Fridge and leisure battery from same split charge

[jimrat]

Hi

I'm in the process of wiring up my van electrics, and I have a question about the 12V supply for my 3 way fridge (Dometic RM123).

The fridge manual says to use a relay, triggered by the alt, to supply 12v to the fridge when driving. My existing split charge relay is the 5 pin type (Lucas 60 Amp), which has two 12V out pins (C2, and smaller C3).

The C2 pin supplies +12V to the leisure battery. At the moment pin C3 is unused. Could I use C3 to supply +12V to the fridge? The fridge will pull 7 Amps when running on 12V supply. What size fuse should I use in my supply wire from the Alt to the relay?

The van will mostly be used for weekend trips, or for a week with hook-up/240 V charger, so I don't expect the leisure battery will ever get completely drained (and draw massive current).

Cheers
Jim

[California Dreamin]

Hi jimrat.....C3 on this Lucas split charge relay is designed as a switched fridge feed....so exactly for the purpose you are proposing. No need for an additional relay or alternator switch supply, if you already have the relay in place and wired up, then all you need to do is add a 2mm2 (17.5 amp wire) from C3, with an inline fuse holder (10 amp fuse) to feed the 12 volt side of the fridge. This 'feed' will only be live when the engine is running so 'as per design' will not flatten your leisure battery, you will just have to remember to switch over onto another power source once you camp up.

Relay same as this one?
http://www.autoelectricsupplies.co.uk/product/824" onclick="window.open(this.href);return false;

Martin

[jimrat]

Yes I have the relay in the link - came with the van, but wasn't connected.

That will save loads of hassle- top man

Thanks

[California Dreamin]

I'm sure you have already worked it out but just in case you haven't.
The 'trigger' or switch wire terminal W1 from the blue alternator exciter (back of alternator) uses 9/0.30 5.75 amp wire (quite thin but it isn't carrying much current)
The local earth from terminal W2 (using the relay mounting point perhaps but make sure the eyelet used is definitely earthed) also 9/0.30 5.75 amp wire.
Starter battery (2) positive terminal to C1 (it specifies 65/0.30 35amps) although I would be tempted to go up to 84/0.30 42amp cable.
Leisure battery (3) positive terminal to C2 uses the same gauge wire as C1.
Add two inline fuse holders (30 amp fuses) located close where each of the positive wires connect to the starter & leisure batteries. Or if you think fitting two fuse holders to this connecting wire is over the top, then just fit the one on the starter battery side (up to you but use at least one)
C3 is the 28/0.30 17.5 amp wire to the fridge (10 amp inline fuse close to the relay)

Martin