Charging power to the new van

Submitted: Sunday, Mar 31, 2013 at 22:43
ThreadID: 101399 Views:3681 Replies:3 FollowUps:9
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Hi guys! Been following this forum for a few months since my family decided to get back into some camping and touring. Love the robust conversation and you have already helped me so much in lots of decisions about equipment etc.
I wanted to ask some of the 12v gurus out there a quick question.
I already have a 105ah Thumper wired into the back of the Pathfinder. Did it myself and it works well! We have recently ordered a camper van which comes with another 105ah plus solar and is Pre wired with Anderson plug for charging from the Pathy when on the move. My question is, do I need to run a new set of wires from the car battery to an Anderson plug on the tow bar, or can I just splice into the existing wiring I have running to the Thumper without compromising charging rates etc. I rang Blue Apple and was told it would be Ok to splice in but they couldn't elaborate on how this will go charging both batteries. I would like to avoid running more wiring if possible as it is quite an ordeal pulling off all the trim whilst worrying about breaking clips etc. Any help suggestions gratefully received. Thanks. Graeme
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Reply By: Member - Andrew L (WA) - Monday, Apr 01, 2013 at 02:16

Monday, Apr 01, 2013 at 02:16
More details are needed to give a definite answer on splicing into the existing cabling:
* What is the the size of the cable you have running from the main battery to the Thumper.
* What is the max. charge rate for the Thumper?
* Does the campervan have any sort of charge controller DC-DC charger? If so what is the current

But my advise would be run a new 6B&S cable from the main battery to the towbar via the chassis. The advantage of this over splicing are:
* Avoiding the need to enter/exit the cabin.
* Providing the best possible electrical installation and charging for the campervan.
* Provides redundancy between two charging systems.

AnswerID: 507938

Follow Up By: ABR - SIDEWINDER - Monday, Apr 01, 2013 at 02:40

Monday, Apr 01, 2013 at 02:40
I agree, you would also need an isolator and a fuse / breaker on the cable.


Derek from ABR

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Follow Up By: Member - John and Val - Monday, Apr 01, 2013 at 08:46

Monday, Apr 01, 2013 at 08:46
I agree with Andrew and Derek, especially since running a separate cable with separate switching will open up some other options. (I use two pairs of heavy cables running from the engine bay to our trailer - one to run the 3 way fridge while on the move, the other to charge the trailer battery. These are individually switched so that the trailer battery isn't directly connected to the fridge. By keeping the two separate the heavy loading of the fridge doesn't affect battery charging).

By providing an independent connection to your trailer you would have the option of including a dc-dc charger there which might prove useful.


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Follow Up By: Pathycop - Monday, Apr 01, 2013 at 12:15

Monday, Apr 01, 2013 at 12:15
John, Andrew and Derek thanks for your replies also. I think this is the way is ill need to go at sometime to make everything a little more permanent.
Just a further question from the points raised by John re the 3 way fridge. Never had one of these before so again just learning. You say you have setup yours with a separate feed to run it when on the move. If I have the thumper 105ah ( which is using 6 B&S plus isolator and fused) and the trailer 105ah batteries connected as described by Sandman, can I assume that the fridge will draw equally from both batteries and both batteries will still take some charging from the tug? Does this eliminate the need for a separate feed from the tug direct to the fridge given the amount of battery power I will have? To throw in another spanner in, I also run a Waeco CF 50 in the back of the car off the Thumper, my kids need lots of food!
The trailer has solar also and all runs through a controller at the trailer battery. Not sure what sort of controller yet as did not ask that question when I ordered it but will no doubt upgrade to the Ctek that more or less everyone recommends once I take delivery.
Again thanks for your time and help. One day I intend to be the guy in in a position to offer the advise too! Not quite there yet though.
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Follow Up By: Member - John and Val - Monday, Apr 01, 2013 at 14:28

Monday, Apr 01, 2013 at 14:28
Hi Graeme,

Three way fridges have the big advantage of being able to run from gas. They are actually heat powered. You can’t run from gas while on the move though, as for safety (and legal) reasons the gas should be turned off while travelling. In any case the flame would almost certainly be blown out if you tried to use gas when moving. To keep the fridge running while travelling, it has an electric element to provide the heat. These fridges aren’t nearly as efficient as compressor fridges such as Engel and Waeco, whose motors cycle on and off, and averaged over an hour or so will typically draw 1 or 2 amps. A three way fridge running on 12V will run continuously and draw about 12 amps!

This raises problems. Not only is this burning energy very fast, but there are resistive losses that reduce the voltage available at the “consumer” end of the supply cable. These losses are directly proportional to the current flow (amps).

If you were to use a single supply cable to the trailer to feed both the fridge and the trailer’s battery, two problems arise. 1) Under these conditions the fridge and the battery are electrically connected to that single supply, and inevitably they are therefore tied to each other. Consequently, when you stop and turn the engine off, the trailer battery will continue to power the fridge – you must find a way to automatically disconnect them once the engine is stopped. 2) Even using very heavy wiring there will be voltage loss in the wiring resulting from the high fridge current. Battery charging is very voltage sensitive. It isn’t easy to fully charge your trailer battery using the full voltage available from the alternator, but with a fridge hanging on the same line, there will not be enough voltage available to provide proper charging to the battery.

So, to stop making words (!) and address your question about adopting Bill’s suggestions:

The 3 way fridge is the problem. The aim is to use the alternator to power it while the engine is running. The alternator will be feeding the battery/s at this time too and consequently they are connected to the fridge. The batteries should never be called on to power the fridge though, and you need some way of automatically disconnecting them from each other when the engine stops. This switching is most easily done in the engine bay.

“can I assume that the fridge will draw equally from both batteries and both batteries will still take some charging from the tug?” Yes and no (does that help?!) With the engine running, the fridge and both batteries are fed by the alternator. (The alternator voltage is a bit higher than the battery voltage, and current (amps) will always flow from a higher voltage to a lower one.) If you were to use Bill’s system AND connect the 3 way fridge to the same line, there would be a small voltage loss in the wiring from alternator to the Thumper, then a further loss between the Thumper and the trailer. Without the 3way fridge, and assuming heavy cables, these losses would be negligible, both batteries would receive some charge (though probably not equally.) This arrangement would also provide extra power to run the Waeco when stationary – the alternator will be powering it when the engine is running.

I 100% agree with Bill’s final paragraph – a dc-dc charger in the trailer is very desirable to ensure good charging. The D250S dual provides the switching, manages charging, and also provides an MPPT solar controller – that’s all the good stuff in one box!

One last thing – you may find Electricity for Camping a useful read.


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Follow Up By: Pathycop - Monday, Apr 01, 2013 at 23:37

Monday, Apr 01, 2013 at 23:37
Thanks again John for all your info. All useful information and certainly assists me in starting to get a handle on the 12 v side of things. Had a read of the link too thanks.
I think once I take delivery of my new camper things will become a little clearer as to what is already in place and what is required to make it all work together. Hopefully I can tap into your knowledge again in a few weeks time and get your advice to get it all right.
Thanks again for your time.

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Follow Up By: Member - John and Val - Tuesday, Apr 02, 2013 at 08:44

Tuesday, Apr 02, 2013 at 08:44
You're welcome Graeme. There's a lot of help and support available here on Exploroz.

Enjoy your rig!


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Follow Up By: CampingTechAust - Saturday, Apr 20, 2013 at 18:20

Saturday, Apr 20, 2013 at 18:20
Hi Graeme,

Further to the excellent follow-ups above (very good advice), I have just completed the task you are about to undertake by running 20mm cable from the battery to an Anderson connector at the rear of my Navara (Not dissimilar to the Pathy).
I have this install documented on my web site with a lot of photos. This is not a business, just my passion!
Have a look at the Installation tips page on: or enter Camping Technologies Australia into Google.

Flick me an email through the web site if you have any questions as posting them here may be considered off topic.

Hope this helps.
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Reply By: Sand Man (SA) - Monday, Apr 01, 2013 at 07:55

Monday, Apr 01, 2013 at 07:55
Hi Graeme,

I believe you can utilise a patch lead like I do, from the Thumper and under the tailgate to the camper lead.
The Thumper has two Anderson connectors on it. (At least mine does)
One is a 50A connector you normally use to connect the charge cable.
The other is a 150A connector for the jumper leads that usually come with the Thumper.

Derek from Sidewinder has a patch lead available Flyer to towbar cable which is terminated in 50A Anderson connectors at each end. Perhaps you just need to replace one end with the bigger 150A connector to plug into the "jumper lead" port.
As the Thumper would come with the car charge kit, I know you would already have twin heavy duty cable from the primary battery to the "black box" which a fuse in it, then to the Thumper.
Obviously, the far end of the camper "charge" lead should also be fuse protected before it connects to the batteries.
The Isolator for the Thumper circuit is in the black box closest to the primary battery end so you will not be compromising anything.

I do this exactly the same thing although in my case I have two circuits from the primary battery.
One for my 75Ah Thumper I take on most trips but only use for the fridge if camping in the tent.
One for my Sidewinder Flyer which is my auxiliary battery in the back of my rig.
The Flyer also has an "output" port on it, bypassing the isolator and I use the patch lead to connect up to my camper charge circuit.
I see no reason whatsoever that the simple addition of a patch lead with a large Anderson connector on one end and the standard 45-50 amp connector on the other would not provide the solution you need.
If you are not handy with a soldering iron, perhaps Derek could provide a patch lead with the different size connectors on it.

Just one last thing you may like to consider as the ultimate addition, is a dc-dc charger in the camper to overcome any voltage drop in the long cable run or the possibility of a lower output charge from the vehicle alternator.
I use a Ctek D250S dual dc-dc charger that gives me a multistage charging process while traveling and the availability of solar input to supply a charge to the battery bank when stationary for longer periods.

Flyer to towbar cable

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AnswerID: 507940

Follow Up By: Sand Man (SA) - Monday, Apr 01, 2013 at 08:11

Monday, Apr 01, 2013 at 08:11

Substitute 175A Anderson connector for the 150A I mention above.

Derek also has these available.

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Follow Up By: Pathycop - Monday, Apr 01, 2013 at 11:57

Monday, Apr 01, 2013 at 11:57
Thanks Sandman! Great simple solution that had not actually occured to me in the many hours spent staring at the thumper setup assuming there must be a way. Always good to hear from someone who is actually using the same setup too and that it works.
I think until we as a family have worked out what our power needs will be, I am always going to carry the thumper with me so this solution fits well for now and involves the least work for me lol.
Thanks again

FollowupID: 785294

Reply By: evaredy - Tuesday, Apr 02, 2013 at 10:06

Tuesday, Apr 02, 2013 at 10:06
I am in a similar situation, I have a 105 ah in the tray of my Dmax and have just purchased a camper trailer, which has a 120 ah installed. It also has 2x65w panels fixed to the roof of the trailer, the bracket the panels sit on allows for them to be swivelled. There is also a Redarc BMS unit installed to take care of the charging, either Solar or from the Alternator.

I still want to have the battery setup in the Dmax for the times when we are tenting it and have a folding 120w panel that will charge the battery.

I was looking at DC-DC chargers and had settled on the Ctek D25OS, I rang Ctek to find out if this would be suitable, they chap I spoke to told me that this unit was not suitable for new vehicles that had ECU.
I then looked at the Redarc and after speaking to them I was told that the BCDC1225-LV is the one to use.

So my plan is to have the BCDC1225-LV installed into the tray, this will charge the 105ah, I will have 1 Anderson plug fitted to the tow bar, this will allow me to hook up a 10 metre cable to power the fridge, lights etc when tenting it.
There will also be another Anderson plug installed on the tow bar that will allow the 120w panel to charge the battery in the tray. I keep the fridge in the back behind the drivers seat when travelling and will have a connection installed to the seat bracket to power the fridge.

It's not a cheap solution, but it should give me trouble free operation.
AnswerID: 508007

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