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morning all.

dumb electrics question coming up.

I want to fit the leisure battery to the camper and get it charged back up as the vehicle moves. I purchased a Combi-master W4. the lad in the shop said that this was connected to the alternator and charged the leisure battery independently of the vehicle battery and that there was basically no contact between the two batteries.

on looking at the instructions it suggests that the Combi-master is connected to the vehicle battery, plus the ignition, and an earth, and then there is a single connection from the Combi-master to the leisure battery. this wasn't how I understood it would go together, so I suppose the questions are - will this set-up actually charge the leisure battery, and will it cause the vehicle battery to flatten if the leisure battery flattens?

many thanks in advance.

Hello soulkitchen.

I don't know about Combi-master W4 in particular.  I would stick to the provided instructions (to start with at least).

What connection on the ignition is specified?

The normal practice is to have a switch (relay) between the poss on starter and the poss on leisure.  This switch (relay) is closed (making connection to leisure batt) automatically when engine (and therefore alternator) is running.  The trigger for making this connection is usually taken from the feed to the ignition warning light.  This means that the switch is closed (putting leisure battery in charging circuit) when the ignition is switched on and the alternator warning light goes out. 

This in effect means that the leisure battery is part of the vehicle charging circuit when the engine is running, but the starter battery is not part of your leisure circuit when the engine is stopped.

Hopfully someone who knows Combi-master W4 will be along soon.

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Steven

i think i see what you mean. when stopped the Combi will not allow power to be taken from the vehicle battery to the leisure battery (effectively the Combi will have an inbuilt relay which closes when ignition off?).

oh, there was no specific wire to the ignition, but I understood this to be any ignition feed wire.

As I said, my description above is just a general description of split charging.  Proprietry units like your Combi or a Zig unit may have variations to this.

With the split charge setup I described, a connection from the ignition would not be a good idea.  It would mean that as soon as the ignition was switched on, the  leisure bat would be in circuit to the starter bat.  Not good for a few reasons.  The most serious being the possibility in some circumstances of a high engine cranking current being passed to starter from your leisure batt.

This is avoided when the relay is triggered by alternator warning light as the connection is not made untill the engine is already running and the alternator generating current.

Your Combi unit may well avoid that senario in some other way but I think we need advice from someone who knows the Combi-master W4.

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Steven

aw jeez,

a weekend later and I'm still confused, duh.

the diagram says there's only one wire from the combi-master to the leisure - I guess this is to the live (?) so do I just earth the negative to the vehicle body?

at this rate I'll be the eejit who has to bump start a T4 all the way to Glasgow first weekend out.

thanks mate, I'll give that a go by substituting the combi-master for the relay on the diagram.

thanks to all who've tried to help.......learning all the time.