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  • 100 foot run

    New member here
    Looking to install solar for battery backup for Ham Radio. Radio s designed to run on 12 volts. Currently, 12awg is suggested from car battery to in vehicle radio

    Best location for my soar panels is about 100 ft from mr radio.

    1. Do I put my battery closer to my panel
    2 Do I ave my battery as close to my radio as possible.

    Thoughts, and thanks

  • #2
    Howdy and welcome. KF5LJW here.

    Sure 12 AWG will work if you want to loose a lot of your power. Exact amount depends on the panel wattage you are using. For example if you use a standard 12 volt battery panel with 100 feet of 12 AWG you will loose over 12% of your power. 200 feet of 12 AWG has .4 Ohms resistance and a 100 watt panel has roughly 5.3 amps of current. Do the math of I squared R = 28 x .4 = 12 watts gone into thin air. Then add the 30% loss in a cheap PWM charge controller and you are down to 55 watts at the battery.

    You want th ebattery as close to the panels and radio as possible. The only way to over come power loss is with larger wire or using much higher voltages or both. Typically you design for 2% or less loss. With a 100 watt battery panel at 100 feet requires a # 4 AWG stranded copper. That is a lot of money.

    Think of using grid tied panels and a MPPT controller.

    73's to you.
    MSEE, PE

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    • #3
      Originally posted by Solardoug View Post
      New member here
      Looking to install solar for battery backup for Ham Radio. Radio s designed to run on 12 volts. Currently, 12awg is suggested from car battery to in vehicle radio

      Best location for my soar panels is about 100 ft from mr radio.

      1. Do I put my battery closer to my panel
      2 Do I ave my battery as close to my radio as possible.

      Thoughts, and thanks
      Actually, there are four components (and therefore three interconnections) to worry about:

      1. Panel(s)
      2. Charge Controller (CC)
      3. Battery
      4. Radio

      A. For best radio performance, you would want the battery close to the radio. And since this connection must run at ~12 volts and therefore be high current, you want to keep it short. The radio, when transmitting, may pull more power than the panels are producing at that moment, so it can be the highest current connection.

      B. The connection from the CC the battery will also be at 12 volts, but if you have a CC with separate voltage sensing wires, it may not be as critical to keep this one short. You will lose charging power, but it will not prevent the radio from working well.

      C. The connection from the panels to the CC is where you have the most freedom. If you use a "12 volt" panel and a PWM CC, the power lost in this wire will not actually hurt your battery charging until it reaches the point where the voltage at the CC is too low for the CC to deliver full output to the battery.
      If you follow Dereck's recommendation and go with high voltage (low current) panels and an MPPT CC (think of it as a buck type DC to DC convertor) this connection is the best one to use to cover the long distance, since it will be low current and high voltage, giving you a double boost in lowering percentage losses for any given wire resistance. If you triple the voltage you can tolerate 9 times the wire resistance and keep the same percentage power loss.
      SunnyBoy 3000 US, 18 BP Solar 175B panels.

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