Control box humming

[phil_o]

I have a PRT 4g circa 2006. Lately, when I turn it on I hear a hum or buzzing coming from the box. If I give the box a light whack the hum will stop. Is this a sign of something I need to be concerned about?

Phil

[jerry_stanek]

sounds like the fan is going out

[phil_o]

Thanks, Jerry. I'll check it out.

Phil

[phil_o]

It wasn't the fan. The fan wasn't even connected. What else might be making the hum on start up? It only hums for less than a minute.

Phil

[jerry_stanek]

Still think it is the fan in the power supply

[MogulTx]

Depending on the era and equipment, it could be the contactor. And electromagnetic contactor whose coil is getting weak can hum or chatter and will eventually kill the contactor. I run some high energy contactors and have had this trouble a few times over the last 25 years. I keep a spare on the shelf, and if I hear it starting to hum, that is the step just before it starts to chatter. You could replace the coil at that time, but I usually just replace the entire contactor. ( and small contactors may not have the option to replace the coil separately from the whole unit)... Just a thought... If you can get it to do it while the controller box is open, you can press a screw driver against it in a non-conducting area- and will be able to feel the hum. (careful of voltage!) Best of luck on it.

[phil_o]

MogulTx. I don't know what a contactor looks like, where it is or how to find it. I'd appreciate a little more information.

Thanks,

Phil

[phil_o]

Still think it is the fan in the power supply
I didn't realize you were talking about the fan in the power supply. I'll check it out.

Thanks,

Phil

[MogulTx]

This is a photo of the contactors in my alpha control box. (Two contactors mounted side by side) This is over the stepper controllers and to the right side of the cabinet. The positioning in your cabinet may vary a good bit, depending on the original equipment bought with the machine or the era of upgrade that your machine may have gone through, etc. But basically, the contactors do not energize all the way through until the control box's blue button on the pendant has been used. Dust and dirt inside the control box can lead to chatter on electromagnetic contactors. Poor quality power (surges and unexpected power ups and power downs) can contribute to contactor hum and chattering... and once a contactor starts to chatter, it is time to replace it. Some folks will try to clean and plane the contacts- but when they are only a few $ it is a "fool's economy" IN MY OPINION... when they start to hum, you should be able to differentiate what component inside the cabinet is humming.... and this is not a musical performance, so you really don't want or need humming!34433

[phil_o]

Thank you, MogulTx for a thorough explanation. I'll let you know what I find.

Phil

[jerry_stanek]

The 4G box does not have a contactor

[phil_o]

The 4G box does not have a contactor
Now I know why I couldn't find one. I think I've narrowed it don to the power supply. It's not easy to check because it only hums from a cold start. If I turn it off and restart it will not hum. I have to wait an undetermined amount of time for it to cool down. I'll investigate further this AM.

Phil

[phil_o]

Before I fired up the control box I removed the power supply and blew it out with compressed air. There was some dust but not much. Put the power supply back in, turned it on, nice and quiet. Thanks to all who replied.

Phil

[phil_o]

Follow up on noisy fan. I thought that I had resolved the problem by blowing out the dust. The noise came back. I found a fix on Youtube that appears to be working. I ws able lubricate the fan bearing. Not difficult.
https://www.youtube.com/watch?v=MH52cMQp2c4&t=402s

Phil