Solar grounding through chassis

[llamafilm]

Hello everyone. I'm planning to install a 100W solar panel on my rig, mostly to power a fridge. The charge controller will go inside the cabin and the battery is under the hood. I will pass 2 wires through the roof to the controller. Then just one positive wire through the firewall to the battery. The charge controller negative output will connect to the car chassis. This is how I wired other accessories including light bars and ham radio, but I've never done solar before so I'm wondering if there is any danger with this plan. Is there any reason to run a separate negative wire from the controller to the battery?

I have a fuse/relay box under the hood. From there I will run one positive wire back through the firewall for the fridge.

This is a Subaru XV hybrid which comes with dual batteries from the factory (engine start and aux). I'm replacing both with AGM type, and the solar will connect to the aux battery. I think I will use 10ga wire for these connections.
Any input is appreciated.

 

[Shakes355]

There are charge controllers designed for both positive and negative ground. Be sure to confirm that you have a negative ground unit, and you should be fine.

To my knowledge, there is no real advantage to running a dedicated line to the B- unless finding a good chassis connection is an issue.

Since you drive a hybrid, it is very important your connections are secure and made of adequate gauge wire. It is important in all cases but if your system isn't sound, any transient voltage could risk some of your vehicle systems.

If you are unsure about your grounding location, stay on the cautious side and find another. If that takes you to the battery, then so be it. And again, make certain to use larger gauge wire if you have to run it over reasonably long distances. Voltage drop along the ground path with decrease the efficiency of the system.

 

[llamafilm]

Thanks. I've ordered a Renogy Rover 20A with negative ground. The seat bolts into the floor have worked well for me in the past. I rough the area up with a wire brush before the ring connector.

 

[NorthWest Xploder]

Most mppt and pwm controllers wont work correctly or at all without both the positive and negative batteries going from solar and then to the battery. They need the battery pos and neg to know the battery condition for charging status and both lines of the solar which then get converted to the batteries voltage parameters.

 

[MOAK]

I just reworked my solar array. Two panels, 100 watt on roof and a briefcase fold out 120 watt. I run a #6 bus line to the rear of the vehicle where I have a four blade fuse block and it continues on to my 800 watt power inverter. I’m using a “ negative ground “ controller with the panels wired in parallel. All the appliances, (two fridges, water pump, inverter for charging camera batteries, cell phones, etc) are grounded on the chassis including the controller. The controller sends power through the system backwards to the optima house battery, and if I choose to, the odyssy vehicle battery (125ah combined) through a manual isolator switch. Using the # 6 positive bus line may seem like overkill, however when checking my system out I lose less than any measurable voltage or amperage, from the batteries or the charge controller. We just got back from a four nighter, in mostly shade with maybe 4 hours of direct sunlight and the voltage never dropped below 12.2 volts in 48 hours of not driving. Good luck !!