Black wire blues.....

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PaulJ
Posts: 598
Joined: 16 Feb 2018, 19:01
Location: Ipswich, UK

Black wire blues.....

Post by PaulJ »

Just about every old set that I have converted has suffered from corrosion of the negative wire, sometimes so badly that it had got to the main pc board and corroded that too....... and now I have even found some on my fullsize boat which uses special tinned "marine" wire. :roll: I have seen a number of theories over the years but does anybody on the forum REALLY know what causes it? :?

Paul
Spike S
Posts: 181
Joined: 16 Feb 2018, 14:59
Location: Salisbury UK

Re: Black wire blues.....

Post by Spike S »

Gremlins ! :evil:
Spike S
(Tune for maximum smoke)
bluejets
Posts: 316
Joined: 19 Jun 2019, 04:09

Re: Black wire blues.....

Post by bluejets »

It's a form of electrolysis ..used to happen in the old 300 ohm tv aerial cables too.
In the rc gear it works it's way from the battery out.
Sometimes one will notice the charge capacity of the batteries seems to be getting low when it fact it's the rotten cable.

Most important thing is, as you found out, get it before it gets to your receiver.

In many instances where it doesn't get to the receiver is when it hits any on-off switch first and there's no receiver left to damage from the crash.

Only fix is find it early and replace it.
Pufango
Posts: 16
Joined: 04 Apr 2021, 12:34

Re: Black wire blues.....

Post by Pufango »

It seems no body knows ,there have been lots of theories from the pigment in the plastic covering ! To some form of electrolysis.
So it’s best to change the negative connections before it’s to late ❌
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Mike_K
Posts: 669
Joined: 16 Feb 2018, 06:35
Location: Hertfordshire

Re: Black wire blues.....

Post by Mike_K »

Hi Paul

I think it should be called negative wire corrosion as it doesn't matter what colour wire is connected to the battery negative, if the battery leaks, the negative wire will corrode. To prove this to myself years ago (in the 70s when NiCD and DEACs were still being used) I used a blue negative wire. And guess what, it got black wire corrosion. Later I tried a white wire and it eventually corroded too.

What is interesting is that the battery can only leak from the positive terminal, but it's the negative wire that always corrode first, so it must be electrolytic with the battery potassium hydroxide electrolyte causing the corrosion. And I tested the mess left of the black wire corrosion in the school chemistry lab and there was definitely potassium salts. Case closed?

Mike
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PaulJ
Posts: 598
Joined: 16 Feb 2018, 19:01
Location: Ipswich, UK

Re: Black wire blues.....

Post by PaulJ »

Hi Mike, I'm in no position to disagree with what you say! :P

Paul
bluejets
Posts: 316
Joined: 19 Jun 2019, 04:09

Re: Black wire blues.....

Post by bluejets »

Main thing used to be to get it early.
In those days it would slowly progress through the switch and even in to the receiver .
Once there it was chuck everything.
Receivers used to be bl***dy expensive back then too.
Pchristy
Posts: 413
Joined: 16 Feb 2018, 13:57
Location: South Devon, UK

Re: Black wire blues.....

Post by Pchristy »

The primary cause in model systems is over-charging! Back in the day, we used to trickle charge our cells overnight, even if they'd only had 10 minutes of flying since the last charge!

Now, when you over-charge a NiCad or NiMh cell, it vents gas - from the positive terminal, as Mike correctly points out. However, the gas has a slight positive charge, and gets attracted to the negative terminal where.... well, I'm sure you can work it out!

The gas itself is only slightly corrosive, however, it dissolves in the water present in the air, and the solution is VERY corrosive!

This is why the worst cases come from systems that have been charged or stored in a damp environment (garage, shed, etc). It also explains why the problem virtually disappeared once everyone started using peak-detect chargers....!

--
Pete
bluejets
Posts: 316
Joined: 19 Jun 2019, 04:09

Re: Black wire blues.....

Post by bluejets »

So how do you explain the black wire in the old 300 ohm TV cable..?
Same thing used to happen there , just the one conductor.
Thankfully no longer used.
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Mike_K
Posts: 669
Joined: 16 Feb 2018, 06:35
Location: Hertfordshire

Re: Black wire blues.....

Post by Mike_K »

Your feed cable are suffering from a completely different corrosion process, but with similar results. If I remember correctly many coax and feed cables use fine bare copper stranded wire and the surface oxidizes and turn to black copper oxide. I can't remember the conditions that accelerate the process, but I remember that being so fine copper strands is one of them. This is why most fine stranded signal cables use plated copper conductors.

Our old transmitters suffer from the potassium hydroxide electrolyte from the batteries, either leaking out of the battery due to the seals failing through age (which is the most likely cause for our 50 year old transmitters) or as Pete reminds us, being vented due to overcharging (which was the main cause during their working life).

Mike
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