email hidden said:
... the difference between primary and secondary lights is the switch.
Running two halogen lights, secondary and primary, they will both
reach full brightness about 12mph. Lower than that and they will both
be dimmer. Which is why some people switch teh secondary light on and
off going up hills or when riding slow, and thus burn out bulbs
switching the light on and off. If you only have the primary on, it
will reach full brightness at about 7mph and be dimmer below that.
With other headlights, it's not difficult to wire a pretty generic
switch yourself. I do this with my old Soubitez bottom bracket
generator on my commuter / utility bike.
I use a three position, single pole, double throw, center "off"
switch. The wiring is a bit odd... let's see if I can describe it:
The main circuit runs from the generator output through one headlight
filament, then through a "center wire" to the other headlight, through
that filament then back to generator ground. (I've isolated the
generator and both headlights from frame ground). If you do nothing
else, running the generator will light both headlights, but as folks
have said, they'll be too dim at low speeds.
The switch is wired as follows: the center "input" terminal of the
switch goes to that "center wire" running between the two headlights.
One "output" terminal of the switch is wired to one generator wire,
and the other "output" switch terminal is wired to the other generator
wire.
I have the switch mounted on my handlebar. If the switch is in it's
center=off position, it does nothing, so both lights still light. But
if you switch it either right or left, it shorts across one headlight
(your choice), taking it out of the circuit. That's useful at low
speeds. IOW, it allows either light to be "primary."
I wired it this way mostly so I could play around comparing headlamp
beams. But it occurs to me, it's also a built-in way to deal with a
burned out bulb. Just switch to the other headlight.
A word on the switch: The standard Radio Shack switch I used has
gotten a bit unreliable, probably from moisture and corrosion. I
noticed my lights looking dim, so I just touched the switch, and they
brightened up to full output. I plan to replace the switch and
weatherproof the new one.
Quoted message said:
But with the new LED generator lights, the primary reaches full
brightness at about 3mph. So if you hooked up two LED lights in
parallel, both getting full power all the time, they would both likely
reach full brightness at about 5mph. With the LED lights, there is no
need to have a series switch on the secondary light since both can
reach full brightness at such a low speed, about 5mph. So I'd just
run two LED lights as primary lights. And if I ever find a grand I
don't need, I'll likely get a Schmidt generator wheel and two LED
lights. Solidlights, SuperNova, etc.
What are the electrical characteristics of the new LED generator
lights? I ask, because with incandescents, you normally wire the
primary and secondary lights in _series_. (The only exception I know
of is the now-discontinued Lightspin.) That's because a generator is
roughly a constant current device, and its voltage output varies with
the resistance it sees. If it sees the double resistance of two
incandescent bulbs, it puts out essentially double voltage to power
them.
So how do the LED lamps behave? Do you really wire two of them in
parallel?
- Frank Krygowski
