NEMA 17 when NEMA 23 was expected.. will it burn up?

I’m in process of constructing a rotary for my laser. I am trying to rule out whether I can use a NEMA 17 stepper motor I have in hand, when the laser cutter likely is sending power for an expected NEMA 23 stepper motor.

I think my 100w laser cutter from omtechlaser.com uses “NEMA 23” Stepper Motors.

The existing Y axis stepper motor is definitely a 2-phase motor. That’s known both by examining the aviation style plug (4 holes, not 3) and info from one of the seller’s websites.

According to some NEMA 23 specs on this site: NEMA 23 Stepper Motor Datasheet, Specs & Applications

“Each phase draws 2.8 A at 3.2 V”

Now, I have some NEMA 17 motors that are designed to draw 1.5 A.

However, according to the above website I used for specs earlier, the NEMA 17 specs shown are:

Rated Voltage: 12V DC.
Current: 1.2A at 4V.

My bottom line question is, would I burn up a NEMA 17 motor if I connected it to the laser machine’s wires that are routed to (apparently, normally) a NEMA 23?

My sense is I would overheat the motor, but the details of electricity and motors are way outside my wheelhouse.

The drivers control the current to the motors. If you can adjust the max current set point on the drivers, you can use smaller motors.

The voltage doesn’t matter at all, unless the voltages are very very different. The voltage is just going to matter to the driver, not the motors.

1 Like

According to this eBay listing, for an “OMTech Rotary Axis” that would be compatible:

…the NEMA 23 stepper motor is compatible with these drivers:
DM542 driver
DM556 driver
(2-phase)

I know the laser machine has a Ruida controller.

I am too new to know if the current to the steppers can be controlled from the controller / software or not. If the current had to be changed by turning a screw on a driver somewhere inside the machine, it’s too much trouble for me needing to just be able to quickly switch into rotary mode and back out again.

Both of those stepper driver modules have small dip switches where you can set the current that the module will supply to the motor, this needs to be set to the correct value for your stepper motor. A NEMA17 motor requires somewhere around 1.2 Amps and a NEMA23 will require something like 2.8 Amps. The DM542 is capable of delivering 4.2 Amps and the DM556 is capable of delivering 5.6 Amps - both are over rated for your application but they can be regulated to a lower value but neither have a desired output of 1.2 Amps for a NEMA17. Also there may well be mounting hole issues for a NEMA17 as the specs for the rotary table specify a NEMA23…I suggest it would be best to go buy a NEMA23 and plug/unplug the Yaxis/rotary table when switching between the two - it’s only a single 4 wire plug.

The laser cutter does not send the power to control the motors, it sends the signals to the stepper driver and the stepper driver controls the power.

1 Like

Thanks for the helpful info! There are no specs for the rotary axis as I’m building it. But I can see I need to get the right stepper for it, that matches the laser cutter’s Y axis stepper. I would like to get a good confirmation that the stepper is a NEMA 23. That’s my best info so far.

Pretty well any 4 wire 2 phase NEMA23 motor will do. They come in a variety of lengths and powers, the shortest being the least powerful (and hence the cheapest) but for your application even the smallest nema23 will have oodles of power. Pick one that requires the same current that your chosen stepper driver has an output setting for.

It doesn’t need to match the Y axis stepper motor as when you are using the rotary table the y axis will be disconnected.

The controller board does not care what driver or motor is connected, it just outputs the signal to the driver. The only thing you might have to watch for will be your steps per mm between your Y axis when in linear mode and the rotary table as they may be different, this should be catered for in the software you will be using and will probably need editing each time you change modes.

1 Like

Thanks for the additional helpful info!!! Much appreciated. When I said “match the Y axis stepper” I simply meant matching from a standpoint of voltage and amperage, so the driver’s switches do not have to be changed each time I go from Y axis to rotary axis.

1 Like

I wound up ordering this one:

You may not get away with not changing the switches. You will need to evaluate the stepper you purchased against the steppers in the machine. You may be able to get away with a lower current to this stepper, but not a higher current.

1 Like

Thanks.

I’m comparing to the laser manufacturer’s rotary as well, to see what thickness of stepper motor they have on what they sell for use on this machine. Just a visual comparison of theirs and the one I ordered, seems favorable. Here are screen shots.

Theirs:

One I ordered:

Nema 23’s at 2.8A are common, and since they look visually similar, then 9 out of 10 you are okay. I just suggest when you get your machine to get the model number off of one of the steppers for the Y axis and lookup the datasheet. If it turns out that the steppers are 4.0A for example, you will overheat your new stepper unless you adjust the driver.

1 Like

Yep, thanks. That sounds about like what I was figuring.

OK, I am back with more info and a quick question.

I found out the following from the manufacturer, which is OMTech Laser.

The laser machine uses “NEMA 57” steppers (I’m assuming they meant 57 mm, which corresponds to approximately 2.3 inches, i.e. NEMA 23), and they are being fed 4.2A from the drivers.

So, my question is, if I find a NEMA 23 that’s rated for 4.2A, instead of a “NEMA 57” rated for 4.2A, I’ll be OK, right? Again this is for a rotary axis accessory.

Yes. That should work fine.

2 Likes

Awesome, thanks.

1 Like

Hey two other quick questions, and here’s an update on my efforts:

After some research I found several helpful bits of info, and also started delving into the “confusion” between Peak Current and RMS Current. In the attached image, the left photo is from my own laser machine’s driver. The right photo came from the vendor, in answer to questions about amp ratings.

One important tidbit is: there seems to a dip switch (#4) that cuts the amps in half.

Could I simply use that switch to make the driver “play nice” with my rotary axis stepper motor that cannot accept amps over 2.8A?

Also, are amp ratings on stepper motor listings shown in RMS? Or Peak? Or does it mean that “neither peak nor RMS should exceed this amount”?