DynoHubs: What light bulbs/LED emitters?



>> SMS <[email protected]> wrote:
>>> Yes, all the effort to avoid halogen based dynamo lights in favor of
>>> LED based dynamo lights is really wasted effort. By the time you
>>> finish with the electronics you need, any theoretical efficiency gain
>>> is lost, and

> bob prohaska's usenet account wrote:
>> That's not true. No "electronics" are needed save for the LEDs
>> themselves. It's just that two or three pairs of LEDs are required.
>> Otherwise the match
>> between a bicycle dynamo and a light emitting diode is quite good.

SMS wrote:
> You can't reverse bias the LEDs, at least according to the data sheets.
> You might get away with it for a while, but you'll greatly shorten the
> service life. For example, the Cree LED specifies a maximum reverse
> voltage of 5 volts, while Luxeon just says 'don't do it.' While it's
> true that if you string three together in series you'll probably not go
> under -15V, the LEDs will only be forward biased and be on half the time
> (actually less) compared to a filament bulb. You're better off taking
> the 20% hit of the bridge rectifier than connecting them directly to the
> dynamo.
> Bicycle dynamos were specifically designed for filament bulbs, and don't
> match very well to LEDs. What's needed is a hub DC generator more suited
> to LEDs, such as the one patented by Nitto, but apparently not yet in
> production.

Regarding "Bicycle dynamos were specifically designed for filament
bulbs", weren't also common AA batteries?
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
 
On Tue, 18 Mar 2008, SMS wrote:

> (PeteCresswell) wrote:
>> Or is there something going on where an unused half of the sine
>> wave doesn't add significantly to the current drawn from the
>> alternator?
>
> The problem is that you'd be reverse biasing the LED that's off, and you'd
> destroy it.
>
> As the Luxeon datasheet states: "LEDs are not designed to be driven in
> reverse bias. Please consult Lumileds' Application Brief AB11 for further
> information." They don't state the maximum reverse bias current, only to not
> do it!

That is a safe though simplistic answer. If you dig a bit deeper (their app-note
AB20-3), they finally reveal the reverse characteristics - which (surprise!) look
like that of an ordinary high-power LED, with a reverse breakdown voltage in the
25V area. Yes, they warn of exceeding 50uA reverse current, but this shouldn't
happen with "antiparallel" connected LEDs.

Having said all that, I haven't actually done it :)

-f
 
> A Muzi wrote:
>> Regarding "Bicycle dynamos were specifically designed for filament
>> bulbs", weren't also common AA batteries?

SMS wrote:
> No.

Which sort of LEDs did they have in the 1950s? AA flashlights all used
to be filament bulb.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
 
SMS wrote:
> With the poorer optics of LED lamps, especially where the beam needs to
> be collimated from multiple LEDs, it's nearly hopeless.

I don't see anything wrong with these beams:

http://ktronik.com/cncdelite/beamshots.html

These lamps can be driven by dynamo:
http://candlepowerforums.com/vb/showthread.php?p=2248317&mode=threaded#post2248317

http://candlepowerforums.com/vb/showthread.php?t=179805

> What would work better if LED lamps are used is to use the dynamo to
> charge one battery while another battery powers the LED. Some
> rechargeable batteries are perfectly happy being charged at a wide range
> of voltages. You can even buy a commercial AA charger that will charge
> four AA cells from a source between 5 and 12VDC, with the higher the
> voltage the faster the charging. So no fancy DC-DC converter is needed,
> you can rectify the output of the dynamo and feed it directly to the
> charger, with only some sort of over-voltage protection being required
> (and practically speaking, no such protection is probably needed, as
> with the load of the charger the dynamo is not going to get over 12 volts.

"Dyno-Batt"
http://www.candlepowerforums.com/vb/showthread.php?t=174596

I'm kind of out of the loop in this conversation, but at least expensive or
do-it-yourself dyno stuff looks to be very capable.
 
Peter Cole wrote:
> The 350ma nominal maximum output current would be too high for safe
> operation of a 1W LED, but well suited to a 3W one. Running this
> unregulated off a SA would be fine, but you're only going to get ~1W to
> it and the efficiency is bad.

Current generation LEDs like the Seoul Semiconductor P4 (or Cree) are not
separated into 1W and 3W classes. As you can calculate from the graph
below, the Seoul P4 (max current rating 1000 mA, what you are calling 3W)
is actually more efficient at around 1W.

http://candlepowerforums.com/vb/showpost.php?p=1794431&postcount=260
 
Andrew Lee wrote:

> I'm kind of out of the loop in this conversation, but at least expensive or
> do-it-yourself dyno stuff looks to be very capable.

Interesting.

I noticed that Wal-Mart sells an Eveready 3 Watt rechargeable flashlight
for about $47, with the charging circuit internal. I don't know if the
circuitry allows charging during use though.
 
Andrew Lee wrote:
> Peter Cole wrote:
>> The 350ma nominal maximum output current would be too high for safe
>> operation of a 1W LED, but well suited to a 3W one. Running this
>> unregulated off a SA would be fine, but you're only going to get ~1W to
>> it and the efficiency is bad.
>
> Current generation LEDs like the Seoul Semiconductor P4 (or Cree) are not
> separated into 1W and 3W classes. As you can calculate from the graph
> below, the Seoul P4 (max current rating 1000 mA, what you are calling 3W)
> is actually more efficient at around 1W.
>
> http://candlepowerforums.com/vb/showpost.php?p=1794431&postcount=260
>
>
>

Yes, I know.
 
On Mar 19, 1:20 pm, Andreas Oehler <[email protected]> wrote:
> 2..."
>
> I won't open M$-doc documents of unknown origin. But those theory seems
> not to fit here. The dynamo delivers 500mA and this current went through
> teh bridge rectifier and the 4 LEDs. 500mA*0.8V=0.4W is consumed by the
> bridge rectifier. 500mA*3.7V*4=7.4W powers the LEDs.
>
> Efficiency is calculated as useful power compared to total power:

In more general terms, efficiency can be broadly defined as "how much
of what you want, divided by how much you have to spend."

That broad definition is important for this situation, a generator-
powered bike light, because we really don't care much about the
efficiency of the bridge circuit. We're spending mechanical power
from our legs - or, IOW, drag. We're wanting good illumination of the
road. (We also want adequate conspicuity, but it's nearly impossible
to light the road well and not be adequately conspicuous.)

If we get better illumination with less drag, nobody cares if a
certain component in our circuit has low efficiency. Freshman physics
students might fuss about it, but practical engineers should instead
look at the overall picture.

In a bike lighting system, the efficiency of an incandescent bulb -
even a halogen one - is terrible. About 90% of the input energy goes
to heat, rather than light. If your emitter does a lot better than
that, you can afford to feed it through a 75% efficient component.
You'll still come out ahead overall.

- Frank Krygowski
 
Andrew Lee wrote:

> Current generation LEDs like the Seoul Semiconductor P4 (or Cree) are not
> separated into 1W and 3W classes.

This is true, but the better bins are more expensive and are used in the
higher wattage lighting products because they are able to produce more
light and less heat at a given current, and heat dissipation is the
biggest issue with LED based lamps.

> As you can calculate from the graph below, the Seoul P4 (max current
rating 1000 mA, what you are calling 3W) is actually more efficient at
around 1W.

Yes, and that's another key difference between LEDs and incandescent
lamps. The incandescents are more efficient at higher voltages, though
it shortens the bulb life.

There are some people that think LED based lamps are efficient because
of the lack of a filament, but in reality they have even more difficult
thermal issues to resolve.
 
Per [email protected]:
>In a bike lighting system, the efficiency of an incandescent bulb -
>even a halogen one - is terrible.

Well, as the OP, I finally shut up and got a system.

--------------------------------------------------------
- SA (recent-model) XF-DD dynohub

- Busche & Muller HL Lumotec N2 halogen head light.

- Busche & Muller TL Seculite Plus LED tail light
--------------------------------------------------------

Coming from a hand-held Lowe's hardware "Task Master" flashlight
with 2 "C" cells and a Cree 4w emitter, I've got to say that the
halogen headlight is just plain pitiful in comparison.

On a scale of 1 to 10
Halogen headlight: .3
Lowe's handheld: 9.5

That's not to say the halogen light is not adequate for the task
- especially since many greater minds (and vastly more
experienced riders) than mine/me think they are.

But, in comparison, the lumens are simply not there.

In fact, I know a guy who injured himself fairly grievously
riding a bike path at night (with a headlight): rode right into
some sort of construction debris and/or hole. Now, having ridden
briefly with the halogen light, I understand how he managed to
do that.

OTOH, it might be an undercover safety feature at my sub-10 mph
night time riding speed: drivers see this wobbly, flickering
yellow light and it gets their attention more just because it
looks so out of place. -)

OTOOH, the tail light seems tb pretty decent. Gives out what I'd
call sufficient light, and has a stand light feature that shines
just as brightly when the bike is stopped.

My original intent was to hang several of those things on the
back, leaving only a token LED front light - all lights always
on.... but my limited knowledge of electricity led me to the
conventional path.

All-in-all, the system does what I set out to do: give my back
some visibility and keep me out of jail of some cop wants to be a
**** about having to have a "real" bicycle headlight.

But in the end, although I'll turn on the dynohub system and feel
better about my visibility from behind, I'll keep using the
Lowe's 4w Cree-based flashlight. That is one *brave* little
flashlight.
--
PeteCresswell
 
On Mar 19, 9:23 pm, "(PeteCresswell)" <[email protected]> wrote:
> Per [email protected]:
>
> >In a bike lighting system, the efficiency of an incandescent bulb -
> >even a halogen one - is terrible.
>
> Well, as the OP, I finally shut up and got a system.
>
> --------------------------------------------------------
> - SA (recent-model) XF-DD dynohub
>
> - Busche & Muller HL Lumotec N2 halogen head light.
>
> - Busche & Muller TL Seculite Plus LED tail light
> --------------------------------------------------------
>
> Coming from a hand-held Lowe's hardware "Task Master" flashlight
> with 2 "C" cells and a Cree 4w emitter, I've got to say that the
> halogen headlight is just plain pitiful in comparison.
>
> On a scale of 1 to 10
> Halogen headlight: .3
> Lowe's handheld: 9.5
>
> That's not to say the halogen light is not adequate for the task
> - especially since many greater minds (and vastly more
> experienced riders) than mine/me think they are.
>
> But, in comparison, the lumens are simply not there.
>
> In fact, I know a guy who injured himself fairly grievously
> riding a bike path at night (with a headlight): rode right into
> some sort of construction debris and/or hole. Now, having ridden
> briefly with the halogen light, I understand how he managed to
> do that.
>
> OTOH, it might be an undercover safety feature at my sub-10 mph
> night time riding speed: drivers see this wobbly, flickering
> yellow light and it gets their attention more just because it
> looks so out of place. -)
>
> OTOOH, the tail light seems tb pretty decent. Gives out what I'd
> call sufficient light, and has a stand light feature that shines
> just as brightly when the bike is stopped.
>
> My original intent was to hang several of those things on the
> back, leaving only a token LED front light - all lights always
> on.... but my limited knowledge of electricity led me to the
> conventional path.
>
> All-in-all, the system does what I set out to do: give my back
> some visibility and keep me out of jail of some cop wants to be a
> **** about having to have a "real" bicycle headlight.
>
> But in the end, although I'll turn on the dynohub system and feel
> better about my visibility from behind, I'll keep using the
> Lowe's 4w Cree-based flashlight. That is one *brave* little
> flashlight.

How's the battery life? (And with what kind of battery?)

- Frank Krygowski
 
(PeteCresswell) wrote:
> Per [email protected]:
>> In a bike lighting system, the efficiency of an incandescent bulb -
>> even a halogen one - is terrible.
>
> Well, as the OP, I finally shut up and got a system.
>
> --------------------------------------------------------
> - SA (recent-model) XF-DD dynohub
>
> - Busche & Muller HL Lumotec N2 halogen head light.
>
> - Busche & Muller TL Seculite Plus LED tail light
> --------------------------------------------------------
>
> Coming from a hand-held Lowe's hardware "Task Master" flashlight
> with 2 "C" cells and a Cree 4w emitter, I've got to say that the
> halogen headlight is just plain pitiful in comparison.

Task Force, not Task Master. Yes, this is true. But you're running the
Cree LED at a much higher current. You couldn't drive the Lowe's Cree
LED flashlight from a dynamo.

Look at Peter White's comparison between the Inolight 10+ and the
Schmidt E6 at "http://www.peterwhitecycles.com/inoled.asp"

"You can see that in the E6 beam on the left, the very top of the beam
is quite a bit brighter than the rest, and brighter than any part of the
Inolight 10+ beam. So the E6 can light up the road further away from you
than the Inolight 10+ can. In other words, you can aim the very top of
the E6 beam further down the road and still have a brightly lit road
surface. That will help if you're riding fast. So for fast cyclists, the
E6 will still be preferred. However, for the slower cyclist, the
Inolight projects a much wider beam, enabling you to see a much wider
section of the road ahead of you. Some of our customers complain that
the E6 isn't as wide as they would like. The bright part of the Inolight
beam is almost 50% wider than the E6, and the total width of the beam is
almost twice that of the E6.

This makes the Inolight an ideal headlight for commuting. Notice that
except for the very top of the E6 beam, the rest of the E6 beam is not
as bright as the Inolight 10+ beam. Overall, when riding, the effect of
the Inolight 10+ is similar to the E6, except for you being able to see
further with the E6. And with the wider beam, you have a better sense of
seeing the entire road ahead, rather than a narrow path through the
road. This is true on roads that are otherwise unlit. In urban areas
with street lights, it's of course very different."

Peter has pointed out the biggest problem with the E6, which is the
narrow path, but that's an intentional design of the E6.

The issue is really that the efficiency of an LED in a dynamo system is
far less than it is in a battery powered system, while an incandescent
bulb is of equal efficiency whether it's powered by a dynamo or a
battery (well not exactly equal, but close).

Actually the most efficient lamp for bicycle lighting at this juncture
is an HID incandescent or an over-voltaged non-HID incandescent, but I
just don't think HID will make it to the mainstream of bicycle lighting
due to cost, and over-voltaging non-HID bulbs results in too-short lamp
life for some (though the lamps are very cheap, so it's really all about
just carrying a spare). There was one company at Taipei Cycle
wholesaling good HID systems for $108. Still, by the time it's shipped
over and sold at retail, it'll be around $200. Within a few years the
LED manufacturers will improve their processes to the point where
they'll get more light and less heat from their designs.

> But in the end, although I'll turn on the dynohub system and feel
> better about my visibility from behind, I'll keep using the
> Lowe's 4w Cree-based flashlight. That is one *brave* little
> flashlight.

Alas, not sure it's still available.

BTW, how did you fasten it to the handlebars? I build a pretty good
handlebar holder from a Driftmaster rail clamp, a piece of aluminum flat
bar, and a pair of Nite Ize Delrin clamps. Took only about ten minutes.
I also built one for an AA flashlight but with a different type of bar
clamp. See: "http://nordicgroup.us/s78/flashlights.html" for details and
photos.

There was a really cool bar mount flashlight holder at Taipei Cycle, and
I may import them soon, but it was only a prototype. I brought along one
of the Lowe's Task Force headlights to the show so I could try various
flashlight holders, but there was only one at the entire show!
 
(PeteCresswell) wrote:
> Per SMS:
>> bins
>
> ?

When semiconductors come off the line, the parts are tested for various
characteristics and divided into bins. I.e. for microprocessors they
test for maximum clock rate and thermals. For LEDs they test for light
output and thermals at different currents. The best quality ones fetch
higher prices.

The no-name notebook computers typically buy the CPUs that no one else
wants because they are higher power with poorer battery life and more
heat to dissipate.
 
SMS <[email protected]> wrote:
>
> You can't reverse bias the LEDs, at least according to the data sheets.
> You might get away with it for a while, but you'll greatly shorten the
> service life. For example, the Cree LED specifies a maximum reverse
> voltage of 5 volts, while Luxeon just says 'don't do it.' While it's
> true that if you string three together in series you'll probably not go
> under -15V, the LEDs will only be forward biased and be on half the time
> (actually less) compared to a filament bulb. You're better off taking
> the 20% hit of the bridge rectifier than connecting them directly to the
> dynamo.
Ahh, but you're missing the whole point: Use a pair of LEDs wired inverse
parallel, and drive the common point with AC. The reverse bias is never
more than the forward drop, which presents no problems. Peak current can
be increased so long as average current is not exceeded. Series pairs
allow increased voltage with no per-diode increase in reverse voltage.

> Bicycle dynamos were specifically designed for filament bulbs, and don't
> match very well to LEDs.

Bicycle dynamos were designed to deliver about half an amp, roughly independent
of speed. That's a near-perfect match to an appropriately-sized set of LEDs
chosen to to match the voltage presented at normal riding speeds.

> What's needed is a hub DC generator more suited
> to LEDs, such as the one patented by Nitto, but apparently not yet in
> production.

All generators produce AC and require some sort of commutation, with its
attendant losses, to make DC. It could be mechanical, it could be electronic,
but why not use the LED as a self rectifier? Simple, cheap and effective:
http://www.zefox.net/~bob/bicycle/

bob prohaska
 
SMS wrote:
> Andreas Oehler wrote:
>
>> I won't open M$-doc documents of unknown origin.
>
> A good anti-virus program will eliminate this concern
>
>> But those theory seems not to fit here.
>
> Then I give up. What I want to say right now I won't say because I can't
> say it nicely. But understand that the 81.2% number is not a theory,
> it's the maximum possible efficiency, with an ideal diode (no voltage
> drop).
>
> If you're really interested in learning about this then you can google
> "81.2% bridge rectifier".

What you are talking about is "rectification efficiency". A rectified
sine wave will have a DC component and an AC component ("ripple").
Rectification efficiency is related to ripple factor, it has nothing to
do with power efficiency.
 
SMS wrote:

> There are some people that think LED based lamps are efficient because
> of the lack of a filament, but in reality they have even more difficult
> thermal issues to resolve.

The thermal design issues of incandescent and solid state lamps are
opposite. A filament works by heating to incandescence, so in effect,
"heat is good", you want to insulate the filament. For solid state
devices, heat is bad, for a variety of reasons. From an efficiency POV,
heat is just radiation in the non-visible spectrum, efficiency just
being the ratio of visible to non-visible radiation.
 
[email protected] wrote:

> In a bike lighting system, the efficiency of an incandescent bulb -
> even a halogen one - is terrible. About 90% of the input energy goes
> to heat, rather than light. If your emitter does a lot better than
> that, you can afford to feed it through a 75% efficient component.
> You'll still come out ahead overall.

All this is true, but the typical bike generators today are designed for
incandescents. With a few design changes they would be much better
(smaller, lighter, cheaper) for driving LEDs.

My ideal bike light would be a sidewall bottle with an
integrated/matched 3W LED. Something like that ought to cost $50 and put
out 300 lumens.

Another interesting option with LEDs is to use a color other than white.
Theory says that our vision sensitivity peaks at around 550nm, dim light
monochromatic vision at around 500nm. That means that a monochromatic
source at that wavelength might be around 2.5x more efficient.
Currently, green power LEDs are available that produce 70 lumens/watt.
This would give an effective (relative to white) almost 200 lumens/watt.
I don't know how well practice would match theory, it would be an
interesting experiment.
 
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