crazy loud minilathe VFD (??) whine - HELP!

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Mr. Science

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Okay - so i bought one of the infamous 8x16 chinese mini-lathes from ebay after getting dicked around endlessly on alibaba. I read a lot of posts here and elsewhere about the various 'what-to-expect's from these things - only to find myself with a totally unique problem. The issue seems to be a loud squeal (electronic - NOT MECHANICAL) from what i am guessing to be the driver board (or possibly motor) but mine is much worse than other examples i have yet heard.

Here is a sample:

I wrote to the seller about this explaining how the sound gets LOUDER as the RPMs go UP (watch end of video) and if they could get me any info about the solution to this. Seller responded thusly:

"my friend,i send the video to the factory,they said the machine works well in your video,about the voice,they said it is normal,you just use it without any worry about that,they said it is the pulse compensation,it is like a technical term,after you use several times,the voice will be decrease,so you do not worry about that "
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i am guessing something is out of spec here - i have seen the same model lathe operating on various youtube videos WITHOUT the offending sound (sounds like an alarm of some kind like a smoke detector) - i'm pretty comfortable with electronics work (power supplies and control electronics notwithstanding) but i'm wondering if anyone might have a clue what this is ... I'm not sure about it being a 'carrier' signal due to the behaviour of the sound ... (seems different in nature to other descriptions of VFD noise) but it would be great if someone had some more insight into this. I estimate the frequency to be somewhere in the realm of 2400 hz if that rings any bells with anyone. Thanks

PS - this is my first post here and the start of an exhilarating and frightening jump into the world of 'machining' ...!
 
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It really sounds like the PWM carrier. 2.4KH would be in the range I would expect. I am guessing there's no way to change it like you could in many VFDs.

Putting a choke between the between the controller and the motor might help. The actual noise could be coming from the motor itself.
 
you are hearing the carrier frequency delivered by the pulse width modulation board.

if you can adjust the carrier frequency to around 8,000 to 10,000 Khz, the whine will be noticeably lower in pitch and it will run a heck of a lot quieter.
 
yes i'd read that elsewhere - not sure how adjustable it is - though i find it hard to believe that EVERY example of the same model has this problem - that's just poor electrical engineering - i'm guessing I'll have to dig through the driver circuit and find the out of spec capacitor or whatever it is ... at worst I'm expecting to have to upgrade the motor and VFD entirely ... but i was just wondering if anyone else had come across this problem - i'd seen videos of others with VFD noise - but NOTHING even close to being this loud
 
I just completed setting up a VFD on a mill and like others said, you're hearing the carrier; you can tell because its frequency never changes. What can make it bad is that some part(s) of the lathe/motor can mechanically resonate at certain frequencies, and yes, it can be loud. Mine was similar until I increased the carrier frequency Assuming your VFD is not user-configurable, your options include trying to get VFD instructions (maybe from the VFD manufacturer), or, replacing it with a more user-friendly VFD (many here use the Hitachi WJ200). A hail-Mary would be to replace the motor, hoping that the next one doesn't resonate the same, or there's just learning to live with it and to wear ear plugs. I know that isn't what you wanted to hear, but non-adjustability is typical on the small units.

Search around the web for something like "mini lathe VFD noise" and see what others have come up with.
 
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You might give a shout to Pete at: www.olduhfguy.com and see what he says about it.
If it is a two wire dc motor as opposed to brushless you could replace the whole controller with an scr type unit such as KB electronics but I suspect it's a brushless type.
mark
 
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kb58 said:
I just completed setting up a VFD on a mill and like others said, you're hearing the carrier; you can tell because its frequency never changes. What can make it bad is that some part(s) of the lathe/motor can mechanically resonate at certain frequencies, and yes, it can be loud. Mine was similar until I increased the carrier frequency Assuming your VFD is not user-configurable, your options include trying to get VFD instructions (maybe from the VFD manufacturer), or, replacing it with a more user-friendly VFD (many here use the Hitachi WJ200). A hail-Mary would be to replace the motor, hoping that the next one doesn't resonate the same, or there's just learning to live with it and to wear ear plugs. I know that isn't what you wanted to hear, but non-adjustability is typical on the small units.

Search around the web for something like "mini lathe VFD noise" and see what others have come up with.
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thanks for the response ... yes i figured it MIGHT have been the carrier - though others have said it should get quieter with increasing RPM - i'm finding just the opposite. It wouldn't be very surprising to find out that it may not be adjustable - i kind of expect that - but i SHOULD be able to change the frequency by subbing in different value resistors or capacitors somewhere it seems to me (?). I was just hoping someone here might know these circuits well enough to get me started in the right directlon - or at least explain how and why this is happening and how it might be avoided ...
 
Mr. Science said:
thanks for the response ... yes i figured it MIGHT have been the carrier - though others have said it should get quieter with increasing RPM - i'm finding just the opposite. It wouldn't be very surprising to find out that it may not be adjustable - i kind of expect that - but i SHOULD be able to change the frequency by subbing in different value resistors or capacitors somewhere it seems to me (?). I was just hoping someone here might know these circuits well enough to get me started in the right directlon - or at least explain how and why this is happening and how it might be avoided ...
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Assuming that it's digital, that's unfortunately unlikely. The whole thing gets dicey when messing with a 230v circuit without a schematic, like walking out blindfolded on to thin ice. Unless you can get information from the VFD mfg, it gets dangerous guessing. Either put in a VFD that can be adjusted, get information from the mfg, or just live with it.

For what it's worth, a friend has a $25k CNC mill and the squeal on his drives him nuts.
 
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