Rotary converter motor question

[maz0]

Hi folks,

I’m going to give building a rotary converter a bash as I have access to a 3 phase motor and its cheaper than the £1000 for buying new.

I just wanted to know if its possible to build one with an idler motor thats 2870 rpm or does it have to be with a 1400 rpm motor? I cant see anything online which stipulates 4 pole vs 2 pole or not.

help much appreciated, thanks

 

[Fazerruss]

I'm interested to know too as I might come across a 10hp 2800rpm motor eventually.
I would have thought it shouldn't make any difference if it has the same connection. The input frequency is still the same.

 

[eddie49]

From "Building a Phase Converter" at

http://metalwebnews.com/howto/ph-conv/ph-conv.html

"The speed rating is not important; from 1100 to 3600 RPM are all fine. The higher speed might produce slightly better phase angles, but the lower speed is generally easier to start."

 

[WorkshopChris]

Out of interest are you going for 230v 3 phase. Or running a transformer to step up to 415v 3 phase.

 

[addjunkie]

The man at transwave advised me too use a two pole motor!

 

[maz0]

Out of interest are you going for 230v 3 phase. Or running a transformer to step up to 415v 3 phase.

I'll be happy just to get it working 230v first, once I manage that, I will see if there is any merit in me going for the transformer type!

 

[WorkshopChris]

I'll be happy just to get it working 230v first, once I manage that, I will see if there is any merit in me going for the transformer type!

There is a youtube video in a post on here somewhere where a guy built a converter that gives 415v ish without a transformer with the star point as neutral so 415v P2P and 230v P2N.
I need to try and reverse engineer to copy it as I still can not get my head around exactly how it works, looks to be too good to be true, there must be a catch, although I hope I am wrong.
I have most of the bits, just not enough hours in the day.

 

[maz0]

There is a youtube video in a post on here somewhere where a guy built a converter that gives 415v ish without a transformer with the star point as neutral so 415v P2P and 230v P2N.
I need to try and reverse engineer to copy it as I still can not get my head around exactly how it works, looks to be too good to be true, there must be a catch, although I hope I am wrong.
I have most of the bits, just not enough hours in the day.

This one?

 

[WorkshopChris]

Yes that's the one, part 1&2 were around for a while, i think he uploaded part 3 last year.

 

[Seadog]

It seems like a good design. You start by applying 230v across two phases ( star connected motor) which provides the initial excitation. The motor is spun up with a donkey motor which then drops out and the 230v supply is switched across one leg and the star point (the star being neutral).

 

[WorkshopChris]

It seems like a good design. You start by applying 230v across two phases ( star connected motor) which provides the initial excitation. The motor is spun up with a donkey motor which then drops out and the 230v supply is switched across one leg and the star point (the star being neutral).

That's how i understood it the downside is it looks like you need a fair size donkey motor, it looks simple but just wondering why no of the commercial versions run this setup?
EDIT> Should read "looks like you need a fair size pilot motor"

 

[Pete.]

Fill yer boots!

 

[maz0]

That's how i understood it the downside is it looks like you need a fair size donkey motor, it looks simple but just wondering why no of the commercial versions run this setup?

In part 2 at 12:16 he says that he has found old motors work the best for this application and explains it a bit. If new motors are too well balanced or constructed to such a high standard then its possible that this application doesn't suit them running as phase converters and hence no ability to churn them out en masse?

 

[Seadog]

the downside is it looks like you need a fair size donkey motor,

Not really, probably a 1/2 hp would suffice. I've a hankering to build one just for the hell of it.

 

[maz0]

Not really, probably a 1/2 hp would suffice. I've a hankering to build one just for the hell of it.

Go oooon, we can make it a group project....

 

[addjunkie]

The belt tension part, doesnt quite do it for me. Very heath robinson.

 

[Seadog]

The belt tension part, doesn't quite do it for me. Very heath robinson.

I agree, but it's a simple, if not elegant, solution. It could be done with an electromagnetic clutch, if you had one laying around. I've a 4kW 3-phase motor and a 3/4 hp single phase motor so have the makings. I'd just need to source some capacitors and belts and pulleys. I'll see if I can find a round tuit in the workshop

 

[addjunkie]

I have a static, and a spare motor....in the roundtooit pile. As my lathe has a two speed motor but only run on one speed with the static.