Originally Posted by
Road Fan
Let me simplify: If I want to build a voltage limiter so I can use a 6 volt halogen bulb with a 6 v bottle or other dynamo, for what voltage should the limiter become active?
If the bulb is rated at 6 volts, I'd limit the voltage to 6 volts.
The circuit is very simple. Take two zener diodes and wire them in series with a cathode-to-cathode or anode-to-anode configuration. Then place these zeners in parallel with the dynamo output, either at the dynamo or at the headlight. Most modern bike headlights already have a zener limiter. The the sum of the zener and forward voltages of the diodes should equal 6 volts, the limiting voltage. The beauty of this limiter is that it does not degrade low speed/voltage performance. The two zeners probably cost less than a single halogen bulb.