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, [EMAIL PROTECTED] 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: [email protected] 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: [email protected] 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
