PWM motor noise

[Bart]

Hi all,
bought a PWM kit ( http://kitsrus.com/pdf/k67v3.pdf ), but put in an
IRF840 & a 630V .1uF cap to run a 108VDC (nom) motor with
rectified/filtered line voltage (~160VDC).
The motor makes a rather loud (pwm) noise when running, is this
normal?
Any way of quieting it down?
Yes, I know I shouldn't be rectifying mains, but this is a test & I'll
use a stepdown/ isolation Xformer if & when it's working well.
TIA!
Bart

 

[phatty mo]

Hi all,
bought a PWM kit ( http://kitsrus.com/pdf/k67v3.pdf ), but put in an
IRF840 & a 630V .1uF cap to run a 108VDC (nom) motor with
rectified/filtered line voltage (~160VDC).
The motor makes a rather loud (pwm) noise when running, is this
normal?
Any way of quieting it down?
Yes, I know I shouldn't be rectifying mains, but this is a test & I'll
use a stepdown/ isolation Xformer if & when it's working well.
TIA!
Bart

High pitched at low speeds,and it gradually gets higher pitched at
faster speeds? Pretty normal.

 

[Jon Elson]

High pitched at low speeds,and it gradually gets higher pitched at
faster speeds? Pretty normal.

What is the PWM frequency? An IRF840 should be able to
switch well above audible frequencies. You might be able to
turn the PWM frequency up by changing a resistor or capacitor.

Jon