Bicycle standlight with SON Edelux II + Supernova E3 Tail Light 2

A day gives you the day and the night. So when you're busy during the day you better make use of the night too. I really like riding bike at night. There's nothing as good as cruising empty roads, passing towns and sleeping villages. People sitting inside, flickering blue TV lights behind windows, dimmed bed lights, calm and sleepy darkness. Long before daylight rises bakeries are waking up, cats and dogs are socialising.

Good lights are essential, since ever I prefer Schmidt. Best generator you can get. Whem I started travelling by bike I was bit surprised that oncoming trucks dimmed their lights before they actually could see me. It was the Edelux, still working on my black tank. On the lighter bikes I used the Edelux II as head light. Schmidt never came up with a tail light as cool as their head lights. So as long as there is nothing better desingned that the Supernova E3 Tail Light 2 I'll stick with that.

And there the confusion begins. None of the both companies ever stated anything regarding compatibility of these lights. No worries, they work excellent together. Bright ahead and behind. Only downside one might need to accept - at very low speed the tail light is blinking and once stopped it goes off. The Edelux itself will provide some standlight, but not the tiny Supernova. It does, but only if wired to the Supernova head light when it's fed by its internal supercap.

So if you bored and fancy some soldering - here you go. The Edelux is connected to the SON dynamo hub as usual. Another cable is running from the Edelux to the tail light. The Supernova got 3 LEDs, a diode for protection and 3 resistors inside its tiny housing. From the Edelux you won't get much more than the 7V.

At first we want to get rid of the flickering behaviour at low speeds. Thus we use a small capacitor eliminating the pulsing DC from the Edelux outlet. Next task is to save some energy in a supercap. They come in standard sizes, one close to the nominal 6V of the tail light is the 5,5V type. Supercaps are a bit sensible regarding overvoltage. A good way to ensure protection is charging the supercap via a fixed voltage regulator. They are cheap and come in standard sizes as well. A 5V type seems suitable. If you take a power supply (a few AA batteries will do as well) you observe that there's not much difference in illuminance between 6V and 4,5V. Just fyi - current is 70mA @ 6V, 40mA @ 4,5V and 10mA @ 3V. This leads to a setup where we charge the supercap with 5V from the voltage regulator. This will be the maximum voltage we can use for the standlight. But as mentioned before, nearby same brightness as running the Supernova directly fed by the Edelux.

The voltage regulator needs some protection from the backside, a standard diode will do the job. This is important because we also will bypass the supercap with the nominal voltage from the Edelux. The layout explains itself.

For the diodes I took some which were laying around here, think it was 2x 1N4001 and 2x 1N4148, more or less standard. Feel free to pick better suiting alternatives. First I just packed everything together an tested the setup in a small plastic bag for rain protection.

After two weeks without any problems the parts were put as close as possible together. Some shrinking tube and some hot glue and ready for its final installation. I run the cables internally in the frame, making use of the Di2 outlets. I placed this little alien in the down tube next to the bottom bracket. Some bubble wrap and you can ride cobbles without any noise ;)

It's running on two bikes so far without any problems, charged in 200...300m. Since there's no cut-off diode in the circuit it's glowing 'til the supercap is empty (>10mins).