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Ethostech
Tinkerer
Username: Ethostech
Post Number: 68
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 17, 2007 - 06:13 am: | 
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I have started this new thread because there have been of late many and varied postings (and responses to postings) which have alluded to "Black Wire Corrosion" within camera circuitry.
As one poster pointed out - this doesn't refer to corrosion of a negative wire but rather to the conversion of multi-strand copper cores into non-conductive black powder - irrespective of polarity. During the timeframe of useage and creeping corrosion the resistance of the formerly good zero ohms gets higher and higher until eventually one ends up with an open circuit. So the camera (or whatever the appliance) becomes less and less operationally efficient until one day - the open-circuit factor kicks in and everything fails.
What causes black wire corrosion (BWC) ?
It is known that the chemistry of rechargeable cells such as ni-cads, is a serious consideration - but it is not the complete answer because non-rechargeable mercury cells are also associated with BWC.
If anybody ever finds a proper technical answer - then such companies as the Japanese Futaba Corporation, the German Multiplex Company and a dozen other manufacturer's of radio-control equipment for model aircraft etc., would surely like to know - because they have been trying to sleutht he issue for the past 50 years .. without success.
The straight answer as to what causes BWC - is that nobody knows for certain. However - part of the inspection pocedure which all model aicraft clubs and their governing national Associations require in the "certification" of RC transmitters and receivers - is that the wire leads from the battery-cell pack to the first soldered connection on a tag or pcb, yield a zero ohms measurement. Otherwise those wires must be replaced.
If a camera stops working due to BWC it is really nobody's neck.
If however a $15000 model helicopter goes berserk and drops out of the sky at a model flyng field the results can be lethal.
( Never mind the expense noise which such a bag of whirling nuts and bolts makes when it hits the ground)
I spent 30 years flying RC aircraft and I can tell you that the number one fear is BWC - and it is vital that the above-mentioned checks are carried out at least annually. I also have some 400 cameras in my "Collection" - every one of which came to me in various stages of "non-working" - and which cameras have been restored to mint or near mint condition and 100% functionalty.
I have never yet encountered a zero ohms (or anything close) resistance on the power supply wires in 20 to 40 year old classic cameras which are of nic-cad or mercery-cell technology.
If I knew the technical answers I would be avery wealthy man overnight. All we know is that it happens and the service solution is to replace wires from the battery compartment terminals to the first tag or pcb solder point. If (as in some cameras and RC equipment) there happens to be a "push-connector" in series with such wires - then those connectors will also be corroded and must be scrapped and replaced with either a new connector or by a sound soldered joint.
There has been some speculation on this forum that the chemistry of the wire insulation might be a contributing cause - but such has been investigated ad nauseam by RC manufacturers and ruled out. Similarly has galvanic corrosion been ruled out. There were also some speculations that such manufacturers as Fuji, Canon, et al .. may have used inappropriate fluxes. (Flux is required to tin the stainless steel tags of mercury-cell battery compartments). It is more than axiomatic that such highly experienced manufacturers do not make such fundamental mistakes - but in any event the fluxes element was eliminated as a BWC trigger ... some 30 years ago.
The short summary is that if a camera tinkerer finds erratic metering readings with cameras of ni-cad or mercury cell technology - the first check should be to disconnect the primary battery-power lead/s at whatever the business end pcb or tag - and check such lead back to the battery compartment tags - for a zero ohms reading. If higher than 0.1 of an ohm .. then renew the wire. Don't worry about WHY the BWC .. because the chances are you will never know the answer.
Hope this helps. |
M_currie
Tinkerer
Username: M_currie
Post Number: 53
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 17, 2007 - 07:34 am: |
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Interesting post. I've sometimes wondered if some of the problem might be in the treatment of the wire itself, or the coating material, or perhaps the local conditions when the wire is made - perhaps the degree to which the plastic or rubber bonds to the copper to seal it? I have seen the beginning of BWC in some automobile wiring, for example, after 10 or fewer years, whereas others show no sign of it after 30 or more. You can peel back the insulation of some wiring on my '95 Jeep and you'll never find shiny (or solder-accepting) copper even three feet back, but the wires on my 1954 Ford tractor and my '72 Mercedes are good as new.
I have several cameras and meters that suffer from this problem, but (knock wood) it has never affected my Nikon FTn's, even in a meter that had once gotten wet enough to lose conductivity at the screw contacts due to rust.
It's a mystery, all right, and an annoying one at that. |
Wernerjb
Tinkerer
Username: Wernerjb
Post Number: 153
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 17, 2007 - 08:26 am: |
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I'm puzzled ... but now I know for sure
- that many obvious commonplace logical reasons can be ruled out.
- that the name for that mystery can be abbreviated (to make it sound familiar? I have a BWC watch) and is often wrongly attributed to the rotting away of black wires.
- that there in no common denominator.
Cameras are full of mysteries (CAFOM) it seems, just think of the currently debated corrosion cases or fungus, another heavily disturbing topic!
No easy way out, but it eases me out. |
Anirban
Tinkerer
Username: Anirban
Post Number: 16
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 17, 2007 - 10:36 am: |
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I think very pure copper tht is pink in colour when freshly rolled, can get oxidised easily by air. If the wire is thicker, it acquires the usual "coppery" colour quickly, but when when each strand is very thin, it can get oxidised to the black copper oxide slowly with time causing BWC. The oxide does not form a tough coating over the pure metal underneath (like aluminium oxide does) and eventually the entire wire withers away.
Anirban |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 275
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 17, 2007 - 08:22 pm: |
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Hi Ethostech:
Your post is indeed interesting, as I have never encountered anyone who was familiar with this phenomenon outside of cameras. Cameras generally have no (+) wire, only a (-), but I imagine that RC aircraft have both polarities as wires from the battery.
So: In aircraft, do you encounter this corrosion equally in the (+) and (-) sides of the circuit? If you do, that would seem to put the galvanic corrosion theory to rest in an instant.
rick : ) = |
Charlie
Tinkerer
Username: Charlie
Post Number: 71
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, May 18, 2007 - 06:17 am: |
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Two qustions-Do the wires to the hot shoe or PC connector (which seldom if ever, or never in my case, carry any current) corrode at the same rate as other wires. And do films or their emulsions outgas? |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 277
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, May 18, 2007 - 08:35 pm: |
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I have never seen a corroded PC wire.
Don't know about the films. |
Charlie
Tinkerer
Username: Charlie
Post Number: 72
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 19, 2007 - 08:18 am: |
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Third question (my mind is working slowly). Do the wires on cameras with selenium meters have black wire corrosion? |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 278
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 19, 2007 - 09:06 am: |
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Can't say for sure but I don't recall ever seeing it. |
Glenn
Tinkerer
Username: Glenn
Post Number: 151
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 19, 2007 - 10:32 am: |
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At the risk of turning this thread into a scientific debate, I will add the following to my original post on the topic.Having worked extensively on a similar problem in the 70s/80s, I am very surprised that this somewhat simple problem, has not been solved by the manufactures of radio control equipment. I suspect the true reason is not the insurmountability of the problem, but rather a question of money and timescale. I have also flown large scale model aircraft - from the days when we used equipment based on vibrating reeds. Whilst a large scale model crashing into a crowd is bound to cause severe injuries and perhaps even death, the thought of 2 or 3 packed commuter trains colliding - all due to a signal cable failure over-riding the fail safe, was not one that could be contemplated. Hence huge amounts of money and time were invested in solving the problem.
Whilst it must be stated that the mode of failure we were studying, finally manifested itself in complete degradation of the insulation. It was proved beyond doubt that the failure started with the onset of black corrosion on the metallic conductors. It was only the fact that the actual conductors were made up from relatively large diameter strands, that stopped the resistance increasing to any extent as the corrosion products built up.
The problem took so long to solve, because there is no scientifically sound method of accelerating the degradation of the conductors. You can only work real time, however a real piece of good luck helped to prove that the potential applied to the cables, did play a significant part. In one particular relay room where the insitu cables were in a very bad state, a roll of the original cable was found behind the banks of relays. This cable was in pristine condition, both externally and internally. Records proved the cables were over 15 years old, the only difference being that the degraded cables had been carrying DC voltage for that time span. Subsequent long term experiments over periods of 5/10 years showed how the degradation progressed.
As the cabling in the battery rooms was also showing degradation, in all our test rigs had the cells contained in specially vented containers. The power feeds were by large section stainless steel bus-bars.
By the use of electron microscopy and other instrumental techniques it was proved that the -ve conductor was corroding at a greater rate than the +ve. It was also suggested that this problem could be triggered by an interaction at the molecular level and that the 'permeability' of the insulation be looked at. In the search for more suitable insulation material, the chemical composition was certainly found to be important.
So where does all this leave the members of this forum? As has been stated by other members, BWC can occur in circuits that do not have Li or Hg batteries connected to them. Anirban hit the nail on the head when he stated that our problem arose from the very small diameter wires used in camera battery leads. This I expect is also the root of the RC problem, bigger diameters could give longer usable life. I have found no tests carried out by camera or RC manufacturers in which the questioned batteries have been physically separated from the powered equipment and long term examination of conductor state carried out. It may be a long term experiment, but it is relatively easy to prove, one way or the other, the impact of cell type/chemistry on the problem.
Modern instrumental analysis may not be quite as simple or as quick as CSI would suggest, but it does give you the results - if you ask the right questions. |
Donnie_strickland
Tinkerer
Username: Donnie_strickland
Post Number: 23
Registered: 09-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 19, 2007 - 11:48 am: |
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Quite enlightening, Glenn.
I have always assumed this is why EVERY instruction manual for battery-powered cameras which I have ever seen stresses that if the camera is not to be used for a long while, the batteries should be removed without fail. |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 279
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 19, 2007 - 03:17 pm: |
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Thanks very much, Glenn and everyone else who has contributed to this discussion. Obviously this is a problem that we have all encountered, and also pretty obviously we are not all equipped, either by training, experience or facilities, to fully work out the cause/effect relationships on our own. Any opportunity to benefit from the experience and expertise of others is gratefully appreciated. |
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