Engine generator wiring

[booster]

We have been having lots of discussions about engine generators, big alternators, etc. Wire sizing, calculators, fusing, switching, ammeters have all come up.

What I haven't heard anything about, or checked myself (didn't even think about it) was if anything needs to be done about the return path the engine generator or big alternator. Obviously, the chassis is part of it probably of little issue (we have discussed that), but the linking from the chassis to the engine to the alternator would still be the stock setup. The older systems I am more familiar with used a battery cable or braided strap to connect the chassis to the engine block, and the alternator negative connected through the mounting bolts to the block. With up to maybe 5X the current, I could see the setup to possibly be undersized, and maybe overloading some of the other ground paths.

Anybody ever seen what the pros do when the put in big charging systems? Ambulances and such must have similar setups.

Perhaps this could be contributing to the cases where there haven't been huge increases in charging speed in some installs.

[booster]

I just dug out the factory service manual for our 07 Chevy Roadtrek 190.

It appears they have #32 metric rated cable from the frame to the engine block, that also goes to the battery on a #19 and to the right inside fenderwell with another #19. The #32 converts to about a #2 and the #19 to between #4 and #5.

These are a bit small for some systems, like those running in the mid 200s for amps. Very close on a 200amp system. Ok at 150, which makes sense as that was the biggest factory alternator.

Of bigger concern to us is that on the Chevy, the body is mounted on rubber mounts, which would probably explain the #19 from the battery to the inner fender. It grounds the body loads.

In our case, on our current setup, the inverter is grounded to the upstream side of the shunt in the negative battery cable. That spot is also tied to the body at a big rear seatbelt bolt location that wasn't being used. I have to assume out ground connection back to the alternator may be running through the #19 fender connection, which would not be good at all.

I couldn't find any other binders between the body and frame on the diagrams. I will have to look at the van and see if I see any. If not, I may add a temporary strap to get by until we do the upgrade when I can fix it properly.

This could easily be a problem in any of the retrofits where they put the batteries in the rear of the van, inside, as the most convenient place to ground is the body.

[markopolo]

Good topic. I'll try to find out what the setup is on my van.

[markopolo]

On mine, (schematics) it looks like:
#50 frame to the engine block
#50 frame to main battery
#50 frame to 2nd battery
#8 main battery to body

#8 main battery to body might need to be upgraded on mine if I can't find a better body to frame connection.

I really need to check the #50 frame to 2nd battery because the 2nd battery was moved inside by the previous owner and grounded to the body where the seat bolts to the floor.

House batteries ground to body in my van at another seat bolt to floor.

Hopefully I'll find that the original #50 frame to 2nd battery was reused as frame to body. It would have been right there available to use and the guy knew his stuff.

Thanks for starting this topic. It's good to check this stuff out.

[booster]

I got a chance to go out and get a good look at the van, and it appears to be wired as the service manual said.

The #19 wire from the body goes to the negative battery cable, which is very close to the tie point on the fender. The negative battery cable goes down to the engine block just above the oil pan. That connection also has a woven wire on it that goes to the frame.

So it certainly looks like whatever we ran on the alternator that was grounded to the body would go through the small #19 wire. Between the inverter and battery charging, that could be upwards of 200 amps. Ouch!

Here is the #19 on the fenderwell

IMG_2890.jpg

The block connection

IMG_2891.jpg

IMG_2892.jpg

The frame connection

IMG_2893.jpg

Out of pix-see next post

[booster]

There was another weld nutted hole right next to the existing fenderwell connection, so I made a #2 cable and put it from that hole to the block connection, leaving everything else in place.

The fenderwell

IMG_2894.jpg

The block connection

IMG_2895.jpg

IMG_2896.jpg

This should cover us for now, glad I found it before our next outing, that will probably have more off grid than ever.

When I do the upgrade, I think I will take everything to the main frame, for the coach battery side. I will also put in a much larger woven ground link from the frame to the block. I think the body to frame connection will be as a multiple tie point where the new woven cable will connect to the frame.

Another thing folks may want to be aware of, beyond the alternator being an issue. The original Roadtrek batteries were grounded to the main frame, so anything that was running in the coach, and was grounded to the coach like most stuff is, would be running through the small #19 wire both when on alternator or batteries. Battery charging would be OK. If someone added an inverter and grounded it to the body, all the current would be on the small wire.

[markopolo]

I checked it today and mine is as spec'd in the schematics with the exception of the removal of the 50 mm2 frame to 2nd battery wire and the addition of the 2nd battery to body ground wire. (two engine batteries in my van, 1st under the hood, 2nd behind drivers seat)

50 mm2 is a bit bigger than 1 AWG
8 mm2 is equal to 8 AWG

There are 6 pieces of steel angle iron used to support the waste tanks and running boards. Those 6 pieces happen to also connect the body to the frame. There are 4 bolts in each piece of steel.

I probably don't have to do anything because of those 6 added frame to body connections but it would be very easy to use my clamp on ammeter to check the current flow on the 8 AWG piece of wire when running the microwave oven with the engine running to confirm it is not overloaded.

[booster]

Originally Posted by markopolo

I checked it today and mine is as spec'd in the schematics with the exception of the removal of the 50 mm2 frame to 2nd battery wire and the addition of the 2nd battery to body ground wire. (two engine batteries in my van, 1st under the hood, 2nd behind drivers seat)

50 mm2 is a bit bigger than 1 AWG
8 mm2 is equal to 8 AWG

There are 6 pieces of steel angle iron used to support the waste tanks and running boards. Those 6 pieces happen to also connect the body to the frame. There are 4 bolts in each piece of steel.

I probably don't have to do anything because of those 6 added frame to body connections but it would be very easy to use my clamp on ammeter to check the current flow on the 8 AWG piece of wire when running the microwave oven with the engine running to confirm it is not overloaded.

It does sound like you are probably OK. I looked all around underneath for likes, but didn't dig up under running boards and side pods. I think the battery boxes may touch both also, and both are in the side skirts.

Good point on the ammeter, I should do that also. If I have small amounts if both wires, I will know there is some other connection someplace.

I do have t say, it doesn't sound like a good idea to tie a rubber mounted body to the frame with rigid bars, though. I would think it would be noisy and flexing.

[markopolo]

I wondered about that too. How are the tanks supported on your Chevy?

Looks like you have frame to body connections here: http://www.classbforum.com/forums/showthread.php?t=1900

[booster]

Originally Posted by markopolo

I wondered about that too. How are the tanks supported on your Chevy?

Looks like you have frame to body connections here: http://www.classbforum.com/forums/showthread.php?t=1900

That was the battery box area I was thinking about. The original wasn't tied to the frame, but now is for the extra weight. Didn't even think about it at the time.

The tanks sit on formed channels, with most areas hung from threaded rods. I will have to look at what the threaded rods connect to. Very possible they could also hit both body and frame because they sit between the frame rails and rockers, although a lot of the body is cut out there for the sidepods and running boards.

We do get a lot of noise from things in the side pods moving on big bumps, always wondered about that. It may be they are directly connected to the outside shell of the van, kind of like a drum.

[booster]

I just went out and crawled under (not on the stands anymore) and got a quick look.

Obviously, the battery box I made connects body to frame.

The side pods and running boards are primarily hung on the body, but they share the tank mount channel supports, which go under the tank and extend out to the pods and running boards. The farthest out of the channel hits on the running board/pod, between the running boards/pods and the the tanks is a thread rod through the channel up to the body, and the furthest inboard support for the tanks are threaded rods through the channels that are welded to the main frame.

So there are mechanical connections between the body and frame. And of course they are in a great spot to transmit lots of noise.

I do remember way back when cars were changing over from body on frame to unibody that there were lots of noise complaints, which is probably why the luxury stuff moved to unibody later. The isolated bodies were probably quieter, until they started mounting the entire front engine and suspension on rubber mounts in unibodies.

[markopolo]

I used the creeper for the first time to check all the wiring and got a bit of motion sickness rolling around under the van

I'm not kidding. Might have to slow down!