Stepper/Driver current and power supply

X-Carve Troubleshooting
1

Hey,
I am about to upgrade my X-Carve to Nema23 steppers. However, I am not sure if power supply fits and therefore measured the current the drivers draw from my power supply as well as the current supplied to the steppers. Well … now I am more confused than before.

The steppers I have:
Manufacturer Part Number 23HS22-2804S
Step Angle 1.8°
Step Accuracy 5%
Holding Torque 1.26Nm(178.5oz.in)
Rated Current/phase 2.8A
Phase Resistance 0.9ohms
Voltage 2.52V
Inductance 2.5mH±20%(1KHz)
Weight 700g

My drivers:
Leadshine DM442

My power supply:
Meanwell 200W 24V

I’ve configured the drivers to output 2.03A RMS current (2.84A peak) and set stepping to 1/8 microstepping.

My measurements:

1. From driver to stepper (measured on a single coil of the stepper)
Idle current: 2.48A (2.7A @ full-step config)
Voltage: 2.8V

This looks fine for me and seems to be within the configured range.

2. From power supply to driver
Max current (trying to stop the stepper with my fingers): 0.42A
Idle current: 0.4A
Drivers configured to reduce current on idle to 40%: 0.15A

Now this seems odd to me. At 24V my drivers just pull 10W from the power supply? However, the measurements I did at a single coil indicate 7 Watt on this coil and I assume the other 3 Watt are spend on the second coil and some loss at the driver.

I’ve done some research and the general estimate for Nema 23s I’ve got was in the range between 30 and 60 Watt. Did I mess up something with my setup as my steppers might get too little power? According to my measurements I should have no problems running 4 of those steppers on my power supply. Am I right? If I have wrong anywhere in this above, give me a hint please.

Best,
Dominik

2

Pololu is my favourite supplier of robotics and stepper boards, this product description has a lot of in depth information about stepper drivers and how to set the current.
Pololu stepper driver

3

Hey Erik, thanks a lot dir the link. I am sorry but it doesn’t really help me.

Maybe I should rephrase my question.

I have two assumptions about the power my drivers will pull from the power supply (assume two coils are fully powered at the same time, so real values should be somewhat lower):

  1. COIL_CURRENT x SUPPLY_VOLTAGE
    2.48A * 2 * 24V = 119W (59,5W per coil)
    This seems way to much Tonne reasonable for a motor of that size. However, i’ve seen similar calculations all over the place on the internet.

  2. COIL_CURRENT x COIL_VOLTAGE
    My steppers have a coil resistance of 0.9 Ohm.
    Therefore: 2.48A * 0.9Ohm = 2.2 V
    Therefore: 2.48A * 2 * 2.2V = 11W

The second calculation is way closer to my measurements, but I couldn’t find this written anywhere and 11W per stepper seems very very low to me.

Probably I am still wrong and miss something here :confused:

4

Re-read the article where it starts with: Please note that measuring the current draw at the power supply will generally not provide an accurate measure of the coil current.

5

Thanks for the hint! This basically matches my observations. However, it still leaves me a bit clueless if my 200W power supply will fit if I run 4 of those steppers. 119W to 11W is more than a factor of 10. That’s why I would like to know what the absolute maximum power consumption of a single driver could theoretically be (even apart from not having two coils fully powered at the same time and losses at the driver)

6

There’s an excellent article about stepper motor power requirements on the Geckodrive site.
It applies to stepper motors in general and is not Gecko specific.