Install Additional/Auxiliary Battery.

[Shadeyman]

I'm not sure I've posted this is in the right place but it seems to me you ICE guys would know.

There's a large powerful auxiliary battery(Bosch) installed in a trailer I just purchased. In order for this battery to be charged from my cars alternator I need something called a "smart battery isolator", I believe it automatically connects and disconnects the auxiliary battery allowing the cars battery to be fully charged first.

Has anyone done something like this?
How do I wire this up(wiring diagram)?
Exactly what do I need(wire size, fuses etc.)?

Any help will be appreciated.

 

[volxstu]

It all depends on how much current you want to pull from it. Obviously the Aux battery will want to pull the same from your front as it is discharging so that will determine the gauge cabling that you need.
We use something called a split charge relay which can be connected to the alternator charge wire or a switch.
http://www.caraudiodirect.co.uk/products/autoleads-split-charge-relay.html

Edit:- I think i may have one spare if you need it.

 

[Shadeyman]

Does a split charge relay automatically detect the voltage of the car battery and switch in and out as required(protecting the car battery) or does it just switch in when the alternator is producing power(charging both batteries at the same time)?

The auxiliary battery power is used only for a backup by the equipment in the trailer. No power from the auxiliary battery is needed by the car, I just want to use the car to charge the auxiliary battery but I do want it to charge quickly so will large cables be required?

Do I need to fuse it all? What amp should I use?

Spare split charge relay, check you inbox.

 

[volxstu]

If you use a relay you should have a fuse at both batteries as potentially the current can flow both ways.
A relay won't automatically detect the voltage of the rear battery but the cost of more complex technology seems a bit over kill for the job. I would just put a rocker switch on it and give it a charge for half hour or so on journeys.

 

[dave]

you need caravan forum

 

[Shadeyman]

If you use a relay you should have a fuse at both batteries as potentially the current can flow both ways.

I understand now, there's potential for a short either side of the relay so both need to be fused.

A relay won't automatically detect the voltage of the rear battery but the cost of more complex technology seems a bit over kill for the job. I would just put a rocker switch on it and give it a charge for half hour or so on journeys.

The smart relay I was told to use isn't supposed to detect the rear, it detects the voltage of the car(front) battery and once it detects its fully charged it activates and connects the trailer(rear auxiliary) battery to be charged. It also disconnects when it detects the car battery drops below a certain level, thus protecting the car battery. I've been looking but had no look finding one yet. Not sure I like the idea of doing.

you need caravan forum

The trailer has a 240v hook up that's transformed down to 12v similar to a caravan. The auxiliary battery is used as a back up for when the 240v hook up fails. So you might be right. :chin:

Edit.
Stu, this is what was recommended for me to use, just cant find a UK supplier that sell something similar.
http://redarc.com.au/news/.....-redarc-smartstart-dual-battery-isolator

 

[volxstu]

I have been led to believe Cole Heerse is the best.

http://www.colehersee.com/home/item/cat/212/48525/

The problem with these are that you have no controll. It's expensive technogy to charge a battery that is only an emergency backup so will only need around 30 mins charge when you use the trailer. The rest of the time it's just puting strain on your engine.
For ease, cost and controll I would just use a standard relay and rocker switch.

 

[Shadeyman]

I have been led to believe Cole Heerse is the best.

http://www.colehersee.com/home/item/cat/212/48525/

The problem with these are that you have no controll. It's expensive technogy to charge a battery that is only an emergency backup so will only need around 30 mins charge when you use the trailer. The rest of the time it's just puting strain on your engine.
For ease, cost and controll I would just use a standard relay and rocker switch.

As the trailer will only be connected once may be twice a week for an hour or two I'm not worried about it putting extra strain on my engine/alternator.

Cost doesn't matter, I just want it done correctly.

Again, I can't find a UK supplier for the Cole Hersee Isolator either.

 

[Shadeyman]

Stu, would one of these marine isolators work?

http://www.ebay.co.uk/itm/370444088945

 

[volxstu]

I cant see a switching mechanism on it. It doesnt look any more useful to you than a normal relay.

 

[Shadeyman]

There's 2 types of smart battery isolator.

Solenoid and diode.

The solenoid type we are all familiar with but the diode type(with small voltage sensor circuits) are cheaper and more widely used because they last a lot longer.

You wont see any switch mechanism on a diode isolator because its a completely sealed unit, thats why they a commonly used in marine installations. The switching is done automatically by small voltage detecting circuit boards and large high amp diodes, no relays and contacts.

You not come accross these before then?

Edit.
Just attached the spec sheet. Would this do the job?

 

[Shadeyman]

Just a quick update.

I purchased a Smart(marine) battery isolator only to find out that the trailer has a built in charger so when its hooked up to the mains the auxiliary battery is being charged. Only problem was the fuse had blown, replaced the fuse and problem solved.