Mach 1 Brakelight Switch

[DewCatTea-Bob]

" I'm sorry if the way I've presented this problem has confused you, but please don't start to question the authenticity of my bike, or my common sense. "

____ It seems our respective posts have been cramped-together out of properly-placed chronological-order, (perhaps leading to a bit of misconception).
__ It really ought be understandable that it would be questionable if your "bike" was really in fact a "Mach-I" , after your posts had come to lead their readers to believe that you had successfully installed a WideCase-type brake-switch on it !
(And I'm now thinking that if I-MYSELF ever posted a picture of any object* that was fairly obviously not quite the very-same style as that which I indicated it to exactly be, [*such as a threaded-rod vs. a smooth rod with a hole near it's tip], then I really wouldn't blame anyone who actually went-ahead & questioned MY common-sense !)

" The simple and most likely explanation is that the previous owner installed the wrong switch "

____ So that's who's to blame !? _ (Not sure that switch could still have been rightfully considered as "NOS" then.) _ But yes, it was indeed the wrong switch-type !


" The simple solution was to reverse the way the switch works as I've done in the drawing above. "

____ Thanks for your drawing !
Could also be of use to someone wishing to do the same modification but in reverse, as well.


DUKE-Cheers,
-Bob

[JasonB]

Hi Octane,
Let me know if you need one as I have one, but I think you have sorted your own drama out, welcome to the world of Italian electrics On hidesight allot better than the prince of darkness "Lucas"

JasonB

[JimF]

I am contemplating the switch reversal myself.

I have the magneto style bike so I should have the NC (Normally Closed) switch wired to ground the ignition, which would then when opened (brake pedal applied) divert the ignition coil current return path through the brake light bulb.

Instead I have a NO (Normally Open) switch now, and because of that I cannot have an incandescent light bulb on the same winding as the ignition since the engaging the bulb filament with the brake light switch (brake pedal applied) emulates a kill switch (a low impedance short to ground.)

One might think a quick answer might be to use a LED brake light, but LEDs are DC animals looking for a regulated voltage and the magneto electrical system is one of AC voltage and completely unregulated.

I don't mind taking the switch apart to see if the switch can be reversed, I just don't want to break the switch and go from having the wrong switch to no switch at all.

I am just asking how many of you might have done this procedure on the stock narrow case brake light switch so I can gauge my odds of success.

Thanks,

Jim

[DewCatTea-Bob]

" I have the magneto style bike so I should have the NC (Normally Closed) switch wired to ground the ignition, which would then when opened (brake pedal applied) divert the ignition coil current return path through the brake light bulb. "

____ If you wish to employ the stock magneto-style/alt.powered-type brake-light circuit, and also feel the need to use only a stock-Ducati B-L.switch,, then yes, you then need the (rarer) n-c.Mk3/Scr.switch of which it's internal-circuit is CLOSED (rather than open) while in it's normal/default-position.
So when THAT switch is left unactivated, the ign.circuit is then directly shorted to ground (and thus the ignition is allowed to function),, whereas when that type switch is ACTIVATED, it then leaves no other choice but for the connected AC.juice to pass through the brake-light circuit's wiring & filament (which is ALWAYS in parallel with the short-circuit made by that switch's internal [default/unactivated-setting] connection,, and-so that switch itself doesn't actually-divert the AC.juice away from the short-to-ground over-to the brake-light, [as that change-over of current-flow occurs naturally] ).


" One might think a quick answer might be to use a LED brake light, but LEDs are DC animals looking for a regulated voltage and the magneto electrical system is one of AC voltage and completely unregulated. "

____ I have no experience with the use of such LED.brake-lights but, I believe that possibly you may simply need a diode to rectify the AC into DC,,
and in the event that you may forget to close-down your throttle when you apply your brakes, (thus expose the LED to excessive voltage),, you could install a simple AC.regulator-unit...
Many Jap.dirt-bikes employ such AC.voltage-limiter/regulators to prevent burning-out of light-filaments (powered by alt.produced AC),
so such an AC.voltage-regulator unit ought to be all that's needed to protect the LED, (although I'd use a 12v.LED-bulb, to be even safer).


Hopeful-Cheers,
-Bob

[Octane]

Hi jim,
I've had no problems since reversing the internals of my switch.
Was simple enough to do, but just be careful not to damage anything when pulling it apart or bending the contact plates.

[JimF]

Thanks,

The previous owner says the switch that is on the motorcycle now is a Cosmo motors sourced reproduction, and as such I am not sure if the internals are re-configurable.

I may have a lead on an original switch - I will know tonight if this fellow found one is his pile of spare parts.


Jim

[DewCatTea-Bob]

" I may have a lead on an original switch "

____ Well Jim, that you currently want such a rather unique switch must mean that you're now intending to go-with the original-type (fairly well dreaded) stock brake-light circuit setup, I presume.
You've already led us to realize that you had wanted to avoid having to use that wacky circuit with the bypass toggle-switch, (which then would've diverted your Duke from remaining as stock),, but now that you seem to wish to use only a stock-type B-L.switch, you've now left us to assume that you must have since become inclined to 'restore' (at least) this (Ducati-rigged) electrical-circuit. _ And if really so, then I'm led to believe that you may be thinking that that more-recently covered (wacky toggle-switch setup) issue is ALL that's undesirable (with Ducati's rigged-up B-L/circuit).
And if that's indeed the case, then I'm thinking that you-yourself haven't had any previous direct experience of your-own with that Mk3/Scr.B-L.function, cuz it doesn't really work (well) as a normal-type brake-light ! ...
Sure, if the revs are kept up high enough when that brake-light is tested-out, THEN it works quite well enough,, BUT, when the revs are down (to about where expected when braking, or at a stop), then that brake-light isn't real noticeable within the light of day (especially in direct-sunlight !). _ (And that's somewhat to do with the fact that it's a rather GRADUAL transition, compared to normal instant-on brake-lights.)
And at night-time when it's dark enough to require having the lights turned-on, then while the taillight is lit-up adequately,
if the brake-light is then activated, then instead of the tail-lamp instantly becoming more brightly lit-up (as is expected), it instead immediately dims-down (momentarily) and then begins to brighten back up to become only slightly brighter (than the taillight WAS just before the brake-light became activated) !
And even when the revs are keep relatively high, that arrangement-type of (AC.powered) brake-light doesn't light-up as instantly as regular brake-lights (that're battery-powered) are well-known to be expected to do.
__ So after you get your wanted (not really 'desired') B-L.switch, you can then get your B-L.circuit all set up like stock and confirm for us all that I've told it (pretty much) like it is. _ (Although there are some mods which can help minimize the undesired effects).
__ Perhaps there's others here (with stock Mk3 or pre-1966 Scr.models) who can confirm the undesired effects of this particular Ducati rigged-up brake-light circuit-setup ?
____ After this stock B-L.circuit has been played-with and then determined to be unacceptable, we can next-then move-onward to other more acceptable B-L.function methods (which I've at least touched-on in previous threads).


Hopeful-Cheers,
-Bob

[JimF]

Well, I had absolutely no brake light with the previous owner's 12-volt LED bulb. It was as you might imagine only working on 50% of the duty cycle, and then only when the bias got high enough to get the LED into light-emitting territory. It pulsed dimly.

The custom tail piece on the bike is fiberglass and not connected electrically to the frame. This allowed me the chance to rig a full wave bridge rectifier, but that didn't help at all. So I kicked the LED out the door.

Reversing the switch was problematic. The plated fingers on the inside have little spring to them. The plunger that shorts the fingers would quickly reshape them leaving the switch a permanent open. I think I have solved that issue. Some testing this weekend will help.

[DewCatTea-Bob]

" I had absolutely no brake light with the previous owner's 12-volt LED bulb. It was as you might imagine only working on 50% of the duty cycle, and then only when the bias got high enough to get the LED into light-emitting territory. "

____ Of-course there's more than one way to connect-up the powering circuit...
I'm left assuming that you simply ran the LED's circuit in 'parallel' with the circuit which powers the ignition. _ In that case, the alt.power-coil's output is either being largely-consumed by the ign.coil, (which is only near 1/16th of the time), AND worst yet, the REST of it's power-output is SHORTED directly to ground (through the ign.points) !!
So then it's really no wonder that there's no significant power-juice left-over to power-up the LED ! _ As the only power-juice available to the LED, is that which it has to share with the (rather high drain) ign.coil, and even that lasts only about 6% of the time,, which is why you saw only pulsed light from the LED, (as it was only fed power at the same [rare] times as when the ign.coil got it !).
__ I've previously mentioned details which ought to have tipped-off a thinking-reader about what's going-on with such.
To let this parallel-type circuit have a chance work, we need to prevent the ign.circuit from WASTING so much power as it does...
A diode (or two) can certainly prevent 50% of the power-coil's duty-cycle from being wasted (through the points), and with that p.juice saved, there ought then be sufficient power to fully light-up the LED. _ As THEN the LED will be fed a FULL* two pulses of power-juice per rev (* that's not shared with the ign.coil), which is at-least 9-times more available power-juice for powering-up LED, (compared to the straight parallel circuit-setup).
And if that still leaves it a bit dim and still noticeably flickering, then a relatively small capacitor should bring the light up to par.


" This allowed me the chance to rig a full wave bridge rectifier, but that didn't help at all. "

____ Well that's of interest ! _ It would've been interesting to see exactly how you found a way to connect-up a F-W.rect (to help-out the situation),, as I would like to determine/double-check if the way you did it would've indeed helped.
(Also hoping that MotoMike still finds such to be of interest as well !)
__ Also, (as I started-out indicating), since there's a number of different ways to possibly power-up the LED.brake-light,, I'm left wondering if you had thought to actually try-out running the LED.brake-light circuit in parallel with the power-circuit for the lighting-system !?
Since the tail & head lights are not short-circuits (like the ign.points are), and also since the LED drains very-little power-juice,, I'd thus-then expect that there would be plenty-enough/spare power-juice to fully light-up the LED.light-bulb, with the sharing of the power-output of the lighting-alt.power-coil,,
(which is why I have assumed that you didn't try that).


" Some testing this weekend will help. "

____ Looking-forward to have you see for yourself how poor the stock brake-light setup actually works !
__ I'm disappointed that nobody (so far) has given any comment on how their-own stock alt.powered brake-light performs. _ As it would be appreciated to have what I've claimed about it's performance either confirmed or modified (or even countered) !


Hopeful-Cheers,
-Bob

[JimF]

I did connect the LED bulb in parallel with the ignition coil. Remember though that the bike came with a 12-volt DC LED bulb, not that 12-volts has much meaning in this application but a 6-volt LED bulb (not easy to source) would likely light sooner but be also be damaged sooner from the peak voltage of the AC.

The power source is AC, certainly the frequency is variable by RPMs, I am not sure if the peak amplitude changes as well, the average voltage is zero, the RMS value is ???, the LED bulb is only every forward biased for only half the time and 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. I suspect several LEDs are connected in series within the LED bulb and so now the threshold voltage just to illuminate the LEDs rises.

This does not even take into consideration any reverse bias threshold voltage before the LEDs are damaged, though with LEDs in series that threshold is probably sufficiently high.

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. That being said I may revisit it in the future when I have a HLPED (High Power current driven LEDs not voltage driven) dual-filament LED bulb avaialbe that runs at full maximum intensity from as little as 4 volts DC to as much as 18 volts DC.