Re: Dangerous Low Voltage (WAS: Power pole for K3?)
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Another low voltage power source that is in common use is the lead-acid
storage battery used on cars and especially the deep cycle marine battery favored by hams for backup. Usually a ring or watchband is not a problem because of the terminal spacing at the battery, but the danger is very much present at the other end of the cables where it may be connected to a terminal strip etc. The added danger of these batteries is they can deliver as much as 800 amps depending on the internal resistance of the battery and cables. If the internal resistance is as little as 1/10th Ohm at 14 volts that is 140 amps. The power generated in the battery under these conditions is 140X140/10 or 1960 Watts. 2KW heating the acid contents of a battery can cause it to explode from steam pressure in a matter of seconds, thus spraying everything in the area with sulphuric acid and hot lead. When this happens in a car the result is usually a totalled vehicle and seriously injured mechanic and passers-by. I never use a wrench which has exposed metal surfaces long enough to short a battery, and I always disconnect the negative terminal (- ground assumed here) and cap it before working around them. Al WA6VNN ______________________________________________________________________ In a message dated 4/19/2008 8:11:26 A.M. Pacific Daylight Time, [hidden email] writes: I see you got plenty of answers about the APPs, Bill. You will need to provide your own suitable connectors for the power supply end of the cable. You mention having high-capacity batteries and a 70-amp Astron supply. It sounds like you have experience with high-current supplies and understand how dangerous they can be, but there are a lot of readers here who may not have that background. I mention it because many Hams think 13.8 VDC is safe to handle. It's *NOT*. It's not the voltage, of course, but the current. A short often produces a flash of molten metal that may continue for a while if the resistance is enough to avoid tripping a breaker or crowbar circuit. It can take off a finger or a hand, or very severely injure a person in an instant should a ring or watch band get across the supply line, immediately transformed by the current into red-hot metal burning its way through flesh. In my days working in the field as an aircraft radio/radar tech I knew some who were missing fingers because they neglected to take off a wedding band when working. It's not a nice way to lose a hand or finger. It's not always quick. It can take a while, with the ring or watch band welded solidly to the terminals by the current as the hot metal eats its way through a finger or wrist. I've seen tempered steel screwdrivers literally explode into a spray of molten metal blobs when dropped across a high-current, low-voltage supply - blobs of molten steel that splatter the face and eyes of the unwary worker not wearing protective gear. Less severe shorts can set wiring, and the shack, on fire in short order, all without opening a breaker or tripping the crowbar protective circuit in the power supply. Even a more moderate 35 Amp supply can start a fire or cause a severe burn under the right conditions. Working on shipboard and aircraft systems using 12 to 28 VDC at high currents, I've learned to treat such supplies with the same respect I do a 3KV high-voltage supply. The concerns and procedures needed to be safe are different, but either a high voltage or a low-voltage, high-current supply is dangerous in its own way. I use soldered-on ring terminals on my Astron supplies that provide large, low-resistance contact areas with the lugs and which cannot be pulled loose without physically breaking the wire, and I make very sure there are no metallic objects (cabinets, connectors, other equipment, etc.) located where they might be accidentally moved and make contact with exposed supply terminals anywhere. And then I make sure the terminals on my power supply (and anywhere else) are carefully covered and insulated from accidental contact, just in case. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com **************Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp00300000002851) _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Hi Ron
I've noticed a lot of us OFs still have the reflex of putting one hand behind us when the other goes inside a piece of equipment. Lot of us learned it the hard way. :-) 73, Bob N6WG ----- Original Message ----- From: "Ron D'Eau Claire" <[hidden email]> To: <[hidden email]> Sent: Saturday, April 19, 2008 2:11 PM Subject: RE: [Elecraft] Dangerous Low Voltage (WAS: Power pole for K3?) I never use a wrench which has exposed metal surfaces long enough to short a battery, and I always disconnect the negative terminal (- ground assumed here) and cap it before working around them. Al WA6VNN -------------------------------- Disconnecting power before working on the gear to remove/replace parts is basic to both low and high voltage supplies. My one up-close and frightening experience with low-voltage high-current supply shorts occurred on an F-86 (Korean war era jet fighter) flight line at Lockheed. It was the middle of the night and bitterly cold as I and another tech worked on two fighters sitting side-by-side. They were powered by ground carts. We had lowered the canopies almost all the way down to conserve a little heat in the frigid cockpits as we ran through the avionics ground checks. Suddenly I heard one of the power carts groan under heavy load. It caused me to look up and out of the cockpit to see what was going on. The plane next to me had smoke billowing from the cockpit, coming out around the almost-closed canopy. I could see the other tech's head lying against the canopy. He was apparently unconscious. I hit the canopy button and clambered out as it slowly wound open, yelling for help, very conscious that these planes were fully-fueled bombs sitting wingtip to wingtip waiting for a fire to set them off. We got the guy out. He was splattered with burns but the plane wasn't on fire. Later we learned that he had discovered a defective circuit breaker. He had a replacement with him, but decided he didn't want to open the canopy and climb down to disconnect the power cart. The circuit breaker connected to power by a wire with a lug on the end that attached with a screw into a threaded hole in a large copper bus bar. As he was turning the screw, he dropped the screwdriver and it fell touching the power bus bar and the aluminum side of the console. He got a face full molten metal blobs as the shaft of the tool literally exploded in his face. He instinctively stood bolt upright in the cockpit, smashing his head against the closed canopy and knocking himself unconscious. Lockheed management and the US Air Force were not impressed. They had a badly damaged jet fighter with molten metal drooled down the side of the console and cockpit and it could have been much, much worse. I think he found a new line of work. Even "minor" short circuits can cause lots of grief. It's very easy to instantly fry a PC board trace with a temporary short circuit. Those can usually be fixed (once you find the break), but it's still a very unnecessary and easily avoided damage by following simple safety protocols, including removing power before touching the circuit to remove parts or taking any other short-cuts. And for those of us who regularly work around equipment with high voltages - a few hundred volts and up - allowing ourselves to be lulled into complacent behavior by the low voltages in most gear today can be dangerous. One time I was troubleshooting a receiver that had something that smelled hot so I was gingerly touching resistors to see if one was overheating when I suddenly remembered I was working on a tube-type receiver with a 250V supply! Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: Dangerous Low Voltage (WAS: Power pole for K3?)
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And not obvious, unless you're seen the results, but removing
conductive jewelry, including your wedding ring, is a highly desireable. I have seen a person who totally lost the use of the appropriate finger because "his wife wouldn't let him take it off". Dual-battery setups require particular care, too. 73, doug From: "Robert Tellefsen" <[hidden email]> Date: Sat, 19 Apr 2008 14:39:44 -0700 Hi Ron I've noticed a lot of us OFs still have the reflex of putting one hand behind us when the other goes inside a piece of equipment. Lot of us learned it the hard way. :-) 73, Bob N6WG ----- Original Message ----- From: "Ron D'Eau Claire" <[hidden email]> To: <[hidden email]> Sent: Saturday, April 19, 2008 2:11 PM Subject: RE: [Elecraft] Dangerous Low Voltage (WAS: Power pole for K3?) I never use a wrench which has exposed metal surfaces long enough to short a battery, and I always disconnect the negative terminal (- ground assumed here) and cap it before working around them. Al WA6VNN _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by n6wg
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Re: Dangerous Low Voltage (WAS: Power pole for K3?)
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In reply to this post by n6wg
Hi Bob,
With mains / battery disconnected, this one uses a "Ground Stick" as well after being bitten hard by a supposedly discharged capacitor too many years ago! 73, Geoff GM4ESD Robert Tellefsen" <[hidden email]> wrote on Saturday, April 19, 2008 10:39 PM > Hi Ron > I've noticed a lot of us OFs still have the reflex of > putting one hand behind us when the other goes > inside a piece of equipment. > Lot of us learned it the hard way. :-) > 73, Bob N6WG _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by AC7AC
I insist on putting a fuse on each battery terminal, preferably fixed right
to the terminal. The additional voltage drop is worth the peace of mind. Car radio shops have big chunky ones at modest prices. David G3UNA _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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I don't know if these are related or not, but #1 when using the monitor function I hear my own voice ON frequency, but I also hear an OFF frequency copy of my signal...like it's about 1 or 2 khz away. I have tried it with and without phones and with two different microphones (MD2 & Elecraft Pro Headset). If I give a whistle in to the mic I hear it off frequency. The higher I whistle, the lower the whistle from the monitor audio, and of course the lower I whistle the higher it is in frequency from the monitor audio. It's disconcerting to say the least and leads me to believe there is something not right.
#2, I cannot get the VOX to work. With the VOX gain set as low as 1 or 2, any amount of mic gain causes it to go in to transmit and will not unkey until I turn the mic gain down completely (3 or so). I can turn the mic gain completely down, as well as the compression, put it in VOX mode, turn the mic gain up to 2 or 3 and it keys right away. this is with the VOX gain set at about 2 or 3 as well. I pulled the front panel off and checked for bent pins, as Gary suggested. Did not find anything wrong. Anyone have any idea?? Stan W5EWA Houston, TX David Cutter <[hidden email]> wrote: I insist on putting a fuse on each battery terminal, preferably fixed right to the terminal. The additional voltage drop is worth the peace of mind. Car radio shops have big chunky ones at modest prices. David G3UNA _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by David Cutter
Camping World and other RV outlets have -nice-
high-current DC items ... including a disconnect switch that attaches to battery posts. I think NAPA stocks the disconnect switches, too. 73! Ken Kopp - K0PP [hidden email] _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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