Secret Scotland

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Black Wire Syndrome returns on my battery terminal

Many years ago there was an odd phenomenon that raised a great deal of discussion and debate amongst RC (radio control) modellers. It may still do for all I know, but I have lost touch with the subject.

The problem was some sort of corrosion or similar that affected the negative wire of rechargeable battery packs. In some cases, the negative wire would turn black and corrode, in extreme cases, or if not noticed, this wire would even fall apart if left for long enough. It came to be known as Black Wire Syndrome, and notably did not affect just exposed wire, but if the insulation was removed from affected wiring would usually be found along the entire length.

I found it myself in some cases, yet could see nothing common in those that suffered from the effect, or different from those that did not.

I also saw it happen to the wiring inside a battery ‘revitaliser’ I built around the same time. This design was meant to extend the life of ordinary zinc-carbon cells, by extracting the last of their usefulness by applying a ‘dirty dc’ current to them (according to the designer). A steady dc current won’t recharge (for want of a better word) such a cell, but the claim was that rapidly varying dc current would excite the remaining chemicals and extract the maximum from them. It may sound dubious, but it did seem to work.

As regards relevance, after building and using this gadget, I found the negative lead inside the box exhibited this ‘Black Death’ and eventually fell apart.

This came to mind recently when I found that a rechargeable carper sweeper would refuse to charge or switch on reliably, and seemed to be underpowered. I’d rewired it to accept a plug-in charger as the original charger failed, so knew the battery pack and wiring were near new, and checked ok.

By chance, I glanced inside the compartment the battery pack slides into – and saw the problem, highlighted below:

Terminal corrosion

Terminal corrosion

As can be seen, the negative terminal is completely covered by non-conductive black surface corrosion, while the positive terminal remains as bright and shiny as the day it was made.

The black corrosion is deep-seated, penetrating well into the metal of the terminal.

It cannot be brushed off, not will it respond to the gentle abrasion of a fibreglass brush, or even a brass brush.

Steel brushing is needed, or the use of a file or abrasive/sand paper to remove the black material and reach clean metal.

The disadvantage being that this removes any protective plating on the contact, and accelerates the return of the problem.

Replacement of affected wiring, or terminals, is the only effective solution.


This quote from 2015 would appear to show that this phenomenon is as unexplained today as it has always been:

There is plenty of speculation, quite a bit of science and a lot of people pontificating on forums about black wire syndrome, black wire corrosion etc, and it has been a known issue for well over half a century,

The reference to ‘pontificating’ is intriguing since there was much pontificating by people where not engineers, or rather literate in any sort of engineering or science, and their ideas about the causes were more related to black magic and witchcraft than anything practical.

While I won’t go so far as to dismiss any of the (non-magical) theories behind the effect, I won’t accept any of them until I see one that includes an explanation which refers to ions (charged atoms or molecules), since the same gasses or similar that are said to cause it will reach all the wires in the enclosed spaces where the effect is found. Yet only the negative wires are ever affected, not the positive, or any adjacent metalwork.

That this article suggest the phenomenon remains unexplained today is… disappointing.

Black Wire Syndrome

This article manages to turn it into Red Wire Syndrome, but only an industrial application that used a -48 V DC system.

Black Wire Syndrome

And leads to this 2001 article (PDF) about the syndrome in RC planes, which claims to explain it – from a description itself dated 1996). It may, but depends on the presence of NiCads (probably faulty or failing), so is at best only a partial explanation.

Black Wire Disease – What’s the Cause?

The pdf article can’t be quoted, so for those interested, this graphic can be read for that explanation:

Black Wire Syndrome 1996

Black Wire Syndrome 1996


March 3, 2017 - Posted by | Civilian, photography | , , ,

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