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Author Topic: Rotary Phase Converter  (Read 5682 times)

Mike Sokol

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Re: Rotary Phase Converter
« Reply #30 on: October 26, 2017, 06:23:52 pm »

Has anyone discussed a big single phase motor and a 3 phase generator, connected with a belt?   I ask because I know a guy who ran a 3 phase c-n-c machine in his basement with one... seemed to work fine


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Of course that works, but it's seen as too expensive and inefficient to be practical. But if I had a spare 3-phase generator laying around it would be pretty cool.
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Mike Sokol
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Stephen Swaffer

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Re: Rotary Phase Converter
« Reply #31 on: October 27, 2017, 04:32:30 pm »

Yeah, that's the first thing I thought of. My thought was since these inverter generators will sync to any parallel source, all you would have to do it build a tiny 3-phase signal generator. That might work with WYE loads, but probably not with Delta motor loads.

So, an inverter genny (I assume) takes DC bus and "Inverts" it into 120 VAC.  Putting 3 of these together and synchronizing them makes 3 phase output.

A freq drive takes an AC supply, converts it to a DC bus, and creates 3 synchronized phases 120 deg apart.

Sounds like we are re-inventing the wheel?

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Steve Swaffer

Tim McCulloch

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Re: Rotary Phase Converter
« Reply #32 on: October 27, 2017, 07:33:43 pm »

So, an inverter genny (I assume) takes DC bus and "Inverts" it into 120 VAC.  Putting 3 of these together and synchronizing them makes 3 phase output.

A freq drive takes an AC supply, converts it to a DC bus, and creates 3 synchronized phases 120 deg apart.

Sounds like we are re-inventing the wheel?

STOP THE MADNESS!!!  The phase wheel is now running backwards!

I hope you kids are happy with yourselves.

/snark
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Mike Sokol

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Re: Rotary Phase Converter
« Reply #33 on: October 27, 2017, 07:50:14 pm »

STOP THE MADNESS!!!  The phase wheel is now running backwards!

I hope you kids are happy with yourselves.

/snark
😊
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Mark Cadwallader

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Re: Rotary Phase Converter
« Reply #34 on: October 27, 2017, 08:21:31 pm »

😊

That's a real fancy-ass bumper car you have, Mike.
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Stephen Swaffer

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Re: Rotary Phase Converter
« Reply #35 on: October 27, 2017, 11:07:41 pm »

I realize that the waveform's on VFD's are designed and optimized for running 3 phase motors (but that is what the OP was about running).  Guess I'm just trying to figure out what the magic device is that let's a Honda inverter genny run an AC unit-starting and stopping motors, etc.  Run power tools-starting and stopping motors, etc. etc.  without blowing up-but a VFD can't do the same?  Down inside the magic box it is physics at work-the electrons don't know if they're in an inverter genny, or a vfd.  It might be a good idea to have load reactor (maybe just a 3 phase iso transformer?) for protection? 
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Tom Bourke

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Re: Rotary Phase Converter
« Reply #36 on: October 28, 2017, 09:14:50 am »

I realize that the waveform's on VFD's are designed and optimized for running 3 phase motors (but that is what the OP was about running).  Guess I'm just trying to figure out what the magic device is that let's a Honda inverter genny run an AC unit-starting and stopping motors, etc.  Run power tools-starting and stopping motors, etc. etc.  without blowing up-but a VFD can't do the same?  Down inside the magic box it is physics at work-the electrons don't know if they're in an inverter genny, or a vfd.  It might be a good idea to have load reactor (maybe just a 3 phase iso transformer?) for protection?
I think it has to do with design goals. If you assume the load is going to be a motor hard wired you design for that.  This let's you use the counter EMF and other characteristics to your advantage for stability or efficiency.   The tradeoffs may include a sensativity to disconnect.

The other tradeoff may be cost of parts vs robustness. The reality is that inverters, audio amps, and vfd all use the same technologies.  Some amps are more robust than others. Overall newer technology has improved costs and robustness.  This is true for all of these applications.
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Frank Koenig

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Re: Rotary Phase Converter
« Reply #37 on: October 28, 2017, 11:15:17 am »

I think it has to do with design goals. If you assume the load is going to be a motor hard wired you design for that.  This let's you use the counter EMF and other characteristics to your advantage for stability or efficiency.   The tradeoffs may include a sensativity to disconnect.

The other tradeoff may be cost of parts vs robustness. The reality is that inverters, audio amps, and vfd all use the same technologies.  Some amps are more robust than others. Overall newer technology has improved costs and robustness.  This is true for all of these applications.

This. Power electronics is a complex, subtle, and, in my opinion, under appreciated business. I'm impressed as hell with the motor drives they're putting in cars that are about the size of a breadbox and can handle a good chunk of a MW at ~400 V while letting you finesse that fixed-gear induction motor to drive smoothly at < 1 mph. -F
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Stephen Swaffer

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Re: Rotary Phase Converter
« Reply #38 on: October 28, 2017, 03:42:06 pm »

I agree-in my day job I deal with inverters from 1 hp to 300 Hp running on both 480 V and 230 V.  The technology has advanced tremendously over the last 10 years-dropping the price to where you can put a drive in instead of an across the line contactor for some loads at a very small increase in cost.  Ten years ago we started using inverter welders where Lincoln could actually design a waveform to minimize splatter-instead of just making a sine wave "work".  Obviously welding is a lot of make and break under load-and the load is actually a short circuit.

How long have Honda genny's been on the market?

I wonder how much of the wisdom that you can't disconnect under load is old thinking-thinking that in 99% of applications is probably best practice anyway?  Often, no good reason to challenge it.

Except for liability when dealing with a hoist (yes I know the ins and outs of overhead hoists), the ideal thing-and probably most cost effective for Mike would be to eliminate the contactors and drive the chain motors with a drive.  Of course, you'd have to wire in limits, etc-but think about the mechanical wear and tear savings as you decel slowly into place and accel slowly to take up mechanical slack. 

The quote I inserted up thread is current from a major manufacturer-and it really doesn't give a stern warning about damaging the drive.  It wouldn't cost a lot to upsize a drive to 300-400% capacity if you were going to "abuse" it.

Not trying to be argumentative-but I can be hard headed when asking "why" at times.  Sometimes it works out, sometimes not.

Actually it looks like someone is already doing this:

https://www.americanrotary.com/products/view/ad-digital-smart-series

A digital 1 phase-3 phase converter 1.5 HP start is smallest they do-$577.  Still pricey-but it would be very portable.

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Steve Swaffer

Tim Padrick

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Re: Rotary Phase Converter
« Reply #39 on: October 29, 2017, 05:20:40 am »

Mike, email me at work, tim at jonas productions dot com.  We have a RotoPhase that we might sell.
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