Z-axis stepper motor is too hot

[gixi]

I manage somehow to catch my ears in calculations regarding resistors, power, etc. for the Z axis :mad:.
The motor I’m using for the moment is getting to hot and I don’t know what is wrong.
In order to get more power from this motor I chose to wire him Bipolar Parallel, and this way the screw mechanism cannot be stopped with bare hands. So its strong enough…
But the temperature of the motor is way to high.
Producer spec for Bipolar Parallel are:
Rated voltage – 2.73 V
Current/Phase – 4.2 A
Resistance/Phase – 0.65
Inductance/Phase – 3.2 mH
Holding Torque – 3Nm
The value for most of this specs are double compared with OM-Unipolar.
So what I should do in order to keep it low the temperature ??? :confused:. With Unipolar it’s not strong enough…

[Gerald D]

You must reduce either the power supply voltage, or reduce the set drive current. Both of these methods will reduce the ouput "power" (torque) of the motor.

What type of drive (eg. gecko) are you using, and what is your power supply voltage?

[Gerald D]

Found this post in another thread:

Hello everybody ! Another small step with Z. I chose to wire the motor Bipolar parallel and is moving quite good. After 4 minutes on jog the motor is slightly warm and the Ghecko is cold. There are something to fix: the resistor is for the moment 60 k.
I'm curios to see is the motor is strong enough to handle everything... For the moment if I try to stop the ballscrew with my hand is not possible. The Romanian supplier buy these motor from http://www.motioncontrolproducts.co.uk/product_info.php?products_id=6.
All Is good for the moment (I hope...) but I don't know much about setting the motor with Mach3 (steps, velocity, acceleration, etc.).
Any suggestions ?
Thanks,
Marius

[Gerald D]

The Gecko resistor must be 70 kiloOhm, or less. Please measure it to check. Many people have made a mistake by believing the salespeople or trying to read the colours.

The power supply voltage must be 57 Volt, or less. Measured on the big capacitor.

[Gerald D]

. . . . But the temperature of the motor is way to high. . . . .

How long can you hold your hand on it? If it is more than 5 seconds, then the motor is not way too hot.

[gixi]

Gerald the motor is not that hot but enough to become woried.
The drivers are Gecko and the specs for transformer are
P=500VA U1=230V
U21=29V I21=16.9A
U22=9V I22=1A
At this momemt I'm using 58K resistor (just for testing because I don't have other resistors near me).

[Gerald D]

It looks like your settings are safe and you are not smelling smoke.

Was your motor getting hot just from switching it on, motor static/idle . . . . or were you running your axis back and forward many times? Your axis could have a lot of friction that is placing a high load on the motor?

[gixi]

So as far I understand using formulas from Gecko instructions I get this values:
Power supply: 32*SQRT4.2=32*2.04=65.28
Next in order to get the proper value for resistor is the next formula:
65,28*4.2/(7-4.2)=97.92
So the resistor should have 97.92K ?:confused:

[Gerald D]

5437

[gixi]

:o :o :o . I'll do the math again...

[Gerald D]

Power supply: 32*SQRT3.2=32*1.788=57 V

Next in order to get the proper value for resistor is the next formula:
47*4.2/(7-4.2)=70.5 kOhm

[gixi]

The resistor should be around 85.5K :D
I'll try this tomorow.

[gixi]

Oh my Good !!! I promise I'll be more careffuly next time. My only excuse is last night I came from my shop at 2 A.M. ....

[Gerald D]

The 47 is a fixed number from the gecko instruction manual. You do NOT use the calculated voltage in that formula for the resistor.

[gixi]

Yes this is what I don't understand from the first begining. But I'm learning as I learned to wire unipolar, bipolar wich is a small victory for me.:)

[Gerald D]

U21=29V
At this momemt I'm using 58K resistor

Therefore your DC voltage is about 40V and your current limit is 3.9A which theoretically is giving you a cool motor.

Have you checked the resistor and voltage with a meter?

[gixi]

I'll do that tomorow. But is very strange because 2 weeks ago using the jog from Mach3 I turn the motor for 4 minutes with no stops and it was a little warm.

[Gerald D]

Your resistor might have become loose and fallen out . . .

[Gerald D]

Any news on this heating mystery Marius?

[gixi]

Sorryyy for forgetting to give a feedback. So...
After several test this is the results:
70k resistor - after 12 min. you can't keep the hands on motor. Even if the motor just stay under power of course.
36k resistor - motor cold but no power.:eek: - no way !
68k resistor - after 20 min. you can't keep the hands on motor case.
55k resistor - after 40 min. the motor is warm but I can keep the hands on it.
But what it maters for my experiments is torque. And the motor is still giving enough torque. I can't hold the Z axis with my hands and yesterday just for testing I hang on Z axis the spindle and it moves without problems.
So for the moment the 55k resistor is the winner.
At my first test I didn't wait enough...:o just 4-5 min.
That's for the moment and after I will finish to mount the spindle I'll give a job to do just to verify the temp.
The major problem is that I don't have this exact values for resistor. To get 55k I mix in serial other resistors.
I'll go shopping for other values of resistors in order to obtain other values.