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QUESTION: Fun with Svetlanas or Staying alive with kV power supplies
My knowledge of vacuum tubes and kV power supplies is limited. I have
been reading an article in the ARRL Handbook detailing the construction of a 1kW HF Linear. I'd like to try my hand at building something like this. I found the article a little intimidating: Ceramic insulators, parasitic suppressors, thermal and mechanical engineering etc. Is there some book that details this type of thing with an explanation of the whys as well as the whats and hows. My priorities a 1) Safety. I'd like to be alive to make my first 1kW QSO 2) Avoiding equipment destruction, arc overs, black smoke, explosions etc 3) Safetly troubleshooting this kind of equipment, loading testing etc. 4) How to deal with tubes: warm up, care, etc... 5) Avoiding TVI (ITV), parasitic oscillations etc. 6) Longevity and Duty Cycle issues etc. 7) Costs and sources. Hope someone can help. Thanks, Tim |
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straydog wrote:
. . . arcs and smoke can be intimidating. Just the surprise from an arc can make you jump in an unpredictable way and if not hurt yourself from the electrical shock, then you'll bang your head or something else. . . In a previous life, I was reaching way to the back of a cabinet of radar equipment for some reason. I was lying on my stomach, my arm was extended all the way, and my head was into the cabinet doorway about at the forehead level, with a couple of inches clearance above and below. Of course all the safety precautions were followed -- some of the heavy ground radar stuff I worked on was easily lethal. But there was some charged capacitor, something hot from another cabinet of gear, I don't recall, and I got a minor shock. My instinctive reaction was to jerk my head up, and it hit the top of the doorway. That hurt and made me reflexively jerk my head downward, hitting the bottom of the doorway with my forehead. That caused a jerk back upward, hitting the top again, and so forth. There I was, oscillating up and down, beating my head to a pulp, knowing exactly what was happening but helpless to do anything about it. It continued for what seemed like a long time, until I was sore enough that I couldn't feel one more whack, when I was finally able to stop and extract my head and arm. I guess I've felt as stupid a few times since, but only a few times. And when you bend your arm every which way in order to get at something, it might go in all twisted contorted, but it comes out fast and straight when you get bit. I've lost a bit of skin that way, too. Roy Lewallen, W7EL |
Ken Scharf wrote:
The filter caps were 10 330uf 450v computer grade units in series, each Probably dumb (and WAY off topic) question: What's the *intended* purpose of a 450v "computer grade" capacitor? -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
On Thu, 14 Jul 2005, Roy Lewallen wrote: Date: Thu, 14 Jul 2005 00:48:01 -0700 From: Roy Lewallen Newsgroups: rec.radio.amateur.homebrew Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies straydog wrote: . . . arcs and smoke can be intimidating. Just the surprise from an arc can make you jump in an unpredictable way and if not hurt yourself from the electrical shock, then you'll bang your head or something else. . . In a previous life, I was reaching way to the back of a cabinet of radar equipment for some reason. I was lying on my stomach, my arm was extended all the way, and my head was into the cabinet doorway about at the forehead level, with a couple of inches clearance above and below. Of course all the safety precautions were followed -- some of the heavy ground radar stuff I worked on was easily lethal. But there was some charged capacitor, something hot from another cabinet of gear, I don't recall, and I got a minor shock. My instinctive reaction was to jerk my head up, and it hit the top of the doorway. That hurt and made me reflexively jerk my head downward, hitting the bottom of the doorway with my forehead. That caused a jerk back upward, hitting the top again, and so forth. There I was, oscillating up and down, beating my head to a pulp, knowing exactly what was happening but helpless to do anything about it. It continued for what seemed like a long time, until I was sore enough that I couldn't feel one more whack, when I was finally able to stop and extract my head and arm. I guess I've felt as stupid a few times since, but only a few times. And when you bend your arm every which way in order to get at something, it might go in all twisted contorted, but it comes out fast and straight when you get bit. I've lost a bit of skin that way, too. Roy Lewallen, W7EL Yep. Great story. Reminds me about that sad/funny joke about the guy, his tower, bucket of tools in a wooden barrel, ropes, pully, and somehow he goes up and down the tower, wooden barrel breaks so the counterweight disappears and he goes down again....broken bones, cracked skull, all kinds of hospital damage. Funny/sad. Similar to the chainsaw joke. Anyone remember or have those jokes stored away somewhere that they can drag them out? I didn't think I had any "funny" jokes like the tower joke, etc., but I definitely had some non-fatal "war stories" to tell. I also built a couple of those "repulsion coils" as a kid. Aluminum ring & coat hanger wire core & couple hundred turns of number 14 gauge wire, plug into AC line and the ring would shoot up 1-2 feet. Neat. Playing around with a high turns coil on it one day and didn't realize my fingers were on some terminals and I must have gotten a thousand volts pressed against my thumb: ergo, two burned spots on my thumb. And, that burnt flesh stench. Gawd did it stink. And, it hurt like hell. Radar? I've heard a couple of stories of guys who walked in front of those dishes not knowing they were putting out KWs of microwaves and they got their tummy microwaved into cooked beef. Killed em dead. Better have a buddy around and you can ask him: "Hey, I think this thing is turned off...Am I thinking right? Please go look at all the switches and check, tubes lit up, fans running, hum from transformers, other noises? Please?" Art, W4PON |
Hi
On Thu, 14 Jul 2005 11:45:41 +0000, straydog wrote: On Thu, 14 Jul 2005, Roy Lewallen wrote: Date: Thu, 14 Jul 2005 00:48:01 -0700 From: Roy Lewallen Newsgroups: rec.radio.amateur.homebrew Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies straydog wrote: . . . arcs and smoke can be intimidating. Just the surprise from an arc can make you jump in an unpredictable way and if not hurt yourself from the electrical shock, then you'll bang your head or something else. . . In a previous life, I was reaching way to the back of a cabinet of radar equipment for some reason. I was lying on my stomach, my arm was extended all the way, and my head was into the cabinet doorway about at the forehead level, with a couple of inches clearance above and below. Of course all the safety precautions were followed -- some of the heavy ground radar stuff I worked on was easily lethal. But there was some charged capacitor, something hot from another cabinet of gear, I don't recall, and I got a minor shock. My instinctive reaction was to jerk my head up, and it hit the top of the doorway. That hurt and made me reflexively jerk my head downward, hitting the bottom of the doorway with my forehead. That caused a jerk back upward, hitting the top again, and so forth. There I was, oscillating up and down, beating my head to a pulp, knowing exactly what was happening but helpless to do anything about it. It continued for what seemed like a long time, until I was sore enough that I couldn't feel one more whack, when I was finally able to stop and extract my head and arm. I guess I've felt as stupid a few times since, but only a few times. And when you bend your arm every which way in order to get at something, it might go in all twisted contorted, but it comes out fast and straight when you get bit. I've lost a bit of skin that way, too. Roy Lewallen, W7EL Yep. Great story. Reminds me about that sad/funny joke about the guy, his tower, bucket of tools in a wooden barrel, ropes, pully, and somehow he goes up and down the tower, wooden barrel breaks so the counterweight disappears and he goes down again....broken bones, cracked skull, all kinds of hospital damage. Funny/sad. Similar to the chainsaw joke. Anyone remember or have those jokes stored away somewhere that they can drag them out? That'd be http://monologues.co.uk/004/Bricklayers_Story.htm - at least, that's the original one from Gerard Hoffnung - which dates back a few years. I used to play the tape of this as part of my 'Quality Awareness' sessions - trying to make the point about forward planning, and avoiding situations that are going to cause problems..... There are further versions of this relating to towers and ham radio - a google for Hoffnung + Bricklayer will turn them up Probably funnier to read about than be involved with g Take care Adrian Suffolk UK ======return email munged================= take out the papers and the trash to reply |
In article ,
Ken Scharf wrote: I always assumed there was voltage across the caps when I worked on the rig. First pull the plug(s). Wait till the voltmeter drops to zero. A trick, courtesy of Bob Pease: whenever you build a power supply circuit which carries line voltage or higher, stick an NE-2 neon bulb and a suitable dropping resistor across the caps, and place the bulb where it's clearly visible when the case is opened. If the bulb is lit (at all) the caps have enough voltage in them to give you a nasty bite. THEN put a heavy screwdriver with a well insulated handle from ground to the HV terminal to be sure! I've heard cautionary notes about this... if you do this prematurely, the arc can be scary (and dangerous in some cases - "arc flash" burns can be severe) and I believe it's possible to damage or wreck some caps as a side effect of a catastrophic high-current discharge. A heavy grounding wire, with alligator clips, and with a current-limiting resistor is another possible solution. You want a low enough impedance to drain away any charge which may come out of the cap's dielectric "soakage", but high enough to avoid a dangerous arc flash when you first hook it up. Keep on hand in the pocket if you need to adjust anything when it's hot. That's one of the best single pieces of advice around! Also, be aware of what sort of grounded metal is around your workbench. Doesn't help much to keep one hand in your pocket, if you lean your belly against a grounded metal bench! HV isn't the only thing that can get you. High current can give you a nasty surprise. Like the guy replacing some batteries on a golf cart. He was using a ratchet wrench to tighten the battery clamps and he ended on the most positive battery terminal. The handle of the wrench hit the chassis of the golf cart putting it between 36 volts and ground of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench glow WHITE HOT? (and melt?) Haven't seen that myself, but I've heard of people who have had screwdrivers, etc. literally vaporized under such circumstances. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Dave Platt wrote:
In article , Ken Scharf wrote: snip HV isn't the only thing that can get you. High current can give you a nasty surprise. Like the guy replacing some batteries on a golf cart. He was using a ratchet wrench to tighten the battery clamps and he ended on the most positive battery terminal. The handle of the wrench hit the chassis of the golf cart putting it between 36 volts and ground of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench glow WHITE HOT? (and melt?) Haven't seen that myself, but I've heard of people who have had screwdrivers, etc. literally vaporized under such circumstances. My brother came home from a business trip once with a scar on his wrist 5/8 inches wide and all the way around -- the truck was having electrical problems & he shorted his metal watch band through the 12V battery (there was a wrench involved in there somehow, of course). I felt for him, but I was very glad that _he_ was the one to learn this first hand, rather than me... -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
Dave Platt wrote:
In article , Ken Scharf wrote: HV isn't the only thing that can get you. High current can give you a nasty surprise. Like the guy replacing some batteries on a golf cart. He was using a ratchet wrench to tighten the battery clamps and he ended on the most positive battery terminal. The handle of the wrench hit the chassis of the golf cart putting it between 36 volts and ground of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench glow WHITE HOT? (and melt?) Haven't seen that myself, but I've heard of people who have had screwdrivers, etc. literally vaporized under such circumstances. The canonical "Take-Your-Rings-Off" reminder in our electronics shop in Japan, back when I was in the AF, was a color image, taken at our base hospital, of a finger burnt to the bone all the way around: one of the techs had got his wedding ring between ground and a high-current low-voltage supply. -- Mike Andrews W5EGO 5WPM Extra Tired old sysadmin working on his code speed |
On Thu, 14 Jul 2005 11:32:47 -0700, Tim Wescott wrote:
Dave Platt wrote: In article , Ken Scharf wrote: snip HV isn't the only thing that can get you. High current can give you a nasty surprise. Like the guy replacing some batteries on a golf cart. He was using a ratchet wrench to tighten the battery clamps and he ended on the most positive battery terminal. The handle of the wrench hit the chassis of the golf cart putting it between 36 volts and ground of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench glow WHITE HOT? (and melt?) Haven't seen that myself, but I've heard of people who have had screwdrivers, etc. literally vaporized under such circumstances. My brother came home from a business trip once with a scar on his wrist 5/8 inches wide and all the way around -- the truck was having electrical problems & he shorted his metal watch band through the 12V battery (there was a wrench involved in there somehow, of course). I felt for him, but I was very glad that _he_ was the one to learn this first hand, rather than me... My dad (the first W3DHJ) told me a similar story. It was in the late 20's. He was working on _his_ dad's Ford utility truck. (Grandpa owned a dairy in Big Bear, Calif.) Six volts here. The truck was parked in the driveway -- just outside the garage. When my dad caught his ring between the positive terminal and the truck frame, my Grandpa picked him up bodily -- ran him over to the rain barrel at the corner of the garage -- and stuffed my dad's entire left arm (and much of his upper torso) into the barrel. ( *The worst* thing you could do in a situation like that is try to _pull_ the ring off.) My dad was a 90-day wonder in WW II. He then spent 25+ years in the U.S. Army Corps of Engineers (we traveled the planet....) Most of his duty assignments were as Post Engineer -- with the added responsibity as Post Safety Officer. I always knew him to be evangelically anal about safety. I'm sure that incident with the old Ford truck had a wee bit to do with it. Jonesy -- Marvin L Jones | jonz | W3DHJ | linux Pueblo, Colorado | @ | Jonesy | OS/2 __ 38.24N 104.55W | config.com | DM78rf | SK |
Doug Smith W9WI wrote:
Ken Scharf wrote: The filter caps were 10 330uf 450v computer grade units in series, each Probably dumb (and WAY off topic) question: What's the *intended* purpose of a 450v "computer grade" capacitor? -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com They were used on the input side of large switching supplies for minicomputers, and some later mainframes. I pulled about 100 of them from the multiple switching supplies in an Amdal mainframe about 10 or 12 years ago. -- Link to my "Computers for disabled Veterans" project website deleted after threats were telephoned to my church. Michael A. Terrell Central Florida |
Don't forget about "soak", also known as dielectric absorption or
dielectric hysteresis. In some capacitors, particularly electrolytics, charge "soaks" into the dielectric and can take from seconds to days to work its way out. The result is a "discharged" capacitor that seems to spontaneously recharge itself. (One story I heard during my broadcast days was someone who put a screwdriver across a "discharged" capacitor. After he picked himself up off the floor, he found just the handle of the screwdriver. He was lucky his eyes weren't hit with molten metal. You'll often find large capacitors stored with a shorting wire across them -- a good idea.) I recommend leaving a heavy cliplead in place across the high voltage capacitors for the entire time you're working on the unit. Put some tape over the on/off switch and/or a tag on the plug to remind you to remove it before turning the power back on. As a side note, the aquadag coating of a CRT is notorious for this. I've gotten a healthy bite off a CRT the day after it was discharged for an hour or more with a cliplead. Roy Lewallen, W7EL |
Mike Andrews wrote:
The canonical "Take-Your-Rings-Off" reminder in our electronics shop in Japan, back when I was in the AF, was a color image, taken at our base hospital, of a finger burnt to the bone all the way around: one of the techs had got his wedding ring between ground and a high-current low-voltage supply. What we got was a nice photograph of a finger in a dish with the ring, right beside the newly customized hand. Roy Lewallen, W7EL |
What's the *intended* purpose of a 450v "computer grade" capacitor? ==================== Switch mode power suppplies ?? Frank GM0CSZ / KN6WH |
On Thu, 14 Jul 2005, Tim Wescott wrote: Date: Thu, 14 Jul 2005 11:32:47 -0700 From: Tim Wescott Newsgroups: rec.radio.amateur.homebrew Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies Dave Platt wrote: In article , Ken Scharf wrote: snip HV isn't the only thing that can get you. High current can give you a nasty surprise. Like the guy replacing some batteries on a golf cart. He was using a ratchet wrench to tighten the battery clamps and he ended on the most positive battery terminal. The handle of the wrench hit the chassis of the golf cart putting it between 36 volts and ground of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench glow WHITE HOT? (and melt?) Haven't seen that myself, but I've heard of people who have had screwdrivers, etc. literally vaporized under such circumstances. My brother came home from a business trip once with a scar on his wrist 5/8 inches wide and all the way around -- the truck was having electrical problems & he shorted his metal watch band through the 12V battery (there was a wrench involved in there somehow, of course). I felt for him, but I was very glad that _he_ was the one to learn this first hand, rather than me... I've got a related story to tell: I saw many years ago two guys try to jump start another guy in the winter time. I only saw a few seconds and surmised the following. These guys must have used the jumper cables to connect the two twelve volt batteries in series, not parallel. Why? The jumper cables were, themselves, literally smoking and not just a little bit. Figure 24 volt power at, what, something like 500 amps(?) split between heating up the interior of the two batteries and those jumper cables (that are usually like #4 or #6 gauge?). How many seconds would it take for on the order of 5000 watts to cause jumper cables to get up to 200-300+ degrees Farenheit? Those guys scrambled to tear those cables off the batteries and I could tell by how they were handling the cable that it had to be hot. They could have warped the lead plates. -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
On Thu, 14 Jul 2005, Roy Lewallen wrote: Date: Thu, 14 Jul 2005 13:27:57 -0700 From: Roy Lewallen Newsgroups: rec.radio.amateur.homebrew Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies Don't forget about "soak", also known as dielectric absorption or dielectric hysteresis. In some capacitors, particularly electrolytics, charge "soaks" into the dielectric and can take from seconds to days to work its way out. The result is a "discharged" capacitor that seems to spontaneously recharge itself. (One story I heard during my broadcast days was someone who put a screwdriver across a "discharged" capacitor. Yep, I can vouch for this effect. I've seen it, too. Short the cap with alligator clip-tipped wire for a few seconds if you want that voltage down to microvolts. I think it is not "soak" but simple RC time constant decay. Just like radioactive half-life. Residual voltage on a cap _never_ goes to true zero, only according to the decay equation. However, there is a so-called "electret" effect which really sounds like your "soak" effect. After he picked himself up off the floor, he found just the handle of the screwdriver. He was lucky his eyes weren't hit with molten metal. You'll often find large capacitors stored with a shorting wire across them -- a good idea.) D'arsonval meters, especially sensitive ones, are also best stored with a shorting wire accross the terminals. I recommend leaving a heavy cliplead in place across the high voltage capacitors for the entire time you're working on the unit. Put some tape over the on/off switch and/or a tag on the plug to remind you to remove it before turning the power back on. As a side note, the aquadag coating of a CRT is notorious for this. I've gotten a healthy bite off a CRT the day after it was discharged for an hour or more with a cliplead. Roy Lewallen, W7EL |
I forgot to tell my "parasitic" story..see below... On Wed, 13 Jul 2005 wrote: Date: 13 Jul 2005 14:05:17 -0700 From: Newsgroups: rec.radio.amateur.homebrew Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies My knowledge of vacuum tubes and kV power supplies is limited. I have been reading an article in the ARRL Handbook detailing the construction of a 1kW HF Linear. I'd like to try my hand at building something like this. I found the article a little intimidating: Ceramic insulators, parasitic suppressors, thermal and mechanical engineering etc. Is there some book that details this type of thing with an explanation of the whys as well as the whats and hows. My priorities a 1) Safety. I'd like to be alive to make my first 1kW QSO 2) Avoiding equipment destruction, arc overs, black smoke, explosions etc 3) Safetly troubleshooting this kind of equipment, loading testing etc. 4) How to deal with tubes: warm up, care, etc... 5) Avoiding TVI (ITV), parasitic oscillations etc. I built this two 811-a linear amplifier way long ago. Basically ave power 300 watts DC input. So, I made my own parasitic suppressors (turns of wire over, say, a ten ohm two watt carbon resistor. Or adjust turns). This was for a 75 meter phone band. So, on launch day it sits there like a scared bird. Turn on fil power, plate power (this is grounded-grid for stability and minimal if not zero need for neutralizations), and tune (no drive) the plate capacitor. Result: dang, RF output through the power meter AND smoke comes out the top of the amp and I stand up, look down, and the coils of wire (made of #22 or 24 gauge wire, can't remember) around the resistors are glowing red hot! Too many turns of wire, so next time around I cut back to half and all was OK. Including no self-oscillation in the two 811-As. That's called trial and error. Or, try, smoke, fix. Like if ready, fire, aim does not work, change the order to ready, aim, fire. Art, W4PON 6) Longevity and Duty Cycle issues etc. 7) Costs and sources. Hope someone can help. Thanks, Tim |
In article g,
straydog wrote: Don't forget about "soak", also known as dielectric absorption or dielectric hysteresis. In some capacitors, particularly electrolytics, charge "soaks" into the dielectric and can take from seconds to days to work its way out. The result is a "discharged" capacitor that seems to spontaneously recharge itself. (One story I heard during my broadcast days was someone who put a screwdriver across a "discharged" capacitor. Yep, I can vouch for this effect. I've seen it, too. Short the cap with alligator clip-tipped wire for a few seconds if you want that voltage down to microvolts. I think it is not "soak" but simple RC time constant decay. Just like radioactive half-life. Residual voltage on a cap _never_ goes to true zero, only according to the decay equation. However, there is a so-called "electret" effect which really sounds like your "soak" effect. Yup. Formally "dielectric absorbtion". In a lot of types of capacitor, enough stored charge can come back out, over the course of a few minutes, to raise the open-circuit terminal voltage of the cap to a significant percentage of its fully-charged level, even if you had previously discharged the cap all the way to a zero reading. It can be enough to give you a nasty bite. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
"Highland Ham" ) writes: What's the *intended* purpose of a 450v "computer grade" capacitor? ==================== Switch mode power suppplies ?? Frank GM0CSZ / KN6WH I thought "computer grade" was either a marketing name, or at the very most defined a certain design of capacitor. In other words, they weren't designed for computers, but saw a lot of use in them. They weren't cheap electrolytics of the type you'd see in the average consumer equipment of thirty years ago. You'd see them promoted in the surplus ads, and the ones I remember were metal-cased, and had screw terminals for connections. I still have one around I bought at a hamfest for a 12V power supply. It was about 10,000uF (which was a fairly large size capacitor circa 1973 or so), had a voltage rating of about 16volts, and was the size of a can of coke. Obviously a lot more impressive than the average electrolytic of the day. So once you had that style, it wasn't whether they were used in computers or not, so of course you could have high voltage "computer grade" capacitors. I have no idea if it was a marketing ploy, "hey those are used in computers [which were still uncommon at the time, and usually big and very expensive], they must be good capacitors", or if there was something about their design that made them better than the average electrolytic of the time. Michael VE2BVW |
straydog wrote:
Yep, I can vouch for this effect. I've seen it, too. Short the cap with alligator clip-tipped wire for a few seconds if you want that voltage down to microvolts. I think it is not "soak" but simple RC time constant decay. Just like radioactive half-life. Residual voltage on a cap _never_ goes to true zero, only according to the decay equation. However, there is a so-called "electret" effect which really sounds like your "soak" effect. No, it's not a simple time constant -- the slope is much different. A reasonably good model of it is a series R, shunt C, series R, shunt C, etc. A large number of Rs and Cs with various time constants have to be used to imitate it reasonably well. I don't know about an "electret effect". An electret is a dielectric with a permanently trapped charge, so it produces a static electric field. It's the analog of a magnet, with permanently trapped flux and producing a permanent magnetic field. A magnet that's not moving can't produce a current (much to the dismay of the perpetual motion crowd), and an electret that's not moving can't produce a voltage. D'arsonval meters, especially sensitive ones, are also best stored with a shorting wire accross the terminals. That's for an entirely different reason -- to protect the meter from damage, rather than the user. Roy Lewallen, W7EL |
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On Thu, 14 Jul 2005, Roy Lewallen wrote: Date: Thu, 14 Jul 2005 19:47:23 -0700 From: Roy Lewallen Newsgroups: rec.radio.amateur.homebrew Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies straydog wrote: Yep, I can vouch for this effect. I've seen it, too. Short the cap with alligator clip-tipped wire for a few seconds if you want that voltage down to microvolts. I think it is not "soak" but simple RC time constant decay. Just like radioactive half-life. Residual voltage on a cap _never_ goes to true zero, only according to the decay equation. However, there is a so-called "electret" effect which really sounds like your "soak" effect. No, it's not a simple time constant -- the slope is much different. A reasonably good model of it is a series R, shunt C, series R, shunt C, etc. A large number of Rs and Cs with various time constants have to be used to imitate it reasonably well. Well, if you want to get technical about it, yes. All those layers of foil all, individually, add up to all of those Cs and Rs. I don't know about an "electret effect". An electret is a dielectric with a permanently trapped charge, so it produces a static electric field. I doubt if there is very much in the universe with a real, practical _permanence_. The second law of thermodynamics says that trapped charge is going to try hard to become untrapped. It's the analog of a magnet, with permanently trapped flux and producing a permanent magnetic field. Most magnets that I've heard about will slowly lose their magnetism via one of many mechanisms. A magnet that's not moving can't produce a current (much to the dismay of the perpetual motion crowd), and an electret that's not moving can't produce a voltage. In a laboratory, once, I made an electret out of, basically, frozen water. The various pieces of these electrets, bathed in liquid nitrogen, behaved, qualitatively, like little magnets. Bring one near another, and whatever "pole" was at some point on one piece would spontaneously jump, appropriately, to the piece I was holding. An electret that is not moving can't produce a voltage? Semantics. There _will_ be an electric field between one pole and the other and it _will_ be measureable and calculable and the results will be in volts regardless of whether the electret is "moving". The units can be expressed in more than one way depending on reference systems, definitions, and goal of the measurement or calculation. D'arsonval meters, especially sensitive ones, are also best stored with a shorting wire accross the terminals. That's for an entirely different reason -- to protect the meter from damage, rather than the user. For many people (since, in my life, it came up many times in conversation), protecting the meter was more important. Roy Lewallen, W7EL Art, W4PON |
On Fri, 14 Jul 2005 wrote: Date: 14 Jul 2005 20:48:16 -0700 From: Newsgroups: rec.radio.amateur.homebrew Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies From: straydog on Fri 15 Jul 2005 00:48 That's called trial and error. Or, try, smoke, fix. Like if ready, fire, aim does not work, change the order to ready, aim, fire. All electronics works on smoke. If the smoke leaks out, it won't work... ;-) Reminds me of another joke I can't quite remember: something dealing with the proof that electricity is really smoke, or something like that. Maybe someone has a reference to that joke. It was pretty funny, too. Art, W4PON |
All electronics works on smoke.
If the smoke leaks out, it won't work... ;-) Reminds me of another joke I can't quite remember: something dealing with the proof that electricity is really smoke.... A local (and now retired) engineering faculty member has an after-dinner speech in which he "proves" that "electricity is black and heavy"! For example, in an automobile, electricity is stored in the battery. What color is the battery? Black! And it is quite heavy for its size. And on and on and on! --Myron. -- --Myron A. Calhoun. Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) |
straydog wrote:
On Fri, 14 Jul 2005 wrote: Date: 14 Jul 2005 20:48:16 -0700 From: Newsgroups: rec.radio.amateur.homebrew Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies From: straydog on Fri 15 Jul 2005 00:48 That's called trial and error. Or, try, smoke, fix. Like if ready, fire, aim does not work, change the order to ready, aim, fire. All electronics works on smoke. If the smoke leaks out, it won't work... ;-) Reminds me of another joke I can't quite remember: something dealing with the proof that electricity is really smoke, or something like that. Maybe someone has a reference to that joke. It was pretty funny, too. Art, W4PON But electricity _is_ really smoke. They burn coal at the generating station and it travels through the wires to your house, where it makes everything work. Then the used smoke goes _back_ through the wires (why do you think they call them "return" wires, eh?) to the generating station where it goes up the smokestack. If something should break then some of the smoke will leak out right there in your house right before the thing stops working. And that's how you know that electricity is smoke. -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
On Fri, 15 Jul 2005, Tim Wescott wrote: Date: Fri, 15 Jul 2005 16:51:21 -0700 From: Tim Wescott Newsgroups: rec.radio.amateur.homebrew Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies straydog wrote: On Fri, 14 Jul 2005 wrote: Date: 14 Jul 2005 20:48:16 -0700 From: Newsgroups: rec.radio.amateur.homebrew Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies From: straydog on Fri 15 Jul 2005 00:48 That's called trial and error. Or, try, smoke, fix. Like if ready, fire, aim does not work, change the order to ready, aim, fire. All electronics works on smoke. If the smoke leaks out, it won't work... ;-) Reminds me of another joke I can't quite remember: something dealing with the proof that electricity is really smoke, or something like that. Maybe someone has a reference to that joke. It was pretty funny, too. Art, W4PON But electricity _is_ really smoke. They burn coal at the generating station and it travels through the wires to your house, where it makes everything work. Then the used smoke goes _back_ through the wires (why do you think they call them "return" wires, eh?) to the generating station where it goes up the smokestack. If something should break then some of the smoke will leak out right there in your house right before the thing stops working. And that's how you know that electricity is smoke. That's pretty good, but I seem to recall another slightly different version of the joke but with some really clever line about the purpose of insulation (and a half-believable rationale [rationale does not mean scientific, however). Anyone else remember more of the details of this joke? Art, W4PON -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
Myron wrote:
A local (and now retired) engineering faculty member has an after-dinner speech in which he "proves" that "electricity is black and heavy"! For example, in an automobile, electricity is stored in the battery. What color is the battery? Black! And it is quite heavy for its size. Sounds logical to me. My favoite is the Dark Sucker Theory (light is the absence of dark, and light bulds suck dark). Do a google on it for lots more info, probably more than you ever wanted to know... :-) And thusly another thread morphs far off topic... |
But electricity _is_ really smoke. They burn coal at the generating
station and it travels through the wires to your house, where it makes .... Did you notice that coal is BLACK? And most smoke is BLACK, too. Insofar as water-generated electricity is concerned, it comes from rain which has FALLEN (it's heavy) out of BLACK clouds and flowed downward (heavy, again) to a sort of centrifuge which spins the HEAVY electricity out of the water and forces it into the wires.... -- --Myron A. Calhoun. Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) |
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