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Old 04-21-08, 04:43 AM   #1
JohnBrooking
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Can capacitors wear out?

Hello,

I was given two sets of Reelights for Christmas. These are small lights that attach to the axle and have an electric charge induced in them by spoke-mounted magnets as the wheel turns. The model I have includes a capacitor in the circuit which (1) keeps the lights blinking at a steady rate independent of wheel speed, and (2) keeps them blinking for up to 3-4 minutes after stopping.

I installed one set on my winter commuting bike and have been using them for about 4 months. They worked great at first. The front one would stay blinking at least 5 minutes after stopping, longer than even the company's website promised. Now, however, I am beginning to notice a decreased duration of blinking after stopping. The front no longer keeps blinking even 30 seconds after stopping, even after my 5-mile commute which used to charge it enough to keep it going for 5 minutes.

Is it possible the capacitor has "burned out" or something like that? It still blinks at a steady rate when I'm riding, but it seems to no longer have any useful life after stopping.

- John
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Old 04-21-08, 05:04 AM   #2
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Old 04-21-08, 07:15 AM   #3
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Are you sure they used capacitors? Good super caps are expensive when compared to small rechargeable batteries. Super caps should last for many years but rechargeable batteries would not in this application. I am sure the electronics are sealed in epoxy so you would not be able to repair them or even determine if super caps or batteries were used. I've never been into a set of these lights so I can't confirm if super caps or batteries were used or if everything is potted in epoxy. If the electronics are not sealed in epoxy you could repair your lights by replacing the super caps or if batteries were used you could replace them with super caps. I did a quick search on super capacitors. Here is the result.
http://www.mouser.com/Search/Refine....user_Wildcards
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Old 04-21-08, 08:36 AM   #4
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I'm pretty sure they would use capacitors in this application, since they only keep them going for 3min after stopping super caps would not be necessary. And we are talking about a blinking light here.

Capacitors most certainly can fail, especially if they are abused (over volted) and they can fail even just due to age. This is especially true of electrolytic (can shaped) capacitors, however thier life span should be measured in 10's of years. So any electronics in which they would fail would be hopelessly obsolete by the time they do.

The problem you are describing certainly sounds like a bad capacitor. It seems abit premature for them to fail like that. You say they were on your winter commuter? Were they subjected to etremely low temperatures?
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Old 04-21-08, 08:37 AM   #5
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Yes, capacitors can go bad.
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Old 04-21-08, 09:11 AM   #6
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I have replaced many cheap, leaking electrolytic caps in dead PC motherboards and power supplies, so yes, they can fail. I don't know what kinds of caps are typically used in this application however, so my experience with electrolytics may not be relevant. Heat certainly is a major factor in the lifespan of almost any electronic component, however.
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Old 04-21-08, 06:48 PM   #7
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Thanks for the feedback. Two things jump out at me. First, as I said, the front one especially would stay on for longer after I stopped than the company claimed it would, so perhaps that it is indication that it was being "over volted", perhaps by being too close to the magnets. Secondly, yes, there were some pretty low temperatures here in Maine last winter. It was ridden (with the lights operating, of course) on several days down around 0F (-17C), and the bike was stored on my unheated front porch overnight, so storage temperates probably got close to that for extended periods of time, although the capacitors would not have been operating.

The company website states "The light stores the energy in a built-in capacitor and keeps flashing for several minutes while the bicycle is stationary." That's all the detail they provide.
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Old 04-22-08, 12:13 AM   #8
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The website description seems plausible enough. Sure capacitors can go bad. So can solder joints and other electronic components. Seems like you can try a warranty repair/replacement. If not, can you open them up? Handy with electronics? If not, you might have to just buy new ones.
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Old 04-22-08, 07:31 AM   #9
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Quote:
Originally Posted by Litespeedlouie View Post
The website description seems plausible enough. Sure capacitors can go bad. So can solder joints and other electronic components. Seems like you can try a warranty repair/replacement. If not, can you open them up? Handy with electronics? If not, you might have to just buy new ones.
If I were replacing these lights I would just purchase regular old battery powered blinkies. I do a lot of riding at night and use my blinkies a lot. I go an entire year on 2 AAA batteries in each one and change them out on my birthday even if there working fine. My little Sony arm band radio uses AAA batteries as well so occasionally I will take the batteries out of a blinkie to use in the radio and replace them when I get home.
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