NiMhs and black wire corrosion

[leccyflyer]

Had an interesting one this afternoon whilst making some long postponed repairs to a slope glider.  I badly damaged the fuselage on my Speedo a couple of years ago, when I dropped it getting it down from it's ceiling hook. I've been repairing the fuselage this week, with epoxy and microbaloons, 0.6oz glasscloth and EzeKote resin and with the structural integrity restored, went to check out the systems. The 4 cell 300mah Nimh receiver pack was much more dead than expected, but not necessaily a problem. Close inspection before attempting to wake it up however, revealed quite severe black wire corrosion on the battery lead. I hadn't seen that in many a year, but this was bad, so I removed the heatshrink and sure enough it was all the way back to the last cell. That pack is now in the bin.

 

That gave me a bit of a problem, with no realistic chance of getting an identical pack by the weekend, when I wanted to fly the Speedo. By chance though, I did have a couple of wee 2s1p 450mah lipos in a stubby block configuration and those actually fitted the very small available space. I found an old GWS ICS100 ESC which could be used as a voltage regulator/BEC and getting everything on the scales there was no significant weight penalty. It was a tight squeeze getting everything back in the Speedo but it all worked out in the end. Since the lipo is a bit further forward than the NiMh pack I didn't need any additional nose weight to counteract the fuselage repairs.

 

Since moving to mostly lipos, even for some receiver packs, it's been years since I've seen black wire corrosion, plus the fact that most of my models that have receiver packs are not stored in the cold, damp conditions of our previous home may well account for that, but I recall it being a fairly common occurrence back at my old club in NW England. Definitely something to do a careful check for on any of my older airframes that might be taken out of mothballs.

[Andy Stephenson]

I would recommend removing batteries from models in storage. If there is no electrical voltage present to drive the electrochemical effect known as black-wire then it can't happen.

[leccyflyer]

That's a valid point Andy. In this case, with no switch, the battery isn't connected, so the BWC was confined to the battery lead itself. The vast majority of my models do not use flight batteries, but the small number that do, will be getting their usual thorough checks before making any trip to the field.

[Andy Stephenson]

I'm not sure if it matters whether there is an electrical connection or not since moisture alone may be sufficient to make enough of a circuit to allow the reaction to take place.

[leccyflyer]

Indeed - but my point was that the BWC can't spread to the wiring loom inside the model if the battery isn't connected to anything else. The usual explanation is that cold damp sheds provide the perfect environment for that black wire corrosion to take place. FWIW when I mothball a model into storage all the gear is taken out, including batteries. It's only a small number of models which are in active service, where they have a receiver pack built in, that would be of any concern and that's what preflights on the bench are meant to detect.

[GaryW]

Black wire corrosion can happen with most battery types including lipos not just Nimh's

[Philip Lewis 3]

1 hour ago, GaryW said:

Black wire corrosion can happen with most battery types including lipos not just Nimh's

I recently did some research on this and from what I could find BWC can only effect NiCad's, NiMh and PB batteries (not so much in cars but has been found on some farm machinery) but does not affect Lithium batteries due to the way that they work.

 

A bit more here, 5th post down,

Edited March 28 by Philip Lewis 3
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[GaryW]

1 minute ago, Philip Lewis 3 said:

I recently did some research on this and from what I could find BWC can only effect NiCad's, NiMh and PB batteries (not so much in cars but has been found on some farm machinery) but does not affect Lithium batteries due to the way that they work.

 

I will therefore stand corrected on lipos

[2.4g Shaun]

And for clarity, it's the negative lead that the corrosion creeps up . The wire insulation can be any colour  but convention dictates that the  -ve lead is generally black. 

[Martin Harris - Moderator]

I've often wondered if it refers as much to the effect on the copper.  It usually manifests as crumbly black conductors.

[Cuban8]

Black wire certainly does exist - I've seen it on my own gear and found it in friends' models that have crashed due to power failure. One chaps tranny's 0V wiring was totally rotten from the battery to the main switch. I can only recall one of my RX packs showing initial signs of it at the connector, but this was many, many years ago on a Nicad that was never fast charged and only ever stored indoors. I remember having to scrap a full reel of new telephone cable at work because the copper conductors had turned black and crumbly. No batteries involved and stored in ideal conditions, so what was going on there?

Anyway........unless someone can say otherwise, i've not seen a concrete, 100% explanation as to why it occurs, and then why it should only happen to some packs and not others. I don't know of any experiment that has been able to recreate the problem under test conditions either. I remember a lengthy article in one of the mags years ago by David Boddington who looked into the problem, but even the great man himself couldn't pin down the culprit beyond a few possible smoking guns e.g overcharging, poor storage conditions in sheds, bad quality copper, even the carbon pigment in the black wire insulation was questioned AFAIR.

One thing's for sure, always check your battery packs for signs of trouble regularly - just flip out the wires from the battery plug and examine with a hand lens or similar for dulling of the connector plating or discolouration of the wiring at the crimp.

 

 

Edited March 29 by Cuban8

[Andy Stephenson]

It has been blamed on NiCads, when charged they can vent some corrosive electrolyte products through the re-sealable vent under the top cap of the positive end.

Another theory I heard is that if the strands of the wire have been plated and not left as bare copper, this can inhibit BWC.

More frightenly, I also heard that it has been found in the wiring of some airliners.

[leccyflyer]

Venting of electrolyte can occur with heavily abused NiCds or NiMhs and I've seen that as white, grey or greenish blue efflorescence- but it will be on the positive lead, rather than the negative lead, as that is where the vents are located. The BWC was definitely more prevalent in the past, hence me starting this thread, as I hadn't seen it in years. Irrespective of the different chemistry of lipos vs NiCds/NiMhs, the different storage regimes would likely not promote the phenomenon in lipos, which really ought not be stored in the model, connected to the wiring loom and likely not in cold damp conditions.

 

As mentioned above it's a simple enough check to make, to bring out the crimped connector from it's housing on the battery and examine it under a magnifier to look for any discolouration or indications of corrosion.

[J D 8]

15 hours ago, Philip Lewis 3 said:

I recently did some research on this and from what I could find BWC can only effect NiCad's, NiMh and PB batteries (not so much in cars but has been found on some farm machinery) but does not affect Lithium batteries due to the way that they work.

 

 

  I was having issues starting my old series 3 Land Rover. [ just a farm run around] Engine would only turn over slowly even with a new battery. Stripped back the covering on the positive cable as could see crud at terminal. Cable was black and crumbly for about a foot. New cable to starter and we were away.

[PeterF]

I have had it once on a NiCad Rx set many years ago. Someone recommended running a dehumidifier in my garage workshop to keep it drier, only run it for 2-3 hours twice a day. I have not had black wire since then, but not sure if that is due to the dehumidifier or the move away from NiCad Rx batteries.

[Andy Stephenson]

Having kept all my models in a centrally heated workshop over several decades, the problem never arises. I'm convinced it has something to do with moisture.

[Denis Watkins]

53 minutes ago, Andy Stephenson said:

Having kept all my models in a centrally heated workshop over several decades, the problem never arises. I'm convinced it has something to do with moisture.

 

absolutely moisture Andy, and temperature

Metallurgists know fully the implications of temperature and moisture making changes to most metals, and surprisingly, non ferrous metals usually more weatherproof, but add polarity and stuff starts falling apart

[Cuban8]

18 hours ago, Andy Stephenson said:

Having kept all my models in a centrally heated workshop over several decades, the problem never arises. I'm convinced it has something to do with moisture.

But I've seen it in one of my own batteries that was always stored indoors in a centrally heated spare bedroom used as my workshop, so I don't see how the cause can be pinned on damp conditions alone.

What about countries that have naturally very humid climates for most part of the year albeit somewhat warmer than blighty? One would assume a plague of BWC in places like that, but I've never heard reports of problems.

Just one observation and that's I'm fairly certain that I've only seen the issue on plain copper conductors - tinned copper wire I've not seen the problem. maybe it  simply hidden by the tinning?

My guess is that the issue is more to do with the quality of the copper used (contaminants?) rather than some outside environmental cause, but who knows?

Edited March 30 by Cuban8

[Andy Stephenson]

Another likely culprit is the chlorine somehow becoming dissociated from the PCV insulation.

[Peter Beeney]

Reading leccyflyer’s OP account regarding the black wire corrosion certainly brings back a few memories. I got into model batteries fairly early on, during the single channel days I guess, probably as a result of my occasional tinkering with full-size cells anyway and also having some bits of kit to be able to check battery condition etc. This snowballed into a Fred Karno style ongoing battery management scheme for a number of fellow modellers right up until lithium replaced nickel.

 

Along the way I did run into the dreaded black wire disaster a number of times and I have to say that I never particularly noticed that it was in anyway the result of any moisture related conditions; but that's not to say that it wasn't of course; and even in it’s very early stages of destruction I think it may have been a bit dangerous.

 

When the Schulze Chamäleon 6-936 charger, the one with the big screen, appeared on the market I instantly bought one, it was a bit expensive at the time but it quickly proved to be a godsend as regards testing battery packs. There was always a charge/discharge curve trace-out on the screen and therefore any faults were instantly plain to see…and it also had a little trick up it’s sleeve that perhaps even Matthias Schulze, the chap that designed it I believe, was unaware of at the time - at least to start with anyway. A helicopter flying friend handed me a receiver pack, slightly bigger than AA size as I remember, and asked if I might check it out for him. He also said he’d bought it new not very long before, it was okay in the chopper but his charger didn't like it too much for some reason. His charger was okay with all other packs so I started to discharge it for a test and instantly the trace on the screen was different, it was decidedly ‘fuzzy’ because it’s edges were very slightly crinkly making it wider and slightly lighter in colour than normal. It was discharging ok however so the next thought was check the wire and after taking a good look at it I noticed that the neg pin in the plug was just a shade tarnished and dull looking but that was the only evidence I could find of any corrosion. However, straight away I renewed the whole wire which I'd done once or three times before on other packs and problem solved! As regards capacity etc. the pack was spot on.

 

In another incident long ago, I’d previously obtained a multimeter which I still have, it lives in a very nice zip up case and it uses a PP3 battery for power. At one stage I thought I was being clever and I gave it a rechargeable to eat which worked fine until I happened to noticed an odd glitch, can't remember now exactly what it was, then that battery came out of it faster than light and low and behold there was the dull appearance on the negative press stud. As you can imagine then and there I made a vow to never again use a rechargeable PP3 in any other test instruments that I owned that used them….

 

I think one of the worst cases I ever saw was in a 40 powered size model that had been hanging up in a model shop for apparently quite a long time. Someone had installed an on-board glow driver, a single nickel cell back on the CoG and I suspect that to try and reduce any vote drop to the plug they’d used a piece of heavy gauge red wire taken from some twin and earth cable used in house wiring. An on/off switch and a recharging socket completed the set up. It had become a bit of a mess really, the top of the cell was completely corroded away and all the metal content of the whole caboodle had completely turned to black stains; I suspect this was not a one off either, I'm sure there must have been other such cases. I also found that once the rot got started in a wire disconnecting it from the battery made no difference at all, even when sealed in a plastic bag it just kept going apace until it was all just a dusty memory……

 

Re the tinned wire, Futaba tried using that idea at one time for the negative leg of the their battery connector wire, maybe they still do, but I saw definite evidence that it could still get attacked; I was going to do a trial with some silver wire but I never quite got around to trying it. Fortunately it's certainly didn't happen to all battery packs by long chalks and I've still got a pack of nicads which are now well over 40 years old and still in the best of health……  
   
Happy days!

 

PB

[Cuban8]

Signs of discolouration on a broken RX charge lead that I was about to resolder this afternoon.

Black wire quite discoloured and broken although red wire still looked bright at solder connection. Stripping back insulation revealed both conductors badly blackened. 

Original charge lead from my first decent Futaba set (Gold) from over forty years ago so can't complain. Still throws up questions as the lead is never left connected to a battery but simply left curled up in the drawer until needed.