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Does the PWM frequency affect the heat of the motor chips?

pwm-frequency

#1

The headline has the question.
Going from low, the comforting ‘Maslow is moving’ sound I know, to middle (motors whistling) to high ( almost silent, very nice!) I am wondering how this effects the chips. My fingertip tests seem to say there is an increase of temperature on the cooling ribs, but I don’t trust them. Enlightenment appreciated.


#2

I think this is a great question. My instinct is that it shouldn’t matter, at least when changing from the 490hz option to the 4100hz option, the 31,000hz option is so far up there that I have no idea. I saw some strange behavior at 31000hz where my sled would drift so I would avoid that one for now except when testing


#3

It could, I would suspect the input capacitance on the MOSFETs of the drivers. The internal MOSFET driver may not as sharp and the MOSFETs may dwell in the land of linearity for bit longer leading to more heat and stress on the MOSFET.


#4

This is true. MOSFET heat dissipation is comprised of two core elements: resistive dissipation and switching dissipation. Switching a MOSFET on or off causes a certain amount of power loss (and consequential heat production) as the MOSFET state transitions on or off. Increasing the PWM frequency will increase this component of the heat dissipation of the MOSFET. This component is typically smaller than the resistive heat dissipation, but it depends on the frequency that the MOSFET is switched at along with the current passing through.

As long as the general PWM duty cycle remains the same, the resistive component will not change.


#5

this man is on the money


#6

Has anyone successfully used 31,000hz for an extended period of time? While working on the optical calibration routine I’ve started to get really annoyed by the motor whine. The ‘silent’ 31kHz is so much nicer on the ears :slight_smile:


#7

I’m willing to test it. 14 to 16 hrs of it a day is wearing on me.

Thank you


#8

I have, though that was with a TLE5206 board. It would be an interesting test to do runs of a subset of your pattern at all three frequencies to see whether they have an effect on your measurements.


#9

Please do!

This is a great idea. I’d love to do this! I want to be confident that my board isn’t going to melt first from the increased switching. I’d be super bummed to burn up my board when it feels like we’re so close to getting this optical calibration stuff right.


#10

I’ve got a spare Maslow v1.2 board I can send you for the test, if you like. Give me an address in a PM…


#11

PM-ing now! Thanks for the offer!


#12

I’ve been running at 31kHz for a few days now and it’s been ok. I even did a cut last night and it came out well.

I’m still using the stock Maslow board and it hasn’t burned up yet :tada: there were a couple times I saw some uneven sled movement / studder that were concerning, but it only lasted for a couple seconds each time. Not sure if it’s related.

@Bee I’ll try your TLE board next


#13

Hi @johnboiles,
3 months later, is 31kHz all good?
:slight_smile:


#14

The stock Maslow 1.2 board has been working just fine on 31kHz. I’m glad to be rid of the PWM whine, especially as I’ve tested @madgrizzle’s WebControl code.

The TLE board couldn’t handle anything other than the default 490kHz unfortunately. I would get sled-not-keeping-up errors sporadically. I think the switching speed of its motor driver is too slow.