Film-Tech Forum ARCHIVE: Rotary phase Converters

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Posted by Erick Akers (Member # 875) on 09-16-2003, 06:22 PM:

Has anyone had any experience with Phase convertors?
I have been considering either building one or purchasing one for those situations when 3 phase isn't available.
Thanks,
Erick

Posted by Paul G. Thompson (Member # 655) on 09-16-2003, 10:24 PM:

I have seen one in the second-hand store a few months back. It was basically a single phase motor driving a 3-phase generator. Obvoiusly, the more power you need, the bigger the unit has to be along with the price to match it.

What is your intent, and how much power do you need?

As far as building one, that's fine as long as you already have a motor strong enough to do the job and a 3 phase generator to go with it.

Here is a link that might be helpful.
http://www.phaseconverter.com/

Posted by Jack Ondracek (Member # 1466) on 09-16-2003, 11:02 PM:

I once moved a radio transmitter to a site that didn't have 3 phase power. We used a rotary converter to run the modulator and final plate supply (everything else was single phase). We got very stable & reliable service from it. The price wasn't all that high, either... I think it was something like $1200 or so for one that could handle a 5kW transmitter (which was a LOT less than than the power company wanted to bring 3 phase to the site). The wiring on the converter was interesting, considering that the 2 220 volt input connections to the converter also acted as 2 of the 3 legs that went to the load. The 3rd terminal was the 3rd leg going out to the transmitter.

More recently, I used a passive converter to run a 3 phase submersible well pump. It also worked very well... no problems.

As far as I can tell, these things are good alternatives for situations where you've got a solid single-phase service but need to power a 3-phase load. However, WHAT you're running and how bit it is will determine the appropriate type & size of converter you'll need. Inductive loads & things that have high starting needs (motors) are determining factors, so make sure you check up on that before you buy one. Because the load an AM transmitter puts on the power source varies with the modulation it has to produce, there was some concern about using a converter for that purpose. In the end though, it did just fine.

Posted by Warren Smyth (Member # 1838) on 09-16-2003, 11:12 PM:

While it is possible to use a motor generator unit to covert from single phase to three phase, the modern approach is to use a converter which does the job electronicly. These units are usually available from electrical supply companies specialising in motor controls. Cost depends upon the amount of current required and the level of sophistication. Some can control the speed of a motor very accurately by altering the frequency.

One version has been used here when running silent films with a symphony orchestra. The projector motor is constantly varied according to a script, to match the required speed of the film in frames per second.

Posted by Greg Mueller (Member # 17) on 09-17-2003, 09:35 AM:

I use 4 three phase "Phase Adders" to power my machine shop. They work fine. I have one for each CNC mill and one that runs my manual lathe and Bridgeport.
They are little more than a three phase motor with some capacitors to start the motor spinning. You can build one out of a couple of power switches, a 3 phase motor and a pull string off an outboard motor or lawn mower. Pretty low tech stuff

Posted by Steve Kraus (Member # 476) on 09-17-2003, 10:16 AM:

That's right, a rotary converter is not the same thing as a motor-alternator set. It's basically a 3-phase motor made to run on single phase with the the other windings generating the other phases.

Which of course begs the question if the motor can be made to run this way why not just run the load in question the same way. I don't really know except that maybe this works only when there is no real outside load on the rotor.

Small 3-phase motors can be run with a gimmicky "converter" consisting of a few capacitors (I've seen a Cinemeccanica run this way).

Posted by Jack Ondracek (Member # 1466) on 09-17-2003, 11:41 AM:

quote:
Small 3-phase motors can be run with a gimmicky "converter" consisting of a few capacitors (I've seen a Cinemeccanica run this way).

That's probably the "passive" model I have, Steve. I think I once heard it was full of caps... never looked, though.

Posted by Greg Mueller (Member # 17) on 09-17-2003, 01:03 PM:

Steve
The 3rd phase is actually "generated" by the motor spinning, so it actually produces a 3rd leg, out of phase with the other two. It's kind of like magic.
Turn on the power, pull the string, alakazam!

Posted by Gordon Bachlund (Member # 124) on 09-17-2003, 04:21 PM:

...and, as Greg says, voila - three phase power. However, the limiting factor is the capacity of the added leg (phase), so be sure to NOT exceed the nameplate rating.

Mine was made by Lincoln, and takes a 220V single-phase input, and yields a 220V three-phase delta output. It then feeds a 7.5-kVA 220V delta to 120/208V wye dry-type transformer.

Works like a charm, though noisier that a solid-state converter.

Posted by Gordon McLeod (Member # 33) on 09-17-2003, 05:19 PM:

Why do you need 3 phase? If it is for a motor get a electronic motor drive that uses single phase to drive a 3phase motor at varrying speeds
If it is for a rectifier you are going about it in a very ineeficient manner and would be better off getting a single phase rectifier

Posted by Steve Kraus (Member # 476) on 09-17-2003, 05:50 PM:

Greg, why do you have to manually start yours? I'm guessing that you're using an actual motor not a converter which, I presume, would come with a start winding.

Gordon: A typical application is when heavy machine tools are setup in private residences. But your idea of the inverter variable speed drive is a good one. Typically these are used with a special 3 phase motor which is designed to be happy with the funky non-sinusoidal waveform these inverters put out but I think there are some now that can drive conventional 3 phase motors. They're computer driven and can be programmed for different speeds, ramp-up and ramp down rates and what to show on the display, such as Hz, RPM, or some multiple (on projectors you can have the display read FPS).

Posted by Greg Mueller (Member # 17) on 09-17-2003, 06:23 PM:

"...Greg, why do you have to manually start yours? I'm guessing that you're using an actual motor not a converter which, I presume, would come with a start winding...."

I don't. Mine have the capacitors built in and are self starting. They are commercial units that I bought so the warranty would be covered on the machines. This brand and type were speced by the machine tool builders so I don't argue. The manual starting kind are the DIYs type that basically only cost whatever the induction motor can be had for. I had friends that have used the pull rope type in their shops. One pull in the morning is all you need

Posted by Erick Akers (Member # 875) on 09-19-2003, 03:50 AM:

My thanks to all for sounding off on this subject. I will be doing mobile projection and as you know, 3 phase power just isn't available everywhere.

My current projection system is totally 3 phase and I am seeking the best all around solution for my situation.

I was considering a smart converter (electric motor drive) to power the projection unit, but when it comes to the
4K lamphouse rectifier??? [Confused]

Any suggestions?

Also, what is the potential accuracy of a smart converter powering a projector motor, for example could one potentially be used to sincronize a dual projection system for 3-D presentations or would you still need seltzens?

Posted by Phil Hill (Member # 371) on 09-19-2003, 03:54 AM:

Running 2 projectors from 3-phase power in no way insures they will both be in sync as they may come up to speed at different rates. You still will need some sort of sync and feedback method. Selsyns or AC vari-drives capable of syncing to each other.

At the DOME, I spec'd vari-drives and brushless motors with both rate and positional feedback for syncing the 3 Century projectors for the Cinerama shows.

The three 6-perf Century projectors were specially picked to be the ones in the best condition from Pacific's "Cinerama basement warehouse" and totally rebuilt and converted to direct-drive to accept the special motors. I do not think these are the same projectors that were used at Crest, from the old Warner Hollywood Cinerama, for the print restoration. These were just the best of the lot of more than 100 in storage.

The vari-drive method is by far the best system for syncing multiple projectors and for dual projector 3D. At the Dome, this also allowed them to run 24, 26, and 30fps.

>>> Phil

Posted by Steve Kraus (Member # 476) on 09-19-2003, 08:49 AM:

100+ in storage! That is simply amazing and wonderful. Amazing because one would have thought those machines would have been long sold off to someone who would rebuild and convert them into normal Century's and garner what cash they could, rather than let them languish for 4 decades with little prospect. But I'm glad they did!

This is like coming upon a forgotten spur track, overgrown with weeds, holding a fleet of PA's, DL109's, Sharks, Centipedes, C-Liners and Erie-builts!

Posted by Jim Spohn (Member # 1547) on 09-19-2003, 09:44 AM:

Erick..Jack and Gregg are right on the money. I run my entire theatre (air conditioning, pipe organ and booth)from a home made three-phase rotary converter. It is as simple as you could imagine, and completely automatic. There are alot of wive's tales about these units from people who know nothing about them, but the real truth is that the three phase output is stable and at precise frequency. All my motors run from one unit. A converter using a 5H.P. Motor will drive FOUR units with 5 H.P. motors on them OR any combination or number of motors not to exceed a total of twenty horsepower (from a unit using a 5 H.P. motor). The unit is simply a three-phase motor with a capictator, timer and contacter. The cap and timer start the three-phase motor turning then drop off line and the motor (any size)will continue to turn acting as a rotary transformer. Motors connected to this unit will start and run just as if they were connected to the three-phase utility. The converter motor just sits and spins. I have built dozens of these units and they work fine. Email me off-line and I'll send you a schematic. Jim

Posted by Pete Lawrence (Member # 130) on 09-19-2003, 09:48 AM:

quote:
I will be doing mobile projection and as you know, 3 phase power just isn't available everywhere.

Neither is 220 volts of sufficient amperage if your planning on 4k lamps. Have you given any consideration to a crystal sync AC generator? Might be a little pricy, but that would make you totally self supported and you could set up anywhere.

Here is a nicely done home-made converter using a three phase motor. http://www.metalwebnews.com/howto/phase-converter/3-phase.pdf

Here are a couple commercial versions with prices. http://www.mscdirect.com/PDF.process?pdf=1421&Section_Id=1117&Keyword=Y

[ 09-19-2003, 11:15 AM: Message edited by: Pete Lawrence ]

Posted by Jack Ondracek (Member # 1466) on 09-19-2003, 08:37 PM:

My rotary converter was made by Steelman Industries of Kilgore, TX. I bought it back in 1982... still works great!

Posted by Erick Akers (Member # 875) on 09-24-2003, 06:14 PM:

Thanks Jim,
That confirms some of what i have been told.
Sent you an e mail, please get back with me.

Also, Is there anything else to share with us on this subject?

[ 09-26-2003, 12:10 AM: Message edited by: Erick Akers ]

Posted by Daryl C. W. O'Shea (Member # 1303) on 07-01-2004, 12:42 AM:

While realizing that running a rectifier off of a rotary converter or phase drive is really inefficient, can anyone recommend a variable phase drive, that they like, that I could use with an Allanson 2K rectifier (220V @ 20 amps I believe). Of course, phase drives are quite common... just looking to see if anyone has a favourite.

Alternatively, a significantly less expensive (solution), equipment wise, single phase 2K rectifier that provides for lamp life in-line with the Allanson.

Posted by Robert DeLoss Marken (Member # 2440) on 07-01-2004, 05:09 PM:

Erick,
Hi! 3 phase is not a big deal unless it is for some huge industrial application. Any 3 phase device will operate on single phase without damage but at reduced efficiency. For a motor it will rotate at the same RPM but at 2/3 of the HP. If 3 phase is needed then a home made phase converter is easy to build. Go to a junkyard and get a 3 phase motor out of some worn out appliance. This motor can be worn out because it is used to supply the third leg and only runs, does not power anything. It must be as large or larger than the working motor. (5 bucks max) It does not have to match the working motor in star or delta. You can get exotic and build a starting system out of capacitors, or do as Greg Mueller does, and start it manually. I can send you lots of info on how to build and wire a converter, but that info is available on the Internet. Just surf phase converters and you will find probably 1K plans and etc.

If your need is an electronic device you can easily convert that device to single phase. I converted a pair of 3 phase tungar bulb rectifiers that power my carbon Enarcs to single phase. You just have to move some transformer wires around. And you can get solid state diodes to replace the tungar bulbs if you desire.

In summery: 3 phase is not a BFD and in most cases is not necessary.

Bob Marken