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

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » Safely Discharging Capacitors on a Scrapped Rectifier (Page 2)

This topic comprises 3 pages: 1  2  3

Author Topic: Safely Discharging Capacitors on a Scrapped Rectifier Chris Slycord Film God Posts: 2986 From: 청주시, 경북도, South Korea Registered: Mar 2007 posted 06-28-2007 03:22 PM                     quote: Mark Gulbrandsen You mean to tell me all those instances on ER where the patient went "flat line" and the drfibrillator was used to re-start the heart were not authentic? Depends on what they show you. A defibrillator, ON IT'S OWN, can't save a flat line patient. In that case, they'll use a combination of CPR and cardiac stimulant drugs. Then, they get it to where they have one of the "shockable rhythms" (ventricular fibrillation or pulseless ventricular tachycardia). Though it's also possible that someone who is flat line actually has a tiny amount of electrical activity. The defibrillator sends out electrical energy that depolarizes the beating section of the heart which stops the arrhythmia and then your SA node (pacemaker) hopefully starts up a normal rhythm. EDIT: In fact, in both of those "shockable" cases the heart is still in activity and might even be beating (they're just in patterns that if left alone will have a major problem for the patient).  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 06-30-2007 07:42 PM                  So CB Shane, what's the final disposition of the PS?  |  IP: Logged Kyle Anderson Film Handler Posts: 86 From: Tyler, TX, USA Registered: Dec 2005 posted 06-30-2007 08:57 PM                     Great way to kill yourself  |  IP: Logged Shane Hoffmann Film Handler Posts: 68 From: Fond du Lac, WI, USA Registered: Feb 2003 posted 06-30-2007 09:33 PM                     I've been giving them a little extra time to discharge somewhat on their own...I'll probably give it a shot sometime during this next week when we're dead and I've got nothing else to do. I haven't decided if I want to go for it with a screwdriver or try the light bulb method. The angle I will have to go at them from is a bit awkward, which is the cause of any remaining apprehension. As far as not having much charge-- my little handheld voltage detector beeps when I put it on the terminals. I don't know what the threshold is for those things to begin registering voltage, but I know when it's minimal it doesn't beep at all...  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 07-01-2007 10:32 AM                     There is no guarantee that leaving them sitting there will discharge them. It may very well have no effect all (or worse). You should measure the voltage with a DC voltmeter. As for awkward angles, well, with two aligator clipsleads, you should be able to solve any such problem. (It's also good practice put a cliplead across the terminals after you have discharged them.) If you've waited this long, take people's advice and don't use a screwdriver. I'm not so sure a lightbulb is a great plan, but I suppose if you burn out the lightbulb it's no big deal. --jhawk  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 07-01-2007 10:54 AM                        They should also slowly discharge when you simple leave the multimeter hooked up to it for a while. If you don't have one to check what's going on, you shouldn't attempt that nayway.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-01-2007 11:20 AM                     quote: John Hawkinson I'm not so sure a lightbulb is a great plan A light bilb is actually a fairly safe way to discharge them but is certainly not the prefered way. A light bulb is a little large and fragile to carry around in the tool kit. quote: Michael Schaffer They should also slowly discharge when you simple leave the multimeter hooked up to it for a while. With most decent DVM's being greater than 10 megohm input it could literally take weeks to discharge them...assuming they are fully charged. Don't necessarily rely on a meter to do that job. Mark  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 07-01-2007 11:43 AM                        What's the typical capacitance of those capacitors?  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-01-2007 12:47 PM                     Christie used 6000uF for the longest time...Strong was normally a bit higher and went to using two devices that when coupled were in excess of 6000uF...I'd have to check to see what they are. Suffice to say, they are not small The screwdriver method is plain stupid...and can often damage the screwdriver too...depending on the charge in the cap at the time. Since the voltage is likely to be low, the wattage of the cap need not be particularly large...a few watts will do it since even if it was at full charage and the lamp didn't strike (125VDC on the high side)...it will quickly drop and with that the power dissapation the resistor must contend with. As for a light bulb it is a good one to use and most booths have them there somewhere...if on a trouble shooting type lamp...then you merely need some clips connect the troubleshooting lamp (Reel lamp)'s power cord to the cap. Steve  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 07-01-2007 05:56 PM                        On large transmitters we used a shorting rod which was permanently grounded before touching any circuit. B+ was 7000 volts. I use a clip lead attached to the sacrificial screwdriver to create a mini shorting rod with good results in this industry. Amplifying Steve: If the last time you powered up actually lit the bulb, the capacitors have 30 volts dc or less; up to 125 volts if no bulb lit. Louis  |  IP: Logged Stephen Furley Film God Posts: 3059 From: Coulsdon, Croydon, England Registered: May 2002 posted 07-01-2007 06:43 PM                     quote: Louis Bornwasser On large transmitters we used a shorting rod which was permanently grounded before touching any circuit. B+ was 7000 volts. In the 60s, during hours when normal programmes weren't being transmitted the BBC wanted some sort of material which could be used for testing and demonstration of the new colour television sets. The answer they came up with was a collection of 'trade test colour films' still fondly remembered by many. These films came from various sources, 'It's the tube that makes the colour', about the making of shadow mask picture tubes was made by Mullard, who may have been owned by Philips by that time, I'm not sure. There were a a number of films by the Shell and BP oil companies, including 'Algerian Pipeline' and one of my favorites, 'The Home-Made Car. I have prints of a few of these films, including one about plastics, and 'We've Come a Long Way, about the design of oil tankers. One of these films was about safety systems and procedures for working on high-Voltage equipment. I can't remember who it was made by, but the title was 'On the Safe SIDE' Switch off Isolate Dump Earth In the film one of the characters has to make some changes to some high-Voltage experimental equipment. He follows all of the correct procedures, but unknown to him, somebody else has made an error in some previous modifications, and the coil he is about to touch is still live. At the last moment he says to himself 'I suppose that Earth is alright' and the camera zooms in on the Earthing hook. The man takes the hook off the point where it was attached, and which would have been directly connected to the coil if not for the previous error. He touches it directly onto the coil, with predicctable results, but at least he survives. Does anybody remember this film?  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 07-02-2007 04:19 AM                        Shane, bring your girlfriend up into the booth -- cautiously tell her to stand back and explain how your are going to demonstrate the incredible power of the equipment you work with and how it stores huge amounts of electrical energy. Now take out a handful of steel wool, and while again cautioning her to stand back, dramatically drop the wad on the cap terminals. It will vaporize in a ball of electrical fireworks. She will ghasp. Reassure her everything is alright and that you have everything under control. She will think you are Mr. Wizard. You might even get laid. And if not, at least you will have discharged your caps.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-02-2007 08:28 AM                     quote: Louis Bornwasser On large transmitters we used a shorting rod which was permanently grounded before touching any circuit. B was 7000 volts. Exactly! The tranmitter I used to work on... a TTU-1000(100kw UHF) had 6 air cooled high voltage supplies (cubicles) that were tied in parallel and could generate a combined total of 20kv at 18 amp . I used to go into each high voltage cubicle(6X6X6 feet in size) and clean them out with a brush and vacuum once a month.... sure they are discharged but you still get the oogies while you're in there. Dust and high voltage don't get along! BTW: The transmitter had a permanently installed grounding rod system and they looked like gates, I believe there were three of them. Each had spring loaded mechanism to hold it grounded once you opened it. They had to be reset by hand to stay open. These were the main path to discharge all the H-V supplies before you could go into the back of the visual or aural cubicles to work. Most of the problems we had were just water leaks in the cooling circuit. This transmitter which went in in 1963 was so large it occupied 1/2 of the 94th floor in the John Hancock building.... The 2 heat exchangers for the klystron cooling circuits which were up on higher levels just below the roof were each the size of school busses. Neat old stuff! Mark  |  IP: Logged German Marin Expert Film Handler Posts: 227 From: Verbania (VB), Italy Registered: Jul 2001 posted 07-02-2007 11:52 AM                     I've discharged that capacitors a lot of times and frequently with a screw driver. When I don't want to see the big spark I've just used a big old wire (the one used for the lamp-rectifier) and touch the terminals without get sparks (just a little non-scared sparks)... if you think longer about this fact, the "fear" take your control and the panic won't let you do it. Have you discharged the rectifier? Saluti  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 07-02-2007 12:49 PM                     Oh, quit being such a baby! Just lick it with your tongue! That's what a real man would do!  |  IP: Logged

All times are Central (GMT -6:00)

This topic comprises 3 pages: 1  2  3

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.