Film-Tech Forum ARCHIVE: Inverter/VFD to power a 3 ph rectifier ?

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Posted by Jonathan Wood (Member # 4614) on 05-08-2015, 10:21 AM:

Hi
This kind of follows on from the previous thread but is really a question in its own right.

Has anyone any thoughts on whether it's possible / advisable to power a 3 phase rectifier from an inverter /VFD ? I have an irem 3ph at home and would like to power a 1k xenon from it. I don't have 3ph but could I use an inverter that takes single ph 230v in and provides 3 phase 415 out ? Given the transformers in the rec , I imagine it would only draw 2-3 amps on each of the primary windings ?

Posted by Steve Kraus (Member # 476) on 05-08-2015, 10:41 AM:

You should do this just for the ridiculousness of it! [Cool]

Inverter/VFD that can put out sine wave power to make tranformers happy is pretty high tech; a transformer-type rectifier is fairly low tech. And all to drive a 1K bulb!

Posted by Sean Weitzel (Member # 244) on 05-08-2015, 02:59 PM:

I've seen a stock Christie SLC console fitted with a 2k bulb powered by a rotary phase converter. The light didn't have any noticeable flicker either so there is always that possibility. There was also a thread on here not too long ago where a gentleman was using a 120v single phase welder along with a capacitor bank to directly power a 1k lamp house. Search for the title "Christie H10 lamphouse PS project" since hot linking a thread doesn't work here.

Posted by Gordon McLeod (Member # 33) on 05-08-2015, 03:14 PM:

With the amount of equipment going in the bin these days getting a single phase rectifier should be cheaper than a VFD for that much current

Posted by Mark Gulbrandsen (Member # 72) on 05-08-2015, 06:48 PM:

Yes, it works fine. Rotary Inverters are actually wound so that third leg will have just slightly higher voltage to compensate for any losses.

Mark

Posted by David Buckley (Member # 2600) on 05-09-2015, 05:15 AM:

Certainly wouldn't recommend a VFD; they put out filthy waveforms. I'd expect a rotary converter to be fine though, based on that small radio station transmitters are sometimes powered this way and work fine.

Posted by Steve Moore (Member # 4753) on 05-09-2015, 06:23 AM:

I bought a three phase converter for our site in Leeds for our Christie CP2000s, after looking up the pricing for getting three phase installed, this seemed like it was worth trying out.

The man at Drives Direct in Nottingham was very helpful and worked out the best model for the current and use required. He did admit he had never built one for a projector lamp, but after looking at the specs of the Sanrex rectifier decided that their model they build for computer CNC machines should do the job.

We have now run the unit for over 2 years between 6 and 12 hours a day without issues, and strangely enough get better lamp life here than at any of our other sites with the same projector!

Posted by Rex Oliver (Member # 7593) on 05-10-2015, 02:23 AM:

Rotary phase convertors and broadcast transmitters--If you use a transmitter on one of these MAKE SURE single phase components of the transmitter are connected to the "real" two phases.Items such as filaments,single phase fans and blowers,bias,and LV supplies.A rotary convertor sure makes a strange noises when it is powering an AM transmitter!For electronic devices you should fight and try to get 3 ph service as much as you can.Rotary and other convertors work really great with motors.I had to deal with one 5Kw AM(Gates 5P) that had to run from a convertor.Just wasn't possible to get three phase at their site.Had to make sure the above mentioned items were connected to the real legs--not to the "Wild wire" as derived by the convertor.They can vary greatly in voltage-esp when put under load-and varying loads like an AM transmitter.Remember when rotary convertors were sold out of the Sears farm catalog!That was their orginal purpose-for powering 3 phase motored equipment in very remote farm areas with single phase services.A fellow that used to work with me here at the transmitter plant uses a rotary convertor at home to power his engine lathe and a milling machine in his garage.He bought the convertor from a pawn shop for $5!!

Posted by Louis Bornwasser (Member # 3063) on 05-11-2015, 07:49 AM:

Harris (Gates) has long promoted an all solid state 3 phase converter for transmitter use. I have a 10 hp one in the garage to run my power tools. (not connected yet due to slow building contractor doing other work who took over the garage.) Looks like a large audio amp in a box.

Posted by Jonathan Wood (Member # 4614) on 05-11-2015, 02:35 PM:

Steve, so that's essentially a VFD you have there ( albeit without the ability to vary the freq,) and not a static or rotary converter ?

Posted by Steve Moore (Member # 4753) on 05-11-2015, 03:37 PM:

No not rotary; the "magic grey box" creates the phase shifts and then various step up transformers and smoothing caps, which i believe are the extras for the smoothing for computer driven CNC machines
They do varying sizes, ours designed to put out 16A per phase at 415v from a 230v input, though we did the calculations on a much larger lamp and the figures quotes on our three phase rectifier. In reality we could have probably got away with their smaller model, as i think we are pulling only somewhere in the region of 4 or 5amps per phase with a 2kw lamp if my mind serves me right. The small grey unit has controls for motor run and startup and direction if you were to use with engineering machines, but as we are wanting it fixed, they just bypass the control panel.

Posted by Rex Oliver (Member # 7593) on 05-12-2015, 12:16 AM:

Never seen the convertors in the Harris catalogs-Special order item?Another trick is to have the power company do a SCott connection involving the single ph distribution primay line and two Scott connected "pole Pigs" for an open delta 3 ph supply.Motors work from these just fine.An RCA 5H AM transmitter ran from it OK as well.At the dump site where I dump my trash their trash compactor motor runs off a Scott connected supply.Power companies don't always like running these-its an alternative to convertors.And FM transmitters run well from rotary convertors becuase they are a constant load-not varying as AM or analog TV transmitters.Haven't dealt with digital TV rigs-they are AM as well.Solid state or Klystrode tube output stages.