One for you electrical geniuses...

Discussion in 'Tech/Mech General' started by Allanm, Feb 6, 2014.

  1. Allanm

    Allanm Funster

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    I need a changeover switch.
    I have just fitted frost heaters to my fresh and waste tanks. At the moment, they are wired up to the Sargent EC500 control panel, which means power is interrupted when I start the engine and drive. I want to be able to switch over to a different power source for travelling, if I need to.
    So, I need a changeover switch. At the moment I have a separate pos and neg feed to both heaters from the panel, I would like to be able to change this to a pos and neg feed to both heaters directly off the leisure battery.

    What sort of switch will do this?

    Allan
     
  2. pappajohn

    pappajohn Funster Life Member

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    neg wire is not an issue....unless the control panel isolates both pos and neg.

    A suitable relay with both normally open and normally closed poles will do.

    Engine Battery wire to n/o pole and panel to n/c pole....a wire from common to both heater plates.
    Just needs a wire from the ign switch to the trigger terminal on the relay.

    Start the engine and the relay will automatically disconnect from control panel/leisure battery and connect to the engine battery.
     
    Last edited: Feb 6, 2014
  3. Allanm

    Allanm Funster

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    Both + and - go back to the control panel. I'm not bothered about automatic changeover with an ign wire and relay, sometimes I won't want them to be on when we are travelling A three position switch, one end connects to control panel, centre all off, other end connects to battery.
    Something like this

    [​IMG]

    Assuming the heater is connected to the centre terminals and alternate power at either end.
    Does that look like it would work?

    Obviously I would need two switches.

    Allan
     
  4. Serendipitous

    Serendipitous Funster

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    Hi if you consider the photo below and change things around a bit. That is consider the lamps as the 2 power sources, (Sargent & vehicle) and then the battery as the frost heaters. Hopefully you see what I mean. If not let me know. Also don't forget to fit fuses.

    (So that's how you get pictures in posts)
     

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  5. pappajohn

    pappajohn Funster Life Member

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    identical setup to the relay...only manually operated and no need for twin switches unless you want to select just one heater rather than both together.

    Problem is it could be left on the engine battery by accident
     
  6. Allanm

    Allanm Funster

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    Thats a point, I'm bound to leave it turned on and come back with no power left. Maybe your relay idea would be best.
    Allan
     
  7. Geordies

    Geordies Funster

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    If you go with either the relay or the switch idea, make sure that they can carry the amps that your tank heaters require. Relay blades have been known to weld together if not rated correctly for the load.
     
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  8. Allanm

    Allanm Funster

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    They are only 2.5 amps each and I was looking at 15 amp switches
    Allan
     
  9. pappajohn

    pappajohn Funster Life Member

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  10. TheBig1

    TheBig1 Funster Life Member

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    go with the standard relay option but add a switch to the ign positive feed for the relay coil so you can choose not to heat already warm tanks etc

    cost about £5 plus cables
     
  11. jonandshell

    jonandshell Funster

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    If the combined current of the tank heaters is only 5amps, why not simply connect them to a relay, switched by the PSU's 12 volt fridge output?
     
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