Electric motor help, please.

[McNamara]

Hello,

I have two electric motors which are capable of single and three phase operation. I have given one a clean and got the bearings rolling smooth, adjusted the wiring to single phase according to the diagram inside the cover and tested it, which after a few blown fuses worked when the black wire was disconnected from the plug (green, brown, blue, black 4 wire).

So I am guessing the black wire is for three phase operation (?)

I would like to know if a capacitor (start,run) should now be used because it was previously used on 3 phase, and why does the shaft alternate direction every time it is switched on?

Thanks to you all, it seems like a good place to ask!

Motors are 2.2kW / 2.5kW MarelliMotori 230 / 400
I'm in England UK if that matters at all.

Ash

 

[Pete.]

Never seen any motor like that - or heard of one. Are you sure they are not just star/delta voltages for 3 phase?

 

[McNamara]

Maybe they are? Identified by a Y symbol (star) and triangle (delta)?
I know very little of this subject but learning.

If that is the case, would it be much trouble to get them operating on 240 single phase? It ran well this afternoon for around 5 minutes!

Thanks again

 

[ronan]

It was only giving one third of its available power if you ran it on a single phase. You need a vfd or rotary phase converter to get it to run more efficiently.

 

[McNamara]

Yes that's how it looks to be, thanks to you both.
Looks like I should trade them in for a single phase instead.

I'll get there in the end!

Cheers

 

[ronan]

Yes that's how it looks to be, thanks to you both.
Looks like I should trade them in for a single phase instead.

I'll get there in the end!

Cheers

Three phase motors are preferred if you want to run a lathe or mill as they give smoother power and this is reflected on the workpiece. If you have a single phase motor you maybe able to make yourself a rotary phase converter to drive the three phase motor, depending on its size. A cheap chinese vfd (variable frequency drive) will drive the motor if you just want something to run a drill press or something simple.

 

[McNamara]

That's an interesting thought, I had been looking at 3 phase generators and rotary converters but the prices are too high for the purpose. I've got an old 1.5 hp single motor which is bigger than these at half the Hp. I'm sure the start windings are faulty in it, though (works with a rope start!)

Something to look into before selling them on I think, cheers Ronan

 

[MattF]

I've got an old 1.5 hp single motor which is bigger than these at half the Hp.

Single phase motor?

 

[McNamara]

Yes it's a single phase 'brook motors' 1.5 hp, 1450 rpm
But I'm sure the the start winding is crap.

 

[MattF]

You'd be using that as the driver to drive on of the three phase motors as the generator then, I assume? Is it a cap start motor? If so, might be worth checking that's not the cause of your starting problem.

 

[McNamara]

It is a cap start motor and I have cleaned it all out last month and tested the capacitor which seemed ok but would hum and blow the fuse in less than a second with and without the cap in place under no load. I tried 15A fuse wire with the same result. I did read something that motors should start without a cap under no load? which is where I decided it must be the start windings.

It has a clutch which I checked / cleaned and I did a light bulb test which someone recommended and I think that did work (I will check that again).

So bit of a story right there but I might aswell inform you!

Perhaps I'm wrong on that too, and again I'm amazed by your help thanks very much.

 

[MattF]

I did read something that motors should start without a cap under no load?

Not that I know of. I may be incorrect, (there are others more familiar with motors who will correct me if I'm wrong), but the cap is necessary for starting, load or no load. It'll just sit there humming otherwise. How did you test the cap? Even with a capacitance meter, you have to take readings with a pinch of salt on occasion.

 

[wheresmejumper]

single phase motors will run without the start cap,but you need to spin the shaft manually to get them going

in the right direction

 

[McNamara]

I checked the cap with a multimeter (something I saw on YouTube)
It seemed to discharge as it should, but now I think I will buy a replacement to make sure. If it turns out that the start windings are no good would this still work for generating 3 phase? It goes by rope! Haha

 

[MattF]

Testing a cap with a multimeter gives no useful indication of condition. Try the motor with another cap.

 

[ronan]

I checked the cap with a multimeter (something I saw on YouTube)
It seemed to discharge as it should, but now I think I will buy a replacement to make sure. If it turns out that the start windings are no good would this still work for generating 3 phase? It goes by rope! Haha

I heard of an owner of a pretty large machine shop in the usa who powered his shop by a rope start motor rotary phase converter, it was there of years and seemed to work fine according to him.

 

[wheresmejumper]

bit of rope is the cheapest,most efficient,most reliable method by far
it stops the lights dimming in the next door neighbours on startup too
i am far too lazy to even considering it though

 

[graffian]

bit of rope is the cheapest,most efficient,most reliable method by far
it stops the lights dimming in the next door neighbours on startup too
i am far too lazy to even considering it though

The lazy people fit a donkey motor to get the idler rotating.

 

[McNamara]

So I have a few things to get on with and learn about,
I'll let you know how things turn out and might be quizzing you again!

Cheers to you all

 

[wheresmejumper]

The lazy people fit a donkey motor to get the idler rotating.

it makes things a lot more complicated than a rope,even more than a start cap circuit.then there is the cost,the extra space,alignment and drag issues.