cali_axela

I've been running a SP dynamo hub for about two years now on my commuter and it has been so great. However, over the past couple months its ability to remain lit while stopped for a minute has been steadily declining, to the point where now it basically only lights up when going over 10mph and will almost immediately flicker and die when coming to a stop.

I'm not sure where to start in diagnosing the problem -- is this more likely an issue with the hub, or the light? It's a PD-8 hub, and an iLumenox Vega light -- I'm leaning towards the problem being with the light itself, but not sure how to tell, or if there's anything I can do to revitalize it. Any ideas would be awesome, thanks!

noglider 

There are two approaches you can use.

One is to swap in and out the suspect components. Not easy. First swap in a known-working light to see if it behaves better. Then swap the old headlight back in and swap in another dynamo wheel. Not easy or cheap.

The other is to take measurements. Hook up a multimeter. You'll need to know what voltages and currents are normal for a given speed.

52telecaster

those super capacitors eventually go bad, but you could have a near short if it wont light up immediatly when your riding. my tailights eventually get to where the standlight fails. this is due to the cap failing. the lights still work however. they light right up when your riding. this makes me think perhaps something else is at fault. you could have a poor connection someplace that is giving you trouble.

noglider 

Yes, and so it's probably the light at fault, not the hub.

52telecaster

yes, i very much doubt the hub is a problem.

Kedosto

Capacitor in your headlight is toast. You're obviously getting juice from the hub. With no reserve in the capacitor, the minute you stop turning the hub there's nothing stored for the stand light.

If you're the DIY type, you might be able to pull it apart and fix it. Be careful, there may be just enough zap in it to get your attention!

-Kedosto

ThermionicScott 

Hmm, paging Steve @steelbikeguy!

FBinNY 

If the light stays on after you stop, you can be sure there's a rechargeable battery or capacitor in the circuit someplace.

Odds are it's battery, since a capacitor would need to be fairly large.

So, like all rechargeable batteries, yours lost charge capacity with age. Find and replace the battery and all will be fine.


BTW, the lithium battery in my 3 year old laptop used to be good for over 4 hours. Now, I'm lucky if it lasts 10 minutes.

twodownzero

WHat was it like when new? Is it an led headlight? It shouldn't take 10 mph to produce enough current to light a few leds.

steelbikeguy

oh.. sorry! I was napping.

My first guess is the same as everyone else's... the supercapacitor is the likely problem.
Any chance that the OP can open up the light and take some photos of it??

For reference, I recently fixed a Supernova Triple dynamo light that had a damaged supercapacitor (along with a ton of other damage). Here's a photo of what's inside the light. There are three capacitors mounted on the bottom of the lower board. The capacitor in the middle is the supercapacitor. It's marked "GC 5.5V 1.0F". This tells us that it is rated for 5.5 Volts, and has a capacitance of 1.0 Farads.



Once the supercapacitor was removed from the board, it could be seen that it was quite bulged, which is a sign of damage.




Another example of a supercapacitor is the deceased B&M Lumotec Eyc that I've received. It is smaller than the Supernova's... 0.47 Farads, and rated for 5.5 Volts. In the photo below, it's the gold colored device in the lower right. There's no sign of damage to the supercapacitor.



side note: I really need to find/make time to put power on this light and see why it's not working....

Anyway... if the OP can open up the light, he/she might find out if there is any obvious damage.
If that's not an option, then the next option is to swap parts until the bad part is identified. i.e. swap the dynamo for a known good one, swap the light for a known good light, and check the wiring very closely.

That's all I've got right now. Let me know how it turns out.


Steve in Peoria

cali_axela

Thanks so much everyone! I'll take apart the light this weekend to inspect, and take pictures. Definitely sounds like that's the culprit.

CrankyOne

Be cautious, you could get a charge out of one of the capacitors.

fietsbob

FWIW, I have 2 B&M top light line tail, and a B&M Eyc headlight, all have stand light capacitors .
none of the capacitors are physically that big..

the model which has the tail light glow brighter as if a brake light adds another battery to illuminate it brighter..


Its not that busy-densly populated here to need that brake light,

standlight in the headlight helps me get the key in the front door lock




got an even smaller Schmidt tail light, it is even smaller, still has a stand light capacitor yet to install it ..

plan to mount it on my Bike Friday , rear facing bottle cage adaptation. behind the seatpost mast..





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sweeks

Low voltage! No worries.
Steve

sweeks

Possibly the capacitor is shorted internally. This would prevent it from storing sufficient charge to illuminate the standlight, and might be shunting enough current to starve the main light until the bike is moving at a higher speed. In this case, removing the capacitor would restore low-speed light performance at the expense of the standlight. You could run it like this until you get a replacement capacitor.
Steve

noglider 

@fietsbob, how do you like your Eyc? My wife has one, but I haven't tried it in the dark. It's a very nifty light, and I saw her once at dusk, and it was a superb be-seen light.

fietsbob

I have it on my Brompton., Fork Crown mount, being closer to the ground , makes it a good see by light ..

Senso T version uses 3 LED, 2 flat ones are day running and the stand light ,
the 3rd is the bright heat sink attached one for the see by in the dark,riding , light focused pattern by the reflector.


mounted higher up it may well be a more seen light, Not to mention all the surrounding city lights..


I have Schmidt eDelux 1, on the fork crown mount of mt 26" wheel Koga WTR..





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jdswitters

Any update? Had this happen on mine two years ago and it turned out to be a bad connection that was not obvious, some of the the wire had pulled loose from the bayonet under the shrink wrap and it happened about the same time at both ends. I'll never know if it was just the installation or if someone was pulling on them.