Lighting

 

This light system is probably a little bit of overkill in that you can achieve the same a lot simpler. However, I want to be able to charge small electronic devices (e.g phone, pda) whilst on tour wild camping, so introduced a battery pack and charging facility. This also saved me a bit of cash when buying the lights as it meant I didn’t have to shell out for the more expensive standlight versions.

 

I have two Lumotec Oval front lights (2.4W bulbs), a Dtoplight plus rear LED light and a standard 0.6W rear light. This brings the maximum wattage to about 6. Obviously this is too much for the Nexus hub dynamo to provide – another reason for the battery pack. My lights are divided into two sets for switching purposes – 1. one oval and the Dtoplight on, 2. the other oval and the 0.6W rear on. Through the two switches in my circuit, it’s possible to have the following combinations:

 

 

I am in no way an electronics expert, but have enough background knowledge to get by and be able to fix faults. Any expert would probably laugh at this circuit diagram:

 larger version available here

 

The battery pack consists of 5xAA 1800mAh NiMH batteries arranged in serial to give approximately 6.6v. The Zener diodes in the front oval lights protect the bulbs from this slightly higher voltage, but I don’t think there would be a problem if they didn’t. The fuses used are 2x500mA (slow burn) to protect the dynamo should something short and 1x5A (fast burn) to protect the battery should the same happen. The switches have a centre ‘off’ position. The battery pack is zip-tied to the underside of my rear rack, the Dtoplight Plus mounted to the back of the same rack, the 0.6W rear light is mounted on the tip of my mudguard and the two ovals are positioned on the top of my front rack for good beam-wheel clearance. The dynamo fuses, rectifier, and SPDT switch are in a box which is zip-tied to the underside of my front rack. One major consideration with running a DC lighting system with components designed for AC is that they are all grounded to their mounts i.e they rely on the bike frame to provide half of the circuit wiring. When running DC through the circuit it’s very easy to get short circuits – trust me, I melted the first battery pack this way! Each light needs insulating from the frame.

 

As for charging small electronic devices… in the case of my mobile phone (Sony Ericsson T610) I found that it charges at 5.2v. Instead of making my own charging circuit I decided to modify the phone’s car charger. The charger accepted the 6.6v from my battery and outputted the required 5.2v fine. It must use some variable input circuitry to achieve this. I’m assuming most step-down car chargers will utilize the same circuitry. I plan to do the same with my pda’s (Palm Tungten E – 5v, 1A charge) car charger soon. These chargers are available at little expense on Ebay and seeing as I don’t own a car, I’m free to adapt them as necessary.