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charging a 12v battery in a trailer

Discussion in 'Automotive Electronics' started by upinthemud, Oct 10, 2015.

  1. upinthemud

    upinthemud New Member

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    I am a cub scout adult leader and we are wanting to hook up a battery in our 14 foot enclosed trailer to run some interior lights for when we are camping so we can see in the trailer. I am wanting to have it charged from the vehicles parking lights at a lower amp, but not have it back feeding back into the vehicle. Has anyone done this before ? What type of diode do I need to do this or what would I need to do this...
     
  2. crutschow

    crutschow Well-Known Member Most Helpful Member

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    A diode will provide isolation but its forward voltage drop prevents the battery from being fully charged from the vehicles alternator.
    You could use a isolator such as this which performs the isolation function without the diode drop but that requires a somewhat elaborate installation in the vehicle's engine compartment.

    However, if you unplug the trailer battery from the car (or use a switch to disconnect it) when you are parked at a campsite, I see no particular need for an isolator.
    It will charge when it's plugged in when the engine is running and unplugging it will keep the vehicle battery from being discharged by the trailer electrical load.
     
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  3. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Trailer batteries never charge hardly at all from the towing vehicle. The towing vehicle's voltage regulator sees the voltage of the engine compartment battery, and adjusts its voltage based on keeping that battery at ~14.4V. The voltage drops in the wiring (and along the vehicle + trailer frame) create sufficient voltage drops such that the trailer battery is lucky to see 13.8V, at which it takes days of towing to recharge...

    The only way to make this work is to put a step-up converter in the trailer. (12 to 13VDC input to make ~14.7V output at ~20A).
     
  4. dave

    Dave New Member

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  5. upinthemud

    upinthemud New Member

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    I have one of these isolators http://www.rvplus.com/sure-power-ba..._source=bing&utm_medium=cpc&utm_campaign=bing but was not really sure how to run it with just the 4 wire hook up from the lights without a dedicated line just for it. Unhooking it from the charging vehicle will not work because they run through the parking light and the battery will back feed and all the parking lights on the trailer will be on and run the battery down quick. don't know might just buy a trickle charger and unhook it all together from the wire harness and plug it in when needed
     
  6. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Since you do not have a dedicated power supply line I would recomend just using a set of larger 5 - 6 amp diodes that tie in all of your electrical lines to the battery so that it can be getting some charge from any light circuit or combination of circuits that is on.

    I've seen a number of trailers that have a fair sized deep cycle battery on them to run a hydraulic pump or winch set up that way and it does work fairly well. The charging rates are not all that great, maybe 3 - 5 amps combined at most, but it does keep the battery topped off well enough to not cause any problems.

    RadioShack used to carry a package of four 6 amp 50 volt diodes for under $5 at one time. Not sure if they still do or not but that's what I would go with.
     
  7. shokjok

    shokjok Member

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    Have you considered using the quick-disconnect hookups found on electric forklifts? These can handle the full current to the trailer battery, adding extra wires to the towing vehicle. A voltmeter should be added to monitor the charge rate. When you park at the site, simply unplug the connectors.
     
  8. Colin

    Colin Member

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    You can use the battery charger circuit on talkingelectronics.com website. It will charge the battery at about 1 amp from another battery. A very clever circuit.
     

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