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Negative Earth Electrics.


Fullwelly

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Nick Fisher and Peter Rosenthal, Summer 2021 Magazine, gave an interesting reply to the question of rusting and wasting of metals. On boats in seawater this is a problem because the whole electric setup and seawater make a situation where metals waste away if it were not for the fitting of Sacrificial Anodes.

Is it beneficial to fit Sacrificial Anodes to all motor vehicles ?

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Fullwelly - 2021-07-17 7:15 PM

 

...Is it beneficial to fit Sacrificial Anodes to all motor vehicles ?

There is online discussion about this.

 

https://tinyurl.com/3442db78

 

20 years or so ago I remember visiting a leisure-vehicle show at Malvern where one of the ‘underseal treatment’ exhibitors was also advertising (not cheaply!) the fitment of sacrificial anodes to motorhomes using marine practice as the argument for doing so. Suitably sceptical I asked what proof there was that this would be worthwhile and whether any visitor to the show had opted for anodes. He laughed and said “I just sell ‘em, but I’ve no idea if they actually work. Nobody so far has bought them”.

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I think the answer is no. A boat is part immersed in water and, in that state, electric currents will flow between the various metals used in its construction. In effect, the submerged parts become a battery, with the water as the electrolyte, and the anodic metals being dissolved to the benefit of the cathodic metals (galvanic corrosion).

 

The big difference between a boat and a motorhome is that, although dissimilar metals are used, frequently carelessly, in constructing motorhomes, the motorhome is not sitting permanently in an electrolyte. It is also insulated from its surroundings by its tyres.

 

Nearly all motor vehicles are prone to some degree of galvanic corrosion, which is why most modern bodyshells are, at least for their lower parts, galvanised prior to painting.

 

Rather than trying to attach sacrificial anodes (which would require good knowledge of the electrochemical properties of the metals used in construction to select the correct metal anode) just be careful when attaching anything to your van externally that you select a metal for making the attachment that is the same as the substrate, or close to it on the electrochemical series.

 

There is a useful guide here: https://www.zygology.com/cms/upload_area/pdf/Zyg-Anodic-Index.pdf

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