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what size wire to use for 30amp 12v circuit ?
Lynn Coffelt wrote: "Eric Fairbank" wrote: Where did you hear that myth??? Iv'e been a marine electronics tech for 30 years and have never heard that one. I know what you stated is total bs but just for drill I did a little test before leaving work today. Hooked up a variable power supply to my Icom 735 with a Bird 4381 power analyst in line (which reads PEP directly). I also verified the wattmeter readings using an o-scope. The power didn't start to drop til the voltage dropped below 10.5v and I was able to receive just fine all the way down to 9.5v. Below that the rig started to die. Eric "Bruce in Alaska" wrote in message ... It is commonly understood that for each volt dropped from 13.6 VDC at the radios PowerAmp DC Terminals, you lose 50% of your PEP Power. So if your at 13.6 Vdc you get your 150 PEP, and at 12.6 VDC you get 75 PEP, and at 11.6 Vdc you get 35 PEP and below 11.0 VDC the internal Voltage Regulators drop out of regulation and the radio goes OFF. It is not a Myth, is is a Fact, and as others have stated, your experiment doesn't prove, or disprove the fact. Also, as Larry stated the 21st Century Icom Rigs have a lot more headroom in the SolidState Amps than just about any other Marine MF/HF Radio, just to deal with this cause. Just try your experiment with ANY SGC designed and built radio. Bruce in alaska I am Old School, and an Old Fart, and I do remember back in the Old Days, before Autotuners, allowed anyone to think they were World Class Radiomen... -- Oh, my gosh, it's just killing me to sit here without jumping in! Then when I heard SGC mentioned, I knew that someone besides me had experienced "Bruce's Law". I am compelled to defend his position and scientific observations without reservation. How much midnight oil I've spent working on the DC supply system on "commercial" vessels, trying to reduce the voltage drop. Until the "code" made batterys in the pilot house almost mandatory, can't you imagine running an SGC711 from engine room batterys? Here's a typical example (it is a genuine "commercial", by the way) of a vessel still using this one time popular rig: http://www.alaskaboat.com/sn033.htm Those SGC711's were hard to coax to even 75 watts PEP with any wire less than #4 if you were more than two feet away from the battery! (OK, stretching a little here) And the built-in wire antenna tuner was a charmer, hey? But as the URL and dozens more can show, that not everyone has yet to install an Icom M802. Some earlier SEA's and Icom's with first generation digital VCO tuning were cool, too. A sneeze or laugh in the mic was as apt to change channels as anything if the antenna was fed directly from the radio, and some joker installed #10 wire for DC power! Early automatic antenna tuners were (are) cool, too. A little pitching and rolling in the North Pacific and they would lock up and refuse to even try to tune anymore. Then the transmitter's fabulous SWR power foldback circuit hit the fan and 5 to 10 watts could be used to heat up the tuner's coils and capacitors. (condensers, actually) Lots of this early stuff is still out there. By the thousands. Modern marine SSB radios certainly have improved their ability to survive poor installations, but is that any reason to go as cheap as possible with DC wiring and antenna installations? (RF ground on "Tupperware" boats is probably just as important, but I digress) Old Chief Lynn (besides, tubes help heat the pilothouse and ease aching joints) Let's just watch out here. I was in a junk shop a while ago and I told the proprietor what was actually hoping to find. We got talking about ships and boats. He stopped and asked if I could tell him about something in back. When retrieved, it turned out to be a marine HF - real live dinosaur (dynosoar?). I think is was Hammerlund or EF Johnson - most of the crystals had been pulled, but it still had a the 2 1625s in the final (and a little burned spot on the tank). I looked at him and said "You know - They haven't made 'em like this for a long time". (Aren't we glad!) Matt Colie - Lifelong Waterman, Licensed Mariner and Perpetual Sailor |
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