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8.15 Yet Another Lighting System


This article is from the Misc Bicycles FAQs, by various authors.

8.15 Yet Another Lighting System

From: arnie@col.hp.com (Arnie Berger)

Since this is the season for posting your favorite homebrew lighting
system, I thought that I'd mention the hybrid system that just put
together. My caveat is that its new this year, so I don't have any
performance data to quote. I call it a hybrid system because I was
able to purchase an existing BLT dual headlight assembly at my local
shop for $60. I already had a battery and charger from my other home-
brew system on my road bike.

After several bad experiences commuting "on the road" to work. I bought
a mountain bike for the express purpose of commuting via a dirt road
through a park. It's worked out well and except for joggers and rabbits,
the trips are usually pretty uneventful. With the return to Daylight Time
fast approaching I was going to move the roadbike light to the mountain

My old light was built from the lamp and reflector of an old emergency
light. The kind that goes above the exits in theaters. It was OK, but it
was big, and difficult to keep aligned. When I saw the BLT lamp assembly
in the store, I felt that it would be the solution.

Many mountain bikes have a recessed allen head bolt that holds the
handlebar firmly to the stem. On mine, the bolt screws in from the front
at an up angle of about 15 degrees. As long as the head of the allen bolt
was recessed into the stem, it was useless, but when I replaced it with
an ordinary hex head bolt, I was able to attach an ordinary angle
under the bolt head. Now, the other arm of the angle bracket could mate to
the mounting bracket of the BLT lights.

All of the above discussion is a bit specific but the key for anyone who
is contemplating something like this is that the allenhead handlebar lock
bolt could be a useful place to hold a mounting bracket for a light.

Next, I found that my little Nashbarbike bag that sits on top of the
intersection of the stem and the handlebars easily holds my 6v, 5AH
lead acid gel cell from Radio Shack ( catalog # 23-185 ). In fact, with
the lamps mounted high on the handlebar and the battery virtually in the
same place, I don't have wiring all over the bike.

The BLT light uses RCA-type phono plugs for power hook-up. I have my doubts
about the long term reliability of these connectors. I may need to
change them. As of now, there is a phono plug mounted on the rear of the lamp
housing. A "Y" connector brings this to one female phono plug. I might
replace these with a wire exiting directly from the lamp, through a
strain-relief type grommet. The battery comes with two spade lug terminals.
I got the mating type and attached them to a phono plug.

For a rear light, I use my Vista-Light, which attaches to my rear rack.
It uses 3, high intensity LED's and works great. I highly recommend this
for your rear light.

The last part of the system is a charger. I built mine from one of those
9VAC plug-in wall transformers. I built a simple DC rectifier circuit and
then copied a nice circuit from the National Semiconductor Linear Data Book.
The charger circuit uses an LM317 3-terminal adjustable regulator that has
a transistor in one leg to set the current limit at 1 amp. It works well,
and prevents damage to the charger or to the battery. Lead acid batteries
like to be charged from a constant voltage source. This is in contrast to
Ni-Cads, which like to be charged with a constant voltage. The charger, by
the way, is the one I built for my old lighting system, and has worked
faithfully for about 5 years.

Only time will tell if the light ( about 10 watts worth ) will be adequate.
My old lighting system was a 12W bulb ( non-halogen ). I'm impressed with
Steve Koren's 35W headlight but, in my opinion, don't minimize the engineering
effort required to find a suitable place to mount the light. As everyone
knows, room in the front is a precious commodity. With Rapidfire
shifter/brakes and my cycle computer, there wasn't much mounting room left.
I was going to mount the lamp assembly onto one of those reflector brackets
that bolts to the fork crown, just above the front wheel. I felt the problem
was that the moment arm would allow the lamp to shake excessively, and either
fail or be useless.

vandeweg@bbn.com (Mike Vande Weghe) writes:
> arnie@col.hp.com (Arnie Berger) writes:
> >Lead acid batteries
> >like to be charged from a constant voltage source. This is in contrast to
> >Ni-Cads, which like to be charged with a constant voltage.
> Did you mean for one of these to be "constant current source", perhaps?

Sorry, for the typo, Mike is correct. The NiCads want to be charged from a
constant current source and, for best results and long life, charging
should be terminated once the cell voltage reaches a maximum and then
starts to fall. This is known as the -dv/dt method . A new company,
called Benchmarq , is producing a NiCad battery charger chip which will
perform all the functions necessary to build a NiCad battery charger with
minimal external support circuitry. I don't have any experience with it,
I've just looked at their data sheets.


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