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Thread: Mini lathe motor whining noise

  1. #13
    Member rdsn's Avatar
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    Default Re: Mini lathe motor whining noise

    Any suggestions, please?



  2. #14
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    Default Re: Mini lathe motor whining noise

    That wiring diagram doesn't help. A schematic of the board is needed, but that's not made public by the seller

    I am sorry, but I only see mounting a standard controller as possibility!



  3. #15
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    Default Re: Mini lathe motor whining noise

    Check if chips on controller board have readable numbers (on my board all chips had identifiers ground off). If yes - try to Google them, they probably used standard pwm controller - there is chance it will have simple rc timing circuit and changing one component will move pwm frequency to inaudible range (inaudible to you - your dog will still don't like it).
    My controller board started "acting" a few months ago - motor lost torque. I reverse engineered the schematic (using "informed guess" on chips without numbers). My board is quite simple - just a phase cut controller (glorified light dimmer) not pwm like yours.
    It "acted" because all electrolytic caps dried out - age and low quality I guess.


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  4. #16
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    Default Re: Mini lathe motor whining noise

    Sorry... been having a few PCB problems of my own here...

    Check if chips on controller board have readable numbers
    Of particular importance in determining what overall type controller you have is the components attached to the heatsinks... if they are SCRs or TRIACs; then that indicates a simple phase-cut type like grg12 has... which shouldn't be capable of making high pitched noises; as they run at 50/60hz....

    If however, as I suspect from the photos, it's got a switching power supply for converting the mains AC into DC; and then a power MOSFET or IGBT that outputs an actual PWM signal to the motor; it may be possible to put a suitably rated capacitor across the motor or a choke inline with it.

    If you are determined to get rid of the squeal; and are willing to replace the motor controller if your modification steps don't work; then you might as well try throwing a capacitor or choke at it "blind"; if the board gets killed in the process (unlikely, but always a possibility when working without a schematic & datasheets) then you are only out the cost of the capacitor and/or choke - as you would have had to replace the PCB anyway...

    Just make sure that anything you buy for it has adequate voltage & current ratings - unless, of course, you wish to have a "Photonic Induction" experience (if you don't know who I'm talking about, look for him on YouTube).



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    Default Re: Mini lathe motor whining noise

    Do not connect random condensators parallel to motor. It may destroy switching elements on controller board.
    PWM controller used in this type of application switches output between full supply voltage and 0V (ground) (for example 0.5ms full voltage, 0.5ms 0V - 50% cycle at 1kHz frequency). If you connect capacitor to output it will try to fully load it at the moment "high" phase starts resulting in short high current spike that may destroy switching elements.
    You can use carefully calculated combination of choke and condensator (LC filter) to smooth output of pwm controller (and effectively convert it to DC power supply) and it will quiet down your motor.

    Wys?ane z mojego SM-N950F przy u?yciu Tapatalka



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    Default Re: Mini lathe motor whining noise

    Do not connect random condensators parallel to motor. It may destroy switching elements on controller board.
    That depends on the output stage of the drive; if it is a MOSFET or IGBT directly coupled to the motor outputs, with no protection... and you put a large enough cap with low enough ESR, with nothing else added... yeah, that'll kill the output switch. If the drive has short circuit protection; it may just shut down. If there is any sort of "line filter" on the output for reducing EMI, that may function to limit the inrush current going into a bare cap bridged across the motor enough such that the switching components aren't over-stressed... or not. It may also mess up any sort of feedback loop it has. Without a schematic I'm just... guessing.

    My suggestion earlier about adding something "blind" is intended as a last resort - that's what I'd do when my next step was to replace the drive anyway.

    I kind of wish I could put the thing on my bench and probe it with my oscilloscope... it would answer a few questions...





  7. #19
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    Default Re: Mini lathe motor whining noise

    I was standing with oscilloscope probes in hand over controllers board - connected to mains and some lightbulbs (dummy load). I wanted to see what's going on... then I remembered that this "light dimmer" doesn't have any real "ground" (it's powered through bridge rectifier so "ground" is half the time connected to phase wire). Luckily I didn't cause any fireworks displays this day
    I managed to repair this thing using multimeter about three days before Amazon package with a isolation trafo arrived.
    Mains voltage (especially 230V) isn't a thing you can be careless about...

    Wys?ane z mojego SM-N950F przy u?yciu Tapatalka



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    Default Re: Mini lathe motor whining noise

    Yup!


    I have both an isolation transformer and variac on my bench for just that reason. Photonic Induction and ElectroBOOM may be fun to watch on YouTube, but I’d rather not have that experience myself...

    I also happen to have one of those cheap Chinese portable battery powered single channel scopes... which would come in handy for something like this (just make sure to double check it’s voltage range - some of them don’t go very high; and don’t have a x10 probe).



  9. #21
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    Default Re: Mini lathe motor whining noise

    Hi again, I have updated the pictures folder with some close ups of what I can read: https://bit.ly/2zyEtXj

    I'm knowledgeable enough to identify if some component is part of a PWM module or not.

    Someone has suggested me this board is not controlled by PWM but by phase control.

    At this point, and to avoid the risk of ending up with a lathe without a controller, I'm thinking about alternatives, ie, starting from scratch with a new board.

    What options are there for a 220V 750W DC motor with reverse/neutral operation and RPM control and readout?

    Thanks



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