my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » Diodes on Kneisley Rectifiers (Page 1)

This topic comprises 2 pages: 1  2

Author Topic: Diodes on Kneisley Rectifiers Elvis Navas Film Handler Posts: 13 From: Caracas, Venezuela Registered: Apr 2003 posted 04-23-2003 12:57 PM                     What´s the optimal value for the diodes in rectifiers of 135amp, 100amp, 75amp, 65amp? what´s the output voltage? thanks for your help.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 04-23-2003 02:00 PM                     Get the highest rating you can get in current and PIV that will fit without modifications.  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 04-23-2003 08:59 PM                     I agree with Paul. The rectifier's open circuit voltage is probably under 200VDC, I would get 400V PIV rated diodes or higher. Higher PIV doesn't radically increase the cost. I suggest at least 10% over the rectifier's maximum output amperage for the diodes' rated current. You may find the highest current diode available in the package used in your rectifier won't allow that safety factor, so use the highest you can get; as long as the diode current is at least equal to your lamp current you should be OK. A slightly higher rated diode should last longer as the silicon chip is a bit larger and the thermal performance a bit better.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 04-23-2003 10:43 PM                     remeber that the diode is only conducting 1/2 the output wave form and in a 3 phase bridge even less I usually use the IR 85amp 600v diode in most recifiers  |  IP: Logged German Marin Expert Film Handler Posts: 227 From: Verbania (VB), Italy Registered: Jul 2001 posted 04-24-2003 12:45 AM                     We've been having problems with one 135A rectifier (it's the only one we keep working) and apparently is fine but the 4KW lamp life is no long than 400 hrs. We think the problems are the diodes but they give us differents values. What should be the exact (or most aproximate) number we get on tester? When the diodes begin to loss its properties? Gracias.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 04-24-2003 01:21 AM                     Why are the bulbs failing at 400 hours? I would look at those areas first, primarly ventilation of the lamphouse. People disagree with me on this, but if one diode goes, replace them all. As far as testing them is concerned, the most accurate way that I know of is testing them under load with volt meters ammeters, and temperature bulbs. Current meters to monitor the current flow through it, volt meters to check the voltage drop across the doide, and a temperature bulb to see how hot the damn thing is getting. High quality meters will give a very good idea but when these diodes are actually in the circuit working under load, things change. It is cheaper in the long run to just replace the whole complement of diodes. In addition, old diodes have been known to fail because of thermal stress over years of operation, and will fail without warning. It always amazes me when some people use a Zillion-Watt Solder Gun to solder a 12 gauge wire to a little stud rectifier without even thinking of using a heat sink to route the heat away from the diode's internal junction. Then they cannot figure out why that diode failed in about a month or so. I tell them they are stupid. The reason why it failed is because it was severely heat damaged when it was installed. And then, they didn't even use new compound when the diode was bolted in and over-torqued, no less.... I once saw a huge shipboard 2-story Fairbanks Morris Diesel Engine in the old Olympic. Each main bearing had a temperature gauge to measure the temperature of the actual bearing. As I looked around, each main bearing had a different temperature, sometimes drastic enough to raise the eyebrow of the Chief Engineer. Get the point? ARG!!!!! Hammer Technicians.....  |  IP: Logged Elvis Navas Film Handler Posts: 13 From: Caracas, Venezuela Registered: Apr 2003 posted 04-24-2003 08:26 AM                     Thanks very much for your help, specially Paul.  |  IP: Logged John T. Mellor Film Handler Posts: 52 From: Htafield, Pennsylvania, USA Registered: May 2000 posted 04-24-2003 08:57 AM                     I agree with Paul , the stress on the remaining diodes after one starts to fail should be reason enough to change them all.Its a lot cheaper than giving out passes on a Saturday night. The Knisley rectifier will take a 150 amp diode with a 3/8 stud there is a company in New England named Edal that makes a very good diode . As a matter of fact they are the ones in a Knisley rectifier.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 04-24-2003 09:02 AM                     I rarely ever change all the diodes out as usually it isn't necassary. When a diode fails (usually open circuit the rectifiers overall output drops proportionally. I use a 100watt Iron to solder the #8 wire onto the stud. #12 is two small as it is rated for 20amps in free air. If a rectifier is repeatedly loosing diodes the culprit is usually a fan cooling issue or High Voltage spikes either from the lamphouse or sometimes due to the failure of the main transformer As for only getting 400 hrs on a 4K lamp I would ask what is the failure mode. If the electrode tips are pitted look for excessive ripple or inrush current. If it is overall blackening then it is probably heat. If they are getting hard to strike then i would be suspisious of the high voltage boast supply that provides the noload voltage. Certain brands of lamps seem to need more noload voltage than others when they get old  |  IP: Logged Elvis Navas Film Handler Posts: 13 From: Caracas, Venezuela Registered: Apr 2003 posted 04-24-2003 10:20 AM                     Hi mr. Gordon, the electrode tips are pitted. The ripple is produced by some diode that is not working properly. I test the continuity of diodes (unplugged) in beep position on the digital tester and it shows me a number measured in ohms, what should be this value?  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 04-24-2003 01:48 PM                     Elvis, I have seen those values "all over the place". But remember, that is a test that uses practically nothing for current and voltage. About the only good that test is is to determine if the diode is open or shorted. in most cases, that's all you need to know. I have not had too much problems if they read somewhere about .375 to .650. Take a bunch of new ones and try them, and plant those figures in your mind. I'll almost bet you will find that each one (even the new ones) will have a different reading. I respectfully disagree with of Gordon's first paragraph when he said it was usually not necessary to change them all. I agree with the rest of his comments, and fully agree with him on his second paragraph. As far as diode lead wire size is concerned, it depends on the power supply. I will agree that a 12 gauge wire is not heavy enough to be using in some larger high current power supplies, but it will probably work just fine in the lower ones such as a 1,000 or 1,600 watt unit. Rarely did I ever see anything smaller than 10 gauge wire anything above 1600 watts. Also, the type of wire used makes all the difference in the world. I would opt for bonding strap style I have seen in some good quality power supplies instead of AWG 12, 10, or what-have-you. Diodes with pigtails already attached can be purchased, and I will go out of my way to get those styles. The price difference between the two is not that big of a deal. I never liked the idea of using soldering equipment on diodes. No matter how good of a heat sink you use, damaging heat can still reach the PN junction inside the doide. At one time, I did just change one diode instead of the whole complement. That was cool, because I knew I would be back in about 2 to 3 months to change another. Good job security.... but non-professional in my books. It is an injustice to that person trying to make an honest "buck" so he or she can feed themselves and their family. I discontinued that "change one diode" practice when I left a theatre supply company I used to work for years ago.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 04-24-2003 03:28 PM                     If it was a bad diode that was causing the ripple there would be a terrible amount of flicker you will need a clamp on ampmeter and measure the AC current value in the rectifiers output. If it is much over 5% then I would suspect a bad filter cap. If it is a 3phase kniesley they don't have an output filter choke and that tends to increase the inrush current  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 04-24-2003 03:35 PM                     Gordon is correct. I might add that the flicker Gordon speaks of would be a strobing flicker caused by the shutter. With the projector stopped, shutter open, CO open, HD open and FS open, you probably will not notice the flicker on the screen. However, the eyebrow raising question would be low bulb current - much lower than normal. I also understand a storage scope is a valuable tool for checking in-rush current, but I never had that luxury to have one.  |  IP: Logged German Marin Expert Film Handler Posts: 227 From: Verbania (VB), Italy Registered: Jul 2001 posted 04-25-2003 01:47 AM                     The lamphouse is a Kneisley The flicker is present but we cannot measure 'cause the "ripplemeter" we have is being repaired.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 04-25-2003 02:06 AM                     If it is a strobing flicker, you either have one or more diodes headed south, or maybe a bad filter capacitor as Gordon suggested. However, to be sure, please indicate if it is or is not a strobing flicker. Some people's idea of a flicker is caused by an unstable drifting arc.  |  IP: Logged

All times are Central (GMT -6:00)

This topic comprises 2 pages: 1  2

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.