WACC'ers Technical Page

Home Page   Technical Index Page

Page Purpose: Technical Info for old moped riders. Send your items to the page organiser.

Rear bulb problems - fixed

Paul thought I should have a better front bulb, and sure enough it's always been pretty poor. Travelling back through the lanes of Warkwickshire hasn't been easy. We find another front bulb and hey presto lights as they should be. A trip back from the Tipperary pub on a summers night through the lanes was great, I could now see the rabbits eyes.

Only problem was rear bulbs were taking a big hit (2 in a week now). I have a supply of screw in 6v 6 Watt bulbs that I don't want to throw away.

Fall back on my electrics training I thought. How about putting a diode in-line with the supply to the rear. That was ok except as we're running AC it's going to cut out 50% of the flow, and it did. The light was too dim now.

Here's the single diode model.



Plan B now comes into play. An array of diodes soldered together, this arrangement allows for current to flow both ways during the AC cycle. As you may, or may not know a diode drops voltage, I measured the voltage drop through the diodes I was using. About .6 of a volt each.

By stringing four diodes together for each part of the cycle I manged to drop the voltage by about 2.5 volts. When the engines moving (23 mph!) it's producing 9.5 volts (AC) approx, that's pushing it for the rear 6 volt bulbs I have. In fact I've had to put on sun block when looking at the bulb. However, the 2.5 volt drop is enough for the bulb to be quite happy with (the current just won't flow). And so far, so good, no blown bulbs.

Here's the Array of diodes complete with shrink rap.




Page Organiser: Laurence
Top Of Page  Home Page