Hot Steppers!

[xitian]

My steppers seem to be getting very hot. They get hot enough where I cant keep my hand on them. Here are the specs i'm using:

Power Supply: 63V @ 15 Amps

Stepper(s): 3.1V @ 5 Amps X 3

Drives: Gecko 203V X 3

I'm using a 120K current resistor as suggested. Should I incease the resistor size and if so how much??

[MarkWink]

...when are they getting hot?

-static no motion?
-rapids?
-cutting?

-how is your motor mounted (the mount helps as a heat sink)

...steppers do run hot, do you have any way to measure the temp to see if your in spec?

[dertsap]

ive found that my 3 volt motor ran far hotter at 48 v than 24v that i am running it at now ,at 48v they got very hot after a period of time , your running your motors to near the max voltage they can handle , i think its a matter of more power more heat , i may be corrected but this has been my experience
what i did to help keep the motors cool was to mount pc fans on the motors ,the fans did the job

[xitian]

They are mostly generating heat during rapids and when cutting it seems. I don't have any tools to measure the temperature but I would say they are approaching their limits.

Can anyone chime in and and let me know if changing the current resistors will help? I'm hoping to not have to go and buy a new power supply.

Fans are a good idea but I dont think they will work well with flood. It would be cool if I could find a heat sink to fit around them..I thought about making some but I think I would need a rotary table to add fins which I dont have....yet...

[MarkWink]

The resistor and voltage are in spec.

- a rule of thumb for voltage - keep the power supply under 25X of the motors rated voltage

- in your case 3V x 25 = 75V the 63V should be fine

- and the motor would be warm or hot if the resistance was wrong when the motor is on but not moving

I run a very similar step up on my router - I can get the motors pretty warm when running at higher ipm (around 200 and higher) and sometimes with a dull bit.

The heat appears to be related to load (or what they call iron losses)

[ger21]

Originally Posted by MarkWink - in your case 3V x 25 = 75V the 63V should be fine

If you lower the voltage, they will most likely run cooler. 25x is the max you should run, but ideally, you'd want to run the lowest voltage possible to get the performance you need. Unfortunately, without trial and error (changing power supplies), it can be hard to know just how much voltage you need.

If you lower the current, you'll also lower the torque, and may not reduce the heat at all. If you can touch them for a few seconds, they're probably not too hot. Most are rated at close to 100°C.

[Glacern]

Steppers typically draw current even when they're not spinning. I run my steppers at 48v... enough power for my needs and I won't burn my hands.

[Mariss Freimanis]

Don't worry about a step motor's temperature unless it exceeds 85C (185F). Step motors are meant to run hot and they do at a 20:1 overdrive ratio. That is why they have Teflon wire insulation instead of vinyl. 185F is hotter than the hottest cup of coffee you'd ever want to drink.

You might want to look at the G203V's yellow indicator LED. If it doesn't light up during a rapid then it means your supply voltage is in excess of what your application requires. That's what it's there for.

Mariss

[sswitaj]

In stepper motors, there are two basic sources of heat. The first is the the straightforward power lost by driving current through the resistive conductors, basic I-squared-R losses, and , for the most part, it's pretty constant with drive voltage.

The second is somewhat trickier. It's the energy lost inside the motor to the constantly-changing magnetic fields in the windings.

With chopper mode drivers, the voltages in the windings are modulated on and off tens of thousand of times a second to produce an "average" motor current. Every time the windings are switched off, the magnetic field collapses a little, and the energy has to go somewhere. A lot of it goes into the structure of the motor as eddy currents. Each transition wastes a tiny bit of energy, but there are zillions of 'em, and it adds up.

This phenomenon rises exponentially with drive voltage, so a 60 volt supply will make a motor run a lot more than twice as hot as a 30 volt supply.

For the most part, as far as stepper drives and power supplies are concerned, current equals torque, voltage equals speed. The natural inclination of most of us is to try to maximize both, but that can generate a lot of waste heat in small motors with high-voltage drives, to the point where it can damage small motors.

If you can live with lower maximum speed, you can come down a lot with power supply voltage, and your motors will thank you (not to mention that you'll burn your hands a lot less)

If your motors are getting that hot, they're probably small (NEMA 23 size?) and have little inductance to begin with, so they're probably plenty fast already even with voltages far lower than 63 volts.

[Mariss Freimanis]

Iron losses (eddy current and hysteresis) increase with the square of the supply voltage, not exponentially with voltage.:-)

Generally a cold step motor is not earning its keep. A hot step motor is delivering what you paid the $$ for.

I mentioned the yellow LED in an earlier post. It is a good diagnostic of how your system is configured. If it doesn't light then either you aren't moving your motor fast enough or your power supply voltage is too high for the speed you need.

If it's the latter and your motor is a 6 or 8-wire motor, rewire it in full-winding or series respectively, set the drive to 1/2 the current it's at presently and your motor will be 4 times cooler.

High power output means running the motor fast enough to have the G203V yellow LED come on. If you don't, all you will have to show for it is a hot motor and little else.

Mariss