Film-Tech Forum ARCHIVE: Electronic retifiers

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Posted by Philippe Laude (Member # 79) on 05-16-2003, 04:06 AM:

Who uses electronic rectifiers? Why or why not?
Could I place one in my sound rack or will it produce interferences?

Posted by John Anastasio (Member # 607) on 05-16-2003, 05:09 AM:

I've often had to move a piece of equipment because of hum caused by induction from another audio device's power transformer directly below it. I'd think that a power supply would have quite a nasty little magnetic field surrounding it with which you'd have to be concerned.

Posted by Ray Derrick (Member # 1001) on 05-16-2003, 05:13 AM:

Philippe why would you want to put a rectifier in your sound rack? Switchmode power supplies produce quite a lot of high frequency energy that can find it's way into sound equipment and produce noise, so it is not a good idea.

Down here in Oz we have had a lot of reliability problems with the Strong electronic units, particularly the high current ones, so we went back to the high reactance types. The switchmodes don't seem to cope too well with the higher mains voltages. (We have 240V 50Hz, that can climb as high as 265V at certain times in some country areas).

Posted by Philippe Laude (Member # 79) on 05-16-2003, 07:06 AM:

Ray,
it was just a matter of saving space in the booth, There is one location left in the sound rack.
I was assuming it wasn't a good idea indeed.
I still need advise on the liability of these units.

Posted by Mark Gulbrandsen (Member # 72) on 05-16-2003, 08:21 AM:

Phillippe,
I've had great luck with many of the early versions, and definately with the later versions(lunchbox version) of the Strong Switchers myself of up to 3kw rating. Its interesting that Iwerks uses three 7kw switchers operating in parallel to run the 15kw lamps on the 15/70 Imax clones. They get excellent lamp life, and so far the units here have not failed!! There have been failures of the high current DC connectors they use, way to small. In the units up to 3kw things are all fine and dandy. Keep in mind that any electronic thing can and will eventually break down due to age. Since you are a long way from Omaha, and the factory service these units would require if they failed, an Irem, or Christie rectifier may be a better choice as you can service any part of it yourself. Ray is also somewhat correct in his statement of their sensitivity to higher mains voltages, especially spikes, so a voltage stabilization system in the rectifier supply mains might be required.
Mark @ CLACO

Posted by Randy Stankey (Member # 64) on 05-16-2003, 08:52 PM:

Do you know why they call them "switching" rectifiers?
Because if they go bad the only thing you can do is "switch" it for another one that works!

[Big Grin]

Either they work or they don't. When they work, they work GREAT. When they don't work, they SUCK! When they quit working there's a chance that the failure will be a "spectacular" one!

I have seen both sides of the coin.

The one in my booth right now has been there 4 years and haven't had a problem. It's almost like it's not even there. When you press the button, the lamp lights... end of story.

On the other hand I have gone into a theater to repair a problem, installed a new rectifier only to have THAT one die on me in just a few weeks. Each one that failed did so with a loud "BANG!!" and a shower of sparks! (I don't know first hand. Only from reports of people who were there at the time. I arrived a few hours later to clean up the messes.)

Repairing them is rather simple: Send it back to the factory and they will send you a another one in its place. [Big Grin]

I think they are good and reliable, PROVIDED you take care of them. Don't push them beyond their limits. Don't run them at or near their limits for long periods of time. Keep the fan grilles and the air passages absolutely clean and clear of obstruction at all times... Do this and they will never spite you.

Posted by Paul G. Thompson (Member # 655) on 05-16-2003, 09:39 PM:

Philippe, I don't think it is a good idea. In view of the high RF signals developed in the switchers as well as extremely strong magnetic fields caused by the reactors and power transformers, this type of interference could induce itself into the audio cinema processors. You will note that ORC, Strong, Christie and others have very heavy shielding protecting the sound processors from the power supplies.

Posted by Phil Hill (Member # 371) on 05-16-2003, 10:02 PM:

I agree with Mark. I had great performance from them. All except a few years ago when Strong had a bad production run and they were failing right and left. Strong immediately corrected the problem and honored their warranty. [beer]

I would NOT recommend using that lame "MS"-type connector for the DC, especially in the higher-power versions. It sucks. Hard-wire it!

I had great reliability and performance from my configuration of three 7kW switchers in parallel to fire a 15kW lamp. It IS important to balance each supply to contribute it's equal share of power!

Although there is no humongus magnetic field like in the brutes, the switchers do radiate a lot of RF hash. I would not put them anywhere near audio or video equipment. The same holds true of SCR/Triac type dimmers. [Smile]

I run a pair of 3kW units @ 2kW at home.

>>> Phil

Posted by Rick Long (Member # 213) on 05-16-2003, 11:05 PM:

Amplifying Mark's and Phil's comments, I service a theatre in Ottawa that has had 3KW switching rectifiers running 2.5 KW bulbs in each of its six Strong Highlight consoles, since Christmas 1989.

They have yet to have a failure and the bulb life is phenomenal.

Keep 'em cool and clean the vents.

Posted by Patrick de Groot (Member # 858) on 05-17-2003, 05:05 AM:

Why should one use those big rectifiers from i.e. Irem if you can do the same with a compact unit?"

What's the difference between these 2 types of rectifiers?
Thanks

Posted by Mark Gulbrandsen (Member # 72) on 05-17-2003, 09:39 AM:

Patrick,
The main problem is servicing them. In the Strong units there are no user replacable parts inside and it must be sent back to Omaha for service. That would be a bit of an inconvenience for someone that lives where you do. Osram made some smallish switchers at one time but I donno if they still do.....
Since I am a Strong dealer if one of my customers units goes down all I need to do is have Strong send hime another unit to swap out!! I than get billed for the repair/exchange unit at a fixed cost.

Mark @ CLACO

Posted by Steve Guttag (Member # 268) on 05-17-2003, 12:05 PM:

I have no use for Switching rectifiers in movie theatres...I have yet to have an installation that has them not go down to the point of needing a replacement. And I don't care WHICH vintage you have.

The only place I use switchers by choice is for smaller lamps (1600-watts and less) and they ALWAYS get a spare rectifier for WHEN it breaks. Shoot I've had them come DOA. The cinema industry does not need non-field servicable equipment and switchers are just that. If theatres were to keep spares like they do xenon lamps, then it wouldn't be so bad. Whereas I use switchers for smaller lamps, I do use the M-S connectors since the end-user can change them out in a matter of minutes.

I've had premiers go down because of the damn things and if not for the spare...it would have made big news. At the Uptown, we could count on them going down at least once a year...after each one (2-projector) died horrible deaths 5-times...we finally went to high-reactance rectifiers...lamp life went up too!

Both Christie and Strong make nice high-reactance rectifiers that work well, and are servicable. Kniesley makes theirs in a rather small package for tight spaces though I don't like its power as much as the other two listed.

Steve

Posted by Gordon McLeod (Member # 33) on 05-17-2003, 12:08 PM:

I have allways been a fan of brute force rectifiers
They don't call them switchers for nothing as you are always switching them out [Smile]

Also there failure mode is often spectacular