Dual battery connection query

[AndyPK]

Following our trip to Warwick, and being jump-started by the site wardens(!!) due to a flat starter battery, the dual battery solar controller no longer ‘sees’ battery 2.

The vehicle battery appears to be ok, but I suspect that both vehicle and hab. batteries are near the end of their life so will need replacing…… With regard to the ‘missing’ battery 2, it’s possibly just a fuse I guess, but following the wiring is not easy without some furniture deconstruction
However, looking at the connections under the solar controller, I do not understand why the black -ve wire on battery 2 is connected to the same terminal as the -ve on battery 1 (see photo)

Am I just being thick, or is there another explanation……??

 

[pappajohn]

Are you sure it is or is it tucked down the back.
If it is and both batteries share a common chassis earth then it will work but be better using is own wire back to the battery.

 

[AndyPK]

No, it’s definitely going to the terminal - all the other wires go through the opening just below the controller…… I wondered if the second battery had been added later but, if that were the case, how has the +ve red been run to it, and why not the -ve black……?

 

[autorouter]

In a vehicle, all the negatives are connected together anyway. The alternator negative terminal is connected to the alternator body, and so to the engine block, then through an earth strap to the chassis metalwork. The starter battery negative is connected to the chassis, so that the alternator can charge it. If you want the leisure battery to be charged from the alternator, either using a s[lit charge relay or a B2B charger, the leisure battery negative has to be connected to the chassis too.

So if the two negatives at the solar controller are connected together, and/or to the chassis, that's no problem at all. Why run a wire all the way back to the starter battery terminal when there is a big solid metal path already connected to it.

In metal vehicles there's hardly any negative return wires. However motorhome bodywork can be coach-built, and it's harder to find solid continuous metal pathways. So negative return wires are often required, especially higher up away from the chassis.

 

[StillGoing]

Following our trip to Warwick, and being jump-started by the site wardens(!!) due to a flat starter battery, the dual battery solar controller no longer ‘sees’ battery 2. The vehicle battery appears to be ok, but I suspect that both vehicle and hab. batteries are near the end of their life so will need replacing…… With regard to the ‘missing’ battery 2, it’s possibly just a fuse I guess, but following the wiring is not easy without some furniture deconstruction

The fuses are probably on the battery terminals so you shouldn’t have to deconstruct anything.

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[StillGoing]

Have you measured the voltage across the solar controller terminals when it’s dark and when it’s daylight?

When it’s dark, there will be no solar! The voltage reading across terminals 1 should be the leisure battery voltage. The voltage across terminals 2 should be the starter battery voltage. If you don’t get a voltage reading on either, you’ll know there isn’t a connection between the solar controller and the relevant battery.

When the sun is shining, and the batteries are not full, the voltage readings will be higher than the night readings if the controller is working properly.

If you don’t have a multimeter, please get one. It is not expensive and is an invaluable diagnostic tool that will easily pay for itself.