Film-Tech Forum ARCHIVE: Switcher vs. High Reactance

This is topic Switcher vs. High Reactance in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Ken Lackner (Member # 1002) on 07-10-2003, 02:53 PM:

I know that this has been discussed many times on this forum. Most of you prefer the high reactance rectifiers because the switchers have a high rate of failure. One question: Why? Is it some design flaw? Is Strong using lower quality parts in the switchers? Why do these things fail so much?

Posted by Jeff Taylor (Member # 443) on 07-10-2003, 03:27 PM:

You're right...it has been discussed a good deal, but I'm not sure that it's fair to say that most people prefer reactance supplies. Frankly, my own experience with switchers has been good. If you want to know why people would feel more comfortable with reactance, however, look at the design of each. The reactance supplies are basically a big transformer, some kind of rheostat, a diode bridge, and some caps. Sure, transformers can short out, diodes can fry, and caps get old, but basically it's simple as can be. It's also big, heavy, and highly inefficient. Switchers are complex--very complex--and got a bad rap initially for a high rate of failures, but my experience is that failure rates are way down, and they are far more efficient, smaller, and lighter than the competition.

Posted by Don Sneed (Member # 955) on 07-12-2003, 04:06 PM:

I think each his own, some people like one or the other....I do not like switcher rect. due to failure rate....yes they are easy to replace (if there is a spare in the booth), you be surprise how many booths do not have a spare switcher rect. On the other hand the High React. Rect. usually has diode failure, Strong beef up theirs & I never had a diode failure that I can remember with over 100 installed...but a diode can be troubleshooted & replaced within an hour, so only losing one show instead of one or two days....my vote is High Reactance Rectifier, by any manufacture....

Posted by Tim Reed (Member # 137) on 07-12-2003, 04:39 PM:

I can't tell you what it is specifically that fails in them, but Don's right. If the switchers were more robust to begin with, you wouldn't NEED to change them!

(I hate the term "robust"... it's so overused today when referring to computers. But, since the switchers are mostly electronic in nature, I figured it deserved it.)

Posted by Steve Guttag (Member # 268) on 07-12-2003, 11:30 PM:

In this year (2003) the high-reactance is the smarter choice for typical cinema applications with film. While the switcher can offer a better quality DC output, it is far less reliable and completely non-field repairable. Two things that the film industry does not need.

The switcher offers the typical theatre owner NOTHING to make up for its high failure rate. So it's lighter...big deal, you only have to schlep it up once. After that about all you will need to worry about are diodes for the HR rectifier.

The only places I use switchers are for low-wattage (below 1600 watts). Strong makes a nice 110V version single phase that will go up to 2000-watts. And then I make sure there is a spare!

For D-Cinema...a switcher is a must for the cleaner power....but since when are the D-Cinema projectors about reliability?

Steve

Posted by Phil Hill (Member # 371) on 07-13-2003, 12:52 AM:

I disagree... the only switchers I have ever had any trouble with are the early 380-volt 50Hz versions. There have been some occasional failures with the 60Hz high-power earlier models, but the latest series seem to be "robust" (Tim!) [Razz]

True, they are not serviceable by the local user, but in keeping with the trend of non-technical people on site, a plug-out interchangeability is OK. I always budget a spare for critical venues.

>>> Phil

Posted by Paul G. Thompson (Member # 655) on 07-13-2003, 01:20 AM:

I prefer the high-reactance type, but I will settle for a switcher if that was the only thing available. The newer model switcher Strong International makes seems to perform very well. I have three of them in Anacortes, and almost lost one. Not be design fault, but some "numb nuts" left one of the internal blower plugs disconnected. It did OK until the intake of the only blower that was working got dusty. The only thing I find objectional is the blower noise of the switcher. It sounds like a swarm of flies in a barnyard.

Posted by Jack Ondracek (Member # 1466) on 07-13-2003, 02:58 AM:

I have both. My switchers are in 7 and 4kW service and have been no trouble whatever (they both use the same model of supply). On the other hand, I have an old, 2kW Strong high reactance supply that started to break down & trip the 125 amp sub-master breaker feeding that whole auditorium. Failures can happen with both types, it would seem.

I like the switchers. They're efficient and put out a good, clean DC. If you're not going to use an old generator to run your lamps, the switcher is possibly the next best output. BUT... it's true that a bunch of diodes and an old, clunky contactor is MUCH easier to service in the field. I've had diodes take a dump on me & I've managed to still save the show (with a good stock of spares on hand). Granted, that would have been less likely if it had been a switcher that had failed. If YOU aren't the one buying the bulbs, but you ARE the one who has to fix the problems, maybe high reactance is a better choice. I'm sticking with switchers whenever I replace or upgrade... but I am also making sure I have at least one spare around that I can run up to any screen, should one crap out on me, which thankfully hasn't happened yet.

Posted by Steve Guttag (Member # 268) on 07-13-2003, 09:37 AM:

Without exception, the only venues I have switcher in that have not had one go and take a show down are the 1KW venues...regardless of model and vintage...even something as simple as a circuit breaker is no longer an easy service item since they are difficult to get into or work on.

I never said High-reactance doesn't have failures...just that unit replacement is not how they are serviced and that within an hour, about 99% of all failures can be corrected by a competent service tech.

What does the switcher get you? Why would anyone prefer it in a fixed installation. We already get 2-3X service life out of the xenon lamps with conventional rectifiers. Strong uses nice 150A diodes that seem to yield excellent service life.

Steve

Posted by Scott Norwood (Member # 30) on 07-13-2003, 10:27 AM:

Semi-related rectifier question: what is the type of rectifier that is basically a metal box that contains several "Sil-tubes," which look like metal cans with Edison screw-type lightbulb bases? Both of the carbon arc houses that I've run use these and I have also seen older exciter supplies that use smaller Sil-tubes. I have never seen these in a xenon house. How do they compare with motor-generators or modern high-reactance or switching rectifiers?

Posted by Don Sneed (Member # 955) on 07-13-2003, 11:33 AM:

Thanks Scott for the memories....Sil-Tubes Rectifiers....almost forgot about those...When I started in the booth in 1970 we had single screen threatres with motor generators with back-up Sil-Tube rect....I remember once helping the sound engineer change out the old Vac-tube rectifiers to the metal can type with a clip wire on top of the tube...back then we would only use these as a back up only, the MG was the main source of power..we were told to use the tube rect. only in emergency, all the theatres was scare of tube rect. over the MG...they thought is wouldn't hold up...(this must have been equivalent our switcher rect. at that time).

Posted by Paul G. Thompson (Member # 655) on 07-13-2003, 12:19 PM:

Hmmm....I have had lots of tungars go south in those old rectifiers, but I hardly ever had a sil tube go south. The ones I did were wasy to fix. Just pop them apart and replace the diode. However, there was a brand that was not possible to fix. Luckly, I have not run into too many of them. Those were [bs]

to begin with.

Posted by Tim Reed (Member # 137) on 07-13-2003, 08:10 PM:

Scott, I believe Kniesley made a rectifier with Sil-Tubes for xenon use, too. Seen a few of those around. The ones in the carbon house are, as Don and Paul touched on, are most likely conversions from Tungar bulbs. I remember converting some of those in the "old days"... you had to lower the input voltage to the rectifier, because you no longer had the voltage drop across the tungar filament. If you find a carbon/Sil-Tube installation that just can't keep the carbons feeding properly, check the input voltage setting of the rectifier.

quote:
the only switchers I have ever had any trouble with are the early 380-volt 50Hz versions

Phil, that's probably because they didn't like 60Hz/208! [Big Grin]

Posted by Alan Gilbertson (Member # 242) on 07-13-2003, 08:58 PM:

I had 3 switchers go out last week at 2 different location. I think you know what I would perfer!!!

Posted by Jack Ondracek (Member # 1466) on 07-13-2003, 10:29 PM:

Sil Tubes were popular replacements in the rectifiers Strong used in their Standard lamphouses. We also had a couple in an old Motiograph exciter/field coil power supply that we used at the drive-in for our exciter lamps. The old merc tubes had finally given out.