Rotary Converter

[Onoff]

I'm not starting this project from scratch I must start out by saying. The "guts" of it, pictured below was thought up by a mate on another forum who successfully used it until he had 3 phase laid on.

It's clever (imo) as it uses a 110V transformer rewired as an auto transformer by connecting primary and secondary in series to give 230+110 so in reality in excess of 350V.

I've a big 5kVA trannie I can repurpose.

Off to the garage to see what that big old motor is I kept and have been meaning to use for "something" for about 30 years!

 

[Onoff]

This is the biggest motor I have:

Windings come out on 3 wires. I presume the star point is buried inside? Between any two phases measures nom. 10 Ohms. Any phase to earth nom. 50 MOhms. It has tbf been sitting in a damp garage for 30 years.

Any good for use in a rotary phase converter? Thinking not...vague recollection the motor wants to be twice the HP of the motor you're trying to run and faster rpm wise is better.

Cheers

 

[ukracer]

This is the biggest motor I have:

View attachment 297614

View attachment 297615

Windings come out on 3 wires. I presume the star point is buried inside? Between any two phases measures nom. 10 Ohms. Any phase to earth nom. 50 MOhms. It has tbf been sitting in a damp garage for 30 years.

Any good for use in a rotary phase converter? Thinking not...vague recollection the motor wants to be twice the HP of the motor you're trying to run and faster rpm wise is better.

Cheers

What do you need 3 phase for then?

 

[Hopefuldave]

A bit small for much more than a pillar drill... I have a pair of motors totalling 11 HP and use an old oil-cooled welder with a rewound secondary for 415v.

Dave H. (the other one)

 

[Onoff]

A bit small for much more than a pillar drill... I have a pair of motors totalling 11 HP and use an old oil-cooled welder with a rewound secondary for 415v.

Dave H. (the other one)

That's handy as the only 3P machine I've got is a pillar drill!

 

[Onoff]

So a rotary converter with a 1.5KW motor should run my 3P drill no problem? Drill motor plate:

Not sure if a 3kVA 110V trannie would do to convert to an autotransformer or whether I need to go up to the 5kVA?

 

[Onoff]

A bit small for much more than a pillar drill... I have a pair of motors totalling 11 HP and use an old oil-cooled welder with a rewound secondary for 415v.

Dave H. (the other one)

Are your two motors matched i.e the same? Could I connect a few different motors to up the HP of the "idler"?

 

[Barking Mat]

As an aside.

My mate runs his huge lathe off a big single phase motor.

His 3 phase mill...

He has a big 3ph motor wired across one of the phases on 220v, he starts it with a powerdrill.

It spins, producing 3ph ,220 volts, his 3ph mill runs, not as quickly as 400 v 3 ph, but it works...

Mental, no clever electrics, motor and powerdrill start.

My thoughts..

 

[graffian]

As an aside.
My mate runs his huge lathe off a big single phase motor.
His 3 phase mill...
He has a big 3ph motor wired across one of the phases on 220v, he starts it with a powerdrill.
It spins, producing 3ph ,220 volts, his 3ph mill runs, not as quickly as 400 v 3 ph, but it works...
Mental, no clever electrics, motor and powerdrill start.
My thoughts..

I ran a cutter grinder using an old three phase motor, I pull started the big motor/converter with a bit of string.

 

[Turbo]

That's handy as the only 3P machine I've got is a pillar drill!

If its just for the drill would it not be easier to buy one of the £30 vfd's on Amazon. That gives you variable speeds with less belt swapping plus fwd/rev.

 

[Onoff]

If its just for the drill would it not be easier to buy one of the £30 vfd's on Amazon. That gives you variable speeds with less belt swapping plus fwd/rev.

Can you point me at one please?

So that'd be 230V single phase in and 230V 3P out meaning I have to rewire the motor in delta?

 

[Hopefuldave]

Yep, pop the cover off the box where the wires go into the motor, if there are 6 terminals with 3 of them linked it's in star connection, change the links from all down one side to three straps across and it'll be in delta, a 230-230 VFD will be perfect

Dave H. (the other one)

 

[Hopefuldave]

Are your two motors matched i.e the same? Could I connect a few different motors to up the HP of the "idler"?

I have a 3hp and a 7hp connected up, not even the same rpm, work fine...

Dave H. (the other one)

 

[not done it yet]

It spins, producing 3ph ,220 volts, his 3ph mill runs, not as quickly as 400 v 3 ph, but it works...

Speed is related to Hertz, for induction motors, so how does it run more slowly?

 

[Onoff]

It spins, producing 3ph ,220 volts, his 3ph mill runs, not as quickly as 400 v 3 ph, but it works...

Speed is related to Hertz, for induction motors, so how does it run more slowly

Speed also depends whether it's connected star or delta.

 

[Onoff]

I have a 3hp and a 7hp connected up, not even the same rpm, work fine...

Dave H. (the other one)

Just connect them in parallel?

 

[not done it yet]

Speed also depends whether it's connected star or delta.

Wrong. Think what VFD means for induction motor speed control.

 

[awemawson]

Speed also depends whether it's connected star or delta.

No it doesn't !

However speed can be changed by 'pole switching' in some motors but I doubt that's what you're thinking about.

As an aside, when I only had a 2.3 KW Transwave static converter to run the workshop, if I wanted to get the big Cincinnati horizontal mill spinning, I'd first start the Colchester Student, then the Bridgeport, as their motors contributed to the 'generated leg' and allowed for the larger starting current on the Cincinnati. Once the motor was up to speed I could stop the lathe and Bridgeport.

 

[Turbo]

Can you point me at one please?

So that'd be 230V single phase in and 230V 3P out meaning I have to rewire the motor in delta?

Thread here.
https://www.mig-welding.co.uk/forum/threads/amazon-1-5kw-220v-vfd.113498/

Just a case of watching out for them on Amazon.

 

[Hopefuldave]

Just connect them in parallel?

Yep, works fine for me and others.
For more than you'll ever want to know, the Practical Machinist board has a forum dedicated to phase converters, VFDs etc with an incredibly long but very helpful thread on DIY rotary converters.

Somewhere on here there are wiring diagrams for my OTT all-the-bells-and-whistles converter, split between AC power and control planes, and pics of my DIY lash-up coil winder for the new secondary winding to get 415v to feed it. I do have a bit of an obsession with gilding lilies...

Nowt wrong with VFDs, I have two on my lathe (one for spindle motor, one for suds pump) but they have to be set up to match the motor, an RPC is plug and play for whatever you like (did the lathe before I knew about RPCs), my RPC does my mill with spindle and feeds motors, suds pump and electromagnetic clutch/brake, pillar drill, 7x12 bandsaw, inverter TIG, yada yada - just plug in an away they go

Dave H. (the other one)