Towing 12S electrics

96griffen
96griffen Forum Participant Posts: 19
edited July 2016 in Caravans #1

I have a 2007 Challenger with a AC50 control panel over the door and a power supply unit NE2006-CWS in the wardrobe. I have fitted an additional 12S socket to the car and checked and double checked the outputs from the socket as per the kit instructions
and caravan club sheet - permanent 12v on 4 with 3 as the earth and switched 12v on 6 using 7 as earth. I now cannot workout what to do with the switches on the AC50 or power supply unit to keep the fridge on. With the car connected and engine running I tried
the 3 way Car - OFF - VAN switch on power supply unit. In the manual it says use Van position to operate fridge when towing but the Thetford fridge works for about a minute then the blue fault LED flashes. In Car position nothing seems to work and yet the
manual says use this to charge the battery. I thought the purpose of the 12S socket into a post 1999 caravan was to provide a switched supply for the fridge and a supply to charge the battery whilst towing. 

Comments

  • EmilysDad
    EmilysDad Forum Participant Posts: 8,973
    1000 Comments
    edited July 2016 #2

    The car/off/caravan switch made no difference in my Lunar to the fridge 12v supply when towing. The spilt charge relay in the car should supply the fridge direct ... obviously as you say whe the car engine is running

  • Snowy1
    Snowy1 Forum Participant Posts: 263
    edited July 2016 #3

    This seems to be a bit strange to say the least, firstly, I agree with MM in the above post; It does not matter which position the "Car/Off/Van" switch is set to because all the caravans' internal electrical supplies are cut off when the towcars' engine
    is started (except the fridge on 12v operation) by (both) the changeover and habitation relays. In other words, the caravans' internal electrics cannot work directly from the towcars' battery, caravans' leisure battery or by the 240v mains as it's not connected.
    To test this theory, try switching on one of the caravans' interior lights when your towcars engine is running.

    Secondly, as MM correctly mentioned; The split charge relay (often referred to as a voltage sensing relay, VSR) supplies the caravans' fridge directly from the towcars' 12s pin 6 (earth return 7), only when the towcars engine is actually running.

    With regard to your handbook saying; Use the "Car/Off/Van" switch to charge the leisure battery, this is when connected to EHU, in other words, you select "Van" position to charge the leisure battery directly from the mains when connected. Again, when you
    say nothing works in the "Car" position, it won't, as previously said, when the towcar is running all internal electrics are cut off.

    Lastly; You say the fridge works on 12v for about a minute then appears to cut off i.e. the blue fault LED flashes. I'm going to have to make an assumption on this one as I'm unable to get "hands on"; Is the power supply that feeds 12s pin 6 via the split
    charge relay (or other means) able to supply a constant 10 amp current i.e. (without going into great detail) if for instance you are using a split charge relay (also known as VSR) and it is supplied from a sorce that cannot supply a constant 10 amp current,
    this can cause the VSR to oscillate thus causing voltage drop, which could be why the blue fault LED starts flashing after about a minute.

    Hope this all helps

    Colin

  • Snowy1
    Snowy1 Forum Participant Posts: 263
    edited August 2016 #4

    PS; forgot to confirm within the above post, when the towcars engine is running, the caravans' leisure battery is switched by the changeover relay (not habitation relay as many think) to recharge from the towcar via 12s pin 4 (earth return 3). Interestingly, both said relays are energised by the fridge circuit (12s pin 6) when the towcars engine is started. Some of the very latest caravans archive this by using a double pole double throw relay officially known as a DPDT Relay, it has 8 contacts including the coils.

  • 96griffen
    96griffen Forum Participant Posts: 19
    edited August 2016 #5

    Thanks Colin. I'll try options tomorrow on the journey. The fault light on the fridge went out when I pressed another button on the fridge so I suppose you have to confirm the source you want the fridge to work from.

  • 96griffen
    96griffen Forum Participant Posts: 19
    edited August 2016 #6

    Been away in the caravan and found that I had to put the CAR/OFF/VAN switch to VAN (which to me makes no logical sense) and select 'battery' symbol on the fridge and all went well.(That is what it says to do in the caravan manual but I originally still got
    a fault on the fridge and did not realise the faults had code numbers ) And yes with engine running no lights work in the caravan as you suggested - which is correct.

  • Snowy1
    Snowy1 Forum Participant Posts: 263
    edited August 2016 #7

    I know your not converting to 13 pin, but it maybe of interest if you read section one and two, as it explains fully how the caravans' auxiliaries work from a connected tow car.

    https://caravanchronicles.files.wordpress.com/2015/06/upgrading-to-13-pin.pdf

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