Setting peak or RMS?

Hello guys,

I have a M542 single stepper motor driver board, and I wonder how to set the motor current. On the driver it has 2 columns, one specifies peak current and the other RMS.

The driver came with 3200 pulse/rev - so I guess this is OK.

Got Inventables NEMA17 motors which are specified to have 1.68 A current/phase. (Doesn’t say if it is peak or RMS)

I have read in other forums that since the board is microstepping, then it would be better to set the current as RMS. ???

Now my options on the board are:

Peak 1.5A = 1.1A RMS
Peak 1.9A = 1.4 A RMS

What would be the best option to set on the dip switch without damaging the motors?

Many thanks


Either would probably be fine. You will experience peak only at stall, and even then your motor should handle it. Steppers are hard to kill. They will heat up, but don’t be frightened unless you cannot leave your finger on the motor without being burned. Motors will withstand heat build up that we cannot withstand by touching it. Worst case scenario, you have to order another $10 nema 17 on Amazon. (but seriously consider Nema 23 motors and more amperage… you will eventually) Actually - looking it up - you would want to set it for: OFF ON ON (sw 1, 2, 3). Peak current would be at 2 amps in this case, but average current would be 1.4 amps. You will be fine here IMHO.

Personally, I would work with the Peak numbers and not exceed the manufacturer’s recommended maximum.

The enemy is heat. If too much heat builds up in the motor windings then you start to have failures in either the insulation on the wires, or melting of the wires themselves. Either one is bad.

So, the part about heat again… if your fingers are uncomfortably hot at those settings reduce the amperage. Smoke is bad. Also, don’t hold a rod over your head in a lightning storm when in contact with you machine, because if you are struck by lightening, your machine is TOAST.

Not always. I have some steppers that run at 80 degrees C. Perfectly within spec and been running for years. I certainly would not hold my fingers on them.

Thanks guys,

@Earwigger - The dip switch setting of OFF-ON-ON (SW1-SW2-SW3) corresponds with 1.5 Amps peak. . . This is exactly what @LarryM recommends :smiley:

Anyway - I will set for 1.5 Peak for now just to be on the safe side and if performance will not suffice I will probably try the next one up.

I am building a small laser machine (Bart’s 2.0) so I guess NEMA17 will do the job.