LED Headlight and generator?

Generators put out AC, LEDs use DC, and polarity IS important...

I'm looking to do the same thing at some point soon. BTW, it looks to
me like many LED "flashlight" setups use 4.5v, so you'd need to add
some regulation as well as a rectifier to make this work. As I said,
I'm just starting to play with the idea right now.

The real question for me is the optics; my Lumotec has a great
reflector and lens...how will even a powerful LED compare?

"Andy M-S" wrote ...

Quoted message said:

The real question for me is the optics; my Lumotec has a great
reflector and lens...how will even a powerful LED compare?

Busch & Müller now offer an LED version of the Lumotec Oval. So the answer
probably is, quite favorably.
--
mark

On Thu, 13 Oct 2005 08:02:46 -0400, E Willson <[email hidden]>

Quoted message said:

Is it acceptable to run a 3 watt, 6 volt LED headlight with an ordinary
6v 3 watt generator?

In most cases, without additional circuitry, no.

Quoted message said:

Do LED's have different requirements than normal
incandescent bulbs for a bicycle application?

Yes. For one thing, they require DC current, and the generators
produce AC. Four diodes (and usually a few other bits) can turn that
AC into DC for the LED, but you have to know how to rig it.

Quoted message said:

I assume that polarity an
issue. What about actual system voltage? Would voltage be different with
an LED compared to a standard bulb?

Most LED units that I have seen (which admittedly isn't many) are
internally equipped with an appropriate ballast resistor now. In
theory, this should make the swap a one-for-one issue, but the AC
output of the generator changes the question.

--
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Words processed in a facility that contains nuts.

Would it work if you had a capacitor between the generator and the
bulb?

Lewis.

On 10/13/2005 4:35 PM said:

Would it work if you had a capacitor between the generator and the
bulb?

Lewis.

No. To block the reverse current you want a diode. Something like a
1N5400 or Radio Shack's 276-1661 would work fine. It wants to be
polarized the same as the LED, with its cathode pointing toward the
LED's anode. There may be some flickering when riding slowly.
Incandescent lamp filaments take a few moments to fade to dark, so
pulsations in the current are less noticeable. LEDs respond quickly.

--

Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana"😉
KG6RCR

Quoted message said:

Would it work if you had a capacitor between the generator and the
bulb?

You need more. A capacitor simply passes AC. You need diodes to pass
current in only one direction. And a bunch of other stuff.

Here's a link to a site (translated from German) that has a circuit
diagram (and much else) regarding LED headlights and generators.

http://tinyurl.com/dczro

- Frank Krygowski

I've seen some LED wind-up dynamo emergency flashlights. After
Hurricane Katrina I couldn't help but notice them.

http://tinyurl.com/cbx7w

I've often wondered about mounting these (with appropriate mods) on a
bike in conjunction with a dynamo hub . Would this be a lousy or a
good idea?

Mike Rocket J. Squirrel Elliott said:

On 10/13/2005 4:35 PM said:

Would it work if you had a capacitor between the generator and the
bulb?

Lewis.

No. To block the reverse current you want a diode. Something like a
1N5400 or Radio Shack's 276-1661 would work fine. It wants to be
polarized the same as the LED, with its cathode pointing toward the
LED's anode. There may be some flickering when riding slowly.
Incandescent lamp filaments take a few moments to fade to dark, so
pulsations in the current are less noticeable. LEDs respond quickly.

Isn't a LED a diode? Why would you need to add a diode if you already
have a Light Emitting DIODE? Can't you use two diodes back to back or
sumpthin?

Marty

E Willson said:

Is it acceptable to run a 3 watt, 6 volt LED headlight with an ordinary
6v 3 watt generator? Do LED's have different requirements than normal
incandescent bulbs for a bicycle application? I assume that polarity an
issue. What about actual system voltage? Would voltage be different with
an LED compared to a standard bulb?

this bulb http://tinyurl.com/7kk4b will replace both bulbs

E Willson said:

Is it acceptable to run a 3 watt, 6 volt LED headlight with an ordinary
6v 3 watt generator? Do LED's have different requirements than normal
incandescent bulbs for a bicycle application? I assume that polarity an
issue. What about actual system voltage? Would voltage be different with
an LED compared to a standard bulb?

TIA,
EJ in NJ

To add to the stuff already mentioned LED's tends to be more sensitive to overvoltages (which leads to overcurrents) than ordinary bulbs, so some sort of active regulator is pretty much necessary. You need to consider the sizeable variations that will occur when running from a dynamo as compared to when running from a battery.

Also, the light output of even the brightest of LEDs is quite small as compared to the light output of say, a 5 W Halogen lamp. Not even the 1 W luxeon diodes comes close. You need an array of LEDs to replace a bulb.

Marty said:

Isn't a LED a diode? Why would you need to add a diode if you already
have a Light Emitting DIODE? Can't you use two diodes back to back or
sumpthin?

LEDs are electrically fragile, asking them to withstand a backwards
voltage of over 10V peak is asking for a breakdown.

Anyway, unless you're using a 2-led-system, you really want a bridge
rectifier rather than a simple halfwave diode. In other words, 4 diodes.
Putting a smoothing cap behind it is the next step up. Shouldn't cost much
more than a euro or two total in parts.

Jasper

dabac said:

Also, the light output of even the brightest of LEDs is quite small as
compared to the light output of say, a 5 W Halogen lamp. Not even the 1
W luxeon diodes comes close. You need an array of LEDs to replace a
bulb.

That's why you use a 3W Luxeon, which is both fairly easily interfaced to
a generator and of the appropriate size.

Jasper

Jasper Janssen said:

Marty said:

Isn't a LED a diode? Why would you need to add a diode if you already
have a Light Emitting DIODE? Can't you use two diodes back to back or
sumpthin?

LEDs are electrically fragile, asking them to withstand a backwards
voltage of over 10V peak is asking for a breakdown.

Anyway, unless you're using a 2-led-system, you really want a bridge
rectifier rather than a simple halfwave diode. In other words, 4 diodes.
Putting a smoothing cap behind it is the next step up. Shouldn't cost much
more than a euro or two total in parts.

Jasper

We're all barking up the wrong tree when we're talking about voltages
and LEDs. LEDs are current devices which is a whole different ballgame.
You need a current regulator not a voltage regulator. This is my setup
on my road bike which is battery powered.

http://www.hyperactive.oz.nf/Lights2/Luxeon2.htm

Ignore any posts from ValleyBiker, he's an idiot.
See here.http://www.hyperactive.oz.nf/Bratton/Roger%20Bratton.htm

Marty

Marty said:

Jasper Janssen said:

Marty said:

Isn't a LED a diode? Why would you need to add a diode if you already
have a Light Emitting DIODE? Can't you use two diodes back to back or
sumpthin?

LEDs are electrically fragile, asking them to withstand a backwards
voltage of over 10V peak is asking for a breakdown.

Anyway, unless you're using a 2-led-system, you really want a bridge
rectifier rather than a simple halfwave diode. In other words, 4 diodes.
Putting a smoothing cap behind it is the next step up. Shouldn't cost much
more than a euro or two total in parts.

Quoted message said:

We're all barking up the wrong tree when we're talking about voltages
and LEDs. LEDs are current devices which is a whole different ballgame.

A bike generator *is* essentially a current source. Very badly regulated,
since it's done by interactions between the coils, the AC frequency, etc,
but it's a current source rather than a voltage source. However, when
loaded with a nominal 3W/6V load, voltage is, depending on speed, between
5 and 8 or so VACeff. Peak voltage is therefore SQRT(2) of that or about
10-12V, which would be what a LED without series diode would be subjected
to in reverse voltage. Regular leds can handle that, just, but Luxeons and
the like should really not have reverse voltages applied of more than a
few volts if you want them to live.

Quoted message said:

You need a current regulator not a voltage regulator. This is my setup

Well, that's not entirely true. Specced voltage drop plus an appropriately
sized ballast resistor will work, but it's not a very efficient way for
Luxeons on bikes.

Quoted message said:

on my road bike which is battery powered.

http://www.hyperactive.oz.nf/Lights2/Luxeon2.htm

Neat. I don't see any discussion of the electronics invovled though.

Jasper

E Willson said:

Is it acceptable to run a 3 watt, 6 volt LED headlight with an ordinary
6v 3 watt generator? Do LED's have different requirements than normal
incandescent bulbs for a bicycle application?

I am not sure whether a homemade set would survive without a capacitor
or some electronics to control (over)voltage.

However, dynamo powered LED headlights are on the market, at least in
Europe:

http://www.bumm.de/index-e.html?docu/ledsw-e.htm

Best,

marcin ha
--
Miasta dla rowerów http://rowery.org.pl http://krakow.rowery.org.pl

Sat, 15 Oct 2005 00:16:08 GMT, Jasper Janssen:

Quoted message said:

On Sat, 15 Oct 2005 05:42:50 +0800, Marty <[email hidden]> wrote:

Quoted message said:

A bike generator *is* essentially a current source.

True for modern gearless hub generators.

Quoted message said:

Very badly regulated,

No. Current ist very good limited to around 580mA. Perfect to run a 3W
Luxeon (or up to three in series) at good efficiency (efficiency goes down
with increase of current).

Quoted message said:

However, when
loaded with a nominal 3W/6V load, voltage is, depending on speed, between
5 and 8 or so VACeff.

With a 12 Ohm load voltag will not exceed 7 Volt. Of course at zero speed
voltage will be zero.

Quoted message said:

Peak voltage is therefore SQRT(2) of that or about
10-12V, which would be what a LED without series diode would be subjected
to in reverse voltage.

No. In reverse direction there won't be any current. So voltage will be
much higher at high speeds. At 50 kmph voltage at no load can be up to 50
Volts rms and up to 100 Volt peak.

But - the use of a bridge rectifier avoids this, also reduces the
flickering and allows the use of a "super"-capacitor to allow some kind of
standlight.

Quoted message said:

Quoted message said:

You need a current regulator not a voltage regulator. This is my setup

Well, that's not entirely true. Specced voltage drop plus an appropriately
sized ballast resistor will work, but it's not a very efficient way for
Luxeons on bikes.

Linear voltage or current regulators are a bad idea to use with a
generator: High losses, the risk of damage caused by high input voltage,
reduced output at slow speed.

Quoted message said:

Quoted message said:

on my road bike which is battery powered.

http://www.hyperactive.oz.nf/Lights2/Luxeon2.htm

Neat. I don't see any discussion of the electronics invovled though.

The biggest problem is to make an efficient optical system to shape the
beam.

Andreas

Sat, 15 Oct 2005 12:34:50 +0200, Marcin Hy³a:

Quoted message said:

I am not sure whether a homemade set would survive without a capacitor
or some electronics to control (over)voltage.

With LEDs forget about voltage. Just make shure the LED(s) are fit to take
the maximum current output of the generator (about 580mA).

Andreas

Andreas Oehler said:

Sat, 15 Oct 2005 00:16:08 GMT, Jasper Janssen:

But - the use of a bridge rectifier avoids this, also reduces the
flickering and allows the use of a "super"-capacitor to allow some kind of
standlight.

The trouble with a bridge rectifier is you're losing power across the
diodes. Why not use two LEDs back to back and maximise energy usage
since the diodes are rectifiers anyway. I have to admit I haven't look
deeply into the problem but a bridge rectifier seems very lossy.

Marty

Quoted message said:

Quoted message said:

Andreas

Marty said:

Andreas Oehler said:

Sat, 15 Oct 2005 00:16:08 GMT, Jasper Janssen:

But - the use of a bridge rectifier avoids this, also reduces the
flickering and allows the use of a "super"-capacitor to allow some kind of
standlight.

The trouble with a bridge rectifier is you're losing power across the
diodes. Why not use two LEDs back to back and maximise energy usage
since the diodes are rectifiers anyway. I have to admit I haven't look
deeply into the problem but a bridge rectifier seems very lossy.

I think this was already answered - specifically, high-output LEDs
don't tolerate much reverse voltage.

- Frank Krygowski