Improving Bodywork Earth

An alchemy of sparks, copper wire and earth

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Mark S
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Improving Bodywork Earth

Post by Mark S »

Ran a Ring Voltmeter connected to cigar lighter and watched the Voltage over a longish journey. Was disappointed to only get 13.5V (this did not vary much with revs). The Voltage also actually went UP for a time when I stopped the engine. Initial inference was that the alternator was shot.

However, I did the same test in the engine bay and all was fine. Getting well into the 14's off the alternator with the engine running. The alternator is connected directly to the battery (+) terminal through a short lead, with a nice meaty earthing strap going back to one of the alt bolts so the connection in that area is as perfect as it can be. NB: this is the only negative connection coming off my battery.

I therefore attribute the lower Voltage at the dash to resistance in the circuit over the length of the bus, and I tend to suspect the earth loop. This is because the return path is through the bodywork, then a strap to the gearbox, through the lump, and back to the battery through the final earth strap on the alt bolts. Any corrosion in this path could add resistance, and I am thinking in particular the body -> gearbox hop.

I thought there is no harm in running a secondary earth strap from some point on the bodywork directly back to the batt (-). I don't want to do any drilling or too much crawling under the bus to route wiring. Any ideas as to the best point(s) to take it from?
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Re: Improving Bodywork Earth

Post by MGP »

Connect your volt meter to the battery - ve terminal and a suitable place on the bodywork, the tail gate striker pin is usually a good spot, now switch on the lights, heater and wipers and observe you voltage reading, if it's less than approx 0.3 volts concentrate on the supply to the fuse box, you can do the same test between battery +ve and the fuse box to see what your losses are but make sure you use a fused lead for your meter.

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Re: Improving Bodywork Earth

Post by CovKid »

I covered this a while back: http://wiki.club8090.co.uk/index.php/VW ... ain_cables" onclick="window.open(this.href);return false;

The problem is mostly down to main cables which by now probably pass less than when new. Good earth sure, but you only need fraying cables at starter. battery or alternator and their capacity is diminished. This didn't matter so much with a cassette player and tungsten bulbs but it will now.

Hope it helps

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Re: Improving Bodywork Earth

Post by RogerT »

Hi Mark
I’m guessing you have a diesel, as you mentioned a short cable from the alternator to the battery. Next to the battery do you have the coolant tank, fixed to a piece of metal coming out from the side of the van? With a hole at the end? I’ve fixed a cable to the hole with a bolt as an additional earth to the battery.
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Re: Improving Bodywork Earth

Post by RogerT »

Badly drawn arrow. Too much stuff in my van for me to get a pic of my setup, but this is where I’ve connected it. I see here it should be for securing stuff as it passes by...
Image

By the way, I’ve followed Covkids advice and the results (to my headlights) was brilliant. No numbers tho so can’t provide empirical evidence.


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Re: Improving Bodywork Earth

Post by CovKid »

Typically just 10v at headlights on a stock system. I ran a voltmeter up front both before and after and saw a rise of at least 2 volts and this increased further once I'd done the dash feed upgrade. Its only then that you realise that fitting brighter bulbs isn't really needed and it barely scratches the surface.

The problem with even minor fraying and damage at connectors is that its accumulative. If it was the same strand broken or corroded throughout, that would be fine, but typically, several strands are affected along the length. What might look like a chunky cable may already be halved in cross section due to the many breaks at various points, as well as the limited capacity it had to start with.
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Mark S
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Re: Improving Bodywork Earth

Post by Mark S »

Thanks, all - useful stuff. Sorry not to reply sooner but distracted by family stuff.

I think I'll have a shot at improving the earth first with a few quick wins around the engine bay. After that, I'll decide whether it's worth looking at the +ve side of the wiring. I'm only losing about a Volt at the dash and everything works OK, so it's not a massive show-stopper.
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Re: Improving Bodywork Earth

Post by CERI »

Could I just jump onto this thread as I have read posts on here previously regarding running additional earth straps from the battery but I cannot now find them. Mine is an 82 air cooled CU. The rewound starter can be lazy from cold and I have already renewed the battery and the positive starter cable from the battery to the starter motor, so I was now thinking of:

1. Changing the braided gearbox earth strap to a more chunky black cable type. Cleaning up the mounting points as I go.
2. Running an additional seperate earth cable all the way from the battery under the driver's seat to one of the starter motor mounting nuts.
3. Running an additional earth cable from the Alternator mounting bolt to ????? any ideas where such a cable should run to?

Any advise on whether any of these will help a faster spin of the starter motor will be greatly apprecicated.



Cheers

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Re: Improving Bodywork Earth

Post by Mocki »

The whole thing about voltage drop is , you need big thick wires to minimise voltage drop under load , so the actual body of the van is the best earth cable you can have, it’s thick, it’s the right length and it’s already wherever you need it , so use it as much as possible, keeping actual earth straps and cables as thick and short as possible .

So running a neg cable down from battery to the starter is not going to do great things ......

Yes clean the gearbox nose earth points well, and fit a nice thick new braided earth strap , a braided earth strap is much better at carrying current because it’s braided multiple strands alll contacting between themselves , and it’s much better at withstanding the vibrations than a conventional stranded rigid cable .

Yes you can add extra earth straps , they certainly won’t do any harm, and will likely help your cause , ideally from the bolt that holds the starter motor to the bell housing to the nearest bit of body you can get to .
You should also clean up the mating face of the starter and bellhousing, since this is how the starter gets its negative connection in the first place .
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bigherb
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Re: Improving Bodywork Earth

Post by bigherb »

CERI wrote: Any advise on whether any of these will help a faster spin of the starter motor will be greatly apprecicated.
Cheers
I ran an earth from the alternator to a nut and bolt through the body.
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RogerT
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Re: Improving Bodywork Earth

Post by RogerT »

bigherb wrote: I ran an earth from the alternator to a nut and bolt through the body.
Image

Maybe a poor photo, herb, but all I see there is a rather weedy brown wire. Is that the earth you are referring to? My understanding is that the earth should be capable of carrying the same current as the supply cable. I see another connector disappearing up at 11oclock, but not the wire it's carrying,vbut even so it doesn't look hefty enough.

Apologies if I've misunderstood.
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Re: Improving Bodywork Earth

Post by R0B »

I think you should be looking at the thick black wire running downwards :)
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bigherb
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Re: Improving Bodywork Earth

Post by bigherb »

R0B wrote:I think you should be looking at the thick black wire running downwards :)
:ok
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RogerT
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Re: Improving Bodywork Earth

Post by RogerT »

Ohhh, right! Sorry. Just coming to realise that my current intake of diazepam and co-codamol 30s (for a back problem that rendered me immobile and in tears on Sunday) are affecting my cognitive abilities quite significantly. I think I should cut down slowly (and don’t worry, I’m not driving)
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