Battery Isolator with Solar PV problem

[SimonSolar2C]

We just got ourselves a 1993 Toyota Hilux Galaxy Fibreglass motorhome with just 46,000km.  

The person that sold it to us installed a 190watt solar panel with a Steca MPPT charge controller which they connected to the new 80AH leisure battery.

I added another 100AHDeep Cycle battery in parallel.

Here's the problem - I'm running a little Electrolux 3 way fridge on the 12v system. (The AC and gas don't work)  It draws about 7amps.  So the solar panel won't be enough to run the fridge and lights 24/7. Therefore I need to run the engine as well to charge up the battery.

For some reason, the battery doesn't seem to charge much off the alternator.  My theory is that the solar panel lifts the battery voltage about 1 volt even at its comparatively low current, and the alternator sees that as a fully charged battery and doesn't send it any power.  Or at least doesn't top the battery up.  

The result is the fridge only runs for about two hours after sundown, until the MPPT regulator disconnects it (at 10.5v?).

Assuming it's all hooked up correctly, is there a solution to this problem?  Or maybe there is an isolator with two inputs, one for solar and one for alternator? Or do I need to disconnect the solar panel when running the engine?

Picture of the existing isolator and a little thing between it and the leisure battery.  Maybe that's a self resetting fuse.

[WME]

Clean all connections, measure voltage at each accessible point. You should have 14v minimum at the alternator when its running. Make sure there isn't a large loss somewhere.

[zero]

14 hours ago, SimonSolar2C said:

 

For some reason, the battery doesn't seem to charge much off the alternator.  My theory is that the solar panel lifts the battery voltage about 1 volt even at its comparatively low current, and the alternator sees that as a fully charged battery and doesn't send it any power.  Or at least doesn't top the battery up.  

 

That doesn't make sense; at least not to me. But who knows? A solar panel would only be able to lift battery voltage by a full volt IF it was fully charged.   Alternator should have an output of around 14.2 volts and there is loss in any of those rectifier-based isolators.  Each output on that isolator should be getting up around 13.5 volts.  Having a solar panel attached to the "house" battery should have little to no effect on the alternator charge.
Easy enough to check. Just read voltage at the "house" battery or batteries when the alternator is not running.  If it is lower then 13.5 volts, then the solar panel is not the problem. If it reads higher - ??  I suggest you just get rid of the crappy rectifier-box and install an isolation relay instead.  That will solve any question of batteries not getting charged and there will be NO voltage drop.

Note that your "rectifier box" only has three terminals and I don't think a three-post model can ever be made to work right on a Toyota with an internal voltage regulator.  If you MUST use a rectifier-box, you need one with the extra 4th terminal that gets hooked to the alternator's voltage sensing circuit.

 

[payaso del mar]

you should have an array disconnect switch anyway for safety.  not too hard to add one....for the amps you're seeing, a simple Cole-Hersee SPST switch will do the job altho it's not code approved.