I certainly agree with running 240V when it is available. However 120V will work just fine with the KPA500. I am testing a KPA500 on a 120V, 20 amp circuit that is fully 50 feet from the breaker panel.
Yes, there is significant droop in the mains voltage when I key down at 500 watts output, but the KPA500 has internal transformer taps that can be chosen to provide the correct voltage under such conditions. There is a limit to the droop allowed as internal voltages in the KPA500 rise when not transmitting (or running at reduced power). The tap is chosen to stay within the upper limit "key up". I submit that my situation is just about worst case - considering that it's only a 20 A (instead of a 30A) circuit and the 50-foot distance from the breaker panel involved, yet I easily found a tap combination that provided the voltage for full output without exceeding the upper limit key up. I have a home built about 30 years ago, and one thing I have noticed that applies here. Commonly used power outlets wear out. Long ago I noticed that I could hear that our vacuum cleaner (which draws 12 amps at 120V) ran more slowly on some outlets than others. Investigation showed that the springs in the outlet itself were weak after many years of having plugs pushed in and pulled out. As they weakened, the contact with the plug got loose, causing heating and further weakening of the springs (there's a reason outlets are mounted in fire-resistant enclosures!). Replacing the outlets cured the problem. It's a simple job for most. Just be certain you have the circuit off at the breaker panel, and everyone in the house knows what you are doing so no one flips it on while you are working (professionals lock the main breaker panel shut and put a big sign on it while working on a circuit elsewhere). Ron AC7AC -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Edward R. Cole Sent: Wednesday, February 16, 2011 10:47 AM To: [email protected] Subject: [Elecraft] 120V vs 240V Important reasons for running HP amps with 240vac. I used to run a smaller PS that provided 2500v at 400mA = 1000w dc input with 600w RF out on my 2m-8877. That PS ran on 120vac and drew 8.3 amps on ordinary house wiring and I saw some flicker in the lights on CW. I don't recall what the voltage sag was. Now I run 3700v at 720 mA = 2664w dc (1400w RF) which represents a 10.9 amp load on 244vac (my line voltage). I see about 2-3 volts line -voltage sag so that is 33w dissipation in the 8-4 wiring. If I had tried running with 120vac the load would be 21.8 amps which would exceed the rating of the wiring and likely trip breakers. The power supply is capable or 1.5amps dc load so represents a max load of 5kW and that hits over 20A which is my current breaker rating. Of course this would produce 2500w RF which exceeds legal level by a lot. Important stuff to consider when running significant RF power. The KPA-500 will likely run on 120vac with no problem but better if run on 240v. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
