12v Electrical Question, any sparkies on here?

Discussion in 'Motorhome Chat' started by paulweller84, Mar 18, 2014.

  1. paulweller84

    paulweller84 Read Only Funster

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    Hi, I would like to install a main switch by the main door on my van so I can switch everything on or off when entering or leaving, this would mean running a switch cable from the main control panel, but my question is what size of cable should I use? I could use something decent sized to remove any doubt about capacity but it needs to be as small as possible to make it easier to route through the van.
     
  2. tonyidle

    tonyidle Funster

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    The simple way is to use a relay. That way you have no cable losses & can use very thin wire to your switch. I can send you a drawing if you wish & it really is very easy to do.
     
  3. paulweller84

    paulweller84 Read Only Funster

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    Thanks, I'm assuming I would need to fit the relay just before the main supply enters the control panel, then run a switch wire over to the new switch. Would I be right in thinking the switch would also need a permanent live feed? If so I think running from the cab interior light would be easiest
     
  4. Wildman

    Wildman Read Only Funster

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    Make sure you don't switch off any charging arrangements , solar etc.:Eek!:
     
    Last edited: Mar 18, 2014
  5. TheBig1

    TheBig1 Funster Life Member

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    Running a trigger wire from the light circuit wont work as the power would be off if the relay is not energised. you will need to run 2 wires to the switch, a live feed and a trigger return to energise the relay

    very simple to do, but there will be a constant drain when the electrics are on because the relay will take power. plus its another potential point of failure as with any moving part
     
  6. tonyidle

    tonyidle Funster

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    You would be better finding the main output & fitting it there. I don't know what sort of control panel you have but most allow you to choose either leisure or start battery to feed the 12v system via a selection switch. The wire from that switch that heads off to the fuses/switches on the panel would be where I'd choose to place a switch or relay. Depending on your panel that may not be easy so your method would work with the proviso noted in the last post re charging etc.

    The best place to take your relay operating supply from would be the wire you break with the relay (before the break of course!).
     
  7. tonyidle

    tonyidle Funster

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    See attachment.
     

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  8. Tmesis

    Tmesis Read Only Funster

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    Have you considered things that need to stay on? Fridge electrics, radio, alde boiler, anything that needs a battery for its memory. Presumably if you have a control panel, it will have a ethos of its own to isolate consumers?

    What control panel and 12v distribution system do you have?
     
  9. paulweller84

    paulweller84 Read Only Funster

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    My idea is to power the switch directly from the leisure battery so when it's open it doesn't draw power. Then when it's switched on it powers the relay and only uses battery power when the leisure battery is powering everything else. If that makes sense? Would that work?

    Also, does anyone know how to bypass the system that cuts off the power when the ignition is turned on? I'd like the option of running the engine to charge the batteries while we are using the van. At the moment all the power goes off which is quite annoying
     
  10. JeanLuc

    JeanLuc Funster

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    I have to admit to being slightly at a loss to understand why you want to do this. I assume you are talking about a master switch for the 12V habitation systems? Our van has a master 12V switch in the control panel above the habitation door, but I generally switch it on when we set off somewhere and switch it off when we get back. So far, the longest elapsed time between those two events is six weeks. I cannot think why I would want to switch it off.

    I realise my motorhome might be wired differently to yours, but the 12V master switch described above does not affect the step, entry light or Truma temperature safety valve; these stay on regardless.
    To isolate all 12V habitation circuits in my van (including the last three above) one has to switch off the main switch on the main charging system which is under the driver's seat. I only switch that off if changing batteries or carrying out any cabling work.
     
  11. tonyidle

    tonyidle Funster

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    Relay current drain would be of the order of 80mA & as you suggest only when domestic power is switched on so not important. JeanLuc's system is exactly the same as mine (mine is Hymer B584). It would be useful to know a little more about your control panel (make & model & any other info you have) to answer your second question - and would enable a better answer to your first.
     
  12. aba

    aba

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    all the power going off doesnt stop the charging of the leisure batteries.
     
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