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Thread: Pragmatic aux battery charging advice please

  1. #1
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    Question Pragmatic aux battery charging advice please

    Hi all

    A previous owner of my D4 installed a Redarc isolator with 100A breaker immediately in front of the cranking battery, with wire to an Andersen plug mounted adjacent to the tow hitch receiver, which I have no use for. I'm about to set off on my first trip longer than 3 days, meaning my 130Ah AGM camp battery is going to require proper charging along the way. I'm leaving in just over a week and need to get something sorted pretty urgently.

    My aux battery is in a Projecta Power Hub battery box which has both an Andersen as well as screw terminals for high current use.
    I've created a very secure mounting for the battery box on top of a false floor immediately behind the 2nd row seats, right in the centre.
    The wire to the trailer hitch Andersen looks chunky to me but I can't tell you what gauge it is.
    The wire runs down the passenger side chassis rail to the back of the compressor, then turns across over the top of the chassis toward the driver side before heading rearwards again past the diff to pop out below the bumper to the right of the tow hitch receiver.

    Questions:
    1. If we're driving for at least several hours most days, can I get away with just charging my aux battery from the alternator via the isolator, or do I really need a DCDC?
    2. What's the best option for getting a wire into the loadspace? Extend from the bumper across and through the RHS tail light grommet, or tap in near the air compressor and run (where?) from there?
    3. Is there anybody in the Brisbane region I could pay to get this done properly at short notice? I'm getting rear control arms replaced at British Off Road on Monday so depending on the answers to 1 and 2 they might be in a good position to run the wire for me.
    4. Any advice on fuse size and location if I'm using an Andersen into the box?

    I've actually managed to keep the battery well charged on trips to Moreton etc by connecting it to the rear cig lighter socket, but what I'm reading now about current draw for battery charging suggests that might not be a wise idea, especially for a two week outback tour! Trying to keep it simple though.

    Thanks in advance for your thoughts.

  2. #2
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    You don't need a DCDC charger at all, the alternator will happily charge the battery.
    Where is your 130ah battery located ?, too big for driver side so is it in front of the main or in the cargo area.
    MY08 TDV6 SE D3- permagrin ooh yeah
    2004 Jayco Freedom tin tent
    1998 Triumph Daytona T595
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  3. #3
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    Quote Originally Posted by loanrangie View Post
    You don't need a DCDC charger at all, the alternator will happily charge the battery.
    That's what I was hoping to hear. The rest of my questions follow on from that though.

    Where is your 130ah battery located ?, too big for driver side so is it in front of the main or in the cargo area.
    "I've created a very secure mounting for the battery box on top of a false floor immediately behind the 2nd row seats, right in the centre."

  4. #4
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    Ok so you want power from up front to the rear, there are grommets either side of the engine bay, 1 beside the brake booster and 1 behind the battery. You can run cable under the plastic door sill panels in the channel and up into the plastic side trims.
    MY08 TDV6 SE D3- permagrin ooh yeah
    2004 Jayco Freedom tin tent
    1998 Triumph Daytona T595
    1974 VW Kombi bus
    1958 Holden FC special sedan

  5. #5
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    It's a shame the cable to the rear has been run outside the vehicle because it would be perfect to splice in to for your internal aux battery.
    This is exactly what I've done recently for a second aux battery, which was fairly straightforward because the cable was already running through the door sill channel.

    I would not necessarily write-off the usefulness of the existing cable either, what if you want aux power in a trailer in the future?
    It would be perfect for that. It's also a handy way to connect solar for cranking battery charging.

    I don't like having cables running underneath but given your short timeframe etc I would splice into the cable outside near the tow point.
    Then bring a new cable in through a rear taillight grommet, along under trim and through to your aux battery.
    If the external cable is well run, protected, etc you could leave it this way long term.
    But remember that cable will need disconnecting if body-off maintenance is ever required.
    Charging this way (via isolator) will be fine, no need to add DCDC.

    Cheers,
    Scott
    D4 TDV6 MY14 with Llams, Tuffant Wheels, Traxide DBS, APT sliders & protection plates, Prospeed Winch Mount w/ Carbon 12K, Mitch Hitch & Drifta Drawers
    Link to my D4 Build Thread
    D3 2005 V8 Petrol
    Ex '77 RRC 2 door. Long gone but not forgotten.

  6. #6
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    I'm happy to be getting upward-pointing thumbs for the cheap and easy option. I'll tee off the cable at the rear and mount another Andersen inside on the rear quarter panel in the space that exists because I don't have the rear AC unit.

    Thanks again.

  7. #7
    DiscoMick Guest
    What the others said.
    No need for a DC-DC.
    Just connect somewhere.
    The existing wire to the rear is perfect for powering a caravan.
    Could you run another one from the Redarc through the firewall to inside the vehicle and to the rear with an Anderson? Then you would be set.

  8. #8
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    Quote Originally Posted by DiscoMick View Post
    The existing wire to the rear is perfect for powering a caravan.
    Yeah I expect that's what it was used for by the previous owner though there's no sign that I can see of a brake controller having been fitted. Caravan is not on my agenda but I appreciate that the possibility is there.

    Could you run another one from the Redarc through the firewall to inside the vehicle and to the rear with an Anderson? Then you would be set.
    Could be done, but I'm in a hurry and trying to spend as little as possible. A quick extension across the bumper and up into the rear quarter will hopefully sort me out, as long as there's not too much voltage drop.

  9. #9
    DiscoMick Guest
    If the wire is a decent thickness, voltage drop should not be an issue.
    You don't say what size is the fuse, but the ones I've seen running to rear plugs for charging caravans are typically 50-60Amp fuses. Mine is 50Amps.
    I put a meter on the Anderson on the rear bumper of our Defender and it makes a steady 8 Amps, which is plenty to charge the batteries in our camper.
    DC-DCs typically are limited to 20-30Amps, a few to 40, so that's way less than you will get from your alternator, even limited by a fuse.
    So, although I'm no expert, it sounds good to me.

  10. #10
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    Quote Originally Posted by DiscoMick View Post
    You don't say what size is the fuse, but the ones I've seen running to rear plugs for charging caravans are typically 50-60Amp fuses. Mine is 50Amps.
    There's no fuse that I can see, just the 100A re-settable breaker up at the isolator end.

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