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'[EE]: LED bicycle headlight'
2001\07\08@004532 by Roman Black

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Patrik Husfloen wrote:
>
> Neat, I was looking to do the same thing, though I have a dynamo/generator driving my bulbs.
> so I guess I'd need some rectifier circuit, using a backup cap to give som glow while stopped might be nice also.
> too bad I have no clue on electronics :)


Hi Patrik, what about a small NiCd or NiMH
battery pack (like the free ones someone gave
to piclisters before?) Small and lightweight.

That gives continued glow when the bicycle is
stopped, steadier glow when moving and is a very
simple way of protecting the LED headlight from
overvoltage.

You need the NiCd battery, LED and it's resistor,
and maybe a protect zener and on/off switch
would round it out nicely. Nothing too complicated
there.:o)
-Roman

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2001\07\09@111324 by Patrik Husfloen

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It seems from the Bulb life thread that there are a lot of drivers ICs for white LEDs
is that for any special reason? I mean your regular red LED never had a driver IC..
are the white LEDs "special" in some way, or can I drive them with a series resistor like I do with all the other LEDs?

I'm not sure how many LEDs one would need to give sufficient lite..I was thinking 4 maybe..and a couple of red ones for the tail light..
you mentioned NiCd, I thought those could only be recharged when they were completly drained or you pretty much ruined them.

I wasn't part of the Piclist at the time for thsoe free cells :/

/Patrik
{Original Message removed}

2001\07\09@121706 by Bob Ammerman

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The white LEDs have a rather high forward voltage (3.6V ?) so to drive them
off one or two batteries you typically need some sort of DC-DC converter.
Also by using current instead of voltage feedback, the converter can be
quite efficient.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2001\07\09@123005 by Patrik Husfloen

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ok, I see,
I wonder if that zentrix or something in that direction offers samples :)
will have to look into that..
would be pretty cool to fit LEDs on the bike for light.
I guess I iwll add it to my giant TODO list..
right after building a new computer case :)

Cheers,
Patrik

{Original Message removed}

2001\07\09@160705 by mike

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I think this is for current regulation - to maximise battery life, and
get a consistent tint - the colour of white LEDs varies with current
as the phosphor characteristic is nonlinear, giving a different
balance between the blue LED colour and the yellow phosphor colour.
You can drive them with resistors in most applications, as slight
colour changes are not often too important.  
On Mon, 9 Jul 2001 17:14:46 +0200, you wrote:

{Quote hidden}

>{Original Message removed}

2001\07\09@172911 by Jinx

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> are the white LEDs "special" in some way, or can I drive
> them with a series resistor like I do with all the other LEDs?

A 330 ohm resistor with a 6V gel cell is fine

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2001\07\09@202450 by Patrik Husfloen

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What is a gel cell, and I can I charge it with a dynamo from a bike?

----- Original Message ----- From: "Jinx" <.....joecolquittKILLspamspam@spam@CLEAR.NET.NZ>
To: <PICLISTspamKILLspamMITVMA.MIT.EDU>
Sent: Monday, July 09, 2001 11:28 PM
Subject: Re: [EE]: LED bicycle headlight


> > are the white LEDs "special" in some way, or can I drive
> > them with a series resistor like I do with all the other LEDs?
>
> A 330 ohm resistor with a 6V gel cell is fine
>
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2001\07\10@012150 by Jinx

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Patrik, further to my last reply, I made this up while watching the
midday news today. I baulked at paying $30 for a lamp I didn't
really like. Used scrap and got exactly what I wanted

http://home.clear.net.nz/pages/joecolquitt/makelamp.html

I've stuck with the plain resistor as the gel cell is rechargeable
and the lamp is used intermittently, but I would consider a driver
chip if either I was running disposables or using the light for long
periods

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2001\07\10@012205 by Jinx

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> What is a gel cell, and I can I charge it with a dynamo from a bike?

A sealed lead battery. The 6V 3Ah I buy is around NZ$22 (US$9).
One thing you need to keep a careful eye on is charging voltage
and limiting the discharge voltage. Go below a certain voltage and
not charge it PDQ and you'll permanently stuff it. Maxim will have
details about battery mangement ICs, which I'd recommend for
getting the best lifetime. I have a smart charger for gel cells so
haven't needed to look into it and can't supply details, sorry. As
for using the dynamo, I've never measured the output of one but
I guess it must be a few volts. If it isn't enough to directly charge
a battery you may need to build a voltage doubler and then regulate
it. It's all sounding very complicated but it isn't really. The money
you'll save over disposable batteries and the piece of mind gained
from having a second source of power will be worth it

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2001\07\10@105647 by Patrik Husfloen

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Well currently I use a dynamo (this is a very old bike, 20-30 years or so) and it has filametn bulbs front and rear, what I would like is a constanst light output no matter how fast I bike, which is not the case atm, and light when the bike isn't moving, in case you have to stop for traffic or something.
One idea would be to have the light on for about a minute after the dynamo stops charging.

I was browsing maxim earlier for those battery ICs, found a few, most were programmable by an SMB bus, I'd rather keep this as simple as possible.

Thanks for the info though,

Patrik
{Original Message removed}

2001\07\10@172116 by Jinx

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> Well currently I use a dynamo (this is a very old bike, 20-30 years
> or so) and it has filametn bulbs front and rear, what I would like is
> a constanst light output no matter how fast I bike, which is not the
> case atm, and light when the bike isn't moving, in case you have
> to stop for traffic or something. One idea would be to have the
> light on for about a minute after the dynamo stops charging.

> I was browsing maxim earlier for those battery ICs, found a few,
> most were programmable by an SMB bus, I'd rather keep this
> as simple as possible

Patrik, the first decision you need to make is whether you stick
with filaments or change to LEDs. That will then help you decide
what back-up supply to use. If you stay with filaments, a supercap
won't do it (two bulbs could use 1500mA). Go to LEDs and you'll
find the current requirements drop dramatically to 20-30mA, which
could be supplied by a battery or supercap. I think this is really a
case of putting aside a Saturday and as Nike would say, just do
it ;-)   BTW, are you using a hub or friction dynamo ?

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2001\07\10@182129 by Patrik Husfloen

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Well I am going to replace bulbs with LED that's already decided.
I don't have the parts to just _do it_ though, I would need to figure out what I need and order it.
I checked white LEDs today, they are about $2-3 (USD) each.
I figure using 3-4 would give enough light to be legal.
I was thinking a supercap would be easier to use, I also read the pulsing the light would be more efficient, in that case just a resistor isn't going to do it..

About the dynamo, not sure really, it's one of those that "leans" on the tire for rotation.
I'm guessing that is friction, this hub thing, what is that?

Any suggestions would be greatly appriciated,

Patrik

{Original Message removed}

2001\07\10@201312 by David P. Harris

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Can you tell me who sells teh super caps?
Thanks, David


Patrik Husfloen wrote:

{Quote hidden}

> {Original Message removed}

2001\07\10@211703 by Patrik Husfloen

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I havn't looked yet but I was planning on buying them from Elfa (.se).
If I decide to use them that is.

Patrik
{Original Message removed}

2001\07\10@220817 by Jinx

face picon face
> Well I am going to replace bulbs with LED that's already decided

That's good. Now, if you want to use the dynamo as the charger
(although honestly I think you'd be better off going to battery power
with a separate charger. After all, you won't be needing all those
amps anymore) then you'll have to do some measurements on it.
I expect it will be AC, so some circuit like that I posted the other
day will do you for rectifying the AC to DC for charging the battery.
The diodes can be 1N4001's or a pre-packaged bridge, the
smallest one on the shelf will suffice. Once you have a DC voltage
to measure, then you can think about what needs to be done with
it to charge the battery properly. If it's a supercap, then you'll need
to limit the voltage, probably with a low dropout 5V regulator.

> I also read the pulsing the light would be more efficient, in that
> case just a resistor isn't going to do it

What I think you mean is that you could pulse the LED with more
energy to make it brighter, but still keep the average power at a
safe level, the same way that IR LEDs are pulsed with high current
to get extra range. However, an IR receiver is not the same as a
human eye, and I couldn't say for sure whether high current pulsing
would necessarily mean a greater perceived brightness. Perhaps
it would be better to start off simply with a dropping resistor and
DC. You may find that's perfectly acceptable. I know I'm OK with
my LEDs

> About the dynamo, not sure really, it's one of those that "leans"
> on the tire for rotation.

Yuck. Haven't used one of those for a long long time. Complete
PITA as I remember. I spend enough time in 1st already on
Auckland's damn hills (for those who don't know, Auckland is
built on around 20 volcanic cones, errr, extinct ones hopefully,
up and down, up and down,........)

> I'm guessing that is friction, this hub thing, what is that?

It's built into the rear axle. If you plan to stick with a dynamo as the
primary supply and you no longer want the extra effort of the tyre
dynamo, maybe you could look for a back wheel with a hub one

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2001\07\11@004242 by Roman Black

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Patrik Husfloen wrote:
>
> Well I am going to replace bulbs with LED that's already decided.
> I don't have the parts to just _do it_ though, I would need to figure out what I need and order it.
> I checked white LEDs today, they are about $2-3 (USD) each.
> I figure using 3-4 would give enough light to be legal.

Check that they are the 6000mCd ones. You can
also get 1600mCd and 4000mCd which are not as good.


> I was thinking a supercap would be easier to use, I also read the pulsing the light would be more efficient, in that case just a resistor isn't going to do it..

Efficiency is not a problem, these leds are MUCH
more efficient than thefilament bulbs you have now.
I've used a 3.3F supercap to drive a led, soon
went back to a few small NiCds. Much better capacity
and flatter discharge curve than the supercap.
:o)
-Roman

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2001\07\11@004845 by Roman Black

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David P. Harris wrote:
>
> Can you tell me who sells the super caps?
> Thanks, David

They have been discontinued from most manufacturers
due to problems with corrosive leakage and failures,
and the high price of course.
We have lots of manufacturer mod notes saying to
replace the supercaps with button NiCds or Lithium
cells. Supercaps are not as good as the concept
suggests, very corrosive electrolyte and fussy
construction to get the capacity, which still does
not compare with NiCd for expected life or
capacity.
-Roman


> Patrik Husfloen wrote:
>
> > Well I am going to replace bulbs with LED that's already decided.
> > I don't have the parts to just _do it_ though, I would need to figure out what I need and order it.
> > I checked white LEDs today, they are about $2-3 (USD) each.
> > I figure using 3-4 would give enough light to be legal.
> > I was thinking a supercap would be easier to use,

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2001\07\11@014632 by Russell McMahon

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> > About the dynamo, not sure really, it's one of those that "leans"
> > on the tire for rotation.

It MUST go - almosty all the energy going into it is lost to mechanical
loss. You will not feel the power taken by a LD lamp if efficiently done.
Try a magnet or a few magnets evenly spaced on the rim and a pickup coil.
You may be pleasantly surprised. This is already done by others.

> Yuck. Haven't used one of those for a long long time. Complete
> PITA as I remember. I spend enough time in 1st already on
> Auckland's damn hills (for those who don't know, Auckland is
> built on around 20 volcanic cones, errr, extinct ones hopefully,

AFAIK there are actually about 100 distinct volcanic cones on the Auckland
field - many are no longer easily distinguishable as such. This is a
hot-spot in the volcanic plate much as that which forms the Hawaiian
Islands - just not so impressive. The field is still live but all past
mounds are dead. The last volcano was about 800 years ago (Rangitoto Island
just off the Auckland City coast). Rangitoto accounts for twice as much
material as all the rest of the volcanos before it combined !!! If we get
another of similar size in the city area proper much of Auckland will cease
to exist.

The good news is that Auckland volcanoes are getting more frequent and
larger with time. The average time between is about 2000 years and recently
its rather shorter. That means we are overdue (honestly) for another one and
it should be a real beaut. With any luck Jinx and I should see another one
here in out lifetimes. The main difference is that he lives on the edge of
the volcano zone and I live comfortably outside it - would do wonders for my
property price :-)

If you want REAL volcanoes a little South from here there is a volcano so
large that the locals don't know it is there !!! Largest volcanic eruption
on earth in the last 20,000 years plus. Closest thing to Olympus Mons that
you are liable to be able to touch in this lifetime. So big that we call it
"the volcanic plateau" - its real name SHOULD be Mount Taupo. Crater is a
lake 25 miles wide and about 40 miles long. Ten miles or so south there is a
5000 foot mountain (Tongariro/Ngaruahoe - one mountain but we think it is
two)) . In the last eruption the ash wave from Taupo overtopped this
mountain by about 3000 feet. You can run but you can't hide. The eruption
would have been observable throughout the world (if you had been there).

.

           Russell

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2001\07\11@171128 by David P. Harris

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OK- I get the picture --- stick with the batteries -- Thanks :-)
David

Roman Black wrote:

{Quote hidden}

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2001\07\12@140644 by Peter L. Peres

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> corrosive supercaps

That's new to me Roman. Most supercaps have a solid dielectric. Can you
quote a make that does not ? The main failure mode is by increased leakage
afaik. This is 'helped' by the long (100ft or more) length of very thin
(10 microns) tape dielectric in them. The slightest material fault causes
leakage or breakdown (at ridiculously low voltages - like 1.5V). Afaik
they don't age electrically, only material breakdown does them in.

Peter

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