240v Motor Speed Controller - Advice required

[Shox Dr]

I need to control the speed of a 240v 1/4hp motor. It's a 3 wire motor ie Live to one wire neg to another with a 2.5uf cap across the neg and remaning wire. To reverse direction swap Neg to other side.

So I bought this controller. However it doesn't work on this type of motor.

It's to build a rotary table for welding. And since buying the above I found these I've emailed them but as usual for a supplier across the water I've yet to get a reply 4 days on

So what do type of controller do I need.

 

[Luke]

any particular reason you didn't use a 3ph motor and standard 1ph-3ph inverter?

 

[Shox Dr]

Yes. It has a 630:1 wormdrive gearbox. Shaft speed is max 2.06rpm I need to be able vary the speed from 0-2.06rpm. Preferably by foot control

 

[Luke]

2.06 rpm output shaft speed?

 

[Shox Dr]

yes, and that is too fast for some apps, you have to think in Inches per minute, so as the Dia of the item you are welding increases the speed needs to be reduced

 

[Luke]

A 4 pole/1500 rpm motor would give you 2.38 rpm maximum, 10:1 turndown would get you down to 0.238 rpm, though you'd have to consider if you really wanted to go that slow, and you'd have to add external cooling for the motor.

Those speeds are synchronous, so the motor would turn slower, due to slip, which will likely be of the order of a % or two.

 

[Shox Dr]

Thanks for the advise Luke but you are missing the point.

I've already got the motor, I need a solution to make this one work.

 

[Archie]

My guess is you have an induction motor so the speed is a constant related to the frequency of the incoming supply i.e 50Hz. In order to control the speed you will need a VFD more commonly referred to as an inverter. This will allow you to alter the frequency from around 0.5Hz to 120Hz and above depending on the model. You'll need a 1ph-1ph jobbie which are harder to come by that the 1ph-3ph ones which are all over eBay. Invertek make some. They are, of course, not as cheap as the thing you've already bought but should allow you to add a standard potentiometer to control the frequency and hence speed. Dunno about the cap though. I have an inkling that may cause issues.

P.S Someone tell me to shut up if I'm talking out of my jacksie. Electrickery not my strongest suit!

 

[Luke]

Yup, you can run some single phase motors off some 3 phase inverters, but the caps do/can cause issues!

 

[Shox Dr]

So the only way to alter the speed is by Hz ie VFD

 

[Archie]

Assuming it is an induction motor (most likely) then yes.

 

[Luke]

As above.

 

[nigelpcat]

Hi. You need a single to 3 phase inverter assuming you have only single phase if you have 3 phase then you need a 3 phase to 3 phase inverter. These will cost you about £100-200 depending on HP rating . They are cl;ever devices and the manual is very complicated but don't be put off. You can probably view the manual on line before you buy just to see if you are up to it ! I have one on my lathe and it's superb the motor speed is variable from say 100 RPM to 3000 RPM all at more or less full power. Once you have one you can vary motor speed with a potentiometer or the controls on the inverter, you will be able yo adjust ramp up time etc as well and time to stop. Try http://www.inverterdrive.com/default.aspx

 

[Shox Dr]

Bit of an old post this one Nigel.* The motor was in fact a 3ph motor been run with a cap. I bought a 240v 1ph to 240 3ph invertor and it works faultlessly.

You can see the use I put it to here



* seems to be happening a lot at the moment

 

[astro_al]

Since it has been completed and dragged up to the top, I will take the opportunity to hijack!

I have a 3 phase motor running off a 3 phase supply that I need to vary the speed of (with a twiddly knob or whatever). What is the best / cheapest way of doing that? It is the fan for my forge, so when I turn it down I don't mind it losing power / torque.

Cheers, Al.

 

[madkayaker]

this might help http://forum.allaboutcircuits.com/showthread.php?t=9832

 

[tigler]

For future ref , with single phase induction motors a light dimmer can be used to control speed !! I've done this a few times with low powered motors.

 

[Shox Dr]

For future ref , with single phase induction motors a light dimmer can be used to control speed !! I've done this a few times with low powered motors.

It will, however you will lose all torque

 

[astro_al]

Is that true with a 3 phase motor too? I don't mind losing torque when its turned down.

Ta Al

 

[madkayaker]

its only a single phase device