speed control for single phase fractional hp ac motor

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BertPage

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I am needing to control the speed of a hoists used to accurately position a 50lb load. It would be used approximately 5 times per hour for less than 1 minute each time. I am thinking there is a device to do this but not sure what. I don't want to spend the money for a variable speed hoist and the space available won't allow a big hoist.

Anyone every use a reliable speed controler on a fractional HP ac motor?

Thanks very much for your help!
 
Since an induction motors speed is based upon the number of poles as well as the frequency there's not much that you can do except to a just the frequency But that you have ruled out as an option.
Some speed control my be accomplished by reducing the voltage which often results is addition motor slip speed.
By ramping the voltage down while there is a load on the more should result in a lower speed but motor heating may be an issue depending upon the duty cycle. If the motor is unloaded or lightly loader there most likely be an insignificant speed reduction as to more will attempt to reach its running speed based upon 60hz.
With smaller motors I know that some speed control can be accomplished with a heavy duty dimmer switch.
I not familiar if there are soft start started for 1ph motors but if I can recall they offer are available with ramp up and down.
It's been a while for me but take a look to see if a soft starter my be available.
 
Type of single phase AC motor is very important in determining how to vary the speed - and some can not really be varied by any significant amount.

If you have a capacitor start motor with governor switch to kick in the starting capacitor below a predetermined speed you are out of luck at varying motor speed. This motor must run at a speed above the governor setting or it will kick in the capacitor to try to increase the torque. This operation was only designed for short duration during starting and not to run in that condition.
 
If you do have a motor that can not have the speed varied, you can switch to either a DC motor with a DC drive or even to a three phase motor and use a AC drive that takes single phase input and delivers three phase output. Of course this is easiest if the existing motor is a NEMA motor and has a standard frame size.
 
What they said. I'll only add that if you happen to find that there are VFDs for single phase motors, it's highly unlikely they will work on the kind of motor used on a hoist.

2nd issue, and a major one. NOBODY should tackle adding variable speed to a hoist motor unless you are a professional hoist control mfr or integrator with years of specific training and experience! The consequences of getting it wrong are dropping the load and possibly killing someone. There is a very specific issue with regard to having a full blown Flux Vector Control drive fed to a 3 phase motor that has a shaft encoder to allow for a "torque proving" routine at zero speed that is necessary before releasing the mechanical holding brake on the hoist. If you don't understand what I said there, stop there. Either hire a pro or do your positioning some other way.

Safety first.
 
Jraef said:
What they said. I'll only add that if you happen to find that there are VFDs for single phase motors, it's highly unlikely they will work on the kind of motor used on a hoist.

2nd issue, and a major one. NOBODY should tackle adding variable speed to a hoist motor unless you are a professional hoist control mfr or integrator with years of specific training and experience! The consequences of getting it wrong are dropping the load and possibly killing someone. There is a very specific issue with regard to having a full blown Flux Vector Control drive fed to a 3 phase motor that has a shaft encoder to allow for a "torque proving" routine at zero speed that is necessary before releasing the mechanical holding brake on the hoist. If you don't understand what I said there, stop there. Either hire a pro or do your positioning some other way.

Safety first.
Click to expand...

I was about to say something similar but he beat me to it. This is not a DIY type project.
 
I will second what was said about getting some who knows about hoist, and many will have a brake that is suposed to engage when power is turned off, and a speed control could burn it out by allowing it to partially engage when the motor is running at a lower voltage, this could end up geting some one hurt.
 
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Jraef said:
What they said. I'll only add that if you happen to find that there are VFDs for single phase motors, it's highly unlikely they will work on the kind of motor used on a hoist.

2nd issue, and a major one. NOBODY should tackle adding variable speed to a hoist motor unless you are a professional hoist control mfr or integrator with years of specific training and experience! The consequences of getting it wrong are dropping the load and possibly killing someone. There is a very specific issue with regard to having a full blown Flux Vector Control drive fed to a 3 phase motor that has a shaft encoder to allow for a "torque proving" routine at zero speed that is necessary before releasing the mechanical holding brake on the hoist. If you don't understand what I said there, stop there. Either hire a pro or do your positioning some other way.

Safety first.
Click to expand...

Kind of depends on just exactly what kind of hoist we are talking about and exactly what the intended load is, but yes definitely worth thinking about. The more directly coupled the motor is to the load the more risk there may be in sudden shift of load if motor fails. If there is worm gear drive between the motor and load, then the worm gear alone may hold the load in place even if the motor disappears somehow.
 
As other have stated, adding a speed control to a hoist will mess up the brake and you are probably violating it's UL rating. Why not add a block and tackle below the hoist? You can rough position the load with the hoist, then place the load with the block and tackle. Sounds dumb, but thats all I can come up with!
 
BertPage said:
I am needing to control the speed of a hoists used to accurately position a 50lb load. It would be used approximately 5 times per hour for less than 1 minute each time. I am thinking there is a device to do this but not sure what. I don't want to spend the money for a variable speed hoist and the space available won't allow a big hoist.

Anyone every use a reliable speed controler on a fractional HP ac motor?

Thanks very much for your help!
Click to expand...

It seems like just a year ago but it's more than that.
My wife bought on ebay a beautiful 1952 sewing machine. Despite the vintage, it was electric. And with a beautiful wooden cabinet. A nice piece of furniture.
The wiring was in a parlous state. And incorrectly connected.
We knew that going in.
The seller said "You need an electrical engineer to check out the wiring."
Mrs B, completely dead pan, "I might know one."
After struggling to get it in the car, we got it home.
I worked out how it should be connected.
It was a simple, single phase universal motor.
Speed control was a series rheostat operated by the right knee pressing a lever under the desk.

OK. After the rewire, the control worked nicely. The machine ran smoothly and quietly. My job done.
But....at the sewing end, there were essential parts missing.

The missus has since bought a new machine. It's also speed controlled and single phase. Unless/until it develops a problem beyond the warranty period I don't need to know...
 
Besoeker said:
It seems like just a year ago but it's more than that.
My wife bought on ebay a beautiful 1952 sewing machine. Despite the vintage, it was electric. And with a beautiful wooden cabinet. A nice piece of furniture.
The wiring was in a parlous state. And incorrectly connected.
We knew that going in.
The seller said "You need an electrical engineer to check out the wiring."
Mrs B, completely dead pan, "I might know one."
After struggling to get it in the car, we got it home.
I worked out how it should be connected.
It was a simple, single phase universal motor.
Speed control was a series rheostat operated by the right knee pressing a lever under the desk.

OK. After the rewire, the control worked nicely. The machine ran smoothly and quietly. My job done.
But....at the sewing end, there were essential parts missing.


The missus has since bought a new machine. It's also speed controlled and single phase. Unless/until it develops a problem beyond the warranty period I don't need to know...
Click to expand...

But that sewing machine didn't have an electric brake to hold a load, like a hoist does ;)
 
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