# Stepper Motor Rating

Hi

I've got a PM2515-03 stepper motor and the ratings are 5V 0.5mA. I use the 5V output from the Arduino with a 10ohm resistor.

If I use those ratings, and I attach a small wheel to it, any tiny amount of force to the wheel makes it stop and vibrate. So like if I hold the motor by its attaching wires and let the wheel roll on my table, it just gets stuck.

But if I use a 1ohm resistor instead, I essentially am putting 5A through it, according to ohm's law. And if I do this it runs perfectly and it doesn't get stuck. Granted it does get slightly warm.

I'm just a bit confused as to the ratings, as it seems what is suggested can hardly hold any force.

That 0.5 mA must be a typo, it's 0.5A per phase in the motor data sheet. You need suitable driver devices, of course.

Oh.. woops. Sorry, I meant 0.5A

I use the 5V output from the Arduino with a 10ohm resistor

You can't drive anything more than 40mA directly using any digital/analog pins, excessive current draw will likely damage your chip.

you can search the forum for a suitable motor driver circuit.

You can't drive anything more than 40mA directly using any digital/analog pins, excessive current draw will likely damage your chip.

Maybe he means the output from the regulator?

Even so, this is really not something that should be done; it is likely that the motor could draw enough current to cause the Arduino to reset or possibly damage the regulator. The motor should be powered separately with its own power supply (just remember to tie its ground together with the Arduino's ground).

:)

But if I use a 1ohm resistor instead, I essentially am putting 5A through it, according to ohm's law.

I am not sure how you get that. If your rating is 0.5A @ 5V then if you put 5V across it you will draw 0.5A. Therefore according to Ohm's law the coil resistance is 10R. It doesn't mean you have to have a 10R resistor as well. If you do then you have a total resistance of 20R and therefore a current 0.25A only half the rated current. Mind you that is still a lot of current so I would be surprised if that gives you the small amount of torque you report.

What are you using as a driver?

That makes sense.

I'm not using the pins, I'm using the 5V output.

Atm i'm not using a driver. I have one, but I'm just using 4 transistors which is working. But I need to put some resistance on it otherwise the transistors burn out. That's why I mentioned the 1ohm resistor.

So, if I use a driver, and put 5V through it directly with no resistance, then it should all be fine? The driver chip won't burn out or anything?

I’m not using the pins, I’m using the 5V output.

Confusion of terms here, you are using pins to control the transistors. Have you got base resistors in the transistors?
How have you wired it up?

But I need to put some resistance on it otherwise the transistors burn out.

Sounds like you have some shoot through rather than a problem of current limit. What transistors are you using?

So, if I use a driver, and put 5V through it directly with no resistance, then it should all be fine?

Providing your driver can take the 500mA current you need.

Yeah I have 220ohm on each pin to base. Not sure if this is correct though. I couldn't find what current I need to turn them fully on. So I just used a 220ohm which gives me 22mA.

Wiring is as follows...

Pins 2-5 go to each transistor, which in turn go to to each wire of the stepper. I put the 5V to the two input wires of the motor. It was here that I put the 1ohm resistor, but now that you mention it.. when I did it previously I did do it wrong, so I think I did have a shoot through.

So it is a unipolar stepping motor not a bi-polar one?

so I think I did have a shoot through.

Only if you were trying to implement a H-bridge with your transistors.

A 2n2222 is only rated at 600mA, that's too close to your required 500mA so you need a bigger one.

I put the 5V to the two input wires of the motor.

Not sure I understand this? What sort of motor have you got and a schematic of how you wired it up would help.

It's a unipolar with 6 wires.

http://www.mantech.co.za/Datasheets/Products/PM25XX-FULL.pdf

I'm planning to use the following driver, L293D.

I'll post a schematic a bit later.

Just tried without the resistor on the the voltage wires and it works hundreds. Thanks for the help.

and it works hundreds

I assume that is good. ;)

Thanks for the help.

You're welcome