Bill, Yes, good lesson in ohm's law, that too often is overlooked.
So the current draw dropped for 20A to 11.7A. That means you were heating your lamp cord with 8.3A at 12.7v (= 105w). Not necessarily bad on a cold winter's night (humour)! But actually a waste of electrical power and perhaps a safety issue. I recently wired a 150w amp to a 28v PS (assume 250w dc load), the wiring has to carry 9A. I ran some #12awg zip cord (red/black). Seeing about 0.5v drop in the cable, which is about 4-foot long, under load. This is temp as the PS and amp will be installed in a 19-inch wide standard cabinet where the dc cabling will be about 12-inch. MY 300w HF amp will also run from this PS and needs about 4-feet dc wiring. I guess a swap is indicated. the 300w amp draws 20A which might even suggest 10awg wiring? The real ohms law test is the 50v 50A draw (2500w) that will be made by the 1100w 6m sspa. I got some #8 for that (doubled up). 73, Ed - KL7UW Thanks to the many who pointed out that the K3 draws a high current even at low power once you get above the 12 watt level, due to the bias for the power amp. I never considered this, and so when I made up a power cable to operate indoors with my MFJ 4225 switching power supply, I used a single light weight lamp cord at six feet long and a cigar lighter plug for the power cord. My reasoning being I would only operate low power, not more than 30-35 watts indoors with my antenna right over my head. So, either the lamp cord was too light, or the cigar lighter plug had too much drop for the current being drawn, and so the current meter in the K3 was indicating 20 amps being drawn at only 30 watts output. Once I fixed the power cord by using two #18 ga. lamp cords in parallel to spade lugs rather than the cigar lighter plug, the K3 now draws 11.73 amps @ 12.7 volts, with 35 watts output, from the MFJ 4225 power supply, which seems more normal than the previous 20 amps at the same power out setting. I hope my experience saves someone else some grief. 73, Bill, k6mgo 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-? DUBUS Magazine USA Rep dubus...@gmail.com "Kits made by KL7UW" http://www.kl7uw.com/kits.htm ====================================== ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
