Filtering DC motor buzz

[slawekgonet]

Hey,

I've got a setup where I'm driving a 105V DC, ~5A pancake DC motor with Parker 512C single-quadrant DC speed regulator. It works fine, but it produces loud buzzing noise (sounds like 50Hz humm): https://youtube.com/shorts/-WkeWhmkcXI?si=uItgNbi35lKAtRch

The speed regulator does not have any significant capacitors on it, so I've tried putting 2x470uF caps at the output and it improved the situation a lot - but I assume that's not the correct and probably not the safest way of silencing it.

Do you have any suggestions for kind of filter I should use?

[Berni]

Looking at the pictures of the Parker 512C it seams to have no capacitors.

So that drive is probably designed to run the motor with a 100Hz hum on it. You don't want to put capacitors across the motor. The correct way to solve the hum is to place the capacitor after the bridge rectifier in the control electronics, or feed it with a 3 phase rectifier that doesn't need smoothing capacitors.

[slawekgonet]

Thanks a lot for response!

This sounds like deeper ingerention into quite expensive unit - I don't think manufactures made any provisions to attach caps anywhere.

I attached block diagram and a picture just in case it helps in any way. I'm using it in AUX + MAINS autotransformer setup, so MAINS is 90VAC for the DC motor and AUX is 230V AC for the control logic.

That being said:
- what are the drawbacks/risks of running the motor with capacitors?
- are there any negative effects of humming motor, other than annoyed operator? :-)

[Berni]

Ah it looks like it is using SCRs as the switching elements. These need zero crossing in order to turn off, so the 100Hz hum must be there for it to work. To get smoother operation you would need a drive based on PWM DC control.

The motor is being controlled by rapidly turning it on and off, adding capacitance to that causes large spikes of current trough the switching elements. While SCRs can handle a lot of peak current, it is not really doing anything a favor in lifetime.

The hum shouldn't harm the motor, it is just slightly reducing the motors potential performance as compared to being run by smooth DC.

[slawekgonet]

Thank you! I've removed the caps, turns out I need to get used to the buzz.

[johansen]

Thank you! I've removed the caps, turns out I need to get used to the buzz.

you can filter the noise with an inductor in series with the motor.

i have a southbend 9 lathe on a relatively light weight bench, and drive it with a 90v dc 1hp ceramic magnet motor. very low inductance, the 60hz SCR control (same as yours effectively) turned the lathe into a 120hz tuning fork. you couldn't set a tool on it, it would move...

a 1KG inductor wound from a 180 watt sized transformer.. rewound with 12 gauge wire and gapped a little.. stopped 95% of the motor's vibration.

[slawekgonet]

Any chance you can capture a photo of that setup so I can get sense of scale?

[SeanB]

Look for a line reactor rated for the current of your motor, a 2 pole version rated for 5A would likely do.

https://acim.nidec.com/drives/kbelectronics/-/media/kbelectronics/documents/white-papers/applications-of-line-and-load-reactors-with-variable-frequency-drives.ashx?la=en

Should provide you with a start.

[johansen]

Any chance you can capture a photo of that setup so I can get sense of scale?

what i suggest you do is find anything in the range of a 24 to 48v 5 amp rated transformer and use a bandsaw or hacksaw to cut as thin as practical gap, a gap in both sides of the E core.

cap off the 120 or 240 primary and don't use it.

3 phase line/load reactors are overpriced, but will work for you.

[slawekgonet]

Choke did the trick. For the reference: 200 turns on a core with a gap made it almost completely silent, only slightly noticeable humm on heaviest loads. 400 turns did not make any difference when it comes to buzzing and started causing what seemed like PID instabilities with 512C.

[johansen]

Choke did the trick. For the reference: 200 turns on a core with a gap made it almost completely silent, only slightly noticeable humm on heaviest loads. 400 turns did not make any difference when it comes to buzzing and started causing what seemed like PID instabilities with 512C.

6mh

The motor was 4mh on its own.