Old Epson Printer Motor Questions

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

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

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James Sweet


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

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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.


Reply to
Chris Jones

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