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Author Topic: Rotary Phase Converter  (Read 1314 times)

Art Welter

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Re: Rotary Phase Converter
« Reply #10 on: October 23, 2017, 11:38:01 am »

I just talked to the marketing/applications department at Phase-A-Matic and they're telling me I need a 20 horsepower rotary converter to run four 1-ton lifts. And it needs a 125-amp/120-volt breaker on the input of the converter. They're just looking at their marketing literature and won't let me talk to an engineer about the application. I need to measure actual current draw when I'm there next week.
Mike,

Sounds like they are going conservatively overboard for 4 two HP motors- 20HP for 8HP?
Also consider that chain motors lift quite slowly, you could run only one pair at a time, alternating stage left and right and use 1/2 the capacity rotary converter.

Art
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TJ (Tom) Cornish

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Re: Rotary Phase Converter
« Reply #11 on: October 23, 2017, 11:55:54 am »

If you want a project I think you can make your own funky phase convertor from a three-phase motor running on a single phase using one of its windings and a small single-phase motor with a belt clutch that you use to start the three-phase motor. The other two phases are taken from the non-driven windings of the the three-phase motor. I'm sure you can find plans with motor sizing guidance on the Internet. While not for industrial use, such a rig might have educational value in and of itself. -F
It's my understanding that this is how all rotary phase converters work - homemade or commercial, though I have never seen the need for a starter motor. 

Making your own is easy, though may require a little trial and error with capacitor values to level the voltages of each phase.
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Frank Koenig

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Re: Rotary Phase Converter
« Reply #12 on: October 23, 2017, 12:17:03 pm »

It's my understanding that this is how all rotary phase converters work - homemade or commercial, though I have never seen the need for a starter motor.

I think that's right. But I'm guessing that the purpose-built phase convertors are optimized (and have a built-in starting winding, etc.). I recall that the home brew ones require a convertor motor with several times the power rating of the motor to be driven, so can be pretty heavy for what they do. -F
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Stephen Swaffer

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Re: Rotary Phase Converter
« Reply #13 on: October 23, 2017, 12:21:16 pm »

Why not use a VFD? They take 3 phase to DC then back to 3 phase.  You can get them that will spec being usable on single phase supplies-usuallu have to oversize them a bit.  Also, you can run mutilple motors on a VFD.  Probably cheaper and lighter than a rotary.
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Tim McCulloch

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Re: Rotary Phase Converter
« Reply #14 on: October 23, 2017, 12:31:34 pm »

Back when I was in highschool and working as a projectionist at the local Rialto Theater we had rotary phase converters for the arc lamp supplies.  Everything else in the booth ran on single phase...

I don't recall that I ever noticed who made them but I know they ran flawlessly for a couple of decades and might still be in use to run the new xenon lamps that were installed 20 years ago.

As for motor load, Columbus-McKinnon publishes full load specifications for all their hoists.  A 1-ton, 16 FPM 3 phase 208v hoist draws <4 Amperes per leg.  Contact Dave Carmack at C-M if you have questions.
« Last Edit: October 23, 2017, 12:34:38 pm by Tim McCulloch »
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TJ (Tom) Cornish

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Re: Rotary Phase Converter
« Reply #15 on: October 23, 2017, 01:02:46 pm »

Why not use a VFD? They take 3 phase to DC then back to 3 phase.  You can get them that will spec being usable on single phase supplies-usuallu have to oversize them a bit.  Also, you can run mutilple motors on a VFD.  Probably cheaper and lighter than a rotary.
VFDs blow up if you disconnect the load while running - the back EMF toasts the IGBT devices.

Mike's application is powering an existing motor controller and setup which would use conventional switches/solenoids to turn the winch motors on and off.
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Mike Sokol

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Re: Rotary Phase Converter
« Reply #16 on: October 23, 2017, 01:37:46 pm »

VFDs blow up if you disconnect the load while running - the back EMF toasts the IGBT devices.

Mike's application is powering an existing motor controller and setup which would use conventional switches/solenoids to turn the winch motors on and off.

Exactly right. I want to provide 3-phase cam outputs with maybe 20 amps per leg at 230ish volts. I've talked to several rotary converter manufacturers today, and they all seem a bit lost with my questions.

Tom Bourke

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Re: Rotary Phase Converter
« Reply #17 on: October 23, 2017, 01:49:20 pm »

One of my hobbies is CNC and machine tools.  The forums I am on for that talks about single to 3 phase conversion all the time.

American Rotary sponsors one of the vintage machine youtube channels.  They also seam to have a good product and service.  I would tend to buy from them if I was not making my own.

I know of several ways to get 3 phase from single phase.

Of them I think a rotary is probably the best.  However I would defer to your chain motor and American Rotary having a conversation.  They have some regulated options.  I just don't know how sensitive a chain motor would be.  For CNC use I hear 2X the spindle current as a common multiplier for sizing a converter to load, regardless of who makes the converter. 

The second kind is a solid-state capacitor bank.  They work like a capacitor start / capacitor run motor only using your 3 phase motors as the motor.  they require tuning to load and are not as smooth as other methods.  The generated leg can get wild with varied loads. 

VFD generally require no switching between the motor and the drive.  They will blow up with a switched load.  Having said that, maybe there are units designed for this?  I have not seen one.  All they really are is an inverter.
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Tom Bourke

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Re: Rotary Phase Converter
« Reply #18 on: October 23, 2017, 01:57:26 pm »

Exactly right. I want to provide 3-phase cam outputs with maybe 20 amps per leg at 230ish volts. I've talked to several rotary converter manufacturers today, and they all seem a bit lost with my questions.
My guess is that a chain motor is not a load they hear about very much, if ever.  Even with a rotary converter the generated leg will be a bit wild.  Controls and electronics need to stay on L1 and L2.  L3 is the generated leg.  You can't really treat them like a generic utility provided service.
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Mac Kerr

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Re: Rotary Phase Converter
« Reply #19 on: October 23, 2017, 03:10:41 pm »

American Rotary sponsors one of the vintage machine youtube channels.  They also seam to have a good product and service.  I would tend to buy from them if I was not making my own.

Keith Rucker?

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