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Old 08-10-2016, 09:16 PM   #301
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I don't think I have an alternator issue actually.......although now I'm curious what other's charging amps to the house batteries are when driving and the batteries are at a low SOC.

On the house battery side of things....I've run both + and - wires everywhere...no chassis ground. However, between the alternator/van battery and house batteries I am using the frame for -ve.

Interestingly, I'm now working on designing and fabricating a custom rear hitch type motorcycle carrier, and I removed and reinstalled the trailer hitch today. In doing so, I had to loosen a factory ground wire to the frame by the spare.......now the van won't start.

I'll look at it tomorrow; I suspect that that ground is for the fuel pump.
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Old 08-11-2016, 08:44 PM   #302
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well, I tightened up the ground on the frame by the spare tire ....van fired up just fine....
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Old 08-11-2016, 10:45 PM   #303
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Simple fixes are the best!
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Old 08-11-2016, 10:54 PM   #304
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Quote:
Originally Posted by ShuttlePilot View Post
I have an opinion on chassis grounds. Chassis grounds are the dirtiest form of under sized wire. It's easy to have a ground strap not get put back after a repair or in many cases rely on a chassis ground to convey large amperage.
When I first got my SMB, chassis grounds were a completely new concept for me, coming from boating, where there is no "chassis" to use (everything just has a same-sized positive and negative wire back to busses).

And I get why they are maybe kind of a lazy way to do things and can be prone to problems, BUT, I have a question for you: If one has made sure that all the short negative wires that lead to the actual frame are equal in size to the positive wires, and if the connections are good (sturdy lug/bolt, not just some wimpy little tapping screws), then would the frame itself be equivalent to a pretty large wire?

Here is an example of what I mean. I put a new 1/0 positive wire in for the start battery to house battery connector wire. Then I also ran a 1/0 cable to the chassis with a beefy lug/bolt for the house battery chassis connection. Then I upgraded the ~10" negative wire that Ford had running from the start battery negative to the chassis. I couldn't fit 1/0, but did manage to fit in 2AWG. (I do have that smaller section accounted for in my fusing scheme.)

But anyway so my question is, would the chassis/frame that comprises the rest of the negative 1/0 run be at least the "gauge" of 1/0 wire? It seems like it would have a big cross section, but I have no idea how to calculate it. And that has always kind of bugged me since I like to run everything through a voltage drop calculator.

(For many things I have simply run an equal negative wire.)

Thanks for your thoughts on it.
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Old 08-12-2016, 09:14 AM   #305
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boywonder, sorry for being an accomplice in hijacking your thread. I can see 90 amps to the house battery when driving if the battery is low enough, and not 20 degrees. 90 amps is only for the first several minutes, will settle in the 60's, and taper as the battery come up to charge. 90 amps might be the upper limit of internal resistance in my battery. Just for reference, alternator is 200 amp, so not real big, battery is a single Chinese UPG 4D, so not fancy, metered with a Bogart Trimetric. I bet the folks with dual alternator Sprinters and Lithium batteries see crazy charge rates while driving.

Viva, Your probably fine with the configuration your describing. When things get ugly is, like in my van, SMB is relying on the sheet metal fender well as the main house ground. Or trying to pass through rubber engine mounts, rubber body mounts, rusted sheet metal body panels, etc. These obstacles are usually bridged over by a ground strap(which may or may not still be there) or the OEM part is designed to convey power through it. Lots of variables to deal with and like you mentioned hard to quantify. Though, 99% of the time no problem, just over looked.

Here is some reading if your interesed in resistance in different metals. Running the numbers is a great place to start but dont over engineer it. Testing shows what's really going on and sometimes shows things I was losing sleep over turn out to be no big deal. I like testing.
https://www.bluesea.com/resources/10...y_of_Materials

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Old 08-12-2016, 09:50 AM   #306
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Interesting! I've spent quite a bit of time on the Blue Sea site, but have never noticed that page (maybe because on a boat I'd just use copper). So as long as the steel frame is 20 times larger than a copper wire... (that's quite a difference in conductivity!).

You know, I thought last night after I posted that "Oh man, that was probably too far off BoyWonder's thread, gaaah, should have started a new one." BoyWonder, I'm sorry to have hijacked.

ShuttlePilot, thanks for the response.
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Old 08-12-2016, 01:25 PM   #307
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Not a hijack at all.....and thanks for the data shuttlepilot!

When I have a few minutes, I'll connect the negatives together using a jumper cable or equivalent...and run my battery down a bit first....
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Old 08-12-2016, 10:40 PM   #308
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Interesting......curious what the current draw of everything else is in the typical E350.....

OK...I can't help myself here....and I understand that current draw is a function of the load resistance......

I have a stock 125 amp alternator...and I'm seeing about 20-25 amps to the house batteries.....so perhaps everything else needs about 100 amps...so about 1200-1300W at 12-13V.....(I have a 2008...and my headlights are on all the time)

Shuttlepilot has a 200 amp alternator....so subtracting about 100 amps for everything else leaves about 100 amps for charging the house batteries....so 90 tapering down is the battery's resistance increases...sounds reasonable..

...just thinking out loud.....
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Old 09-01-2016, 01:20 PM   #309
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Great build thread Boywonder, I got lots of good information to help me with my 94 sportsmobile rebuild, thanks for all the documentation. So much to do, so little time. How is your penthouse modifications holding up, I want to add all the nylon washers and everything like you did, do you feel the inner sleeve is worth the extra $100? Have you ever heard of anyone having a failure or bending the crossbars?
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Old 09-01-2016, 01:39 PM   #310
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Have you ever heard of anyone having a failure or bending the crossbars?
Crossbar bending is fairly common.. Usually, but not always, due to operator error.
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