So, this makes sense to me in theory but I just wondered if anyone had actually done it in practice;
If you take a 12v supply from a standard car 12v socket and attach it to a 1000w inverter, then plug a 240v powered leisure battery charger in to the inverter, then attach the battery charger to a 110Ah leisure battery, will it charge it? (with the cars engine running i.e. out for a day trip for example).
Why mess about when you can connect your car battery to a leisure battery directly with jump leads and boost the battery by also running the engine/alternator
Quote: Originally posted by Big Al on 10/4/2013
you would be better off sticking a set of jump leads on and letting your car run for ten minutes
I was thinking that! But my car is unable to jump anything as its one of those BlueMotion technology engines! Had already tried last year when the wife's car had a flat battery!
on another point,driving around with a bloody great battery in your car charging is a very dangerous thing to do.in the event of an accident,you would stand very little chance if that hit you.
have a split charge relay fitted in the boot,and strap the battery down.
The usual way of doing this is to wire something into boot to charge battery. It is no different from towbar wiring that charges leisure battery in caravan.
Thirty years ago most people used the method Tentz suggested and some people (my dad included) even fitted a split charge relay in the boot of the car leading to a battery box with restraining straps on it. The box had a socket on it and it was a simple case of unplugging the box containing the charged battery and plugging it in to the caravan. There again life was simple back then with no confusing habitation relays etc to prevent you doing what was simple. I guess you could do something similar for camping and if possible avoid the use of crocs to ensure you get good contact on the terminals.
------------- 'A sure cure for sea-sickness is to sit under a tree'
Firstly, thank you all for your replies, though I don’t think that I've explained myself fully or particularly well on this thread.
I drive company cars, seldom the same one from one week to the next so the idea of the split charge relay is not feasible, hence my question regarding the 12v socket.
I wouldn't really want to be putting jump leads on to it as the idea was to charge the battery whilst driving, for example on a day out; two birds with one stone you might say, in a safe way obviously with the battery strapped in to the boot of the car.
Most of the vehicles that I drive have a 12v socket in the boot and strapping points, which is what gave me the idea.
The inverter may be 1000W but the battery charger is only 10amp (less than the fuseable rating of the socket).
The reason that I want this to be mobile is that I'm using it in a tent; it isn't fixed.
If it’s simply a case of connecting a positive and a negative from a 12v socket insert directly to the battery, then I’ll give it a go. It just doesn’t seem as controlled as using an intelligent leisure battery charger?
Effectively the charging intelligence is already in the car. The only issue with a direct connect via the 12v boot socket is the potential difference between the two batteries. If you are not careful the current drawn while the two equal out could blow the fuse to the socket.
There are ciggy to ciggy adaptors for jump starting cars and these have current limmiters inside that prevent fuses blowing... take a look at this
I had a portable hook up for a while a bit like this where I fitted the leisure battery with a permanent 12v ciggy sockets for lighting and USB chargers
You could use a split-charge relay in a small enclosure, supplied from a 12v ciggy plug and outputting to battery clamps.
In my experience ciggy socket circuits are normally rated at 20 amps where there are multiple outputs so you are unlikely to overload the system.
You want to ensure that you are not drawing current from the leisure battery when starting the car - a split charge relay, or remembering to unplug it when you stop will deal with that.
you do not need a 1000w inverter to run a 240v smart charger. A cheaper 150/300w would do. I have an emergency battery pack that has a 300w inverter, tyre pump & fluorescent light
this has a 20ah battery & is more than enough to charge my leisure battery, I then recharge the battery pack from the car while we are running around