mastakebob

Do SKS Chromoplastic fenders burn out? My tail light stopped working and, after some troubleshooting, I isolated the problem to my rear fender. Bypassing the fender part of the circuit with normal wires causes the tail light to work as normal.

Taking a closer look at the copper leads on the inside of the rear fender, it looks like they burned/corroded away near the forward grommets. See below picture. Has anyone else heard about this happening before? I find it hard to believe that copper strips can be damaged by the levels of current (dynamo-generated, through a B&M front light) that I have flowing through the fenders. I scrubbed/degreased the grommets thinking that they might have corroded over, but that didn't solve anything (still no connectivity between front and rear grommets).

imgur: the simple image sharer

Reddy Kilowatt

Dear Mastakebob:
I used to work on boats and there's a condition known as galvanic corrosion. It's caused by two metals of differing "nobility" in contact with each other in a wet area or underwater (especially prevalent in the presence of salt water). I don't know what kind of terminals are in contact with the copper strips in your fender, but if they're tin-plated ring lug connectors or such, you've got the a perfect environment for galvanic corrosion in a fender that's subjected to salty road spray, no?
That's why boats and ships have "sacrificial anodes" (most often made of pure zinc) attached to the costly bronze propellers, rudders, and drive shafts underwater. The zincs are much less noble so they get eroded by the stray electrical currents. They're also way cheaper than those expensive bronze hardware items. (A bronze boat propeller could easily cost more than a carbon fiber road bike with the most expensive components.)
Here's the deal: you don't even have to have electricity flowing to make this happen (remember the potato or lemon battery kits with the zinc and copper strips? Galvanic corrosion makes its own current.
You can use an ohmmeter or a test light to check the copper strips and the rest of the circuit in your bike. If the copper strips have good continuity, you can restore the circuit by cleaning the terminals and the "lands" where they attach with a wire brush, then coat the connections with a brush-on dielectric goo in a can. Heat shrink tubing can also be your friend if the connectors are the crimp-on type.
I see that Amazon sells Star Brite Liquid Electrical Tape, which is what I used to use on boat connections. If there's a boatyard near you, you can probably buy a can of the stuff there. It even comes in different colors though I always used the black. Liquid Electric Tape is a brush-on product in a little screw top can with the brush attached. After you apply it to the nice, tight, and clean connections, it dries and cures to a watertight coating that conforms to weirdly shaped connections.
Once a year or thereabouts, you have to wire brush it off, clean the connections, and reapply. (Maybe even more often in the presence of grit being slung up by your bike's tires; especially if you ride in winter with salt and sand on the roads.)
Good luck; galvanic corrosion never sleeps.
Allen

mastakebob

Reddy,
Interesting thought. I had heard of galvanic corrosion before, but it didn't occur to me to consider it in this situation. I guess I assumed that a widely used fender made by a reputable company wouldn't have such a fundamental design flaw (corroding under normal use situations). I mean, I'm not a heavy user. I commute daily about 3 miles round trip in DC. This type of light use should be well within the specs of any fender. Or maybe I just got a slightly defective version, a manufacturing flaw that allows water to seep into the copper strips via the grommet holes.

Thanks for the suggested fixes. I can't get to the copper strips (they're layered in clear plastic). I 'fixed' the problem by skipping the fender entirely and running a patch wire along the frame to the rear light. Not as sleek anymore (zip ties messing with the bike's lines), but works fine.

wesmamyke

Are the grommets something you installed? I have the P-65 Chromoplastics on my mountain bike and they didn't have any grommets for wiring. I was also under the impression that the stripes on the silver model were just decorative, not functional for wiring lights.

I'm honestly curious if this is common, the wiring lights through Chromoplastics. I always assumed the thin strip on metal inside the fender was aluminum, as they are pretty easy to trim if needed. Aluminum seems like it would be pretty bad for wiring purposes, is it actually steel or copper as you said?

gsa103

Something could have shorted the two channels together. The dynamo will generate plenty of current to cause damage if its driving across a short rather than a load.

noglider 

@Reddy Kilowatt, great explanation.

The solution might be interesting, but would it be so bad to use insulated wire attached to the fender or somewhere else on the bike?

pdlamb

I'm wondering if the conductor burned or shorted out, or whether the plastic just cracked and took the thin foil with it. It's possible the fender cracked internally, broke the conductor, and eventually the break oxidized to the point it won't carry any significant current.

fietsbob

the foil strips inside the mudguards are conductive, too . the copper ones were aftermarket modification perhaps?

road crud made the grommet to foil strip inside the mudguard corrosion inevitable, then contact between them was broken..

Why sweat the why ? fix it.

I've hot melt glued wiring runs inside SKS mudguards before, so the look can be unchanged .

mastakebob

Negative, grommets are factory.

mastakebob

That's what I'm doing now. Have a 24-guage wire pair running from my bottom bracket, along the chain stays, up the inside of my rack 'legs' and then under the rack surface to the rear light. Works fine, just isn't the most aesthetic solution. Where before I had no wires, now I have wires and zip ties.

mastakebob

This is what bugs me. The whole point of SKS Chromoplastics is that they (1) get road gunk on them, and (2) conduct electricity. It seems odd to me that SKS would release a product that fails to achieve (2) in the course of achieving (1). Also odd that I haven't been able to find any other threads about failed Chromoplastics which leads me to believe its not a design flaw, but rather something I broke or a defective unit.

Regardless, my tail light works again. Just in time for the approaching winter and its short days.

fietsbob

I had grommeted SKS as part of the Koga WTR build the copper strips on the inside were not done by SKS..

only the aluminum foil inside between the layers of plastic is OEM .. the external strips were added (IDK when or where)


Having a Corespondent in NL Who had a Custom Bike Business not far from Koga's in Northern NL

I Asked him .. he suggested dont bother .. I ran wiring from the back of the headlight,

wound it around the shift cable via down tube, left chainstay, to the External shift Box on my R'off , then up the mudguard strut to the Rack Mounted Toplight.
lots of second-guessing manufacturer's choices happens on this Forum , as if people just buying stuff, not working for the producer, knew.

wesmamyke

Interesting, reading that and looking at the picture again I see now that the strips are on the inside of the fender. That is not something I have ever seen in the wild.

unterhausen

I have seen very old SKS fenders that were still perfectly conductive. I'll have to grant that this is often a surprise given their physical appearance. Saw a set just last week

noglider 

How would you have seen it? It's on the underside to hide the wiring.