120V vs 240V
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I recently wired my ham shack for 240vac for supplying my 4500w HVPS
that supplies HV for my 2m-8877 (full QRO). I went to Home Depot and bought 150-feet of 8-4 cable (actually three #8 awg wires and one #10 solid-conductor safety wire). This runs from my service box to a small load center (40amp breaker box which I have equipped with a 240-20A and two 120-20A breakers). This does not exceed the 40amp rating of the box or wiring (35-foot run of 8-4). I run all my shack power supplies from this source: HVPS on 240vac, 12v-50A PS and 28v-25A PS. The filament transformers and bias supplies. This is grounded thru a second ground rod outside the shack as well as thru the 4th safety wire via the service ground. This lessens the electrical loading on the 120v house circuits in the bedroom converted to shack. Those circuits power the computer stuff, lights, antenna rotators, and some test equipment at the work bench, plus bench 0-30vdc power supply. 73, Ed - KL7UW ------------------------------ Message: 44 Date: Tue, 15 Feb 2011 17:17:42 -0800 (PST) From: ab2tc <[hidden email]> Subject: Re: [Elecraft] 120V vs 240V To: [hidden email] Message-ID: <[hidden email]> Content-Type: text/plain; charset=us-ascii Hi all, I was not advocating using the safety ground of the 240V cable for a neutral return for a 120V outlet (clearly against code). I have not done a a combined 120/240V run myself but I thought it was possible to get a complete red/black/white/blank cable to do this in a single run. Rummaging around in my supply of electrical wire I found a red/black/white piece of cable but curiously it had no safety ground wire. Anyway, I suppose running two cables from two breakers is still not too much trouble. AB2TC - Knut 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 [hidden email] ====================================== *temp not in service ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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> This lessens the electrical loading on the 120v house circuits in the
> bedroom converted to shack. Those circuits power the computer stuff, > lights, antenna rotators, and some test equipment at the work bench, > plus bench 0-30vdc power supply. Many good suggestions here. If for no other reason, running dedicated branch circuits into the shack will often eliminate light dimming. My shack occupies a spare bedroom and the 120V receptacles were at the end of a shared branch with an adjacent room. Keying at 100W would cause the room lights to noticeably dim. Now add a 500W solid-state amp to that circuit and not only will the lights dim, but voltage regulation on the branch suffers. This is one of those projects where it will often pay off to run multiple branch circuits into the shack. If you need one, it takes little effort and cost to pull a couple more. I did all my attic work in the middle of the hot Florida summer. I tried to start early and finished by 11am when temps really start to climb. The job was split into two days but there's now two separate 120V branch circuits into the shack that only power equipment. A 30A, 240AC 4-wire circuit was pulled ten years ago. I now wish I had pulled a few more to have dedicated 240V receptacles for each amp. It's easy to quickly run out of panel space. I had already maxed-out a sub-panel and for better or worse, I used a tandem breaker for the two 20A shack feeds since I had a single remaining position available in the sub panel. Paul, W9AC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Edward R Cole
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 <[hidden email]> Subject: Re: [Elecraft] 120V vs 240V To: Elecraft Reflector <[hidden email]> Message-ID: <[hidden email]> 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 [hidden email] ====================================== *temp not in service ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Edward R Cole
Ed is giving you excellent advice. It is just about as easy to pull
a heavy feeder ta sub panel as it is to pull a couple of branch circuits. In my unfinished basement there were only three 15 amp 110 v circuits. Furnace, sump pump and lights. The main entry was in the garage. When I finished the basement there was no way to run wires from the garage to the basement. I pulled a run of #6/3 w/ground to a sub panel near the furnace. I moved all the old basement circuits to the new panel. This allowed me to install a new 220 v breaker in the main entry to feed the new sub panel. There are plenty of slots in the new sub panel to make all the 110 and 220 v circuits I need. I used #6 which is oversize to make the voltage variation from no load to full load as little as possible. The value of the breakers in the new panel can add up to more that the capacity of the cable you just ran. The breaker in the main panel protects the feeder. The breakers in the sub panel are sized to protect the final branch circuits. If your new wiring only supplies the shack you might wish to consider using a main breaker rather than a main lug box for the sub panel. Maybe it is not so important now as when we had so much high voltage running around, but the old safety recommendation was to have the wiring set up so that a single switch would kill all the power in the shack. Some notes: the bare grounding wire is connected to the box itself. The white grounded (neutral) wire is supposed to be connected to the grounded wire only at the main entry and not in the sub panel. This has been code for a long time. Also the rules for wring in bedrooms and basements has been changing over the last two or three editions of the electrical code. There are probably professionals on the list who can correct any errors I have made and are more qualified on the details than I am. David K0LUM At 3:25 AM -0900 2/16/11, Edward R. Cole wrote: >I recently wired my ham shack for 240vac for supplying my 4500w HVPS >that supplies HV for my 2m-8877 (full QRO). I went to Home Depot and >bought 150-feet of 8-4 cable (actually three #8 awg wires and one #10 >solid-conductor safety wire). This runs from my service box to a >small load center (40amp breaker box which I have equipped with a >240-20A and two 120-20A breakers). This does not exceed the 40amp >rating of the box or wiring (35-foot run of 8-4). <snip> > >73, Ed - KL7UW > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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