Vehicle battery / leisure battery select switch

[Steve wilcox]

I have a 2003 Elddis suntor. I’m trying to locate a wiring diagram. My fault is that when I switch to vehicle battery I have no volts to the panel. There is a green wire coming to the switch which disappears down the wall. 

[Keithl]

Start at the vehicle battery and look for obvious added on wiring and follow it to look for a small fuse box then check the fuses.

[Steve wilcox]

Update. In the bulkhead near the battery were 2 relays both with heavy green wires the same as the wire to the switch panel. The relays are fuse connected to the green wire. The back fuse was blown. It is marked 25 amp. That’s a lot of current to cause a fuse to fail. I have replaced the fuse and the fault is rectified. The old fuse plastic was melted. Could have been a poor connection. For now fixed. Watch this space. 

[Alanb]

On 08/07/2023 at 11:33, Steve wilcox said:

Update. In the bulkhead near the battery were 2 relays both with heavy green wires the same as the wire to the switch panel. The relays are fuse connected to the green wire. The back fuse was blown. It is marked 25 amp. That’s a lot of current to cause a fuse to fail. I have replaced the fuse and the fault is rectified. The old fuse plastic was melted. Could have been a poor connection. For now fixed. Watch this space. 

This sounds as though the relays could be split charge and fridge relays.  This would explain the fuse rating. If a 3 way fridge draws about 15A when travelling, then it does not leave much to charge a depleted habitation battery. The popular CBE 12V systems suggest a fuse rated at up to 50A in the connections to the habitation and starter batteries.  However while cable sizes need to be suitable, even 6.0 sq mm thinwall cable could carry this current. The rating the split charge relay would also need  to be considered before increasing the size of fuse.

Alan