Wiring Query

[jonbowen]

Just curiosity really - my starter battery has 2 leads attached to the +ive terminal, plus an extra one that feeds the camping interior. There's 1 big thick lead which I presume feeds the engine compartment, starter, instruments etc ... and then there's a thinner red lead ... anyone know what it's for?
Best wishes, Jon

[pocolow]

The big thick one feeds the starter motor, the the thinner one feeds the rest of the vehicle electrics and the last one as you said goes to the leisure battery.

[jonbowen]

Thanks - I guess this was more than curiosity really: I have a leisure battery which charges from a "Smart Relay" (which also drives the fridge). I think the idea is that when the engine's running the relay flips on, and when it stops running the relay flips off again. However, if the leisure battery gets really low, next time I run the van (if it's just a short distance), the starter battery discharges, presumably into the leisure battery, so *next* time I try to start ... flat battery. Putting a 90A alternator in doesn't seem to have helped very much.
If I could wire an "alternator -> 2 battery" power diode in the circuit (it looks like you can get marine ones that would do the job), this would prevent the problem, but it looks like the alternator "Out" merges with the rest of the electrics somewhere in the engine compartment. To get this to work, I guess I'd have to run a spur off the alternator all the way to the relay (under the driver's seat with battery), which looks like quite a daunting task of running a long length of armoured cable through a couple of bulkheads and over the top of the fuel tank.
Has anybody actually done this, and is there another solution to the problem?
My temporary solution is to mount an isolator switch between relay and leisure battery, which I only turn on when I'm going on a long journey. Works OK, but depends on me remembering what I'm doing ...
Best wishes, and looking forward to ingenious suggestions ... !
Jon

[VWCamperfan]

The main alternator output runs down to the startor motor and then supplies power to the battery through the starting lead.
The charging indicator lead runs from the alternator to the dashboard connector (Blue cable). This can be used to switch a split charging relay.

[bigherb]

Split diodes work well. Sterling Power do some low voltage loss ones but they are a pain to wire up on T3's due to running heavy cable from the front to the rear. Your problem should'nt be happening if your split charge relay and alternator are working correctly. I think you need to check through your system first.