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[victor6.7y]

Might also be that the LED headlight was drawing so much current that de DC/DC converter was able to supply current but not able to keep de voltage at 12V.
Hopefully the problem will not come back

[erensi]

Glad to hear your 12v is working again.

LED headlight bulbs normally have a constant current driver between the source voltage and the LED element.
If the driver is starting to fail they can produce a buzzing/humming noise. Can also cause a lot of "noise" (EMI or RFI) in a circuit that can freak out other devices like the DC DC.

What do you mean by "freak out"?

[Crissa]

Loads that are inconsistent are not nice to dc-dc converters.

-Crissa

[Demoni]

What do you mean by "freak out"?

Into the weeds we go...

An incandescent bulb uses a filament (normally tungsten) to create light. This filament has a fixed resistance so if you double the voltage the current would also double (V=I*R) because the resistance of the filament is constant. 
6v = 2A x 3 ohm  vs  12v = 4A x 3 ohm

Led's are an variable impedance load, their have a fixed voltage drop. So if you doubled the current it would half the impedance.
6v = 2A x 3 ohm  vs  6v = 4A x 1.5 ohm

As a LED heats up its resistance is reduced, this allows more current to flow to the diode (because the voltage is fixed), more current causes more heat and lowers the resistance. This continues till the load going through the LED gets too high and it fails.

This is where a constant current driver circuit comes in and is what protrudes from the back of the bulb. These use a feedback loop circuit that passes the voltage through a resistor (value can be changed to adjust the current), this fixes the current provided to the LED. Depending on what part of your LED bulb circuit is failing it may can cause spikes in its current draw on the circuit. The sound you are hearing is created by the LED driver circuit switching at a high frequency. This can cause interference (EMI) that can wreak havoc with other components like the DC DC converter.

DC DC (Buck) converters use a PWM signal to adjust their duty cycle, this duty cycle is adjusted based on the circuit load requirements. This adjustment is based on a feedback loop that uses voltage as a reference. Your failing LED driver may be causing current fluctuations faster than the DC DC circuit can adjust for this might cause some sort of fail safe. The circuit also uses an inductor (coil of wire) to smooth the output voltage waveform. Inductors create a magnetic field that can be impacted by EMI.

These videos probably do a better job explaining how each circuit functions.
https://www.youtube.com/watch?v=iuMngik0GR8

[erensi]

 

The problem is back.   The 12V circuit randomly turns on and off while I'm riding now.  Last night it cut out as I was riding home along Skyline Blvd where there are almost no street lights.   I know the road well and went slow but I'm gonna need to figure this out.   Could it be the DC-DC inverter itself?  Has anyone experienced this?

[Auriga]

Yep, intermittent DCDC failure is a somewhat common DCDC failure mode. If you're certain the DCDC connection is good and secure, replacing it would be the next step.

[DonTom]

The problem is back.

As I expected (see reply 13 in this thread).

The 12V circuit randomly turns on and off while I'm riding now.  Last night it cut out as I was riding home along Skyline Blvd where there are almost no street lights.   I know the road well and went slow but I'm gonna need to figure this out.   Could it be the DC-DC inverter itself?  Has anyone experienced this?

Yes, it could be, but it also can be after the DC2DCC, check all connectors and other connections where possible.


Such intermittent electrical issues are very common in many  vehicles. Various reasons, including solder shaking off a printed circuit  board caused by vibrations. Some stuff is designed better than other stuff  to deal with vibrations, but often the best ways make it almost  impossible to repair except by replacement of the entire assembly. That could be how your DC2DCC is.


Unfortunately, such an intermittent issue as yours is almost impossible to repair on the web.  All we can do is tell you to check various connections and such. Do it with the bike's  lights on and wiggle the wires and such inside the headlamp assembly is where I would start.


If checking where the DC2DCC is located, be sure to stay away from the high voltage input an such.


Skyline can be a dangerous place to lose your lights, especially when foggy up there.  I used to live in the west bay area.


One of my best friends was killed on Skyline back in the 1970's. He just turned 21 years old then.


-Don-  Reno, NV