[stargeezer]

Hi guys. Today I smoked two steppers on my x axis with very little run time. As soon as I felt the first stepper warming up I started checking for a problem and found nothing amiss. The leadscrew was free, the bearings in the gantry uprights were free turning and the ballnut was not tight. I am just getting this CNC operational and have been playing with the microsteps, but I don't feel this was a cause of the problem because there has been no real run time on the machine.

The first two steppers were recycled nema 23 steppers running 2.4 amps. On the last stepper I was watching the heatrise very closely and cut the current settings down on my driver board as far as I could and it still got hot enough to burn out while I was eating dinner, with the machine at idle. I had turned the power to the machine control panel when I left the garage and it was smoking as I returned 15 minutes later. Following the demise of the last stepper I replaced it with a totally new nema 23 425 ozin stepper motor that had never even been powered up and 5 minutes after the power was turned back on, it was heating to a serious temp. That's when I killed the power and got on the forum.

I do have the driver switch turned on thats supposed to disable the stepper when it's at idle - but either the x axis was NOT fully at idle, or perhaps my driver board is not doing what it is set to do.

I'll respect any and all suggestions folks, I can't afford this problem.

[ger21]

What voltage are you running at, and what are the motor specs?

The leadscrew was free, the bearings in the gantry uprights were free turning and the ballnut was not tight.

Binding in the drive system will not cause any damage or excess heat in your motors.

[dram]

Please do not pay any attention to this post. BUT.........

Somewhere I read that a servo/stepper can and will draw heaps of current whilst not working and vice versa, will draw even lots less when at full torque.

I believe that you can limit this max current, but not sure how.
I am an old electrician who was brought up on Ward Leonard Control systems, and did my apprenticeship on The Ark. ( wasn't a good cruise, bloody rained all the time)

As, I warned, be careful how you treat this post.
Cheers,
Mark Needham
PS.I posted this and then I just googled "Stepper at stop current" and came up with this.
http://www.phidgets.com/docs/Stepper...troller_Primer
...the first bullet point confirms my "supposition", but MAY not be the cause of your problem.

reading further,"" using a bipolar controller to run a unipolar motor, even though it is theoretically possible."" in the "Types of Stepper Motors"
....also you indicate that a motor "Became Hot" doing bugger all. So it has to be a problem of driving, and not the load.

[jfong]

First of all what type of stepper driver, make/model, would help in diagnosing the problem. Power supply voltage etc. More info please.

[stargeezer]

I'm running a 36v power supply, the stepper driver is a Wantai Dq542ma, the steppers that failed were Minebea Motor 23km-k036-p13v.

As for the voltage that's supplied to the stepper from the driver, I'll have to check that by measuring it since I don't see a voltage output on the driver board.

[stargeezer]

Dram - I've heard it said that there are no dumb questions - but I always point out that there are truly a lot of inquisitive idiots.

After the day I've had I can appreciate any effort to give me a smile and a ray of sunshine. Thank you sir.

Larry

[ger21]

Do you have any specs on those motors? And how do you have them wired?

I'm guessing that the motors current rating is much lower than 2.4 amps?
Are you sure that the current is set correctly?

What are the motors mounted to? They should be mounted to solid aluminum, which will draw some of the heat out of them.

In 10 years here, I don't recall seeing anyone burning up a stepper motor.

[jalessi]

Gerry,

Based upon the specifications in the attached pdf I am guessing the stepper current is 1.5 amps.

Jeff...

[stargeezer]

Thanks guys. The stepper is mounted on an aluminum mount. It's wired as bipolar (center tap unused). The current was set to 1.5 amps on the driver when the stepper smoked and locked up. I had found the specs on this specific motor and they listed it at 2.4 amps. The odd thing is that I'm running two more of these same steppers on the y axis with no over heating issue at all. The drivers are setup exactly the same.

The 425ozin motor I just switched to, that is also overheating is certainly a 3 amp motor, is also over-heating just like the . I'm going to try switching to another driver after lunch and see if it reacts the same. If so that would seem to indicate a software (Mach 3) setting issue.

[ger21]

There are no Mach3 settings that will have any effect on motor heating.

Sounds like you might have a bad drive?

[stargeezer]

That seems to have been the problem Gerry. Switching to the unused A drive I'd mounted - just in case - seems to have corrected the overheating issues. I've got it in idle mode and I'll monitor it for a few hours before pronounceing it "cured".

[stargeezer]

I decided to look at the waveform of the voltage out of the driver with my ancient O Scope. For a DC line it has the most trash filled signal I have ever seen. Looks like a AM transmitter signal with about 50-75% modulation. At idle the "trash" looked like 120% modulation on the modulator tube thats gone very, very leaky.

I guess I had better order a backup driver board. I might never need it, but on the day I don't have a backup, I'll lose two.

[James Newton]

I decided to look at the waveform of the voltage out of the driver with my ancient O Scope. For a DC line it has the most trash filled signal I have ever seen. Looks like a AM transmitter signal with about 50-75% modulation. At idle the "trash" looked like 120% modulation on the modulator tube thats gone very, very leaky.

I guess I had better order a backup driver board. I might never need it, but on the day I don't have a backup, I'll lose two.

Well... pretty standard... crap design chopper driver.

And... you are rewarding the mfgr by purchasing /another/ of their products?

You obviously have electronics experience, you can solder, right? Buy one of my THB6064AH kits, build it and give it a spin. Publish your results here within 30 days and I'll refund your purchase price.