I recently got some 3-4 RPM motors to turn some small mirror balls.
They spin a little too fast for my liking.
I have a variable frequency AC supply I built using an old Bogen 60 watt amp, a 15Vac to 120Vac transformer and one of those cheapie function generator kits I bought from Amazon which I made to run a record player that's slightly too slow. I tried the motors on it and found 40Hz makes them spin just about right.
So I'm thinking of building another variable frequency AC supply only this time I want to try one of those class D amplifier boards I can get from Amazon or Parts Express and a similar function generator kit along with a power transformer run in reverse to develop the voltage needed as the class D board will be a good bit smaller than the Bogen and a lot more efficient.
How well would a class D amplifier board do feeding a signal into a transformer driving a minimum 52 watt load?
As I do with everything involving audio power amps I will use my oscope to view the waveform while I do extensive testing under load to be sure the amp does produce a clean sinewave.
Before I go and order a power transformer I'll try some I already have.
The motors do run a bit warm on 120Vac, but do run on 100Vac so I'll run them on the lower voltage.
I'll also figure out some sort of voltmeter to use so that I know what the output voltage is.
They spin a little too fast for my liking.
I have a variable frequency AC supply I built using an old Bogen 60 watt amp, a 15Vac to 120Vac transformer and one of those cheapie function generator kits I bought from Amazon which I made to run a record player that's slightly too slow. I tried the motors on it and found 40Hz makes them spin just about right.
So I'm thinking of building another variable frequency AC supply only this time I want to try one of those class D amplifier boards I can get from Amazon or Parts Express and a similar function generator kit along with a power transformer run in reverse to develop the voltage needed as the class D board will be a good bit smaller than the Bogen and a lot more efficient.
How well would a class D amplifier board do feeding a signal into a transformer driving a minimum 52 watt load?
As I do with everything involving audio power amps I will use my oscope to view the waveform while I do extensive testing under load to be sure the amp does produce a clean sinewave.
Before I go and order a power transformer I'll try some I already have.
The motors do run a bit warm on 120Vac, but do run on 100Vac so I'll run them on the lower voltage.
I'll also figure out some sort of voltmeter to use so that I know what the output voltage is.
I'm thinking of using these parts to build it.
Amplifier
https://www.amazon.com/HiLetgo-TPA3116-Amplifier-TPA3116DA-Channel/dp/B082F7P184
Power supply
https://www.amazon.com/gp/product/B08Z7X9F1V/ref=ox_sc_act_title_1?smid=A2JL7VEXKVJYVZ&th=1
Function generator. Even though I could go with a much simpler design for this specific purpose, this one permits setting an exact frequency for use with playback or recording devices with an AC motor that run slightly fast or slow.
https://www.amazon.com/gp/product/B08NSR5GYR/ref=ox_sc_act_title_1?smid=A2QLMFTY03XGKY&psc=1
Voltage regulator for the function generator.
https://www.amazon.com/gp/product/B0D3BLVWH4/ref=ox_sc_act_title_1?smid=A340R8AE7I6WOL&th=1
Amplifier
https://www.amazon.com/HiLetgo-TPA3116-Amplifier-TPA3116DA-Channel/dp/B082F7P184
Power supply
https://www.amazon.com/gp/product/B08Z7X9F1V/ref=ox_sc_act_title_1?smid=A2JL7VEXKVJYVZ&th=1
Function generator. Even though I could go with a much simpler design for this specific purpose, this one permits setting an exact frequency for use with playback or recording devices with an AC motor that run slightly fast or slow.
https://www.amazon.com/gp/product/B08NSR5GYR/ref=ox_sc_act_title_1?smid=A2QLMFTY03XGKY&psc=1
Voltage regulator for the function generator.
https://www.amazon.com/gp/product/B0D3BLVWH4/ref=ox_sc_act_title_1?smid=A340R8AE7I6WOL&th=1
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Instead of the listed voltage regulator I may use this one.
https://www.amazon.com/Converter-DROK-Voltage-Regulator-Waterproof/dp/B07P663XJV
https://www.amazon.com/Converter-DROK-Voltage-Regulator-Waterproof/dp/B07P663XJV
1 - Be aware, running at 40Hz, a mains transformer will be significantly derated to avoid saturation.
2 - Ensure the amplifier will provide the required power continuously and not rated on music.
2 - Ensure the amplifier will provide the required power continuously and not rated on music.
1. It definitely will for sure. I also know that as the frequency goes lower, the signal level fed to the mains transformer has to be reduced as well in order to avoid issues with the amp.
I do have a 200 watt 70 volt audio distribution transformer somewhere I may try, however I know it likely won't generate the needed output voltage. Worth a shot though as the motors run just fine at 40Hz on 81Vrms. If that transformer does work I won't need to worry as much about derating given it's designed for audio frequencies specifically.
2. Pretty sure 100 watts is not the continuous power, but as long as it can do 65 watts that's all I really need.
The parts will be here Monday.
I do have a 200 watt 70 volt audio distribution transformer somewhere I may try, however I know it likely won't generate the needed output voltage. Worth a shot though as the motors run just fine at 40Hz on 81Vrms. If that transformer does work I won't need to worry as much about derating given it's designed for audio frequencies specifically.
2. Pretty sure 100 watts is not the continuous power, but as long as it can do 65 watts that's all I really need.
The parts will be here Monday.
For the same flux at 40Hz, the rated voltage would have to be 4/5th of its 50Hz value or equivalently 2/3rd of its 60Hz value,
That would explain why with the variable frequency AC supply I am testing the motors on complained when I lowered the frequency without lowering the input voltage to the mains transformer.
Hopefully that 200 watt 70 volt distribution transformer will produce enough output voltage with the class D amp module.
Hopefully that 200 watt 70 volt distribution transformer will produce enough output voltage with the class D amp module.
I might do just that if the 70 volt transformer doesn't produce enough output voltage.
Also it's likely the 30V to 250V transformer would be designed for 50Hz so would operate better at 40Hz than a 60Hz transformer.
I also ordered one of these AC voltmeters to use on the output.
https://www.amazon.com/Baomain-DH-670-AC-0-150V-Rectangular/dp/B0CM8HDKSR
Also it's likely the 30V to 250V transformer would be designed for 50Hz so would operate better at 40Hz than a 60Hz transformer.
I also ordered one of these AC voltmeters to use on the output.
https://www.amazon.com/Baomain-DH-670-AC-0-150V-Rectangular/dp/B0CM8HDKSR
If you are not already aware of vfd's, these are available ready made and may be a better solution. Granted most are made for high power 3-phase motors, but cheaper smaller units are available. Note that reducing the voltage inversely proportional to frequency is a standard feature because the current varies inversely as the frequency. https://www.amazon.com/Cozyel-Variable-Frequency-Converter-Single-Phase/dp/B0BHMZ8YXZ/ref=sr_1_36?adgrpid=1335907193780293&dib=eyJ2IjoiMSJ9.lXDwXcZtnvMtr-ht6EoOc6fJezvr9KkrFYybrioGBY1Kx7rnZS7Q-F7piej2zkWOcnO2Py_yhVMV7fwoiXYqtwFQBDbNZsGOiFCJRwnCL6KcVmAyMFiNhUXbXpyCrCzqipt3_hhOYacw5iXRsGN_KSBLeSMws7hpligUIkuqSFiQb7AS7vb49nv3XLxJD7tjPIrbOuRaSi7gXiGZe7ndlKIm_P3Z-AIC3ra6wdH3Va-OurZoOf9GLqWu7-izHtuHndQdBtxEaqRpmHP9b4Xc2TuKrGyS8mxBR1z8UwWtwBI.Tl5yFGO_XaOII-FY5WDKtJclPjAZ0Ku9Xd5PZnDav8I&dib_tag=se&hvadid=83494440362837&hvbmt=be&hvdev=c&hvlocphy=90944&hvnetw=o&hvqmt=e&hvtargid=kwd-83494548729306:loc-190&hydadcr=19831_13385594&keywords=vfd+drives&qid=1730570792&sr=8-36&th=1
I had thought about using a VFD, but I wasn't sure whether or not it would produce RFI nor do I know if it puts out a sinewave and if the motors can run on anything other than a sinewave.
The motors I got are these.
https://www.amazon.com/dp/B07QMCF2SX
Will there be any damage done by running them on a lower frequency at a lower operating voltage?
https://www.amazon.com/dp/B07QMCF2SX
Will there be any damage done by running them on a lower frequency at a lower operating voltage?
The transformer I have is either this one or very similar.
https://www.planetdj.com/qsc-ot-300a
I forget exactly how the transformer would need to be connected, however I am not so sure it will work as the ratio may not be high enough.
I probably have a transformer that might work though. I suspect that a transformer from one of those more modern receivers made to run on 120V or 240V would work just fine.
https://www.planetdj.com/qsc-ot-300a
I forget exactly how the transformer would need to be connected, however I am not so sure it will work as the ratio may not be high enough.
I probably have a transformer that might work though. I suspect that a transformer from one of those more modern receivers made to run on 120V or 240V would work just fine.
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Got the parts in.
Two issues.
1. Ordered from Amazon a new 24V 6A supply. Instead got a used 24V 2A supply so I will return to Amazon.
2. The function generator while it will produce the frequency I need it does not have a way to store the frequency so that will be a no-go. That one is my fault though as I failed to read the description fully.
1. I have one of those old EICO variable 0-6 0-12V battery chargers that produces up to 30Vdc at 6A with a bridge rectifier instead of the original selenium it came with so that will power the amp temporarily.
2. I have a Heathkit audio signal generator that I can use to drive the amp for now.
Two issues.
1. Ordered from Amazon a new 24V 6A supply. Instead got a used 24V 2A supply so I will return to Amazon.
2. The function generator while it will produce the frequency I need it does not have a way to store the frequency so that will be a no-go. That one is my fault though as I failed to read the description fully.
1. I have one of those old EICO variable 0-6 0-12V battery chargers that produces up to 30Vdc at 6A with a bridge rectifier instead of the original selenium it came with so that will power the amp temporarily.
2. I have a Heathkit audio signal generator that I can use to drive the amp for now.
What I think likely happened is someone ordered a 24V 6A supply to replace their 24V 2A supply, did a return sending back the 24V 2A supply to get the supply free and nobody checked the box to verify it was the right item.
I tried two transformers and they didn't work.
I then remembered I have a toroidal transformer with dual 15V 3A secondaries and dual 115V primaries.
I was hesitant to try it as I tried that one with my other variable frequency AC supply that uses power transistors and it wouldn't work with that.
Tried it with the class D amp and the amp itself just does have enough oomph to make the mirror balls spin on 40Hz.
I used one 15 volt winding with the 115V windings in series.
The heatsink gets real warm though and I'd need to use a fan.
Here's what I thought of doing. Given I got a two pack of the amps and both secondaries are isolated from each other, I can put one amp on one secondary and the other amp on the other secondary. I'd then feed both amps the exact same signal. That way each amp will carry 1/2 the load
Would that work or will that cause a problem?
I then remembered I have a toroidal transformer with dual 15V 3A secondaries and dual 115V primaries.
I was hesitant to try it as I tried that one with my other variable frequency AC supply that uses power transistors and it wouldn't work with that.
Tried it with the class D amp and the amp itself just does have enough oomph to make the mirror balls spin on 40Hz.
I used one 15 volt winding with the 115V windings in series.
The heatsink gets real warm though and I'd need to use a fan.
Here's what I thought of doing. Given I got a two pack of the amps and both secondaries are isolated from each other, I can put one amp on one secondary and the other amp on the other secondary. I'd then feed both amps the exact same signal. That way each amp will carry 1/2 the load
Would that work or will that cause a problem?
Put a series capacitor to reduce the fan speed. Those are common in fan speed controllers, the older triac based designs should work as well.
Start at 1 mfd / 400 or 600 V, go up to 4.5 if needed, the 'regulators' are like 75 cents here.
Just put one in series and vary it till you like the speed.
And speed contollers are very common in industrial drives, VFD starts from about 100 Watts.
Starting price is like $40 here, Allen Bradley, Delta, Noritake and other local makes are sold here, see what you get in your area.
As usual, just being helpful, no ties to any names here.
Start at 1 mfd / 400 or 600 V, go up to 4.5 if needed, the 'regulators' are like 75 cents here.
Just put one in series and vary it till you like the speed.
And speed contollers are very common in industrial drives, VFD starts from about 100 Watts.
Starting price is like $40 here, Allen Bradley, Delta, Noritake and other local makes are sold here, see what you get in your area.
As usual, just being helpful, no ties to any names here.
The motors you linked to are quite low rated, the series capacitor regulator is one I have used at home for over 15 years on cieling fans without any issues, see on line, capacitor makers in fact used to offer sets for regulator makers...
These motors rely on the AC line frequency to set their speed so a simple capacitor dropper won't work.
I first had thought of using a VFD, but I do not know if they put out a sinewave or squarewave and I don't know how these motors would work on a squarewave. Also I don't know if the VFD would cause any RFI issues.
I first had thought of using a VFD, but I do not know if they put out a sinewave or squarewave and I don't know how these motors would work on a squarewave. Also I don't know if the VFD would cause any RFI issues.
For now I can use that function generator, but it would need to be powered 24/7 which I can do from an extra USB port I have on a powered USB hub connected to my PC.
I may try using the two amps just to see what happens. They were cheap so it won't matter if the amps fail.
Tried both amps and I am able to get more output power to a load, however while trying to run the motors at 30Hz I discovered I had to lower the voltage and I wound up dropping it to 48Vrms and the motors spin at 30Hz. They also spin at 60Hz at the same voltage. The best thing is the amps aren't even drawing an amp of current.
So I connected the motors to just one primary winding and I can easily get 48Vrms with some to spare. I may try connecting the windings in series like I did initially and see if I can still get the motors to spin on 48Vrms. If so that will be good as it won't be running the amp nearly as hard. Plus the substantially reduced voltage to the motors will likely keep them running cool, unless the lower frequency causes the windings to still heat up about like they did on 120V 60Hz.
I may try using the two amps just to see what happens. They were cheap so it won't matter if the amps fail.
Tried both amps and I am able to get more output power to a load, however while trying to run the motors at 30Hz I discovered I had to lower the voltage and I wound up dropping it to 48Vrms and the motors spin at 30Hz. They also spin at 60Hz at the same voltage. The best thing is the amps aren't even drawing an amp of current.
So I connected the motors to just one primary winding and I can easily get 48Vrms with some to spare. I may try connecting the windings in series like I did initially and see if I can still get the motors to spin on 48Vrms. If so that will be good as it won't be running the amp nearly as hard. Plus the substantially reduced voltage to the motors will likely keep them running cool, unless the lower frequency causes the windings to still heat up about like they did on 120V 60Hz.
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