trailer electrics

[sclater85 Lurker Find all posts View Profile Close sclater85]

hi all,

first i want to enquire what is the specific purpose of an anderson plug near a towball is, i imagine its a supply of 12v to the trailer and a hard supply at that,

if you want to run a dual battery system and then tow a trailer that also has batteries in it how do you charge the trailer batteries via your alternator, is the alternator big enough to handle that task and is it even possible,

what specific product would you use to ensure all batteries are charged properly and power to them distrubuted equally, and similary when the alternator is not being used that the starting battery does not empty , would the redarc bms 1215 do the job? does it have enough facilities to manage the two car batteries and the batteries in the trailer

[Matty80 Avid PP Poster! Find all posts View Profile Close Matty80]

Re: trailer electrics

hi all,

first i want to enquire what is the specific purpose of an anderson plug near a towball is, i imagine its a supply of 12v to the trailer and a hard supply at that,

if you want to run a dual battery system and then tow a trailer that also has batteries in it how do you charge the trailer batteries via your alternator, is the alternator big enough to handle that task and is it even possible,

what specific product would you use to ensure all batteries are charged properly and power to them distrubuted equally, and similary when the alternator is not being used that the starting battery does not empty , would the redarc bms 1215 do the job? does it have enough facilities to manage the two car batteries and the batteries in the trailer

1. the anderson plug at the rear is generally used for power connections to the trailer or for higher load devices such as portable air compressors which may be used while stopped. Handy for when the appliance is of a load rating greater than what the internal 12v sockets are rated for.

2. if you visit the www.redarc.com.au, they have in there technical section a variety of different dual & triple battery arrangements and the setups (complete with general wiring diagram) as PDFs. These should be able to help answer your question.

It is important to note, that due to internal cable resistances, the further a battery is from the alternator (longer cables required), that the charge current diminishes reducing the full charge capacity - ie. the closer batteries charge better than the further away ones. To combat this, DC-DC battery chargers can be used as an alternative. If you look at the dual battery installs on the forum (and there aare lots of them) them you can see that both methods are used. Very easy to apply a third battery in a similar or different combination.

That is - the aux battery gets charged via the alternator, and the anderson plug at the rear connects to a DC-DC charger with chargers the CT battery. Or a DC-DC charger can be used for the Aux and another can be used for the CT. Will depend entirely on how you want your setup to work and in what way you will use it.


3. Again, best look at the dual battery setup that members have already in their vehicles, or checkout the redarc website. (Or other dual battery manufactures website).

[sclater85 Lurker Find all posts View Profile Close sclater85]

Re: trailer electrics

http://www.exploroz.com/Trader/Accessor ... x?id=10795

found these units that alter the output voltage of the alternator to increase charging in dual battery settups just wondering if anyone has experience with these.

i am aware of cable lengths/voltage drop and current draw etc, but im not talking about a backup battery mounted in the trailer it is only thier for the electrical system within the trailer, all i am talking about is providing a top up charge to those batteries via the alternator so when you open you camper trailer the batteries are charged ready to go.

[Matty80 Avid PP Poster! Find all posts View Profile Close Matty80]

Re: trailer electrics

i am aware of cable lengths/voltage drop and current draw etc, but im not talking about a backup battery mounted in the trailer it is only thier for the electrical system within the trailer, all i am talking about is providing a top up charge to those batteries via the alternator so when you open you camper trailer the batteries are charged ready to go.

Mate, call it whatever you want - be it back battery, ct battery, 3rd battery, 1st battery, main trailer power source battery - its still a battery and its in your trailer, it still provides a source of power, and it still requires it to be charged and it gets connected to the car... Yes?

1 SBI with 2 auxiliary batteries.


2 SBI’s with 2 auxiliary batteries.


Images Courtesy of Redarc

I will note that this is only 2 of the many possible ways that this can be done, any dual battery system (tri battery) will work... As I said before, visit the redarc side and have a look at the ways they do things, or view what others have used for their own dual battery (tri battery) setups, vary the system to meet your needs, using a combination of the methods stated. Keep your protection correct and adequately sized.

[AJ120 Out of control poster! Find all posts View Profile Close AJ120]

Re: trailer electrics

As far as the voltage booster you linked to goes, have a look here viewtopic.php?f=16&t=7939 lots of good info in this thread regards dual batteries. One of the guys who posts a lot in this thread LieghW actually makes and sells the diodes on ebay. Lots of us run them including me, they are simple to install and work well.

As Matt said search for info on dual battery systems as there are lots of different ideas and ways on how to do it. I like to keep these things simple, I have a triple battery system that works roughly like this.
Standard Toyota cranking battery, second battery fitted in rear cargo area in custom made drawers (but you can put it wherever you like) is a 100ah AGM battery isolated and controlled through a redarc SB112 controller.
Third battery in trailer is a normal cranking battery 600cca sealed, I also have a tip trailer that runs the same size and type of battery. My third battery in the CT only runs a couple of lights and the 12v water pump from my tank so it doesn't need to be overly big or expensive hence the standard battery. If you wanted to run a fridge or something else that draws a lot of power a deep cycle battery or similar may be better. To charge the trailer battery i simple have a cable running from the cranking battery through a fuse to the Anderson plug at the rear, the CT battery is much the same, Anderson plug running back to a fuse near the trailer battery and then to the battery.
The Anderson plug is always live so power will flow either direction from trailer to cranking battery or vice versa, whenever the anderson plug is attached depending on which battery has the most charge. The cables i have used are probably a bit small but it seems to work OK. I have on occasions flattened the trailer battery after a wire has come loose but it seems to charge up well enough just by hooking it back upto the vehicle for a day. I have never had this flatten the cranking battery.
This set up seems to me to be almost as simple as you can get and it has worked well for me for quite some time now. hope this helps.
follow the link to my build up in my signature below for a bit more info.

Cheers Andrew