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Argh! My car has a split charge relay because my caravan doesn't. Problem is I can't adjust the screw to get it to stay on when the car is running and stay off when it's not.
What the Jeff? Already replaced it, no joy.
Right, I think I figured it out. I think the car's been wired up badly.
The relay is voltage sensitive. So when the alternator voltage goes up above the threshold it comes on. But the voltage it's testing is the supply voltage for the fridge (and the charger, but more on that later). So when the fridge draws power, the voltage drops below the threshold and it goes off again. The relay only has one input terminal which is both power and sensing, so I'm not sure how that's meant to work.
The power to both the fridge and the battery charging circuit comes from the input wire to the relay. And this is some nice thick wire that is connected via one of those press click connector things to some rather thin wire that then comes all the way from the front of the car where he's spliced it into the fuse box. This seems rather crap to me. Surely the resistance of that long run is what's causing the voltage to drop so much when the fridge comes on?
The battery charging circuit is another matter. The battery is mostly charged but not fully - and it's drawing more than 30A! That doesn't make sense, does it?