Dirty alternator output fries LEDs?

 So, I got some fancy LED tail/brake lights for my Yamaha XS400, but I
was reading online about how "dirty" the power from motorcycle
alternators is... It was mentioned that the the resistance in
headlight and taillight filaments help damp down some of the nasty 20v
and up spikes that the alternator can produce.

I've noticed how my neutral light will pulse in time with engine RPM,
which certainly looks like voltage spikes to me. Should I wire up a
10W power resistor inline or across my taillight leads to soak up some
of these spikes so my LEDs don't fry, or do you think they will be ok
by themselves? Anyone else running the 3W Luxeons from
superbrightleds.com on a bike?

 

I don't know about running LED's, but the voltage from the alternator is
strictly a function of the engine speed.  It's the job of the rectifier and
voltage regulator to keep the voltage at a specific range.  So if anything
you should be blaming them - not the alternator.  One thing I should note,
in older bikes the voltage regulator and rectifier are separate objects -
whereas in modern bikes (like post 1980's) the alternator, rectifier, and
regulator are all integrated together.  If I had to guess I'd say the LED's
were undersized for the bike's voltage output, the bike's fine it's the
LED's that are not.

 


It's alarmist hype.  A healthy battery will provide an effective filter.
The voltage variations don't really qualify as "spikes".  The "pulse" you
see is probably due to the voltage falling below 15V as the alternator
ceases to produce enough to provide a charge.  Consider turning UP your idle
speed (for lots of reasons).

I've been thinking about supplementing my brake lights with LEDs.  What's
your source ??

 
http://www.superbrightleds.com

I'm told that only the 3W and 5W Luxeons are worth your time, the
others they sell on that site just aren't as bright or are only bright
directly where the LED is pointing (narrow beam angle). However since
you'll be keeping your stock lens, it will diffuse the beam a bit so
their next-brightest 30-LED units might work ok too. The 3W I just got
are at least as bright as the stock bulbs, though there's not as much
differentiation between tail and brake as I might like -- in other
words, the tails are too bright.

At the same time, I also got their WLED-x5 wedge-base to use as side
markers for my car -- they're also at least as bright as the stock
incandescent. The frosted BA9S I got as license plate lights were
disappointing though.

 

All LEDs are directional, you need a diffuser of some kind with them.
Anyway, they only sell one brand of power LEDs, for modding my
brother's Maglite 3D I bought SSC P4 3W LED at www.dealextreme.com
- 3W SSC and Cree LEDs are also quite nice. You'd have to google
a bit to find information about which one is the least directional,
or ask someone over at candlepowerforums.com ;-))

Then there are the REALLY BRIGHT power leds, like the Osram Ostar
or SSC P7 <http://www.dealextreme.com/details.dx/sku.11809> .
The problem with high power LEDs is that you need
to mount them on a really efficient heat sink, because when
they overheat they damage themselves.

Leslie
--
Leszek "Leslie" Karlik
NTV 650