Mini DC and common negative and grounds

[ClassicCrazy]

A couple years ago I updated a friends PV system - replaced the Outback Controller with Classic and mounted it on a Midnite Mini DC disconnect box. I used a Midnite PV6 combiner box as DC breaker box - split with half 12v and half 24v .

I am now adding some more panels to their system and will use the Outback Controller since the Classic is maxed out.  I am going to use PV12 combiner because I needed more breaker room for the Outback PV in and Battery breakers. 

My question is , do all the negatives from Classic system have to be isolated from the Outback controller ?  What about the grounds - can they all be combined ?  The system is not negative or positive grounded. 

I am also wondering about wiring the negative battery charging from Outback controller to the shunt with Whizbang . Not sure if that would mess up ending amps that the Classic uses - I guess I would have to set the setpoints on Outback so it goes to float before the Classic does - haven't thought this part out very well yet but maybe someone else has ?

Thanks,
Larry

[dgd]

The neg from the OB should go to the shunt high side, where Classic and other Negs connect to.
That way the Classic will see the total battery current and adjust its output appropriately.
The OB may stay in bulkmppt even when the Classic gets to Absorb and float, but as you suggest you could make the set points slightly lower on the OB
All earths should be connected together.

Dgd

[ClassicCrazy]

Thanks dgd.

Larry