gna

My new-to-me winter bike came with a Shimano dynohub and front and rear lights. They are wired in parallel to the hub. The gentleman I bought the bike from used incandescent bulbs in his lights, which were a bit dim. The hub is 3W and 6V. I tried some of the E10 LEDs which have a screw in base, as it was a quick and dirty replacement. I made sure to get 3W models, and they say they can handle 6, 9, 12V. They are very bright, but they don't last long.
https://www.amazon.com/gp/product/B0...ZW43EHC9S&th=1 , for example.

Is it likely that they are getting overheated and failing? Would wiring the lights in series help?

Tourist in MSN

Decades ago when people were using incandescent bulbs in lights like yours, some people would wire in a pair of zener diodes (about 8 volt) to protect against overvoltage. Over a decade ago I did that with a bottle generator type headlight but it has been so long ago that I do not recall how I wired it.

The hub puts out AC and LED bulbs typically are DC. Your Amazon listing says they should work with AC. I do not know if they are really good for AC or not.

I know I did not answer your question, but I think you would be a lot happier with new lights with built in LEDs. On the newer lights, the taillight wires are plugged into the headlamp, the headlamp draws power from the hub. The headlamp has overvoltage protection to protect both lights when you go fast, e.g. down a hill, etc.

The on/off switch on the headlamp controls both lights. On the newer systems, the taillight lacks overvoltage protection, you can't run the taillight alone without the headlamp.

In the old days when incandescent lights were the norm, your light system would be wired in parallel. The taillight would be 0.6 watt and the headlamp 2.4 watt, for a total of 3 watts. If one bulb burned out, all the power would go through the other and the other would soon follow due to excess voltage.

Good luck getting this figured out. If you decide to replace your lights with modern ones, the website that Peter White has describes how to wire them up. I have no connection to Peter White, just citing it as a lot of good info.

I described how I wired up my rando bike for dyno powered lighting at this link if you are curious,
https://www.bikeforums.net/electroni...b-charger.html

VegasTriker

You are right in suggesting that overheating is a leading cause of LED failure but if this is a winter bike in Minnesota, overheating should not be a likely cause. It is actually 1.6W LED and the rest of the 3W is probably used in the control circuit. One possibility for failure would be the electronic circuit designed to convert to DC and regulate the voltage to the LED. It was designed for a flashlight which is not subjected to much shock compared to a bicycle. It may be a failure in the control circuit rather than in the LED itself. LEDs themselves are pretty rugged.

gilesa

My guess would be that excessive voltage killed them, which fits with "very bright". If that idea is correct the problem would only occur beyond a critical speed.


The 6V/3W rating of the dynamo applies only to the specific load presented by the original bulbs, otherwise much higher values are possible and can be measured. The bulb replacements likely draw constant power: as speed rises, so will the voltage and the current will fall, causing a further rise in voltage ... Wiring in series would probably help, but will reduce the amount of light at low speed, raise the starting speed ,and does not really solve the problem.


As suggested above, voltage regulation with Zener diodes is probably the simplest solution. A pair of wire-ended (through-hole) diodes rated at 7.5-12 volts (12 for maximum output) and at least 1W should be connected back to back (there is normally a stripe to indicate polarity) across the input, downstream from the switch. If lacking soldering tools, screw down terminal strip should work. These parts are cheap, about 25 cents even from the big distributors like Mouser. I have not actually done this, but have used a similar arrangement with a self-built LED bulb replacement for about 10 years.


Alternatively, there is a UK Ebay vendor, bikeco_uk selling ready-made regulators for this. They also have some bulb replacements specifically for dynamo lights, but do not say what is different.

gna

I took the bulbs that didn't work apart, and you are correct--voltage directly to the LED lights up the LED. Not sure if the tiny control circuit board is burned out or damaged, but that seems to be the problem.

I may just give up and use Pilom.de to build up lights for this bike. I could try #4...

gna

Not sure what you mean by back to back. Do you have a wiring diagram?

gilesa

This should be a small addition to your existing wiring so a diagram is difficult without knowing what you already have. The usual arrangement is that there are two wires from the dynamo, and one is routed through a switch. Then the pair splits to feed front and rear bulbs. The regulator should be wired between the output side of the switch and the non-switched wire from the dynamo ("common"), so regulator and both bulbs are in parallel. If the regulator is not controlled by the switch it will be active with lights off, wasting a little pedalling effort and will need higher-rated (wattage) diodes.


An image search for "Zener diode" shows a lot of small glass or plastic cylinders with wire ends. One end has a stripe. Back-to-back means: connect the two striped ends together, then connect the remaining free ends to the switch and "common".

gna

Got it. Thanks.

randomgear

Bring yourself into the 21st century and upgrade your lights to LED. Just plug into your dynamo and ride away: no worries about overvolting the lights. Since many of these are made in Germany, they adhere to the German requirements for what resembles a low beam on a car which puts the light where it's needed. They also tend to measure brightness in Lux, not Lumens. Personally, I tend to prefer a minimum of 60lux for commuting - YMMV.

Busch & Muller are perhaps the biggest name: https://www.bumm.de/en/
Peter White has a great website showing beam patterns: https://www.peterwhitecycles.com/