Dual Battery - Towball Question

[ozguy7]

Hi All,

I'm running a simple dual battery setup at the moment using a VSR to ensure the start battery doesn't get drained.
I'd like to run an anderson plug to the towball so I can also charge a camper trailer when the engine is running.



I've got a three way Anderson cable splitter installed under the car per the diagram above. If I run a cable straight to the towbar is that all I need? I know the VSR will stop the camper or dual battery from draining the start battery, but what's to stop the trailer draining the second battery?

Do I need a second VSR connected to the second battery to stop outward drain too on this circuit or something else?

Cheers

[Intruder]

I personally wouldn't be doing it this way as your actually asking the VSR to charge two additional batteries - which it probably isn't designed to do. Potential also being you'll just end up draining your start battery anyway. If you are going to drain a battery - you want it to be your second battery.

If you want it simple, run your cabling direct from the second battery to the towbar with an inline circuit breaker at the towbar end installed for safety. Worse case scenario here being you drain your second battery, start battery is fine though.

If you think you may want to add additional power options to the vehicle down the track, in the tub for example, then run cabling direct from second battery to a fuse box, then cabling to your anderson plug direct to the fuse box. I've done that by using one of these, https://www.whitworths.com.au/blue-sea- ... fuse-block , with one of these being used as an earth connection point next to the fuse box as well https://www.whitworths.com.au/blue-sea- ... -plus-5-16.

If you want to get fancy, I'd be installing a ctek or redarc dc-dc unit in your camper which then allows for solar connection for charging your camper's battery.

Otherwise you could place a relay in the the anderson plug cable run, with the relay connected to your car's ignition, thus anderson plug only gets power when ignition is on. Alternatively you could go old school, and just disconnect the anderson plug when you park the car.

[ozguy7]

Thanks for the feedback.

My original thought was to install a one way diode between the branch off and the second battery. This would allow current into the second battery (from the alternator) but not allow any current out.

You do raise a good point about the VSR / Alternator being able to handle the additional load.

[ag9111]

Your alternator will be able to charge both batteries at the same time and if both batteries are down about 11.8 volts will pull about 20 amps.
Do not use a diode as they produce a 0.6V approx accross them.
My suggestion would be to install a second vsr feeding the towbar but this of the assumption that all aux batteries are deep cycle. If AGM then you need to go to dc to dc convertors.
My concern is the splitter under the car. It will be subject to water dust etc and the contacts will tarnish even if they silver flashed.
Tarnished contacts will produce a voltage drop.

My particular set up is a vsr under the bonnet, good for 250A. 16mm2 cable to the aux battery in the tub, 100A wet cell deep cycle, so it can be used for starting in an emerg.
This cable is fused at both ends with 150A CAL2 fuses. I then have a 30A CAL1 fuse feeding the 175A anderson on the towbar direct off the aux battery.
The camper is another 100A wet cell deep cycle fused with another 30A CAL1 fuse. No vsr or dc to dc between the 2 aux batteries.
When i leave on a trip all batteries are fully charger and remain that way when driving.
If i pull up overnight i just disconnect the towbar andersons for isolation and then reconnect in the morning after i have the car started. Simples.

[Quinny]

Simples.

I had to read it twice

[ag9111]

Simples.

I had to read it twice

Your from qld so congrats on only needing two goes at it.
Round of applause for encouragement.





Sorry Quinny, Can help myself

[Quinny]

I've been here for only 10 years ... I didn't think it would happen that quickly

[ozguy7]

Both are AGM Deep Cycle batteries. Just did some research on your comment about using a DC DC charger rather than the alternator. Might need to get one I think.

Looks like the alternator can overcharge an AGM? I know it sits around 14v when charging

[mowerman]

ML dual cab.
I ran 6B+S cable from the crank Batt to a vsr.
Circuit breaker either end of cable.
The Vsr and 2x80 amp AGM Batts are behind the back seat.
A tight fit but they do fit.
From there, thru 2 more circuit breakers, 6 B+S from these batts to an anderson plug at the tow bar.
There are also anderson plugs in the tub and down the side of the rear seat. A fridge usually sits on the back seat. It doesnt whinge like the kids did.
The camper trailer carries 4x80 amp AGM batts.
Haven't had any problems with the alternator keeping up the charge to this lot.

Overkill?
Beer should be cold.

Rod
.

[ozguy7]

ML dual cab.
I ran 6B+S cable from the crank Batt to a vsr.
Circuit breaker either end of cable.
The Vsr and 2x80 amp AGM Batts are behind the back seat.
A tight fit but they do fit.
From there, thru 2 more circuit breakers, 6 B+S from these batts to an anderson plug at the tow bar.
There are also anderson plugs in the tub and down the side of the rear seat. A fridge usually sits on the back seat. It doesnt whinge like the kids did.
The camper trailer carries 4x80 amp AGM batts.
Haven't had any problems with the alternator keeping up the charge to this lot.

Overkill?
Beer should be cold.

Rod
.

Hey Rod, do you just unplug the trailer when the engine isn't running?

I'm going to wire it the same way you have but add a second VSR between the second battery and the trailer plug. That way it should only charge the trailer when the second battery is full or being charged (I hope anyway)

[mowerman]

.[/quote]
Hey Rod, do you just unplug the trailer when the engine isn't running?

I'm going to wire it the same way you have but add a second VSR between the second battery and the trailer plug. That way it should only charge the trailer when the second battery is full or being charged (I hope anyway)[/quote]

No.
We do a lot of overnighters on our trips and I just leave everything hooked up.
All of the batteries are downstream of the vsr. Its mainly for keeping the crank battery for being run flat.

Rod
.