MPPT Solar Controller Load Out to Starter Battery

I've ordered the MPPT Solar Controller which a few have recommended on this forum - https://www.ebay.co.uk/itm/130616352324

I currently have a very cheap looking device which seems to step down the 20v to 12v (or thereabouts) to charge the leisure batteries. I'm sure there's some other tech in there to monitor the battery etc.

Since the new controller I've bought has a "load" output which I assume is enabled when the leisure batteries are fully charged, could I:

• Run the MPPT "load" output to the cheap controller
  
• Run the output of the cheap controller to the starter battery so it charges from the solar panels
  

Thanks....

I have ONE OF THESE it keeps the battery in top condition.

Jason, your "custom set up" doesn't sound right to me. Would it not be more logical for the Split Charge Relay to be energised by the voltage output from your Alternator when the engine is running and therefore supplying the charging current through it's, now closed, contacts? The relay, in this configuration, would de-energise when the engine is switched off and charging of the batteries would cease at the same time. I don't think that normal battery voltage is sufficient to keep the Split Charge Relay energised.
I stand to be corrected, but I think that most of these MPPT controllers will charge the vehicle battery only after the leisure battery has reached it's optimum charge level.

That’s pretty much what I have if we ignore the solar side of it for the moment. With the engine switched off, the starter battery voltage is below the voltage of the split charge relay ‘on’ threshold and the relay is open. Engine then switched on, the alternator pushes the voltage up to about 14.4V, now the relay is closed. The engine is then switched off, the starter battery voltage present at relay will eventually drop below the ‘off’ threshold and the two batteries are isolated. It takes a few seconds after the engine is switched off before you hear the relay click.

But with the solar panel and controller in circuit, if I then turn off the engine, the solar controller could well be keeping the starter and leisure battery voltage above the relay threshold and the relay will never open until either the sun goes down, or I remember to open the relay. I can open the relay either by flipping the PV isolator switch, or just turning on the fridge 12 V power. As the fridge will draw about 10 amps, if the engine is not running this will be enough to pull the battery voltage below the relay threshold in a matter of seconds.

It’s not a big issue. Often the fridge will be on 12 V power anyway when on the go so when I stop the engine the relay will open. And even if I forget about it, the worst case scenario is my solar panel is charging the two batteries until the sun goes down. Once the sun comes up the solar controller would not be capable of closing the relay. Only the alternator can do this. To avoid all this, ideally I would take an ignition on signal to power a relay and do away with the VSR, but I haven’t been bothered.

So is this wired between your Maximum Solar MPPT controller and the leisure batteries?