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Author Topic: Measuring Amperage  (Read 1598 times)
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Hello, I'm using some motors that I pulled out of an old printer and I don't know how many volts or amps they need. How would I find this out? Is their any equipment I could buy that I could use to test the Motors with?


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Drew Davis
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Also, they have no markings or model numbers.
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You can measure the winding resistance with a multimeter, and from that calculate the maximum current they will take at a given voltage. You could try driving them at 5V, but they very likely need 12V, perhaps even more.
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Thanks!
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You can measure the winding resistance with a multimeter, and from that calculate the maximum current they will take at a given voltage. You could try driving them at 5V, but they very likely need 12V, perhaps even more.

Huh??? The winding resistance has absolutely no correlation to the voltage or current a motor requires!
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If you know the resistance of the winding and the size of motor (which correlates with power dissipation) you can make
an informed guess.  Many electric motors are limited by thermal considerations.
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This is the multimeter I have…  http://www.sears.com/craftsman-digital-multimeter-with-ac-voltage-detector/p-03482146000P?prdNo=1&blockNo=1&blockType=G1

What selection do I need to put it on to get the winding voltage, or if thats not the best way to find the amperage/voltage of the motors how would I find it out?

Also, what is winding voltage?

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Drew Davis
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What selection do I need to put it on to get the winding voltage
The motors must be powered to measure the "winding voltage."

way to find the amperage
Measuring Current requires you to "break the circuit" and measure current in-line with a power source.

Also, what is winding voltage?
The intended operational voltage of the windings inside the motor.
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If you know the resistance of the winding and the size of motor (which correlates with power dissipation) you can make
an informed guess.  Many electric motors are limited by thermal considerations.

The DC resistance of a permanent magnet motor will be very low. The resistance IN NO WAY correlates to it's operating parameters. Not even close enough to make an "informed guess".

Do you not know how motors work?

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My experience with printers is that printer motors are almost always steppers, so that the paper and the optics can be positioned within the required tolerances

Post a pic...
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My experience with printers is that printer motors are almost always steppers, so that the paper and the optics can be positioned within the required tolerances

Post a pic...
Are you living in the 90's?  I haven't seen a stepper in a printer since old dot matrix printers.  Certainly all the inkjets I have worked with over the past 5 years or so have been normal motors, not steppers.
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Well I joined Xerox in the 80s....

But I did just take our immediately past printer at home to pieces, and it had a bunch of steppers in it; it wasn't that old. That was iirc a Lexmark laser printer, copier, fax, scanner, liquidiser, blender etc.
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Well I joined Xerox in the 80s....

But I did just take our immediately past printer at home to pieces, and it had a bunch of steppers in it; it wasn't that old. That was iirc a Lexmark laser printer, copier, fax, scanner, liquidiser, blender etc.
Ah, it'll need the stepper for the blender.

Lasers do sometimes have steppers, yes, but there are 10000x more inkjets around, so chances are it's an inkjet
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I don't think it is a stepper motor, but I have never really seen one. It just has two wires and it comes from the part of the printer that goes back and forth applying ink to the paper. I can't figure out how to post a picture, but i'm pretty sure it is just a regular dc motor.

Thanks!!!
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I don't think it is a stepper motor, but I have never really seen one. It just has two wires and it comes from the part of the printer that goes back and forth applying ink to the paper. I can't figure out how to post a picture, but i'm pretty sure it is just a regular dc motor.

Thanks!!!
Yes, that will be normal DC, and either 12 or 24 volts - probably 12, but without markings it's pretty hard to tell.

A stepper motor has more than two wires.
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