# It is a jungle out there: Phase converter, 208 motor and a headache.



## gnuuser (Jan 13, 2013)

buck/boost transformer can be wired between the phase converter and motor to bring the voltage closer to the motor requirements.
this info should help
https://cdn.automationdirect.com/static/manuals/buckboostinstallguide/buckboostinstallguide.pdf


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## splatz (May 23, 2015)

https://www.americanrotary.com/blog/balanced-voltage-claims-truth-or-fiction/


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## sparkiez (Aug 1, 2015)

splatz said:


> https://www.americanrotary.com/blog/balanced-voltage-claims-truth-or-fiction/


funny enough, it was one of their phase converters and idler/generators. I figured it had something to do with the capacitance in the circuit. I mean, we are dealing with a 5% imbalance, which would bug me coming from utility. But some of the other equipment seems to be handling it just fine.


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## splatz (May 23, 2015)

http://www.phasetechnologies.com/phaseconverterinfo/phaseconverter_voltagebalance.htm


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## macmikeman (Jan 23, 2007)

I didn't click on any of the links but I know what they say. Derived phase will swing around some on that brand of phase adder until it is loaded up at which time it will sync the derived phase to the other two and output the proper voltage. They tell you not to bother reading the derived to ground, just phase to phase.


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## tmessner (Apr 1, 2013)

On the output the voltage on the generated leg will be all over the map. I would not be surprised to see up to 300 volts with no load. When load is applied the voltage will even out some, still not equal on all three legs. It does not matter if you measure line to ground (heaven forbid) or line to line. The current measurements will also not be equal on all three lines. As the converter is loaded to fla things even out some. I hate rotary converters.Try this instead: http://www.phaseperfect.com/p/t/overview


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## sparkiez (Aug 1, 2015)

Well, I was measuring phase to phase, not phase to ground. Got some documents from the manufacturer as well. I should be able to read them tonight.


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## macmikeman (Jan 23, 2007)

Make sure none of control wiring or control transformer or time clocks etc., are connected to the derived phase. If it is "C" put the control transformer across A and B.


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## telsa (May 22, 2015)

sparkiez said:


> So, I'm on a job, and installed a rotary phase converter. This is going from 240V actual single phase and outputting 240V three phase. Today, a piece of equipment was hooked up, a small filtering machine.
> 
> I noticed upon inspection, that phase to phase (I'm thinking B-C, but can't quite remember) was 250V, which is 10V higher than the other two. This this normal for a rotary phase converter?
> 
> Also, I'm not liking running a 208V 3-phase motor on 3-phase 240V 3-phase. That is a lot of difference in voltage and the equipment was getting quite hot. I've talked him into replacing the motors with 230V 3-phase motors, and that should solve that problem. Thoughts?


For trivial 3-phase loads with non-complex loading, one should seriously consider the bargain priced VFDs coming out of Red China.

They are CHEAP.

They are idiot simple to install.

And they are usually superior to rotary phase converters, which is a largely obsolete technology.

BTW, you don't even have a problem.

You have a perfection fetish. :biggrin:


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## sparkiez (Aug 1, 2015)

telsa said:


> For trivial 3-phase loads with non-complex loading, one should seriously consider the bargain priced VFDs coming out of Red China.
> 
> They are CHEAP.
> 
> ...


I didn't spec equipment, I'm just getting it all running. VFD's weren't acceptable for this application due to having multiple devices on the system. I was informed that, "It's three phase right? Its just four wires. It will work." 

Also, yes, I'm quite the perfectionist. I try to do every single job I can to the best of my ability. That doesn't mean that it turns out that way, but I try :vs_laugh:

Also, here is where I went with it. I did some research on these stupid add-a-phase black boxes, saw what is going on with the different voltage readings and the crazy current draw I took, and that it was normal, and got to thinking about the motor in terms of power and determined it was being starved for current due to the voltage increase. Two more used machines arrived today that need to be gone through this morning prior to startup. Perhaps I'll FINALLY get to programming the PLC and HMI this weekend.


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## paulengr (Oct 8, 2017)

VFDs as power supplies work just fine on multiple devices. In V/Hz mode with no slip compensation, vector mode, etc. the drive just stupidly outputs voltage. Feedback is for protection only. Turn off things like open phase detection, or current imbalance.

The big disadvantage of VFDs over rotary phase converters is size. Single phase ones top out at about 5 HP.

Above that if you want stable 3 phase the only other option is an MG set. These are vastly more expensive but give you rock steady output. They are still used for some large aviation/military 400 Hz systems. Many test labs use them to isolate themselves frequency m noisy or unstable input power especially radio equipment. 90% of the fleet of dragline excavators running 6000 A peak DC output to DC mill motors used as servos, and the same design on some very old elevators. There are lots of these around the surplus market for DC and 400 Hz. Most of the 60 Hz ones have largely been scrapped out though. I’d say we get a few come through the shop a year. I probably see more long ago abandoned and rusting away in a corner where the cost to haul it out was more than the scrap value so they kind of become museum pieces.

So if you can find one there is a third option but they’re hard to find.


Sent from my iPhone using Tapatalk


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