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

[JimDawson]

yes some sort of blocking filter (cap or coil) was my first idea - but doesnt' the motor need to receive that signal for whatever reason? (minilathe voodoo? doesn't it need the PWM signal?)

No, the motor does not need the squarewave to run. So knocking the corners off of the spikes won't change the operation. Given that it apparently a brushed DC motor, it will run on pure DC. The PWM is really just controlling the torque, while keeping the voltage at maximum, but changing the wave duty cycle. Gives better low end torque performance.

 

[tq60]

Imagine flipping a light switch really fast.

The light is now dim.

Regardless of how fast it is same.

Leaving it on longer the light is brighter.

This is the pwm process in a nutshell.

The pulses are exciting something as they are full voltage but very little duration.

The motor does not spin up as the shirt period of full voltage does not create enough force to do anything.

But anything with a coil will move or try to move.

Given you have electronic toys and your handle you already understand pwm...we are helping others too.

Locate a microphone, tiny from headset or old school ear bud.

Connect this to your o-scope or an audio amp and attach the item to a pencil.

Now get the lathe to make the noise and with the microphone Starr touching things to find it.

Could be motor windings as well as inductors on the control board.

If motor many things to do from epoxy to filtering and coils on control board may need to be epoxied in place.

Touching them with the eraser end of pencil to see if sound changes is simple test.

Lots of possibilities....enjoy the hunt!

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

[Mr. Science]

Imagine flipping a light switch really fast.

The light is now dim.

Regardless of how fast it is same.

Leaving it on longer the light is brighter.

This is the pwm process in a nutshell.

The pulses are exciting something as they are full voltage but very little duration.

The motor does not spin up as the shirt period of full voltage does not create enough force to do anything.

But anything with a coil will move or try to move.

Given you have electronic toys and your handle you already understand pwm...we are helping others too.

Locate a microphone, tiny from headset or old school ear bud.

Connect this to your o-scope or an audio amp and attach the item to a pencil.

Now get the lathe to make the noise and with the microphone Starr touching things to find it.

Could be motor windings as well as inductors on the control board.

If motor many things to do from epoxy to filtering and coils on control board may need to be epoxied in place.

Touching them with the eraser end of pencil to see if sound changes is simple test.

Lots of possibilities....enjoy the hunt!

Sent from my SAMSUNG-SM-G930A using Tapatalk

yes good idea with the pencil eraser thanks

hoping not to have to pull the motor apart to find the ringing bit ... I just spent two weeks trying to get my table saw motor back together after replacing the bearings ...

 

[Mr. Science]

snooped around inside - definitely coming from the pulley end of the motor ... if i'm going to go through the pain of removing the motor i wonder if i should just wait and put up with the noise for now until i opt to replace the motor and drive circuitry with something better ... only issue with replacing is that it looks like quite a tight fit!

i may end up just trying the filter-the-signal option .. for now

 

[macardoso]

Hate to say it, but that is just an example of a low quality VFD generating excessive switching noise. If it is programmable, you can change the carrier frequency to a higher value to bring it out of the audible range for you (but maybe not your dog's). Inadequate grounding/bonding of the VFD may also play into it.

If you are putting a choke between the VFD and the motor, be careful. There are components specifically designed for this purpose and standard line filters are typically not designed for the large voltage spikes.

Edit: Just read it is a brushed DC motor. Whoops!

 

[stupoty]

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.

Interesting side note , the PWM frequency can sometimes be worse at higher Hz depending upon how good your ears are, I was watching a video on the u tubes where someone sets the frequency higher and then declares it to be silent whilst I was watching the video going "owch that noise is offending my ears"

I have my inverters set to 1.5khz (possibly 1khz) which I find to be the most comfortable for me.

I stop hearing it somware after 17khz might vary depending upon speakers/headphones etc.

Stu

 

[Mr. Science]

Hate to say it, but that is just an example of a low quality VFD generating excessive switching noise. If it is programmable, you can change the carrier frequency to a higher value to bring it out of the audible range for you (but maybe not your dog's). Inadequate grounding/bonding of the VFD may also play into it.

If you are putting a choke between the VFD and the motor, be careful. There are components specifically designed for this purpose and standard line filters are typically not designed for the large voltage spikes.

Edit: Just read it is a brushed DC motor. Whoops!

how would that affect your advice (brushed vs brushless)?

 

[macardoso]

how would that affect your advice (brushed vs brushless)?

Totally different control strategies. A brushed DC motor controller uses a unipolar PWM (fixed frequency) signal to set the speed (unless reversed) while a 3 phase induction motor VFD uses a variable frequency bipolar PWM signal which aims to generate sinusoidal current.

If this were a 3 phase VFD for an induction motor, the sound you hear would be a the switching carrier frequency which remains constant (typically 4kHz) regardless of the output frequency of the drive (think of it like an overtone).

A brushed DC motor also has a PWM carrier frequency, but I don't know nearly as much about the operation of these motor controllers, so I will leave the troubleshooting to someone else

 

[stupoty]

A brushed DC motor also has a PWM carrier frequency

The PWM for a brushed motor is just duty cycle so the sound may vary as the percentage of full power to the motor is changed, at full speed it's the normally Full DC voltage and shouldn't "whine" (their may be exceptions to that but generally). It can be a fixed frequency or variable frequency.

Stu

 

[Mr. Science]

for those interested in this lathe ... i found a guy on youtube with the EXACT same build who is going over it in detail ... I feel lucky not to have the QC issues he seems to have (but then again I haven't totally taken this thing apart yet!) - though he has the same motor whine too (and says it toned down after some hours - which is nice to hear)

there are fifteen parts to this series.