Reduce AC motor speed

Thread Starter

manumaanumanumanu

Joined Oct 11, 2019
8
Hi friends, I have an audio echo machine and I want to reduce the motor speed. It is 220V, 50HZ, 2MF.
I have no idea. I read and I try 3 options between the wires on the photos:
. Motor speed control CA 50-220V, 2000W: it reduces very few rpm and it turns off at some point of the potentiometer.
. Diod 1n4007: veeeery slow and unconstant speed.
. Potentiometer: on on the max, and off on the rest.

I don't know what to do. Thanks a lot.
 

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jpanhalt

Joined Jan 18, 2008
7,697
That looks like an eBay "motor speed controller" that someone added. Was that you? Maybe (probably) it's the wrong type of controller for that type of motor? Can you provide a link to the controller and better pictures of the motor?
 

jpanhalt

Joined Jan 18, 2008
7,697
That's an SCR controller which clips the AC and effectively reduces the voltage. That will work with some motors, like brushed AC motors. It will not work well with synchronous motors as their speed is determined by the frequency. If you decrease the power to that type of motor, eventually it cannot overcome frictional losses and slows. But that is not a good way to slow them down as they then have no power.

This describes how they work: https://www.nutsvolts.com/magazine/article/scr_principles_and_circuits
Scan down about half way to Variable AC power control.
 

Thread Starter

manumaanumanumanu

Joined Oct 11, 2019
8
Thanks to all.
So, I have a synchronous motor.
I prefer to regulate the speed, but if there is an easy way to reduce it to half or something I would be happy to. Maybe a resistor?
In that thread he solved it with an scr, but the link is down, don't know if it's like mine.
 

MaxHeadRoom

Joined Jul 18, 2013
18,864
It looks to me as though it is a PSC (permanent start cap), Asynchronous motor.
And as suggested, appears to be a Triac controller, these usually have to be on high to get the motor to turn and can, and will often drop out of run when the rpm is reduced, this is a typical condition when trying to control the speed of a 1ph induction motor, also why you very rarely see the more sophisticated VFD versions, which are generally used with 3 phase motors.
If you want some precise control look at converting to a brushed DC for cheapness.
This way a cheap PWM (Ebay) controller could be used.
Max.
 

Thread Starter

manumaanumanumanu

Joined Oct 11, 2019
8
Thank you very much for the reply.
Unfortunately, I am afraid that I cannot replace the motor, because it is a very precise device and it does not seem easy to find something of the same measurements but in DC.
Any possibility that the regulation is not as precise or even a fixed reduction?
 

MaxHeadRoom

Joined Jul 18, 2013
18,864
If you only need a fixed reduced speed and have no use for the maximum, then a output reduction method could be used if necessary, belt, gearbox etc.
Max.
 

shortbus

Joined Sep 30, 2009
6,885
When you say it's an "audio echo machine" do you mean it is a tape loop or are you talking about something like a Leslie speaker?
 

thedoc8

Joined Nov 28, 2012
127
Hi friends, I have an audio echo machine and I want to reduce the motor speed. It is 220V, 50HZ, 2MF.
I have no idea. I read and I try 3 options between the wires on the photos:
. Motor speed control CA 50-220V, 2000W: it reduces very few rpm and it turns off at some point of the potentiometer.
. Diod 1n4007: veeeery slow and unconstant speed.
. Potentiometer: on on the max, and off on the rest.

I don't know what to do. Thanks a lot.
I read through the post, but did not see why you wanted to slow the motor.
 

MisterBill2

Joined Jan 23, 2018
3,721
My guess is that you want to slow the echo operation, and so the simple way to do that is to put a slightly smaller pulley on the motor shaft. But if the mechanism is direct drive, with the tape driven right from the motor shaft, then that is not possible. Probably the motor is like Max stated, a capacitor split-phase type, in which case reducing the speed can be a challenge if you want to reduce the speed very much. Dropping the voltage some will slow the motor some, but it reduces the torque a lot more, and so the motor will stall and stop at that point.
Do you know the voltage the motor is supplied with? That will affect the possible methods of speed control and the way to implement those methods. So can you let us know that, please. And also, does the system use a drive belt, or is it directly driven?
 

shortbus

Joined Sep 30, 2009
6,885
This isn't meant to be a mean statement, let me say that up front. Unless this is meant to go into a museum of audio equipment, you would be farther ahead to buy a digital echo module. For, I'm guessing, less money and work than it will take to change this to what you want you could buy one that will do more. I'm also assuming this is why the people you got it from sold it, it was too costly to modernize.

That said if you want to proceed with this I'd remove the motor. Doing this will allow you to make some necessary measurements. Length and diameter of the motor shaft. With those measurements you can look for a DC motor that has the same sizes, then you would need to design a way to mount the DC motor to align with the way the original one was mounted and in the same place. Then you would need to buy a DC speed controller for the motor and mount it in the console.

But I'm betting when you start to disassemble this to remove the motor you will find some sort of drive system , an electric motor direct driving a tape loop would more than likely make a warbling sound not an echo sound, due to speed. Can you give a make and model of the machine so we can understand better what your up against?
 

MisterBill2

Joined Jan 23, 2018
3,721
This isn't meant to be a mean statement, let me say that up front. Unless this is meant to go into a museum of audio equipment, you would be farther ahead to buy a digital echo module. For, I'm guessing, less money and work than it will take to change this to what you want you could buy one that will do more. I'm also assuming this is why the people you got it from sold it, it was too costly to modernize.

That said if you want to proceed with this I'd remove the motor. Doing this will allow you to make some necessary measurements. Length and diameter of the motor shaft. With those measurements you can look for a DC motor that has the same sizes, then you would need to design a way to mount the DC motor to align with the way the original one was mounted and in the same place. Then you would need to buy a DC speed controller for the motor and mount it in the console.

But I'm betting when you start to disassemble this to remove the motor you will find some sort of drive system , an electric motor direct driving a tape loop would more than likely make a warbling sound not an echo sound, due to speed. Can you give a make and model of the machine so we can understand better what your up against?
Why would you think that a split-capacitor motor driving a tape loop would produce a warbling tone?? Some expensive and high quality tape machines use a direct drive off the motor shaft, and the wow and flutter specs are quite good. Of course they also include a bit of flywheel to help them remain stable. If the amount of slowing is not that much then it5 should be possible to slow the motor speed some by reducing the voltage. A greater speed reduction would take a reduction in frequency. A low power inverter should be able to do that. But why does the TS want to slow the echo speed??

Of course it is always possible to solve a problem by throwing enough money at it, but I usually find that approach as almost offensive in it's simple-mindedness. Anybody can fling money, that takes no insight or knowledge at all. Understanding a system and then having the insight and ability to change it to do what you want is far more creative, PLUS it keeps things out of the waste stream. Disposable everything is the problem that we have now.
 

MaxHeadRoom

Joined Jul 18, 2013
18,864
My recollection of tape transport units use the same as the LP turntable, IOW a small synchronous motor.
Not asynchronous as the OP one appears to be.
Max.
 

shortbus

Joined Sep 30, 2009
6,885
Why would you think that a split-capacitor motor driving a tape loop would produce a warbling tone??
Because unlike you usually do I read the thread from the first post and look at the attachments.

Of course it is always possible to solve a problem by throwing enough money at it, but I usually find that approach as almost offensive in it's simple-mindedness. Anybody can fling money, that takes no insight or knowledge at all.
And your trying to make me look bad and not knowing what I'm talking about is offensive and simple minded. You should know by now when you try to make me look bad you always end up being the one who does. Talk about simple mindedness. Like I've told you many times read and understand before posting.
 

MisterBill2

Joined Jan 23, 2018
3,721
Because unlike you usually do I read the thread from the first post and look at the attachments.



And your trying to make me look bad and not knowing what I'm talking about is offensive and simple minded. You should know by now when you try to make me look bad you always end up being the one who does. Talk about simple mindedness. Like I've told you many times read and understand before posting.
I did read through everything, and what I came across was that some speed controllers do produce small rapid variations in the speed.
I did not come across anything about warbiling, although some controllers would cause such an effect, probably. There has not been any explanation about the reason for wanting to reduce the speed, which is sort of important.
I was not trying to make you look bad, just pointing out that there are reasons for not replacing things, but repairing them.
 

shortbus

Joined Sep 30, 2009
6,885
I was not trying to make you look bad, just pointing out that there are reasons for not replacing things, but repairing them
If not meant for me, why quote me?

I did read through everything, and what I came across was that some speed controllers do produce small rapid variations in the speed.
I did not come across anything about warbiling, although some controllers would cause such an effect, probably. There has not been any explanation about the reason for wanting to reduce the speed, which is sort of important.
So you don't think "small rapid variations in speed"(your own words) would make a warbling sound from a tape?
 
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