Pololus overheating with heatsink and fan?

peqo

Pololus overheating with heatsink and fan?
April 19, 2012 12:56PM

Registered: 12 years ago
Posts: 22

I'm building a Prusa and I get this problem on all my axis when I have them move. They stutter when they move. I tried adjusting the trimpot which helped partially. Now it can move once or twice without stuttering and then it starts stuttering. If I keep moving it after that it stutters more. Then, If I turn it off and back on again, the process repeats. The reason for this that I can think of is that the Pololus are overheating and turning off and back on, even though I have heatsinks and a fan on them.

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brnrd

Re: Pololus overheating with heatsink and fan?
April 19, 2012 07:00PM

Registered: 13 years ago
Posts: 1,780

Did you measure Vref on the Pololu carriers? You want to adjust it to 0.4 V. If not, turn down your trim pot to around the 10 O'clock position. If your axes are binding at that setting, then you either have too much mechanical resistance or you have the wrong motors.

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peqo

Re: Pololus overheating with heatsink and fan?
April 19, 2012 07:10PM

Registered: 12 years ago
Posts: 22

yeah i tried 0.4V. It doesn't bind at that voltage, just stutters. Turning it up a bit more somewhat improves the stuttering. My axis are well oiled and slide well. These are the motors I have: [www.ebay.com]

edit: i posted a link to the wrong steppers! Mine are NOT 12v

Edited 1 time(s). Last edit at 04/20/2012 04:46PM by peqo.

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rhmorrison

Re: Pololus overheating with heatsink and fan?
April 20, 2012 02:50AM

Registered: 14 years ago
Posts: 3,742

Those are 12V steppers - eye popping smiley

- what voltage are you driving them at?

For those of us using 12v we use steppers that are for 4 or 5 volts.
Plus the holding torque is a little bit low though it might be sufficient for X, Y and Z.

Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

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Leeway

Re: Pololus overheating with heatsink and fan?
April 20, 2012 06:36AM

Registered: 12 years ago
Posts: 18

It's not uncommon on CNC machines to go 20 times the rated voltage of the stepper motor. You don't want to provide more than the rated amps, but for voltage this is typical.

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Traumflug

Re: Pololus overheating with heatsink and fan?
April 20, 2012 07:13AM

Registered: 13 years ago
Posts: 7,616

True about the low voltage steppers, still a 12V-stepper should run with 12V. Just with less tourque at higher speeds.

Regarding "stuttering" - is this at a frequency like once a second? Then it's indeed likely an overheating Pololu. To start finding the issue I'd start with running the motors without mechanical load. This would require only a very low current and thus producing almost no heat.

Generation 7 Electronics	Teacup Firmware	RepRap DIY

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VDX

Re: Pololus overheating with heatsink and fan?
April 20, 2012 07:19AM

Admin
Registered: 16 years ago
Posts: 13,889

... yes, my CNC-repstrap has drivers cpable of 70 Volts and 6 Amps, but the used motors are rated with something like 3 Volts and 2 Amps ... but i have other driver+motor(NEMA23)-combinations with 325Volts@1.75Amps too!

You have to optimize your parameters by adjusting the motor-current ... the voltage adjusts automatically according to Ohms law: U=I*R (with R=coil-resistance)

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

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nophead

Re: Pololus overheating with heatsink and fan?
April 20, 2012 07:35AM

Admin
Registered: 17 years ago
Posts: 7,879

The resistance is too high to be able to overheat the Pololus.

12V motors do not work well with a chopper driver and a 12V supply as the switching frequency tends to 0. To get correct microstepping you have to set the current a little less than 0.4A so you can't get the full torque.

[www.hydraraptor.blogspot.com]

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peqo

Re: Pololus overheating with heatsink and fan?
April 20, 2012 04:47PM

Registered: 12 years ago
Posts: 22

Sorry guys! I posted the wrong link to the steppers I have. Mine are 3.4v , not 12. Here is the right one: [www.ebay.com]

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peqo

Re: Pololus overheating with heatsink and fan?
April 24, 2012 09:42PM

Registered: 12 years ago
Posts: 22

I still have not found a solution.

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nophead

Re: Pololus overheating with heatsink and fan?
April 25, 2012 03:44AM

Admin
Registered: 17 years ago
Posts: 7,879

If the pololus are overheating reduce the current. They won't overheat when the current is below 1A even without a heatsink or fan. With a heatsink and fan you will be able to get about 1.5A. You must have the current set even higher than that if they overheat.

As brnrd said, try setting vref to 0.4V to get 1A and see if you have enough torque.

[www.hydraraptor.blogspot.com]

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Traumflug

Re: Pololus overheating with heatsink and fan?
April 25, 2012 05:31AM

Registered: 13 years ago
Posts: 7,616

Quote

I still have not found a solution.

You have to describe what you tried, how this failed and try to answer the questions raised here smiling smiley

We have no crystal ball to watch your lab and there is very likely no click-here-and-everything-is-solved solution smiling smiley

Generation 7 Electronics	Teacup Firmware	RepRap DIY

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