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Author Topic: ORC rectifier goes on fire Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 07-26-2005 07:45 PM                        I have no IREM's that make any form of noise. Yes, ripple is high on IREMs. So is bulb life. Therefore ripple is good??? Seems not to matter. I, too, have the ORC ripple meter. FWIW, I have never changed an IREM capacitor...they must last forever...some from the 1960's. Changed many onKneisleys and Christies, though. Also note the power draw IREM vs Christie for a given wattage. Louis  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-26-2005 08:30 PM                     Another controversy... As to switchers...I only use them when I have wattage below 1600-watts or there is no choice (it is in the specification that I can't change). I've watched switchers (current ones) die within 5-minutes of installation and no surge supressor was going to save it. Think that is bad...got a replacement...same thing happened. Most failed rectifier based on brand/model...for us switchers...any generation. They are like ticking time-bombs with all their clocks set differently. The big kicker is that they are not servicable. I require that if a switcher is to be in the specification, they must have a spare, just like the lamp. As to IREMs...I've never been the big fan of them. They have that Italian elegance to them though. They cut their wires way too short and specify their components marginally. Their wire gauge and contactor choices seem to be based on the 380 voltage without any concern that more current is going to flow in countries that have 208 (nominal). The contactors that are in them now...the A16 for under 3K is only a 16A contactor and is marginal. The A30 is a 30-amp contactor and is marginal for the larger currents. We generally replace them with A26s and A40s and have cut those problems to non-existance. Likewise, on diodes, we go to 85A/1600 PIV. IREM does charge extra for their "AFU" (aka choke) on the smaller rectifiers but it is standard on the N3-150 and up. It should be standard on all of them since they can be rough on lamps. I have had IREMS that just sit there and do the job and those that HUM and Buzz wildly. Those that hum and buzz...it seems that even when you adjust the hum-out screws...it will just come back in a bit. To their credit, the current adjustment just can't be beat. We have one theatre that has been chewing through diodes on the IREMs...installing surge supression has effectively arrested the problem. I have had good and bad lamp life out of IREMS. The one location mentioned above has routinely attained greater than 5000-hours on their Christie lamps...in fact, I just changed one with 9000 hours on it! A tribute to the lamp but if the retifier was horrible, it would not have lasted either. As to Christie rectifiers...for whatever reason, they have yielded the longest life lamps on average though they seem to be the most plagued with diode failure. Like the IREMs, upon surge supressing the power...the diode problems have gone away. Kneisley is a rectifier that has routinely provided me with the worst lamp life so I don't know what to say about Mark's measurements...the lamps don't agree, regardless of lamp brand. Strong's high reactance rectifiers seems to be somewhere in the middle. They do okay without much complaint. However the current version Strong decided to omit the output choke...that just can't be as good for the lamps so I expect to see shorter life spans due to lack of filtration and increased diode failure from lack of protection from the igniter coming back down the line. MIT is the new kid on the block and they seem to have a promising rectifier. It uses SCRs instead of straight diodes. This lets them be contactorless and their troubleshooting circuit has LEDs to let the tech know which device has failed. Current is adjusted with a lever external to the unit and has 5 or so positions. I am curious about anyone that has used it and what kind of lamp life they are getting.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-26-2005 09:13 PM                     quote: Steve Guttag As to Christie rectifiers...for whatever reason, they have yielded the longest life lamps on average though they seem to be the most plagued with diode failure. Steve, The single biggest problem with Christie rectifiers is the lack of sufficient heat sinking. Do the math, I know you can. The real joke is that the sinks they provide are super innefficient, have low dissipation ability! You'll find that at an average power setting for a given model that only have 1/5th of the amount they really should have. You have to keep device temperature within a reasonable 30 to 40 deg. C. limiit that semis like that can stand over long periods of time. Indeed the majority of failed diodes in Christies that I replace are mechanical junction failures from repeated thermal cycling. Thank god they got smart and added a fan, but I also seem to replace ALOT of those. A smallish squirrel cage blower as was used on the old ORC rectifiers would have baan a better choice. quote: Steve Guttag The big kicker is that they are not servicable. Wrong on that one, they are usually VERY easy to repair. Believe me Strong makes a pile of $$ on repairs. Shorted switching transistors account for the majority of problems with them. Unless the traces of the boards are seriously burnt off repair is simple although not as easy or as fast as working on say a Christie but it is really quite basic electronic repair. I like to think of them as huge Class D power amplifiers. The majority of time I've spent repairing them involves removing and replacing the two pounds of screws holding them together. The other thing that one must do is match the switching transistors for a VGS of about .01 volts so that all share the same amount of current. Doing so is VERY simple and the devices are also dirt cheap... far less expensive than replacing all the diodes in a Christie rectifier. Only some of the very old Strong larger power switchers cannot be repaired because of semiconductor obsolescence. I have quite a number of locations that get great lamp life with the Kneisleys... sold a boat load of them back in the Midwest area and customers report excellent lamp life. Might be more attributable to the hurricane blowers I always spec in on the lamphouses. I suspect that perhaps your problem may be with dirty power. quote: Louis Bornwasser I have no IREM's that make any form of noise. Louis, I just tightened up a buzzing Irem this past Saturday. I've had my share of buzzing units, especially the contactors in humid areas like yours. In all fairness ditto for Kneisley and loose cores! As for the MIT units, its definately NOT a new idea but it does get around the expensive high current tap switch but who knows if the company will be around in a couple of years, they are a watch and wait type of thing for us. I hate selling equipment, no matter how good it is, from conpanies that then disappear in a short amount of time. Changing from diodes to SCR's is also something that can be done to just about any rectifier. All you need is a simple circuit to properly fire the gates. Many very high tech welding supplies have used scr rectification for years. Before SCR's they used Thyrister vacuum tubes. Mark  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 07-27-2005 12:12 AM                     Okey..let's get a bit "ancient" here and have to ask this one as well: How did the old "Tungar bulb" rectifiers work and how reliable were these old monsters compared to generators and then, the newer diode rectifiers? -Monte  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-27-2005 02:30 AM                  When I was a mere teen, I *REALLY* liked watching the Motor-Generators. They gave me a hard-on just watching them with their sparking brushes. The 866 Mercury Vapor rectifiers used in broadcast transmitters did the same thing for me...Hubba Hubba! OBTW: It's "Okay" or "OK", NOT "Okey"! JEEEZUS!  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-27-2005 07:46 AM                     Kniesley rectifier I have had almost always poor bulb life Sanrex has been using SCR's for years in several models of there rectifier  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-27-2005 07:56 AM                     Mark, The VAST majority of diodes I've changed in Christie's and IREMs have not died in a thermal fashion. It is true that the inner plate does get warmer and those that died thermally tend to be the inner plate diodes. As to Strong's switchers...just how much are your trasistor devices costing you? I know that 85A diodes are not THAT exepensive. As to matching the Vgs...is that a thing with the devices themselves? As in matched transistors? How many devices is Strong using (I have not even looked)...how many devices must you have in order to always have a matched set? However, it is quite understandable why one would want as closely matched devices as possible.  |  IP: Logged Mike Babb Master Film Handler Posts: 250 From: Norwich UK Registered: Jul 2002 posted 07-27-2005 06:56 PM                        Some of the most interesting conversations happen in topics after the initial problem is addressed... Those Strongs should have more comfortable handles on them, it would make it easier to carry them in and out which I tend to do more often than I should have to. They kind of dig into your fingers. On the other hand, I do carry one in my van and it has saved a show several times.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-27-2005 07:13 PM                     quote: Steve Guttag As to Strong's switchers...just how much are your trasistor devices costing you? Steve, Well under 3.00 each in 100 quantity. There are very few left over after matching to .01 volts as long as you get devices from the same code lot. Actually .05 volts is probably also close enough but I have a habit of matching to .01 from building alot of Class A power amps. It takes about 4 to 5 hours to match up 100 devices, its very easy but boring. The MOSFET devices in the switchers are indeed very similar to but not the same ones I use in the power amps, IRFP240. The amount and type of devices depends on the model number. There are only several models of them that I will repair, and quite frankly I don't get to work on them very often. I've never had to repair the newer compact model at all. I also do mods to the older ones so that BOTH internal banks of caps drain down in the 20 minuite time period so one can install a new fuse and not have it blow. There was something I posted about doing this mod in a thread about this a while back. I would say that at least 70% of the diodes in Christie and Strong that I have changed have failed mechanically from thermal cycling. The rest are shorted or open devices. I can usually wiggle the stem of the diode quite easily as the epoxy eventyually contracts around the stem and allow the device to fail. Christie and most others use pretty crappy diodes. They are epoxy encapsulated instead of the higher quality glass type seal that rarely ever fails from thermal cycling. I once met a semicontictor engneer that was near my shop when I was back in Elgin. He got took a look at some samples I sent him of the diodes that the manufacturers were using and told me about the higher quality glass sealed diodes. He sold me a couple hundred of foreword and reverse 85 amp diodes at a very resonable price, I think less than 5 bucks each. He said it would be the last diodes any rectifier got and he was absolutley right. I've never had to replace one of those. I will take photos and post them here of the next switcher I get in and do a repair to or do the mod to. They are really very simple once you understand them. Steve, There are many parameters to matching transistors but in heavy current devices VGS is the most important matching criteria. This is done so all the devices share equal amounts of operating current. Or so one device isn't handling alot more current than the other devices. This would lead to premature failure of that device since its douing the brunt of the work. There are also plus and minus sides to the switcher amplifier just like in a power amp. Its not that important that both sides be matched to each other but that all the drvices on one side be matched and sharing the load equally on that side. Mark  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 07-27-2005 11:18 PM                       quote: The 866 Mercury Vapor rectifiers used in broadcast transmitters did the same thing for me...Hubba Hubba! Oooh, yes! Altec 287-W amplifiers had those, too (at least, I think they were 866's, if not, then similar HV rectifiers). That's one of the first things that caught my eye in drive-ins!  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-28-2005 05:24 AM                     There must be some close relationship between these two types of glows? A large Mercury vapor rectifier tube....... Maine Yankee de-comissioned reactor core lining.......  |  IP: Logged Stephen Furley Film God Posts: 3059 From: Coulsdon, Croydon, England Registered: May 2002 posted 07-28-2005 10:11 AM                     quote: Mark Gulbrandsen A large Mercury vapor rectifier tube....... Mark, that's not large, that's tiny. A little two anode single phase job. You can get a rough idea of the size from the light bulb package behind, even if that's a large light bulb. I've seen glass bulb rectifiers over a metre high, and 12 anode steel tank ones about two metres high, and 2.5 metres across. The modern technology just isn't as interesting There used to be a substation on the London Underground that had rows of very large glass bulb rectifiers. At night you could see this wierd blue glow from ventilatation openings high up in the building. All long-gone now, just a few trays of solid state diodes replaced it all. Where is that by the way? It looks like it's working, but it doesn't seem to be in the usual cabinet, with the cooling fan underneath. And what's that picture on the wall behind, it looks like Bin Laden!  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-28-2005 10:46 AM                     Actually that rectifier tube is available from that place in the UK that I posted the link too that sells the steam engines. So its not all that far from you Stephen. If you want one go for it..... I doubt that the steam engine dudes are much interested in Bin Laden...... except to hang him bvy his b#lls! The New York Subways also used banks of those larger tubes up till the mid 80's. I suppose they last a very long time but knowing this government they made them pull them because they have mercury in them. Mark Mark  |  IP: Logged

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