Headlight Pulser: What Should It Do?

I am thinking of building a headlight pulser sircuit. Would like some info on what they typically do or should do.

Do you usually pulse the low beam or high beam?

Does it leave the low beam on continuosly and "pulse on" the high beam as well?

What pulse frequency? Halogen sealed beam lights come on kind of slowly so very fast pulsing will not show up, it will look more like steady light. Is three pulses per second about right?

I am thinking of bulding one and I want it to be automatic.... I was thinking of using a solid state pulser in line with the high beam. When I shift to high beam, it would pulse the High beam during the day, just go steady on at night.

I would use a light-sensitive resistor to disable the flasher at night.

There is a federal law that mandates how headlight modulators work.

See it here: tinyurl.com/2urmh

They are LEGAL in all 50 states.

Very interesting, one thing I wondered: does pulsing the lamp shorten it's life compared to just letting it run normally?

bountyhunter wrote:

Very interesting, one thing I wondered: does pulsing the lamp shorten it's life compared to just letting it run normally?

Interesting question. My guess would be it shortens the life because of the cycling temperatures affecting expansion and contraction in the filament material. But it's just a guess.

Just make sure it doesn't flash too deeply or at the right frequency to set off emergency traffic signals. It'd be a shame to always have a green light...

bountyhunter wrote:

Very interesting, one thing I wondered: does pulsing the lamp shorten it's life compared to just letting it run normally?

It depends on the circuitry. If you pulse 100% voltage to it, yes it shortens the life. If you pulse 80% voltage to it, the life should be close to the constant on hour rating.

robjonrik wrote:

bountyhunter wrote:

Very interesting, one thing I wondered: does pulsing the lamp shorten it's life compared to just letting it run normally?

It depends on the circuitry. If you pulse 100% voltage to it, yes it shortens the life. If you pulse 80% voltage to it, the life should be close to the constant on hour rating.

Yeah, problem is pulsing 80% will make the circuitry a lot more complicated. It's very easy to use a power P-FET to pulse the 12V onto the bulb (which is 100%), not so easy if I have to drop voltage in series as that will require a power resistor to dissipate the power.

You could use pulse width modulation instead of a dropping resistor. Then just vary the duty cycle to find the amount of reduction you want. The FET would be full on or full off. You'd probably only need 100 hz or so. High frequency modulation shouldn't affect a filament's life as much (as slow cycling like in turn signals), because the filament will remain glowing during the off-time, just not quite as brightly.

loudhvx wrote:

You could use pulse width modulation instead of a dropping resistor. Then just vary the duty cycle to find the amount of reduction you want. The FET would be full on or full off. You'd probably only need 100 hz or so. High frequency modulation shouldn't affect a filament's life as much (as slow cycling like in turn signals), because the filament will remain glowing during the off-time, just not quite as brightly.

I see what you mean. Have a free running osc set at maybe 100 Hz to prevent flicker and adjust the duty cycle of that guy to be fixed 80%. And, use another 555 oscillator (set to about 3 Hz) to power the one running at 100 Hz to get the pulsing mode of the light. That could work.