Mach 1 Brakelight Switch

[DewCatTea-Bob]

By: JimF...
" I did connect the LED bulb in parallel with the ignition coil. "

____ Then now we can confirm that the poor results you got was (as I had to assume before) due to your LED-bulb being expected to run in parallel with the short-circuit* (through the ign.points) the majority of the time, and also having to share the power-source with the ign.coil the rest of the (relatively slight!) time. _ Thus understandably only pulsed dimly !
* I had already mentioned that oversight once recently before, (back when you thought you could get-away with wiring-up your brake-light in PARALLEL with the ign.circuit, and then discovered for yourself that your B-L.switch would then act like a kill-switch), so it seems you forgot about that already.



" The power source is AC,
I am not sure if the peak amplitude changes "

____ Yes, the v.tension-amplitude increases with raised RPMs.



" the RMS value is ???, "

____ While 'RMS' voltage is certainly applicable with normal/old resistance/filament-type light-bulbs, I believe that only the 'peak' voltage is the equivalent main-concern with LEDs.



" the LED bulb is only every forward biased for only half the time "

____ Right, in this case your LED is self-feeding only the negative half-cycles of the full-AC it's exposed to, thus powered-on only half the time.



" even during that half time that it is forward biased the voltage needs to be above some threshold determined by the value of current limiting resistor and the forward voltage of the LEDs. "

____ It's been my limited experience with modern LEDs that they still light-up fairly-well even with considerably less voltage than they've been rated to work with.
__ The parallel connection of a capacitor would make quite a notable improvement towards making it irrelevant
that the supplied power is only half-wave !



" This does not even take into consideration any reverse bias threshold voltage before the LEDs are damaged, "

____ I agree that it's questionable as to how much voltage-abuse LEDs can handle, so it would be added insurance to run them in series with a regular diode in line.



" As the LED's forward current is likely set by a fixed resistor expecting a regulated DC voltage value (say 12.8volts), then any over-voltage (voltage above 12.8 volts) will result in a life-shortening over-current condition in the LEDs.
This is why I abonded the LED solution (for now) on an AC bike. "

____ Well, I've never advised that the LED-bulb HAS to be powered by the same alt.power-coil as the stock brake-light circuit,, and since the LEDs consume so very much less current, it should thus-then be no-problem to have the brake-light circuit powered (in parallel) by the same alt.power-coil which powers the tail & head lights.
And when the headlight is kept turned-on, the lighting-system's system-voltage is then always kept well below any voltage that could possibly be harmful to the LED !
And for running with the headlight turned-off, a simple Zener-diode (like used on many Brit.bikes), would certainly protect the LED (from higher voltage), quite well enough.
__ Indeed the (current standard) LED.tail-bulb can provide such worthwhile advantages, that it's well worth adapting one for use on any Duke-model !
I'll provide the related details for anyone interested.



Fun-Cheers,
-Bob

PS... In the other related thread, rather than starting another post somewhere-else, I've instead updated the same posting with additional info.details...
QuickLink - viewtopic.php?f=3&t=1043&p=7065#p7065