping motors. Does anyone know the approximate
voltage used to drive these motors?
I can play around with them, but would feel better knowing about what
they should be driven with.

H. R. (Bob) Hofmann

From: James Sweet on 8 Aug 2007 03:21

"hr(bob) hofmann(a)att.net" <hrhofmann(a)att.net> wrote in message
news:1186554398.231835.186070(a)j4g2000prf.googlegroups.com...
>I just scrapped the two motors out of an old Epson printer. Markings
> on one are EM-289, 940906B, the second is marked EM-293, 940903B Each
> motor has 4 wires going to the motor. From the feel of the rotors,
> these may be stepping motors. Does anyone know the approximate
> voltage used to drive these motors?
> I can play around with them, but would feel better knowing about what
> they should be driven with.
>
> H. R. (Bob) Hofmann
>

They sound like bipolar stepper motors. What is the impedance of the
windings? Most of these are 12V.


From: hr(bob) hofmann on 8 Aug 2007 14:03
On Aug 8, 2:21 am, "James Sweet" <jamessw...(a)hotmail.com> wrote:
> "hr(bob) hofm...(a)att.net" <hrhofm...(a)att.net> wrote in message
>
> news:1186554398.231835.186070(a)j4g2000prf.googlegroups.com...
>
> >I just scrapped the two motors out of an old Epson printer. Markings
> > on one are EM-289, 940906B, the second is marked EM-293, 940903B Each
> > motor has 4 wires going to the motor. From the feel of the rotors,
> > these may be stepping motors. Does anyone know the approximate
> > voltage used to drive these motors?
> > I can play around with them, but would feel better knowing about what
> > they should be driven with.
>
> > H. R. (Bob) Hofmann
>
> They sound like bipolar stepper motors. What is the impedance of the
> windings? Most of these are 12V.

Jim:

Thanx for the info, I'm on a vacation and don't have any of my stuff
with me, so it will have to wait till I get back home. I didn't have
any way to measure the power supply voltages before I scrapped the
motors, but they look pretty substantial and I will play around with
them when I get home. Based on the construction of the printer, I can
see why Epsons cost more than Lexmarks.

BOb Hofmann

From: Chris Jones on 8 Aug 2007 19:13
hr(bob) hofmann(a)att.net wrote:

> On Aug 8, 2:21 am, "James Sweet" <jamessw...(a)hotmail.com> wrote:
>> "hr(bob) hofm...(a)att.net" <hrhofm...(a)att.net> wrote in message
>>
>> news:1186554398.231835.186070(a)j4g2000prf.googlegroups.com...
>>
>> >I just scrapped the two motors out of an old Epson printer. Markings
>> > on one are EM-289, 940906B, the second is marked EM-293, 940903B Each
>> > motor has 4 wires going to the motor. From the feel of the rotors,
>> > these may be stepping motors. Does anyone know the approximate
>> > voltage used to drive these motors?
>> > I can play around with them, but would feel better knowing about what
>> > they should be driven with.
>>
>> > H. R. (Bob) Hofmann
>>
>> They sound like bipolar stepper motors. What is the impedance of the
>> windings? Most of these are 12V.
>
> Jim:
>
> Thanx for the info, I'm on a vacation and don't have any of my stuff
> with me, so it will have to wait till I get back home. I didn't have
> any way to measure the power supply voltages before I scrapped the
> motors, but they look pretty substantial and I will play around with
> them when I get home. Based on the construction of the printer, I can
> see why Epsons cost more than Lexmarks.
>
> BOb Hofmann

It's better to think of the limitation being on the current in the winding,
because the current determines how hot the motor will get and how much
torque you will get. The current and voltage are not in a fixed
relationship because of the inductance of the winding which causes a time -
varying relationship. Higher performance stepper motor driver circuits
normally work like some sort of current source.

Too little current and the motor will lose step with relatively little
torque, too much current and the motor will get hot. The amount of heat
will depend on the current squared multiplied by the resistance (I^2 * R)
of the winding. You can measure the resistance with an ordinary
multimeter.

To try out the motor you could try connecting the motor to a power supply,
and increasing the voltage gently until you can't turn the shaft easily but
there is a reasonable amount of torque required, then you could leave the
motor on, checking the temperature every minute to begin with, then every
few minutes, for an hour or so. If you're happy that the motor is not
getting too hot then the current should be safe. Remember that sometimes
two windings can be switched on which increases the heating effect, so that
would be a good condition to test.

High resolution (1.8 degree or 0.9 degree) motors intended to do high
numbers of steps per second tend to have low resistance windings, maybe
only an ohm. Low-resolution (7.5 degree) motors tend to have higher
winding resistance and so need higher voltage and lower current.

Chris


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