I don't want to assume but I would think engine battery and coach battery

negative (ground) is electrically the same right? I haven't verified, doesn't make sense if one was isolated from the other from the chassis.  The pain of having zero electrical diagrams

Yep, you assume correctly.

Yup, a ground is a ground is a ground.

What are your electrical issues?

True, but on my coach (no diagram, traced the cables) the engine battery is grounded to the engine block.  The coach battery and the rest of the 12v system is grounded to a stud on the frame near the battery bay, even though both sets of batteries are nearly side by side.

Bobtop46 said:

True, but on my coach (no diagram, traced the cables) the engine battery is grounded to the engine block.  The coach battery and the rest of the 12v system is grounded to a stud on the frame near the battery bay, even though both sets of batteries are nearly side by side.

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The coach battery was grounded by the company that built the chassis. The house battery ws grounded by the company that built the coach. Two different companies who are not in communication with each other. But they both go to the same place so all is good.

If you look around the engine compartment, you'll find bonding straps connecting the engine block to the frame, thus making the whole thing one giant bus bar.

I'm leaving nothing to chance as I'm doing an addition of a solar panel dedicated to charging the coach and engine battery banks while the RV sits in storage. I got all the parts coming in next few days and will start laying some of the wiring in.  The main problem was selecting a place to mount the solar panel that I can access for quick setup but not so easy for a "sticky fingered" person to get to.  Found a pole mount for solar panel that I can attach to one of my telescopic antenna mast and raise it up and point south easily.  Still need a way for a quick connect of the panel to the mount that makes it easy for me.  Will have better idea after all the parts are here.  My biggest hurdle is time as weather is closing in and I have to soon winterize the beast and get it out of my driveway.

thanks for the replies.  I rather be safe than a fireman

You need to worry about the positive sides of both batteries interacting with each other.  You'll either need a charge controller with two isolated outputs, or an isolator after the controller to provide two outputs.  You don't want to connect both sets of batteries to a common point.

If you tie the positive sides of both batteries together, you create a bridge between them and they'll both discharge when the solar panel isn't charging them.

More to the point, unless you put a fuse appropriate to the wire size at both batteries, you risk a short circuit or a heavy draw like an inverter or the starter motor overloading the interconnecting wires and creating a very real risk of a fire.

Lou Schneider said:

You need to worry about the positive sides of both batteries interacting with each other.  You'll either need a charge controller with two isolated outputs, or an isolator after the controller to provide two outputs.  You don't want to connect both sets of batteries to a common point.

If you tie the positive sides of both batteries together, you create a bridge between them and they'll both discharge when the solar panel isn't charging them.

More to the point, unless you put a fuse appropriate to the wire size at both batteries, you risk a short circuit or a heavy draw like an inverter or the starter motor overloading the interconnecting wires and creating a very real risk of a fire.

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Yup  )

If it were me, I'd buy two units from Harbor Freight, and be done with it.  Certainly would be good to disconnect the batteries and have the chargers simply keep the batteries charged, not to worry about parasitic loads.

On most all american made vehicles yes. NEgative is connected direct to chassis ground.

NOW.. Not all vehicles are AMERICAN MADE.. Sherlock Holmes (The fictional British Detective) and I both drove the same make and model for a while.. IT Was NOT Negative ground (English Ford)  But for US built it's been negative ground as long as I can recall.

(Fun with that car. I eventually "Flipped" the electrical system)

Lou Schneider said:

You need to worry about the positive sides of both batteries interacting with each other.  You'll either need a charge controller with two isolated outputs, or an isolator after the controller to provide two outputs.  You don't want to connect both sets of batteries to a common point.

If you tie the positive sides of both batteries together, you create a bridge between them and they'll both discharge when the solar panel isn't charging them.

More to the point, unless you put a fuse appropriate to the wire size at both batteries, you risk a short circuit or a heavy draw like an inverter or the starter motor overloading the interconnecting wires and creating a very real risk of a fire.

Click to expand...

I bought a solar charge controller made for dual battery systems.  Everything is wired up and functioning great.  My 25 watt panel is doing the job well.  It was a pain in running all the cabling as expected. But now, I can store the beast for a couple months at a time and not have dead batteries,

Negative grounding in vehicle has been an industry standard since about 1950, about the time they switched from 6v to 12v.  The Society of Automotive Engineers (SAE) standardized on negative ground around that time.  However, American brands such as Packard, Nash & Studebaker retained positive grounds until the mid-50's, and some English cars used positive grounds up to the 70's.  European cars built for export to the US often had negative grounds, while the same models built for domestic use were positive ground.  Negative ground is pretty much universal nowadays.

Many older farm tractors, generators and such used positive grounds.

John From Detroit said:

On most all american made vehicles yes. NEgative is connected direct to chassis ground.

NOW.. Not all vehicles are AMERICAN MADE.. Sherlock Holmes (The fictional British Detective) and I both drove the same make and model for a while.. IT Was NOT Negative ground (English Ford)  But for US built it's been negative ground as long as I can recall.

(Fun with that car. I eventually "Flipped" the electrical system)

Click to expand...

Many American cars built before 1955 were Positive Ground.