Charging a leisure battery from car

[PeterHunter]

Hi All,

I'm in the process of converting my 806 into a 'basic' campervan. I have a new 110ah leisure battery that will give power for internal lights etc. But I also want to power a small 12v fridge (47 watts). My initial plan is to plug the fridge into the accessory socket in the rear of the 806 whilst traveling, and then connect it to the leisure battery during the night. I'm sure there must be a better way of doing this, just not sure how.
The problem with this is that I will very quickly drain the leisure battery if it's not re-charged. So how can I do this from the car's battery?
If and when I pull into a campsite I can use the electric hookup and use the mains charger. But I don't very often use campsites.
Any help or advice would be most appreciated, as long as it's simple and cheap !!!

Regards, Peter

[citronut]

u have never done this,

but what about the likes of one of these


http://www.ebay.co.uk/bhp/leisure-battery-charger" onclick="window.open(this.href);return false;

and you might need one of these

https://www.google.co.uk/#q=campervan+c ... t&tbm=shop" onclick="window.open(this.href);return false;

[PeterHunter]

Thanks for the research and info Malcolm. I already have a mains charger for leisure batteries, but didn't know that did them for connecting to car batteries. Worth considering. Yes, I had thought about the need of a fuse box / isolator. Probably even consider a multi-connector junction box of some type as well when the time comes.
Regards, peter

[Peter.N.]

The easiest way of charging your leisure battery is to connect it to the car system via a relay which is activated by the ignition switch so that its only connected when the engine is running. Providing you are doing a reasonable number of miles that should keep it topped up. You will need quite a heavy relay and cable.

Try not to fully discharge it, the battery life is based on the number of complete charge/discharge cycles, the deeper you discharge it the shorter will be its life.

Peter

[PeterHunter]

Hi Peter.N. and thanks for the reply.
I had thought about a relay of some sort, but not sure what to go for. I would only want the charging to happen whilst driving - and I do drive long distance when I go camping. At all other times I wouldn't need to use the fridge etc. anyway, so that wouldn't be a problem.
However, if it's got to go through the ignition then it obviously wouldn't be connected directly to the battery. Am I right in guessing that the accessory socket (10amp max (I think!)) wouldn't be up to the job? So, where would I connect the relay to?
Cheers
Peter

[Peter.N.]

You really need to connect a lead direct to the battery or even better still the alternator because the voltage increase necessary to charge the battery is quite small so if you connect it to a light duty cable the voltage drop due to its resistance could substantially reduce the charge rate.

You need something like a 50 amp relay and also cable capable of carrying that sort of current, not because you will be charging at 50 amps, well not for long anyway, but to make sure you don't lose most of your charge in the cable.

If you can't find a readily available ignition switched feed the radio is probably the easiest place to pick it up. The supply to charge your aux battery will need to come from a source close to the battery, its only the relay switching lead that will come from somewhere else.

Peter

[BX]

Go to your local autofactor or to Hal***ds and buy a split charge relay kit. They are designed for operating the fridge and charging the leisure battery in a caravan whilst it is on tow. In your case you will have the fridge and battery on board as in a camper van. One can just use a 40Amp or larger relay operated by the no charge warning lamp instead if you want to be very thrifty. However the split charge relay has the advantage that it is voltage sensitive and allows the engine battery to at least partially recharge before charging the leisure battery. Many also have a seperate connection for the fridge. The split charge relay kit should include wire, connectors and instructions.
Before you do anything measure the current drawn by your fridge. It is often in the region of 4 to 12 Amps. This gives very little running time even off a fully charged 110Ah battery. Even the best leisure batteries can only withstand a limited number of deep discharges. A lifespan of 150 deep discharge cycles would be good. As a rule of thumb do not frequently discharge your battery below 50%. This means that if your fridge draws 10 Amps you only have 5 hours useful charge in the 110 Ah battery. Unlike domestic fridges camping fridges are generally either absorbtion or peltier units that run continuously. The most common ones used in campers and caravans are usually absorbtion units where the heat source can be provided by 12V or 230V electricity or by LPG. 12V is only used whilst travelling and either LPG (gas) or 230V is used whilst parked.
If you want to use the simple 50A relay switched by the ignition you must make sure as in all cases that the cable is up to carrying the current. However I recommend using quite a long lead from the engine battery. In this case you will be using the cable via the relay between the two batteries as a type of resistor. This contradicts the practice of maximising charging current by lowering the resistance. In this case using long positive and earth leads helps to prioritise charging current for the engine battery. Remember if you have a flat leisure battery you can always start the engine to charge both batteries but if your engine battery is flat due to getting insufficent charge you are stuck.

PSI Should have read the original post more carefully with this fridge you are good for about 13 hours or occasionally even 24 hours (110 A/h is only nominal and only whilst new) Remember even after running for 13 hours it could easily take 2 hours driving to restore the charge depending on the exact voltage- charge curve of the battery

[PeterHunter]

Hi BX,

I've just checked that out. They are a reasonable price and seem to be the ideal choice for the job. I'm not so sure about the fridge idea now though (although I still need the leisure battery for other things). If the current drain is going to be that high it looks as if it will be out of the question. Unless I get a fridge that runs off gas. I'll have to look into that option.

Thanks for the info anyway.

Peter

[citronut]

Hi BX,
I'm not so sure about the fridge idea now though
Peter

Peter
you missed out on the obvious option for a fridge


http://www.frenchcarforum.co.uk/forum/v ... =3&t=46925" onclick="window.open(this.href);return false;

[Peter.N.]

There are quite a few second hand 3 way fridges on ebay, some for very reasonable prices.

Peter

[PeterHunter]

Yeah, thanks Malcolm, very funny. I'm surprised you didn't suggest taking the windows out !

Good thinking Peter, I'll have a look on eBay if I decide to go that route. I only really want the fridge in case it gets hot enough to melt the butter !!

Peter

[citronut]

spoz you could always make sure you weigh anchor were there are freeeez shams in the next field

for the milk at least

[PeterHunter]

Yeah, and if they run fast they'll be passed your eyes !!

[Peter.N.]

Hi Peter

I sent you an email, did you get it?

Peter

[PeterHunter]

Hi Peter. Yes, I did, thanks. I'll reply later. Been a bit bogged down with holiday preparations. Sorry.
Peter