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Author Topic: Power in Lamphouse After Breakers are Cut Aaron Mehocic Jedi Master Film Handler Posts: 804 From: New Castle, PA, USA Registered: Jun 99 posted 03-29-2003 02:09 PM                     We have a problem. There is still DC power in our Xenex II Kniesley lamphouse, but all breakers are cut. Yes we checked all breakers and they are if the OFF position, so thats not the situation. Understand this is a bulb change after the 3000 Watt ORC failed to ignite after serious attempts and reasoned thinking. Our multimeter is showing 250 Volts of DC power still held up in the machine. Anybody ever seen this before?  |  IP: Logged Aaron Sisemore Flaming Ribs beat Reeses Peanut Butter Cups any day! Posts: 3061 From: Rockwall TX USA Registered: Sep 1999 posted 03-29-2003 02:17 PM                     The filter capacitors in the power supply will hold the DC charge for some time after power is cut unless discharged in some fashion. Most power supplies have 'bleeder' resistors across the capacitor terminals to drain this latent charge off. I cannot remember if the Kniesley supplies had these or not, and if they do then its likely that the resistor is open. If you need to access the lamp and the charge is there, simply jumper a 10k 5 watt resistor across the + and - terminals for several seconds and recheck to see if the charge is gone with a multimeter. -Aaron  |  IP: Logged Aaron Mehocic Jedi Master Film Handler Posts: 804 From: New Castle, PA, USA Registered: Jun 99 posted 03-29-2003 02:58 PM                     Thanks! We did something similer to what you just recommended and it worked. The manager and myself have changed a lot of bulbs, but you can immagine our surprise when we both got shocked. Oh yeah, I mistakenly typed 250 Volts, it was much less than that, but still we felt it.  |  IP: Logged Don Bruechert Mmmmmmmmm, bird! Posts: 340 From: Manitowoc, WI, USA Registered: Jan 2003 posted 03-29-2003 03:04 PM                        Joe's booth training video makes fun of this situation, but is a good way of making a memorable presentation of the danger. We have kniesleys too and I believe somewhere on them there is a label that says to wait a minimum of 10 minutes after power down before accessing the bulb area... I saw it on the video, but when I showed that video to other staff they told me they found it out the hard way!  |  IP: Logged Darryl Spicer Film God Posts: 3250 From: Lexington, KY, USA Registered: Dec 2000 posted 03-29-2003 06:31 PM                    Like Arron Stated, These capasitors do holed a current for a brief time if the bleeder resistors are good there will be no charge after 10 mins. This held voltage usually runs around 25 DCV.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 03-30-2003 02:25 AM                     As a rule of safety is, in addition securing the power to the appartus, discharge ALL capacitors in the power supply before servicing. True...the voltage might be low...but what about that gold ring on your finger when it comes in contact with a huge capacitor terminal? The current flow on discharge can be enough to fry the ring's imprint on your finger permanently. Sometimes (notice I said "sometimes") it is not the electrical shock that does the damage. It is the reaction of the human body that can cause some REAL problems. When I was in the US Navy in a training command, metal jewelry of any kind was forbidden to be worn while working on electronic equipment. I support that. Try get hitting with a -27,000 volt pulse from the pulse transformer of a radar set. If you think about it, even the ignition phase of the standard Xenon lamphouse can be triple that amount. In a thread on FT, I described the results of getting "hit" by an ignition pulse of a Xenon lamphouse. It is quite "electrifying" just to put it mildly. Back to the subject at hand.....Only a fool will trust a bleeder resistor. Safety first!  |  IP: Logged Rick Long Jedi Master Film Handler Posts: 759 From: Toronto, Ontario, Canada Registered: Nov 1999 posted 03-30-2003 12:17 PM                     Paul's post is worth re-reading (the voice of experience). Like pilots, there are old technicians and there are bold technicians. There are no old, bold technicians. Always, when I am about to work on a circuit I am 150% sure is "dead" I first put two fingers of one hand on the terminals I am about to work with. (The other hand is in my pocket). The worst that could happen if I am wrong is a sudden muscular reaction and bite in my fingers, coupled with a remark like, "ouch, sonofabitch", rather than provide a circuit for heavy current through the heart. One should NEVER wear any jewlery or neckties while working on projection equipment.  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 03-30-2003 12:50 PM                        Please explain bleeder resitor. My English is failing me here. I think I know what you mean from the context, but I want to be sure that I understand it correctly.  |  IP: Logged David Stambaugh Film God Posts: 4021 From: Eugene, Oregon Registered: Jan 2002 posted 03-30-2003 12:58 PM                        A bleeder resistor can be installed across a device like a capacitor. The resistor will have a high resistance value so that it doesn't pass much current and thus has no effect on the active circuit. However when the circuit is powered down, the resistor provides a controlled current path across the + and - terminals of the capacitor and allows the cap. to slowly and safely discharge its energy, rather than storing it indefinitely and discharging it through an unwary technician.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 03-30-2003 01:02 PM                     Typically a bleeder resistor in normal power supplys are across the filter capacitors. They serve two basic purposes: 1. Better power supply regulation. A correct bleeder resistor value is supposed to handle 10% of the total current through the power supply. However, for xenon power supply units, this may not be the case. 2. Safety of maintenance personnel in high voltage applications. Rick, I never use my fingers to test a circuit to make sure it "dead". I usually have a little "Missouri Ignition Key" (a small jumper lead) to do that for me. I can visualize the results if I got a small jolt across the fingers, and my arm reflexed backwards with the elbow hitting a curious onlooker behind me right square in the <ahem> By the way, I have heard stories about that... The "one hand in the pocket" technique Rick speaks of is well worth following. I might add this: If you are making screwdriver adjustments on electronic equipment, keep your fingers off the metal shank of that screwdriver, and keep the other hand in your back pocket. Rick also said: quote: One should NEVER wear any jewlery or neckties while working on projection equipment. This has been one of my pet peeves for many years. I was at odds with Regal on this one....they required neckties in the booth. I refused to wear them. I don't know if Regal has reversed that requirement, but I hope they did. Neckties are a definate safety hazard around any machinery. I am sure there are other corporates that require neckties in the booth. It is pure and simply stupid! If their job requires a necktie if on the floor in public view, fine! But it should be removed before running the equipment.  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 03-30-2003 01:19 PM                        Thanks, I know now what it is, in German it is called "Entladungswiderstand", "discharge resistor".  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 03-30-2003 01:23 PM                     Michael, pronounching some of the German words are really a "mouthful"...  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 03-30-2003 01:31 PM                        It seperates the men from the boys! Ant-laa(with a as in father)doongs-veeder-stunt  |  IP: Logged Michael Harlow Expert Film Handler Posts: 170 From: Faversham, Kent, UK Registered: Jul 2002 posted 03-31-2003 12:17 PM                     Paul, I have searched for your post about getting "hit" by a Xenon pulse. Can you bump it up or link to it please?  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 03-31-2003 01:48 PM                     Michael, it has been a long time ago when I posted that, and I don't know what thread it was in. Basically, my hand was in the Xetron XH-2000 lamphouse "fired", and the ignition came around the front bulb support and nailed me. The projectionist that was in the booth said it literally picked me up and threw me against the wall without my feet touching the floor. It even tore a hole in my pants leg, but I don't know how that happened. For two days, I was walking around with my hair standing on end, and I could not comb it down! It was a bad experience I don't ever want to repeat. I was lucky on that one.... This incident would have never happened if I was not in a hurry. There was nothing wrong with the lamphouse. I just got foolish and bypassed an interlock for some stupid reason.  |  IP: Logged

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