Film-Tech Forum ARCHIVE: Converting 3 phase rectifier to single phase

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Posted by Jonathan Wood (Member # 4614) on 04-16-2014, 10:06 AM:

Hi all, has anyone got any experience of converting a 3 phase rectifier into a single phase (230v) rectifier ? I am looking for a single phase rectifier for portable use and I have an Irem 3 ph (3/400) rectifier which is sitting idle. It seems to me all the components must be in there , could it be converted ? Single ph recs seem pretty rare. Cheers Jon
Apologies if this has been posted before, I searched but couldn't find anything. [Smile]

Posted by Mark Gulbrandsen (Member # 72) on 04-16-2014, 02:08 PM:

If it's for portable use then I suggest looking on Ebay for a Strong Switcher. There should be some of those in your neck of the woods. Portable as in 60 pounds for a 4kw rectifier even lighter if you choose the 2.5kw version at 40 pounds. They are fairly easy to repair when they go down and Strong also still repairs them.

Mark

Posted by Geoff Newitt (Member # 6663) on 04-18-2014, 01:17 PM:

What size lamp do you want to power?

There are plenty of T&R 123s around if you know where to look (I have at least three or four in storage). OK, so they're more 'moveable' than 'portable', but they're simple and reliable. Not so hot for big lamps, though.

Posted by Steve Kraus (Member # 476) on 04-18-2014, 01:37 PM:

I don't know about IREM as that may be a weird thing with the variable core transformer but what happens if you take a conventional transformer-based* 3Φ rectifier and run on single phase? Assuming you added some capacitance to the DC output, what's the difference between that and a single phase transfomer-based rectifier? If it had separate transformers, maybe there is a way to use the unused one as an inductor to further smooth the DC.

* Sorry but "high reactance" sounds like a made-up term.

Posted by Mark Gulbrandsen (Member # 72) on 04-18-2014, 03:05 PM:

That all depends on what era IREM you try it with. Before a certain time IREM's had very low start voltage because they were would for a 380 volt three phase primary. That problem led a few companies to come out with accessory start boxes to help with hard starting. Installed quite a few of those boosters in buildings that had 208 volts three phase where lamps simply wouldn't light at all after several hundred hours. Later IREMS were wound for 240 volt three phase primaries and didn't require any booster on 208 volts. So early ones may not work too well but later ones may well with a little bit of flicker.

Mark

Posted by Jim Cassedy (Member # 4115) on 04-18-2014, 04:27 PM:

I think I've mentioned this in a previous post, but I know of several a couple of
old theaters here that have been running Christie 3phase rectifiers on single
phase for over 20 years. It's done by using a large capacitor bank across the
single phase line to create a 'phantom' 3rd phase. If you poke around on the
internet, there's information on how to wire up an arrangement like this to run
3phase motors on single phase. Be aware that this method is somwewhat inefficient,
from an electrical standpoint, and you will have to de-rate the rectifier output
by approximately 25%.

Also,at one theater they also had to add a large inductance coil between the rectifier &
the xenon lamp to remove ripple from the output that was showing up in the lamp.
Not sure why it was only a problem at this one location, as the rest of the
equipment was identical at all locations.

Also, the rectifiers will run with a very loud & annoying appx 120hz 'buzz'.
I find it disturbing enough that I can only spend a few minutes in the booth
when one of those things is running before it really gets on my nerves.
. . and if your projection room isn't well soundproofed, it might possibly be
heard in the auditiorium.

I do not recall the size of the capacitors used to create the phantom phase,
but they were pretty friggin' big. I'm pretty sure the guy who put these systems
together over 20yrs ago got the caps at some sort of industrial electrical equipment
surplus store. New caps that size are probably pretty expensive, and given the
advances in technology, it might just be cheaper to buy a solid state phase converter now.

Posted by Mark Gulbrandsen (Member # 72) on 04-18-2014, 09:50 PM:

Yes, that can be done but there is a lot of loss and low efficiency on that leg. A rotary phase converter works better and provides almost the same efficiency (Up to the rating of the converter) as real 3 phase.

Mark

Posted by Steve Moore (Member # 4753) on 04-19-2014, 06:22 AM:

I bought a digital converter to run my three phase Christie CP-2000SB from these people in the UK http://www.invertersdirect.co.uk/ which takes my 240V single phase and inverts to 415v 3 phase.

Their 10HP-CNC rated unit has run my 2KW lamp perfectly for 12 months now and would have enough capacity to run up to 3.5kw. They do make bigger ones too (though note it's certainly not portable!)

Posted by Jonathan Wood (Member # 4614) on 04-19-2014, 01:38 PM:

It's only a 1kw lamp I will be running maybe a 1.6, I already use a 1/2hp inverter to power the motor but the 10hp vers is just too expensive and big. Had thought about the capacitor method , same as running 3ph motor off 1ph supply with a cap across the unused leg, but someone else told me it might be pretty noisy . Was hoping for a quick fix but I guess there isn't one. I think the best bet is just to hold out for a portable single phase rec. thanks for the input guys . [Smile]

Posted by Edgar Prass (Member # 7558) on 04-19-2014, 02:05 PM:

http://www.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=011497#000001

Posted by Steve Moore (Member # 4753) on 04-20-2014, 06:28 AM:

Have you tried contacting Omnex in Stockport? I have purchased, in the past, a pair of single phase compact (movable by one person) rectifier from them which is branded Omnex. They may still have one possibly.

Posted by Pete Naples (Member # 761) on 04-20-2014, 11:35 AM:

Those were designed and manufactured by ourselves Steve.

We're not making them anymore, but we might have a good old T&R.

Posted by Jonathan Wood (Member # 4614) on 04-21-2014, 03:54 AM:

Was hoping to find a used one lying around as new ones are pretty expensive.

Geoff- which T&R 's do you have? I seem to remember they did a reasonably small one , which would be manageable .

Jon

Posted by Pete Naples (Member # 761) on 04-21-2014, 04:02 AM:

123B/ 2 or 3 is the common T & R

Posted by Jim Henk (Member # 3628) on 04-21-2014, 11:23 AM:

Hey, this is a family show. Let's not have any talk about T & R! [Razz]

Posted by Geoff Newitt (Member # 6663) on 04-29-2014, 11:32 AM:

Pete's right - I have various 123Bs; I can't recall off-hand which ones exactly. I have a little Omnex rectifier that I might be persuaded to part with as well, if Pete can't sort you out. That one is definitely smaller and might be more portable than a T&R! Come to that - I think there's a switcher in a store room in Greenwich that I had forgotten about 'til just now! I have to be a little careful about what I let go - some of it is still useful to us.

T&R - Transformers & Rectifiers - got out of supplying cinemas a long time ago, but are (or were, at least recently) still around and based in Guildford. They provided some of the equipment for the third rail power supply upgrades in the 00s.

Posted by Pete Naples (Member # 761) on 04-30-2014, 02:50 AM:

http://www.transformers.co.uk/

Still around Geoff.

I've two Strong switchers in my workshop, unfortunately I'm not for parting with them as they power my TIG welding plant.

Last time I was in the Stockport office there was at least one T&R sat there gathering dust.