19-08-2020, 12:40 PM
Hi Howard
LEDs can produce noticeable light with very little current, and can turn on and off incredibly quickly. I suspect you have voltage spikes on the switched side of the wiring which are coming across the open switch from the battery/dynamo side. This is most likely via the small capacitance across the switch contacts, or capacitance between switched and unswitched wiring running alongside each other. Simplistically these spikes/pulses are AC, which unlike DC can flow through a capacitor. All A7's have voltage spikes on the 6V line, coming mostly from the ignition coil (if fitted) and the dynamo.
I recommend you connect a capacitor from the switched side of the coil to ground. This will short circuit the rapid spikes whilst not affecting the steady DC. You could also try capacitors on the switched side of each lighting circuit. The capacitance value isn't critical, anything between 0.1 uF (microfarad) and 10 uF would probably do. Radio type capacitors would work, but aren't as easy to get since Maplin disappeared. Automotive suppressor capacitors are more convenient to mount and wire in. They aren't so prevalent these days but can be found online. An ignition condenser (= capacitor) would also work. Keep the ground lead short.
Rather less likely is direct interference from the HT side of the ignition, radiated by the copper HT cables used by A7s. In this case, I find resistor suppressors of 5000 to 10000 ohms mounted between the leads and the sparking plugs are quite effective. "Champion" style right angle types ought to work, but beware that many of them are poorly made copies. I suggest checking their resistance with an ohmmeter before fitting, if you go down that route. Be aware that it's generally reckoned not to be a good idea to fit resistor suppressors to Magneto systems.
With all problems of this nature, some experimentation is needed, so best to "tack on" components initially and then make a more permanent solution when the best setup is found.
LEDs can produce noticeable light with very little current, and can turn on and off incredibly quickly. I suspect you have voltage spikes on the switched side of the wiring which are coming across the open switch from the battery/dynamo side. This is most likely via the small capacitance across the switch contacts, or capacitance between switched and unswitched wiring running alongside each other. Simplistically these spikes/pulses are AC, which unlike DC can flow through a capacitor. All A7's have voltage spikes on the 6V line, coming mostly from the ignition coil (if fitted) and the dynamo.
I recommend you connect a capacitor from the switched side of the coil to ground. This will short circuit the rapid spikes whilst not affecting the steady DC. You could also try capacitors on the switched side of each lighting circuit. The capacitance value isn't critical, anything between 0.1 uF (microfarad) and 10 uF would probably do. Radio type capacitors would work, but aren't as easy to get since Maplin disappeared. Automotive suppressor capacitors are more convenient to mount and wire in. They aren't so prevalent these days but can be found online. An ignition condenser (= capacitor) would also work. Keep the ground lead short.
Rather less likely is direct interference from the HT side of the ignition, radiated by the copper HT cables used by A7s. In this case, I find resistor suppressors of 5000 to 10000 ohms mounted between the leads and the sparking plugs are quite effective. "Champion" style right angle types ought to work, but beware that many of them are poorly made copies. I suggest checking their resistance with an ohmmeter before fitting, if you go down that route. Be aware that it's generally reckoned not to be a good idea to fit resistor suppressors to Magneto systems.
With all problems of this nature, some experimentation is needed, so best to "tack on" components initially and then make a more permanent solution when the best setup is found.