There's two problems here; gratuitous feature-itis, and failure to waterproof. The actual power circuitry carries enough current that a thin film of water is not going to make that much difference; what does you in, is when there's some tiny e-brain that makes the light blink, or senses daylight, etc, and it runs with itty-bitty currents (normally you like that, itty-bitty current means low power overhead). Get those wet, and they think bad thoughts.
I've done some homemade circuits in the first category (dumb power) and they just work. My "smarter" circuits are inside sealed containers (e.g., Rubbermaid, Tupperware) with all the wires going out through a hole, and then the hole sealed with silicone rubber, AND the hole in a draining orientation anyway. The biggest problem is vibration.
If you wanted to do some after-market waterproofing, I think your friend is lanolin grease (Rivendell / rivbike.com has carried this in the past). Gummy, waterproof, ok for humans. Just gob it into all the cracks where water might get in.
Stuff that I don't have to take apart, I use a combination of:
- silicone (prefer Silicon II, it does not outgas acetic acid when it cures)
- thick epoxy (e.g., JB Weld, JB Quik)
- nail polish (on any exposed connections).
I tried potting a circuit in paraffin wax on my son's bike, and "something happened" and it failed. I still have not melted the wax off to see what went wrong; instead, I did a quick replacement with a "stupid" circuit (4 diodes, 3 caps, all soldered and ziptied to a PCB), and stuck it in a Trader Joe's Peanut Butter jar wired through a hole at the bottom when the jar is mounted in a bottle cage. If this gets wet (if he leaves his bike out in a flood), I can restore it to working order by taking the top off the jar, pouring in clean water, and waiting for it to dry. (And I am thinking, I'll bet I could just hit the whole thing with Clear-Coat, and it would even work pretty well underwater).
I also tend to use excess silicone rubber and heat-shrink tubing to help with strain relief on some of the wire connections. If you look at this picture http://dr2chase.files.wordpress.com/2010/11/img_0352.jpg
you can see the nail polish on the exposed circuit metal, but you can also see the un-strain-relieved wires soldered to the puck. That won't last in real use; you've got to do something to cut down on the flexing and vibration right at the solder joint.
This stuff is tedious and hard to get right. I'm not surprised to see it done wrong on cheap electronics, but see previous rant about failure of expensive electronics.
On 2011-05-08, at 2:37 AM, Cara Lin Bridgman wrote:
> What I don't understand is why bike electronics (i.e. lights) aren't
> made waterproof. Over the past 10 years I've wasted a lot of money on
> headlights that whack out after the first downpour. Taillights tend to
> do much better.