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Homemade rotary phase converter

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Joshjosh

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Hi has anyone had any experience building a rotary phase converter? I’m currently weighing up my options of running a 3 phase wadkin bao and considering this
Thanks josh
 

SammyQ

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Not worth the candle. Motor power rating goes down, there are usually balancing problems, you have to run two motors with attendant lecky costs.
Only reason it keeps getting talked about is the Murricans - with cheap power? - bigging them up.
VFD's rule!

Sam
 

wallace

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If you plan on just having one 3 phase machine then a vfd is possibly the best option.
If your going down the wadkin slippery slope then a rotary converter is a good option. A static is a poor second place but works.
 

Joshjosh

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wallace":vyzxozb9 said:
If you plan on just having one 3 phase machine then a vfd is possibly the best option.
If your going down the wadkin slippery slope then a rotary converter is a good option. A static is a poor second place but works.
Yeah from what I’ve read a vfd would be a lot simpler solution but the bao has two motors plus I think they’re 400v. So standard vfd isn’t an option. Which led me down the route of building a rotary phase converter. From what I’ve seen online they seem not too hard to put together provided I follow a plan accurately
But wondered if any one had first hand experience building one? Or had a simpler low cost solution to powering a dual motored 400v 3 phase machine?
Thanks for the help I appreciate it
Josh
 

Ttrees

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Sorry, I can't give much help, but just to let you know there's newer VFD's on the market,
that will power 400v motors.
For a Chinese 3hp, it costs under £150, compared to under a £100 quid for the more typical 240v voltage out.

Tom
 

Trevanion

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The only awkward bit is the Wadkin BAO part. The separate 400v (I don't think either is dual voltage) motors make it a royal pain for conversions to single phase power. The machine is also very awkward to change motors to 240v from what I understand from when I was looking into it and the machine ideally needs to be stripped down to take them out.

I would personally avoid going down that route (As I did in the end) and keep an eye out for a single phase machine / a more easily converted one. By the time you've put down the money and time into a rotary phase converter you might as well have bought a single phase machine.
 

Joshjosh

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Trevanion":1qteaq0l said:
The only awkward bit is the Wadkin BAO part. The separate 400v (I don't think either is dual voltage) motors make it a royal pain for conversions to single phase power. The machine is also very awkward to change motors to 240v from what I understand from when I was looking into it and the machine ideally needs to be stripped down to take them out.

I would personally avoid going down that route (As I did in the end) and keep an eye out for a single phase machine / a more easily converted one. By the time you've put down the money and time into a rotary phase converter you might as well have bought a single phase machine.
If I could get the stepped vfd that produces the 400v 3phase then would this then become an easy operation? Or is the feed motor hard to access? I’m presuming I’d need 2 different vfds calibrated to each motor, although if it’s possible to run off one vfd and have less controllability of feed speeds I might consider that
Thanks for everyone’s help
 

Joshjosh

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Ttrees":2ei5l0vl said:
Sorry, I can't give much help, but just to let you know there's newer VFD's on the market,
that will power 400v motors.
For a Chinese 3hp, it costs under £150, compared to under a £100 quid for the more typical 240v voltage out.

Thanks I didn’t realise they were that cheap. Where have you seen them? eBay?
Thanks josh
Tom
 

Zedheadsteve

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Not tried to build a rotary converter, but i have been using an analogue 15hp rotary (good for running up to 7.5hp motors) for around 20 years. Balance between phases is ok to about 10% or better which has been fine for a conventional milling machine, bandsaw, hones and a Colchester Triumph 2000 7.5 hp lathe. Will support several machines at once without need to worry about variance in demand as long as no more than 7.5hp starting up at same time ( but I can only really use one machine at a time!). I have been told that normal true 3 phase commercial supplies may not achieve much better than 10% balance at all times. Not sure how true this is.

Also using my rotary convertor to drive a 32cfm Ingersol Rand variable speed rotary screw compressor rated at 12.5hp 3 phase. The ‘soft’ start of the VFD compressor has proved to be no problem for my nominally rated 7.5hp rotary convertor and works just fine. Had no problems whatever in 20 years. A genuine full 32cfm is pretty handy from a domestic 240v supply! (Piston compressor rated at 14cfm 3hp 240v will only deliver around 8 or 9 cfm for real, rotary screw provides it’s full cfm rating).

CNC machines can require a 5% (some3%) phase balance. Digital rotary convertors can achieve this. Also many CNC machine controllers will run with 240v so only the machine drive motors use the 3 phase. Out of balance phases do result in less power - and rougher running motors.

Unfortunately as with running my 3 phase vfd compressor on my rotary convertor, no guarantees will be provided by the equipment suppliers - all you can do is pay the money and have a go! For me, it has worked just fine.
 

Ttrees

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Joshjosh":1zbtixzf said:
Thanks I didn’t realise they were that cheap. Where have you seen them? eBay?
Thanks josh
Tom
[/quote]

Sorry, was away for a bit.
Here is the VFD I was talking about, selling for 150 euro's in Ireland.
vfd 380V OUT.jpg

VFD 380 out label .png


The seller keeps putting these up, although knows nothing about them when queried.
Well, the specs pulled off of his computer states 380v out, but that's no guarantee, that could be for another VFD I suppose (hammer)
These are probably all over eBay, I haven't looked yet.
Bob Minchin (9fingers) has been talking about them for some time, though I'm unsure if its this
brand he was on about.

Tom
 

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wallace

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Just because a motor tag just says one voltage ie 400v doesn't always mean it isn't dual voltage. I've done 5 motors recently on machines that just needed the connections changing in the box. I've also taken motors to a winders to have them bring out the star windings to make it low voltage. I've just had a motor rewound to 240v at a cost of £350.
A static converter is cheapish and will work. I run an 18" p/t on one and it works well and I don't notice the lack in power
 

Joshjosh

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memzey":1nf0132a said:
If the motor is wound star and 400v on the plate, you can actually take out the star joint and re configure it delta/240v yourself. See my thread here for a quick and dirty how to -> star-point-in-three-phase-motor-t113222.html
Thanks for the help I’ll have to wait till it’s delivered and see what access is like to the motors
 
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