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Split combiner box feeding 2 SmartSolar mppt controllers off a common negative bus bar?

Hi, I am wondering if it is ok to use a Midnite Solar 6 breaker combiner box with the positive bus bar split in two and use it to feed two Victron SmartSolar mppt charge controllers using the common negative busbar? Each controller would receive their own positive and negative cables, only the negative busbar would be shared.

The arrays would be different sizes feeding into a Victron 150/100 and a Victron 150/70 feeding into a single battery. Midnite Solar states most charge controllers can work in this configuration with a few named exceptions (Victron not being one of them). There is a diagram similar to this setup on page 5 of this document:

I just want to make sure before I make a potentially expensive mistake! Thanks in advance for any help.

MPPT Controllerswiring
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wkirby answered ·

I would advise against this option. I'd prefer to split the negative PV busbar also, or install a second negative busbar in the combiner box.

Both the PV negative and Battery negative are common on the Victron MPPTs (and also the Midnite MPPTs). So on the surface, a common PV negative doesn't seem like a problem.
However, the battery negatives also go to another negative busbar. If you have the negatives common in two different places, you end up with a loop, which is not good.

It's better to keep the PV DC circuits separated from one another. The PV negatives will ultimately be commoned via the MPPT to the battery negative busbar which is fine as this is a single common point and there would be no loop.

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Makes sense, thank you