Question about grounding

[thomasluce]

Hi everyone,

I think I already know the answer to this question, but I wanted to ask people with more experience than myself before setting my truck on fire. The wife and I are building an RV out of an old surplus military vehicle (an M934.) I'm installing a solar setup to run the non-propane appliances and lights, basically. The truck's already installed electrical system is a 24 volt system (28 nominal), but the solar setup is a 12 volt system; so I'm running a separate bank of batteries for the solar that never the twain shall meet (ie, the solar panels will never charge the truck batteries, and the truck batteries will never run systems hooked to the solar). So far so good.

My question is: Even with the voltage difference, I should still be able to run standard chasis ground where needed for everything, right? I know in DC circuits in general having a common ground for differing voltage sources is okay, and I know that, technically, a 12v system doesn't need grounding anyway - I just want to get my assumptions checked before I do something that I don't live long enough to regret. Any input from folks is much appreciated.

Cheers,
-Thomas

[bcroe]

All the 12V systems I've seen use the vehicle metalwork for return, so it is very important. RVs like to have 2 batteries, a stationary
use for appliances, a starting battery, and also an electrical isolator that allows the engine alternator to charge both. The grounding
properly done should be no problem, but I'd want to be able to charge both batteries with the engine. You might consider changing
both to the same voltage; another solution is add a common 12V alternator for that battery. Bruce Roe

[thomasluce]

I can't really change to the same voltage now; I have the equipment that I had available to me. Putting in a 12v alternator isn't a bad idea, but doesn't really address my question, so let me rephrase: given what I described, is there any danger to equipment or humans having a common ground for both systems?

[bcroe]

The grounding properly done should be no problem.
Bruce Roe

[Mike90250]

With a 24V vehicle power system, you could be way ahead of the game, if you make the choice to have the solar gear 24V. It could charge from the vehicle if needed, and it's much safer and reliable. You should ground the - to the chassis, but you may also want to install - return lines and avoid running high current through the chassis. High end boat and RV shops would have 24v gear, or you just wire up a sinewave inverter and have nice AC power throughout.

[Sunking]

Don't be silly, make it a 24 volt system unless you have some reason to have 12 volts. Get a 24 volt battery isolator so you can charge the house battery while the engine is running. You do that before you even consider any solar. If you drive at least every other day, you have no need for solar. The engine alternator generates more owner in 1 hour than your panels can generate in a week.

You have been confused because you do not know the difference between a Ground Systems, and Ground. Autos. Trucks, and Rv's quit using vehicle frames and chassis as Battery Return Conductors with one exception the Starter Motor. It raises hell with Electronic Ignition Systems and Electronic Gizmo's. Everything gets a Return Conductor just like the Positive Hot Conductor.

What you are asking is how are you going to apply Fault Protection for the wiring. You can either Ground the System by by bonding the Battery Negative Term Post with a Short Heavy Bonding Jumper to the frame of the vehicle. That allows you to use only 1 single fuse on each circuit.

The other method which I do not recommend for you and is almost impossible to do because equipment manufactures bond Chassis to Bat Rtn inside their boxes. Floa the system which mean syou have to use a Fuse on Both Positive and Negative.

But under no circumstances do you use the vehicle Chassis or Frame as a battery return conductor. You want something like this.