Film-Tech Forum ARCHIVE: Single-phase Rectifier question

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Posted by Justin West (Member # 920) on 05-09-2004, 12:36 AM:

Hi, all...I contacted a theatre supply house in search of a single phase 2kw rectifier. I asked if they had any of the newer Strong switchers and they said NO and suggested I stay away from them (due to failure rate concerns). They said they did have a couple used Strong (non-switcher) units for $400 each but forewarned me that the previous owner had said he was disappointed in the reduced life of the xenon bulbs with this pair of rectifiers. In other words, the xenon bulbs were not typically lasting as long as they they were rated to last (although he did not say how much bulb life was shortened) when they were run in these units. Is that something that is a fact of life with single-phase recifiers or could there be some other undiscovered problem? Thanks for the advice.

Posted by Steve Kraus (Member # 476) on 05-09-2004, 12:52 AM:

Well of course there could have been other problems such as inadequate cooling.

Besides AC ripple and in-rush current, is there something else a rectifier can do which would affect bulb life? Regulation or lack of any I suppose but besides the effect of regulation on reducing ripple does overall gross current regulation influence bulb life (considering so many rectifiers are completely unregulated)?

Posted by Mark Gulbrandsen (Member # 72) on 05-09-2004, 08:21 AM:

Well, here we have another dealer thats again giving out WRONG INFORMATION and I've got to wonder if this is the same guy that trashed the Panastereo??? There are DEFINATELY NOT any high failure rates with Strong Switchers. In reality what it seems to amount to today is that there are people that hate them or people that love em somewhat based on the problems thay may have had with the early units. Yes, there WERE many mechanical type problems with the early Strong switchers but that was a long time ago and definately not so with the new units. The downside is that you can't repair it if it does break down. Simple as that!! I can think of only one location here in SLC that had many problems with them. Since they do their own service work I can't honestly say what the problem was, but I suspect that it was not the rectifiers. A good example of the reliabliity of these units are the Phil Hill designed Iwerks 15/70 installations that have three 7kw units in parallel cranking out 375 amps all day and night long with out any failures.

Out here in the mountain states we have probably close to 150 Strong switchers in just about every type of cinema situation you can imagine and we have less trouble with them than we do with standard rectifiers and failing diodes with the remainder of our close to 400 locations. We have sites that run switchers that have had them for a decade and had zero problems....and those are some old switchers by todays comparisons. Keep in mind that they are in plex's, in small town situations, and situations with occasionally dirty power.... overall we see one or two switchers a year get exchanged.

As for the older Strong high reactance units, they only have barely passable ripple and inrush current levels when in good running condition while the switchers high frequency ripple is pretty much invisible to the lamp and inrush current is very well controlled. Being more efficient they also put out far less heat and draw far less current. Obviously Strong had to do something about these old Hanovia built high reactance designs and decided to go the switcher route.

If you want a good iron core rectifier then look for a Christie, an Irem, or a Kneisley ...prefrence in that order. Far as I know Christie never made any single phase 2kw units but the other two companies did and still do.

Here are some advantages and disadvantages of each type......

High reactance type...

Advantages....
Easy to repair, cheap to buy used

Disadvantages...
Extremely heavy, can be very power hungry, higher ripple, genreally around 10% and high inrush currents that can go to 5 to 6 times the operating current, poor lamp life, transformer windings that come loose and buzz, diode failures, blocking diode failures, noisy whining fans.

Switcher....

Advantages...
Light in weight, smaller, high frequency ripple is invisible to the lamp, well controled inrush current levels, extremely long lamp life if you want to push it there, low power consumption, low heat produced, same unit runs on either single or three phase, LED array to aid in over the phone diagnostics. Flat R/A price charged by Strong for an overnight replacement.

Disadvantages....
Can't be field serviced easily but it is possible, Sensitive to dead short circuits on the DC line, Lots of hardware to remove to get inside unit, uses solid state relay instead of a regular contactor eliminating the usual clunk sound that some techs normally use for over the phone diagnostics. Some of them have the noisy whining fans.

Hope this helps....

Mark

Posted by Gordon McLeod (Member # 33) on 05-09-2004, 01:45 PM:

ORC/LP associates has/had a single phase 2K rectifier
I have had a higher level of failures with switching rectifiers than for the same number of transformer styled in the past

Posted by Richard Fowler (Member # 893) on 05-09-2004, 02:31 PM:

LPA 8502 2KW rectifier 25 amp draw from a single phase line. I used to use two with balancing variacs + meters for 4Kw use when 3 phase was not available.

Posted by Sam D. Chavez (Member # 1841) on 05-09-2004, 02:51 PM:

Everything I've heard is that customers are getting away from the Strong switchers due to high failure rates.

I like them and have not personally had problems but I tend to sell to screeing rooms where they don't operate 12 hours at a time.

Posted by Jack Ondracek (Member # 1466) on 05-11-2004, 10:28 PM:

I have two of the older Strong switchers. Other than keeping the input grates clean, I open them up once a year to make sure the DC connections are tight (which, by the way, is recommended by Strong). I have had zero problems with these power supplies. I recently purchased two of their newer 7kW supplies, so I could retire some very old ORC and Strong supplies I have at the drive-in. Zero troubles with those switchers, too.

On the other hand, I have replaced diodes in every model and size of high-reactance supply I've ever owned... Strongs at 2 and 4kW, and a couple of ORC 4kW supplies. Nothing in the booth may be fail-proof... but over the years, I haven't had to pay nearly as much attention to my Strong switchers as I have my high-reactance supplies.

Posted by Will Kutler (Member # 770) on 05-12-2004, 01:34 AM:

I installed a brand new single phase LPA in a theatre a few years ago and have never been alerted of any problem.

Mr. Pincus was very polite and professional in working with me to solve this theatre's problem...I received an emerengcy call and had to come up with a solution quick. Mr.Pincus helped save the day.

If I remember correctly, the new rectifier was somewhere around $1800.00 new. Single phase and I believe it was a 2K.

Posted by Mark Gulbrandsen (Member # 72) on 05-12-2004, 08:03 AM:

I'm not surprised at your lack of problems Jack, nor at the fact that you've replaced alot of diodes. As I mentioned we've had very good luck with switchers. I only know of a few places that have had problems and stopped using them and went back to high reactance in new builds. They now pay the premium with very poor lamp life. Christie rectifiers are the exception though I wouldn't consider them a "High Reactance" type of design.

The reason there are few switcher problems even over the long haul is because the diodes do not produce as much heat and experience the drastic rhermal cycling that high reactance units do. Its drastic thermal cycling that kills the diodes over time in "iron core" rectifiers... on top of that most rectifiers are way under heat sinked and rely on forced air for better cooling.... well if the fan dies which frequently happens in this neck of the woods then semicinductors really experience drastic temperature swings amnd will fail quickly.

Mark

Posted by Gordon McLeod (Member # 33) on 05-12-2004, 09:27 AM:

You know the worst bulb life I see is tpically with switching rectifiers and the best life has been on many older units
The Allanson rectifiers built locally (copy of the Sanrex) and the newer sanrex SCR rectifers seem to get terrific lamp life