Greetings. Recently I bought a LED light for AC 9-18V for my moped. It uses AC which gives about 9V when at high rpm.

I installed this LED light. It worked fine for the first 15 mins. It dies out suddenly after. Opening the driver I noticed that one of the diode has blown up and two of the capacitors are swelling. There seems to be some liquid around the driver (it is not water as it was still there even after few days)

I have bought 2 of these LED and both ended its life after 15 mins or so. Why does it happen? Is my bike giving too much voltage?

 

Welcome to AAC!

Is my bike giving too much voltage?

Probably. Does it have a voltage regulator?

 

Welcome to AAC!

Probably. Does it have a voltage regulator?

Thank you for the warm welcome Alec! the bike itself or the led driver? As for the led driver, the only components that I could identify are
- 2 copper windings
- 4 470uf 25v capacitors
- SS34 diodes
- SMD resistors

I dont see any voltage regulators like the LM7805

 

It does look like over volts from the bike.
They usually rely on the headlight drawing enough current to keep the volts down. And if they have a voltage reg, the power is still often very spikey. The LED lamp probably will not draw enough current.
A voltage regulator looks to be needed.
Can the lamp run on DC? If so, add a rectifier and capacitor circuit along with a 3Amp EBay DC regulated power supply board to drive the lamp. Or a power Zener made with a power transistor and Zener diode and resistor all inside a 25A bridge rectifier so it will clamp the AC from the bike alternator to a safe level, like 12V or 15V.

 

It does look like over volts from the bike.
They usually rely on the headlight drawing enough current to keep the volts down. And if they have a voltage reg, the power is still often very spikey. The LED lamp probably will not draw enough current.
A voltage regulator looks to be needed.
Can the lamp run on DC? If so, add a rectifier and capacitor circuit along with a 3Amp EBay DC regulated power supply board to drive the lamp. Or a power Zener made with a power transistor and Zener diode and resistor all inside a 25A bridge rectifier so it will clamp the AC from the bike alternator to a safe level, like 12V or 15V.

Im actually on a project to covert the bike's AC to DC now. I've found a link where someone has done it without having a voltage regulator. Thank you for the suggestion

I'm a little baffled at how the LED which could receive 9V ~ 18V died when my bike barely gives out 9V. It is usually lower (4V ~ 6V). at lower rpm

 

It may be just transients at much higher voltages getting through.
Something to investigate.

 

the bike itself or the led driver?

The bike.

my bike barely gives out 9V. It is usually lower (4V ~ 6V)

How did you meaasure the voltage? An inexpensive digital multi-meter doesn't give accurate AC readings unless the waveform is a pretty good sinewave.

 

The bike.

How did you meaasure the voltage? An inexpensive digital multi-meter doesn't give accurate AC readings unless the waveform is a pretty good sinewave.

I don't think the bike has a voltage regulator as with normal halogen bulbs, the brightness of the bulb varies with the engine RPM

Unfortunately an inexpensive digital multi-meter is all I have.. So I can't say for sure

 

It may be just transients at much higher voltages getting through.
Something to investigate.

It could be. I wish I had an oscilloscope to further investigate it.

 

Welcome to AAC!

Probably. Does it have a voltage regulator?

No idea what they use now - but in my day. the battery gassing expended enough energy to 'control' the voltage when the main beam wasn't being used. Some have a series pair Zener module to clip the AC output. cheaper models usually switched in a ballast resistor when the headlight was off.

Half wave rectification is/was the norm for the DC parts of the system - its not at all like a well behaved bench supply.

 

my bike barely gives out 9V. It is usually lower (4V ~ 6V). at lower rpm

What load did you have when you measured the voltage?

 

It could be. I wish I had an oscilloscope to further investigate it.

Identify the ignition part before worrying too much about spikes. the old energy transfer ignitions were totally separate from the lighting etc and DC circuits. CDI with a high voltage winding on the generator became popular, they're also separate. starter solenoids and indicator relays can generate spikes, but those events aren't easy to sync a scope to.

In your OP, its not crystal clear what's AC - you're not stuffing AC generator into a driver module that expects DC are you?!

Even an AC module would be expecting 50 or 60Hz - you need to find out how many poles and the generator has and calculate frequency from expected RPM range.

I'm kinda thinking towards a buck/boost converter charging 7 or 8 nickel chemistry cells.

 

Identify the ignition part before worrying too much about spikes. the old energy transfer ignitions were totally separate from the lighting etc and DC circuits. CDI with a high voltage winding on the generator became popular, they're also separate. starter solenoids and indicator relays can generate spikes, but those events aren't easy to sync a scope to.

In your OP, its not crystal clear what's AC - you're not stuffing AC generator into a driver module that expects DC are you?!

Even an AC module would be expecting 50 or 60Hz - you need to find out how many poles and the generator has and calculate frequency from expected RPM range.

I'm kinda thinking towards a buck/boost converter charging 7 or 8 nickel chemistry cells.

My bike uses fuel injection. I can get DC from the dash/gear wiring but then I wouldn't be able to control hi/low beam

The AC is from the H4 female plug

 

Edited

 

Im actually on a project to covert the bike's AC to DC now

I don't see how the circuit in post #14 can work. What supplies the power, and where does it connect?
You're no doubt aware that on most motorbikes/mopeds the AC generating coil has one terminal grounded inside the magneto? That, and the fact that the common terminal of the bulbs is also grounded, make conversion by full-wave rectification to DC tricky.

 

I don't see how the circuit in post #14 can work. What supplies the power, and where does it connect?
You're no doubt aware that on most motorbikes/mopeds the AC generating coil has one terminal grounded inside the magneto? That, and the fact that the common terminal of the bulbs is also grounded, make conversion by full-wave rectification to DC tricky.

Initially I was afraid of discussing this because IIRC it is against the rules but..

The circuit works fine. It manages to give a constant power that lit up a great beam on the LED

The right side is from the bulb plug and the left side is the LED

However using that configuration, even when I take off the low beam source on the right side, the circuit will lit up both high beam and low beam. I am guessing because the ground is connected at the same wire on the High beam rectifier, thus providing power on the low beam LED as well