240V vs 120V vs Dedicated Line

Discussion in 'Amateur Radio Amplifiers' started by N4UP, Jun 5, 2012.

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  1. N4UP

    N4UP Premium Subscriber QRZ Page

    My apologies if this has already been asked and answered ( I looked but didn't find ).

    I have a new 1000 W solid state amplifier ( 10A 240V or 20A 120V ). Is there any REAL advantage to having a 240V dedicated line over a 120V dedicated line? Seems to me that the real issue is having a "dedicated" line. My amplifier manual says 240V is preferred for "stability" ... but wouldn't ANY dedicated line do that?

    From earlier experience ( 1960s ) I know that using such an amplifier on a non-dedicated ( 15A ) line will cause problems ( light-dimming, etc. ) but I wouldn't expect any of that with a dedicated ( 20A ) line.

    My ( non-ham ) electrician says I only have room in the breaker for adding one 120V dedicated line ( and no room for a 240V breaker ). The run would be 100 feet or less. Romex 12-2 wire with ground.

    Any advice or insights would be appreciated.
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    You will have less Voltage drop when operating at 240V and can use a smaller wire gauge, because the current is half.
  3. W1QJ

    W1QJ Ham Member QRZ Page

    Unless your breaker panel is loaded with split breakers already you can ALWAYS squeek in one space. I would go for a 240v line every time. It is the same run of wire either way. Got to be a way to to get another 240 line in there. Tell him to use a "quad 240" breaker with another 20A 240 breaker for a pump or something.
  4. N4UP

    N4UP Premium Subscriber QRZ Page

    Don and W1QJ, thank you, that is helpful.

    Don, I assume then that less voltage drop means more stable. Now I wonder what would be the effect on the amplifier or RF output for a "larger" voltage drop? Would it influence the signal "quality" or frequency stability? I'm just trying to understand the consequences of using a dedicated 120V line. The answers might influence how much power I actually run.

    W1QJ, thanks. Time for me to have another talk with the electrician ...
  5. K5VWZ

    K5VWZ Ham Member QRZ Page

    My 2 cents worth. Most big box house have circuit breaker boxes that can hold 2 or 3 circuit breakers. You could run from your main panel the proper sized wire with ground for 240 volt. for example, you could put 2 120volt breakers and 1 240 breaker in the new box and have all the outlets you need and not crowd the existing panel. I persoanlly would run 10/3 so as not to have any concern about voltage drop...
  6. N4UP

    N4UP Premium Subscriber QRZ Page

    Tom, thank you. I have now had another conversation with the electrician, and if I understand him correctly, I have a large older home with 100A service that is already "maxed out" ... and in order to get a new 240V line I should to upgrade to a 200A "service" ...
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    You could get by operating the amp only on a 120V feed.

    Frequency stability should not be a issue with a amp, unless you are also dropping voltage to your transmitter.

    You should try to rearrange the breakers that you have and you will be better off in the long run.

    It never hurts to do some overkill and not have to worry about voltage drop.

    240V is the best way to go, If possible.

    As long as you do not have electric heating, Then you may be able to use your 100A panel, But 100A service is marginal now a days.
  8. N4UP

    N4UP Premium Subscriber QRZ Page

    Thanks, Don. What baffles me is how a 100A service ( in the garage ) can even work with what I have, given that I have two heat pumps, an electric stove, electric water heater, and dryer, all on 240V lines. There is a box or breaker ( sub-box ? ) outside, so maybe that is where the heat pumps tie in and maybe that is in addition to the 100A service. So then the question is can they add another box and run the feed from there, under the house, then up into the third floor attic, and down to the 2nd floor radio room ( right now they are running the 120V line from the garage to the attic and then down to the radio room ).

    The utility feed ( or whatever it is called ) is all underground and presumably as old as the house, so there may be limits to what they can do without replacing that as well. But either way, it looks like I am already pushing the limits even without a new 240V line. I suppose these are the perils of buying an older home.

    So. I may have to live with a 120V 20A dedicated line for now, then see about upgrading the overall service to 200A, and then add a 240V line.

    In any event, thanks Don, Tom, and W1QJ for your advice and insights.
  9. KA9JLM

    KA9JLM Ham Member QRZ Page

    It sounds like they split the Main load to 2 different panels.

    Be careful when working on something like that because the main in the main breaker panel may not kill the power in the other, and the Meter may need to be pulled if you work on the Heat pump panel.

    You could maybe upgrade the Heat pump panel and use that one. Put one in with a main cutoff, if it does not have one.

    Heat pump systems normally have electrical heating strips and are rated for a bunch of current.

    Be careful playing with electricity.
  10. KD4MOJ

    KD4MOJ Premium Subscriber QRZ Page

    Some amps that cover HF/50Mhz are half output rated using 120v vs 240... may not be your case but thought I would mention it.

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