Blowing headlights

[Guest]

Hey fellas. After at least a year (maybe multiple years - can't even remember when I replaced it last) on the same H4 headlight bulb, my low beam quit on me last week. I switched to high, and that was out I think before I got home. Picked up a Silverstar at Walmart, carefully (no touchy! Used gloves.) installed the replacement, and was up and running again.

Went for a longish ride in the country over the weekend, and I don't know if the new low beam was working when I got home, but it wasn't working this morning when I fired up the bike to head to work. Turned on the high beam, and that was blown before I even left the parking lot.

I've read through the threads on this topic, and based on my experience so far I'm leaning toward the Regulator Rectifier, which is to say that the long life of my previous bulb and the fact that I keep my carbs in sync makes me think it's not a vibration problem.

I'm open to defective bulb, but before I go try to convince Walmart to replace it (with a receipt but without the package), I'd like to check the voltage at the headlight. As as basic as that sounds, I'm not sure how. There's three contacts - how do I tell which two to check, and do I check with the bike running (about what RPM?) or not?

If it helps at all with the diagnosis, for as long as I've owned the bike the headlight gets brighter at higher RPMs. That doesn't mean much to me, but it seems like it might be significant.

Thanks!

Edit: Additional notes based on other threads - forgot to add... I have a 1-year-old sealed battery, works and starts like a charm.

[hampshirehog]

I would check the voltage at your battery at tickover, 4k rpm and turned off. Blowing headlight bulbs can be a symptom of the R&R playing up and you'll find a clue to that at the battery.

[tom203]

Do the stator tests- you might find your charging voltage is too high! headlight getting brighter at high revs points to this, though with all the connection losses, you'd think it wouldn't effect bulb life but rather torture battery.

[Roostabunny]

I would check the voltage at your battery at tickover, 4k rpm and turned off. Blowing headlight bulbs can be a symptom of the R&R playing up and you'll find a clue to that at the battery.

Cool. What's tickover? As you crank the engine?

[Roostabunny]

Do the stator tests- you might find your charging voltage is too high! headlight getting brighter at high revs points to this, though with all the connection losses, you'd think it wouldn't effect bulb life but rather torture battery.

Connection losses, you mean extra resistance or voltage loss from corrosion, age and such?

Sorry if I'm misusing those electrical terms, BTW.

[Steve]

Those guys "across the pond" use 'tickover' for IDLE.

.

[barnbiketom]

ALSO if your battery is weak ..it can be weak in terms of cranking and taking a charge..( as in not taking a charge correctly) it will not buffer the voltage correctly and the rect/reg may end up overcharging..
make SURE your battery passes all tests and then I'd place a digital voltmeter on it and ride it for a while.. see if the voltage rises above 14.5 V.. if not then buy a different brand bulb hahah

[MisterCinders]

To test the power at the light, check your diagram. Usually black/white wire is the ground. The others will be hot.

[OldVet66]

Too much voltage will blow the lights quite nicely. Mine would take out the low beam every three or four months toward the end. Then it started boiling the water out of the battery. I installed the Compufire charging System, and so far the same type H-4 bulb has lasted long enough to have been changed two or three times with the old system. At the price of +50 H-4 bulbs alone, it will pay for the Compufire in several years or less.

[koolaid_kid]

So, everyone is pointing to the R/R, so I thought you might (or not) appreciate an explanation what the R/R does. The Rectifier converts the AC output of your stator into DC voltage that your system uses. The Regulator limits the output voltage to ~14.5 volts. Too high of an output voltage will tend to burn out lights, as you have observed. This is an indication the that Regulator portion is no longer regulating.
The Honda R/Rs are a favorite replacement for the OEM R/Rs.

[trippivot]

where is the fuse in this story..

we protect our circuits with a fuse to prevent problems like this. So if the fuse is letting you bulb zap.. Where is it? and Why is it not doing it's job?

I suggest looking at some other things where the fuse wont help

if the ground to your light opens and closes like a slightly broken wire it will kill many light bulbs. H-4s are not strobes - fuses can handle the strobing.

short circuits on the power wire will zap a fuse before your lighing element..

Excessive vibration to the bucket while riding can do this too -- I have had strutted bikes - you probably dont . but bad rubber dampeners that finally gave up the ghost. Road vibration hits different than engine vibration.

Finally you could put a voltmeter in place of the headlight and take note if the voltage exceeds 17 DCV When revving the engine and twisting the bars. but if you have this senario you got more problems to sort out AND I gotta ask why have a great big fuse where a little one needs to be?

[MisterCinders]

we protect our circuits with a fuse to prevent problems like this. So if the fuse is letting you bulb zap.. Where is it? and Why is it not doing it's job?

I suggest looking at some other things where the fuse wont help

if the ground to your light opens and closes like a slightly broken wire it will kill many light bulbs. H-4s are not strobes - fuses can handle the strobing.

short circuits on the power wire will zap a fuse before your lighing element..

Excessive vibration to the bucket while riding can do this too -- I have had strutted bikes - you probably dont . but bad rubber dampeners that finally gave up the ghost. Road vibration hits different than engine vibration.

Finally you could put a voltmeter in place of the headlight and take note if the voltage exceeds 17 DCV When revving the engine and twisting the bars. but if you have this senario you got more problems to sort out AND I gotta ask why have a great big fuse where a little one needs to be?

I doubt he has a short, because that would blow the fuses. If he is getting too much voltage, that doesn't mean he is pulling too many amps. Amps blow fuses, not voltage.

That said, if you cannot sort this out, a low-amp fuse at the light end of the wire might help as a stopgap. Basically, if you are getting more amps than the lightbulb can handle, but not the 15+ that will blow a main fuse, drop a smaller fuse into the lighting wire (3-5 amp?). That way, you will have the small fuse blow when the problem emerges, preserving the light while you are tracking down the problem.

At least I think that would work. But I am pretty dumb.

[koolaid_kid]

An H4 high beam in the US draws 65 watts by law. This is the total power it can dissipate. Since P = I*V, Power (measured in Watts) = Current (measured in Amps) times Voltage (measured in Volts), we can calculate the following:
At a nominal 12V, the current draw would be ~5.5A, since the filament cannot dissipate any more than 65 watts of power. However, let's theorize that his system is over voltage, let's pull 15V out of the hat. Now it is only drawing ~4.3A for 65W, so the fuse would not blow. However, the bulb is not rated for this high of a voltage and has the potential to burn out due to over-voltage.
Also, being an 81 I suspect it has a separate 10A blade fuse for the headlight like my 83.

[OldVet66]

Now you know why they use 480 volts to run large commercial three phase ac units on buildings on 15amp circuits. Higher voltage less current, less copper cost in the wiring, more efficiency etc. Higher voltage will not blow your fuses unless it is extremely high.

[Roostabunny]

This is awesome, fellas. Getting a mild EE lesson with my troubleshooting help. I took Physics 101 a long time ago, so some of it sounds vaguely familiar.

So to ask a total newb question, I figure I'll set my multimeter on V DC in the 20 range to measure at the battery and at the bulb socket? I assume 20 means up-to-20V?

Also, Steve, thanks for translating "tickover"!