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. ------------------------------ Message: 16 Date: Wed, 16 Feb 2011 10:35:27 -0600 From: Scott Ellington <[email protected]> Subject: Re: [Elecraft] 120V vs 240V To: Elecraft Reflector <[email protected]> Message-ID: <[email protected]> Content-Type: text/plain; CHARSET=US-ASCII Actually, the percentage voltage drop at 120 V is FOUR times that at 240 V. (For the same power, wire gauge and length.) Since the KPA500, like most tube-type amplifiers, uses an unregulated power supply, the extra drop can significantly reduce output. For example, suppose the amplifier can put out 500 W with a perfectly regulated input of 120 or 240 V. Say the line voltage, at 240 V, drops 6 volts at full output. That's a 2.5 percent drop, which reduces RF output by about 5 percent, to about 475 W. At 120 V, the drop is 12 volts, 10 percent, which reduces the output by about 20 percent, to about 400 W. You just lost 75 more Watts, each of which cost you $4. Keep in mind that 500 W output requires about 1 kW input, that the power factor of the power supply is considerably less than 1, and that the high peak currents make the effects of line voltage drop even worse. When calculating effective line drop for the KPA500, I would use something like 2 kVA, about 17 A at 120 V. The above example corresponds to a run of 220 feet of AWG 12 (440 feet total), admittedly a very long run. Bottom line: If you are adding wiring, use 240 V. Run the amplifier on 120 V only if you have no choice, or if the run from the distribution panel is under about 50 feet. Scott K9MA 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 144-1.4kw*, 432-100w, 1296-testing*, 3400-winter? DUBUS Magazine USA Rep [email protected] ====================================== *temp not in service ______________________________________________________________ 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
