WBX Gearbox starter earth bypass cable

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itchyfeet
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WBX Gearbox starter earth bypass cable

Post by itchyfeet »

I remember this being suggested before but I don't remember any details given of the cable.

Reason being that Galvanic corrosion is accelerated with DC currents and the aluminium gearbox suffers, bypassing the starter earth path away from the gearbox helps to reduce the corrosion.

It looks to me that the easiest bypass cable would be from the lower starter bolt ( as the upper one won't come out without removing starter) along the top of the gearbox ( cable tie to pipe retainer) to the existing earth point.

Existing earth braided cable then needs removing or this is pointless, also good to add nylon washers between mount and box both sides to increase insulation, then use nyloc nuts as nylon washers won't hold a torque.

You could drill a hole but I'm interested in a solution anybody could and will do.

So this needs a 1metre cable with an M10 ring one end and an M8 ring the other, you could use an M10-M10 and fit a large washer but not ideal.

You can get these made but I'm wondering on spec of cable, is 16mm2 enough? should it be braided with no PVC to help prevent corrosion?

Any pointers from those that have done it?

thanks

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Last edited by itchyfeet on 09 Mar 2015, 21:21, edited 1 time in total.
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Re: WBX Gearbox starter earth bypass cable

Post by CovKid »

16mm should be enough although you could double them up if you wanted to. You're correct on the location. You could ground from alternator too.
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Re: WBX Gearbox starter earth bypass cable

Post by itchyfeet »

I hadn't thought about alternator :shock:

Never occured to me that some of the voltdrop we are all chasing could be happening at the alternator mounting bolts

when did you ever hear somebody saying, 'make sure you clean up your alternator mounting bolts'

It's not going to fix low cranking voltage but may help push up charging and headlight voltage.


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Re: WBX Gearbox starter earth bypass cable

Post by CovKid »

Was just thinking it might be easier to run one from there to side of engine bay rather than have to crawl underneath. Don't have one myself but if I were to fit one, pretty sure thats where I'd stick it.

As you know, I've beefed up everything now - main cables, heavier guage to dash etc so probably pay me to fit one now.
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Re: WBX Gearbox starter earth bypass cable

Post by itchyfeet »

Problem I see is corrosion of the aluminium but also corrosion of the contacts leading to volt drop, if you just link from the alt to body the starter current has to pass from gearbox through engine and those surfaces and bolts will be or get dirty and corroded.
I'm thinking two is best, one from alt to body and one starter to body ( or daisy chain alt to starter like pos leads) so each high current device has a cable link to the chassis which is easy to clean up periodically.

Need to scan the engine bay for a suitable point, but I'm still leaning to existing earth under as its on the chassis, I think a 0.5m m10 -m8 would connect starter to alt
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Re: WBX Gearbox starter earth bypass cable

Post by CovKid »

Makes perfect sense to me to have the two. Don't forget Toolstation if you need more connector eyes - cheapest I've found. Bought loads last time I went. Bit of a bind soldering them up but at least its done properly then.

Do the battery to dash cable beef-up if you haven't already. That was by far the biggest improvement I did on the electrics. Awesome power up front now:

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Re: WBX Gearbox starter earth bypass cable

Post by itchyfeet »

I'm not making my own because I can buy a custom made lead cheap enough and I'm short on time.

I'm thinking 25mm2 170A may be better for starter as the lead will be long, 16mm2 is only 110A, fine for alt but perhaps a bit thin for starter which can pull very high amps.

Almost never drive the van at night but I'm planning to upgrade lighting cables one day, just not a priority right now.
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Re: WBX Gearbox starter earth bypass cable

Post by irish.david »

Galvanic corrosion is only an issue when there are two dissimilar metals that are linked with an electrolyte. It's a big issue for ships with metal hulls as the sea water acts as an electrolyte and and you get electrons flowing from the metal higher up the galvanic series to the one lower down. The solution for ships is to fit sacrificial anodes which are designed to corrode and be replaceable at set intervals, or an impressed DC current system to counteract the flow of electrons that causes corrosion.

The good news for your gearbox, galvanic corrosion isn't an issue as there isn't an electrolyte between the aluminium gearbox and steel body to allow ion migration between the two. The only issues you might have are where there is physical contact where you get the standard reaction between dissimilar metals, but most of these points are fitted with vibration mounts which act as a galvanic barrier and the others (such as the earth cable connections) are easy to take apart and clean from time to time.

Long story short, the corrosion on your gearbox is nothing to do with your earth connections.

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Re: WBX Gearbox starter earth bypass cable

Post by ghost123uk »

If I were doing this, and I well might when the weather warms up, I would put the chassis end under one of the bolts holding the engine cross member to the chassis. As for the engine end, there must be lots of candidates only a short run from the aforementioned cross member bolt, but right now I'm not sure which I would use and it's cold a dark outside at the moment ;). Hang on, how about the bolt to the crankcase that the engine mount is secured with?
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Re: WBX Gearbox starter earth bypass cable

Post by itchyfeet »

irish.david wrote:Galvanic corrosion is only an issue when there are two dissimilar metals that are linked with an electrolyte. It's a big issue for ships with metal hulls as the sea water acts as an electrolyte and and you get electrons flowing from the metal higher up the galvanic series to the one lower down. The solution for ships is to fit sacrificial anodes which are designed to corrode and be replaceable at set intervals, or an impressed DC current system to counteract the flow of electrons that causes corrosion.

The good news for your gearbox, galvanic corrosion isn't an issue as there isn't an electrolyte between the aluminium gearbox and steel body to allow ion migration between the two. The only issues you might have are where there is physical contact where you get the standard reaction between dissimilar metals, but most of these points are fitted with vibration mounts which act as a galvanic barrier and the others (such as the earth cable connections) are easy to take apart and clean from time to time.

Long story short, the corrosion on your gearbox is nothing to do with your earth connections.

Dave

not sure I agree with you, you have a steel gearbox mount in direct contact with an aluminium gearbox, these metals are dissimilar and exposed to water and salt spray, the current flows here and the corrosion can be seen.
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Re: WBX Gearbox starter earth bypass cable

Post by ghost123uk »

It might not be galvanic corrosion, but you certainly get corrosion :twisted: I seem to remember our gearbox guru Aiden talking about this.
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Re: WBX Gearbox starter earth bypass cable

Post by itchyfeet »

ghost123uk wrote:If I were doing this, and I well might when the weather warms up, I would put the chassis end under one of the bolts holding the engine cross member to the chassis. As for the engine end, there must be lots of candidates only a short run from the aforementioned cross member bolt, but right now I'm not sure which I would use and it's cold a dark outside at the moment ;). Hang on, how about the bolt to the crankcase that the engine mount is secured with?

would not wan't the connection on the engine bar, wants to be directly to the body away from the wheel spray.
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Re: WBX Gearbox starter earth bypass cable

Post by itchyfeet »

ghost123uk wrote:It might not be galvanic corrosion, but you certainly get corrosion :twisted: I seem to remember our gearbox guru Aiden talking about this.


Ok lets call it bimetallic corrosion accelerated by dc currents and a salt solution, oh hang on thats an electrolyte isn't it?

what would help further is plastic washers between gearbox and mount once earth is bypassed.
Last edited by itchyfeet on 09 Mar 2015, 21:03, edited 1 time in total.
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Re: WBX Gearbox starter earth bypass cable

Post by irish.david »

Where the metals are physically joined you'll get very localised galvanic corrosion, but any corrosion elsewhere on the gearbox isn't due to that and the corrosion where the metals meet has nothing to do with your earth connections.

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Re: WBX Gearbox starter earth bypass cable

Post by ghost123uk »

Didn't say on the bar ;) Said on the bolt to the chassis rail that holds the bar. I see your point about it being open to the elements though, mind you, there would be easy to get to for routine cleaning and it's a very solid earthing point. A hole drilled into simple bodywork, with a bolt, wouldn't be as good an earth (imho and being a bit nit picky I suppose :roll: )
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