Variable frequency AC power supply design

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#41
These little motors I'm using use a magnet for the rotor. Forget what type of motor that is.

I do still hear noise from the motors at 30Hz and it seems to be once per rotor revolution of one motor as it does not sound like multiple motors.

I might pull the stuff down again and see if I can find the noisy motor. My dad does have a stethoscope he used for automotive work and if it is still good maybe I can use it to find the issue.

I do know one motor doesn't start up on the same lower voltage as the others requiring a little higher voltage so maybe that's the one with the problem.

I did open one spare motor up to see if there was anything that could possibly cause noise and I didn't see anything immediately obvious.
 
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#43
If is a permanent magnet motor, then it is most likely a DC motor, there should be a tiny PCB inside to convert line supply to DC.
Check, it is easier to change a low voltage (?) DC supply.

The air conditioner blower motor in my car uses a permanent maget motor, the coil is fed by brushes...the toy motors use that too.
Magnet for the rotor means electronic commutation in the stator to move the rotor?

And the lube may be less in the 'sticky' motor, which needs higher voltage.
 
#46
See an old movie like 'Saturday Night Fever', disco was popular at that time, some film may have used that effect, strobes on mirror balls.
Laser on mirror ball is also a possibility, and narrow focus lenses on LEDs...technology advance is fast these days.

There was a celebrity place called Studio 54 in NY City, landing lights from aircraft were a light source...
 
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#48
It is a completely different aspect of appreciation that I might have for at least some visual effects. Like just about everything else, it can be poorly done. The 70's scene made me sick. Gaudy, blurry, and salesmen loved it.
 
#49
Here's the AC power supply. It's a bit ugly but it works. That function generator is only temporary until I find one that can store frequencies like the function generator I use in my other AC supply does.

The mirror balls all start up fine on 30Hz at 40Vrms. The amp heatsink just does get a little warm.



20241107_153950.jpg
 
#51
#52
I have a cheap box fan that I put in my bedroom window on summer nights. I run it off a variac that I set about 90 VAC for a nice quiet slow fan. So it's running from 60Hz, just at a reduced voltage. Induction motors just run with more "slip" at reduced voltage. Of course, TRIAC based fan controls buzz like hell because they chop up the sine wave. If you knew the voltage you want, you could use a ~24VAC HVAC transformer from the home improvement center to buck the 120VAC down to a lower voltage.

Before I retired, I wrote a power line test suite in VBA that controlled either a California Instruments or an HP/Agilent 681(123) AC source, but they are large KVA powerful and expensive.

https://variac.com/staco_3PN10_20.htm

https://www.valuetronics.com/power-supplies-loads/ac-source
 
#54
steveu said:
I have a cheap box fan that I put in my bedroom window on summer nights. I run it off a variac that I set about 90 VAC for a nice quiet slow fan. So it's running from 60Hz, just at a reduced voltage.
Click to expand...

Note that many induction motors run at lower than rated voltage can pull a lot more current (and physically stall), risking severe overheating. By varying the depth of the embedded conductors in the squirrel cage the stall-current to run-current ratio can be tuned, so some motors are able to handle this by design, others may not.

Large industrial induction motors can have a rating for the maximum re-starts per hour, since exceeding this can cook the motor due to the massive losses at start up (both due to large currents at low speed and the work needed to accelerate the load).

So you should be wary of abusing induction machines like this...
 
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