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Main
Date: 13 Sep 2006 01:56:19
From: Gooserider
Subject: Wind powered bike light
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Hmm. Wonder how it compares to a hub dynamo?
http://www.treehugger.com/files/2006/07/a_double_whammy.php
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Date: 13 Sep 2006 13:18:25
From:
Subject: Re: Wind powered bike light
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peter wrote:
> chuck wrote:
>
> > How long would a typical dynamo take to charge a 6V battery pack?
>
> Depends on the charge capacity of the battery pack.
>
> > Too me
> > a 6 watt bulb seems to be the minimal needed for my purposes. It'd be
> > nice knowing that on a 5 hour ride the last 3 in the dark will be
> > lighted.
>
> When riding at reasonable speeds (say over about 10 mph) you can get 6W
> directly from most dynamos just by giving them the right load. Some
> riders attach two 3W headlights in parallel and have a switch so only
> one operates at very low speeds but both can be turned on at cruising
> speed when desired.
That's correct, except the two headlights are in series, not parallel.
It's counterintuitive, but true.
As mentioned in another thread, typical bike generators are, roughly
speaking, constant current devices. They try hard to put out 0.5 Amp,
no matter what. If you give them twice as much resistance (two bulbs
in series) they put out roughly double their normal voltage, to pump
that 0.5 Amp through the doubled resistance.
It's not perfect, of course. Current drops a bit. And it works only
at high enough speeds. And only if the increased resistance torque
doesn't make the generator slip. (Most sidewall generators will slip.)
But it works.
> That would provide you with the 6W you want and
> would be much simpler than combining a charging circuit with a dynamo.
> The latter requires that the AC output of the dynamo be rectified to DC
> and then further regulated to avoid damage to the battery pack. That's
> not very convenient to do with the way dynamos are generally wired,
> typically using the bike frame as part of the current path.
Yep. As a general rule, the simpler the system, the more efficient it
will be. This little windmill headlight is just silly. It introduces
several extra losses.
I think it's intended for the people who power their sailboats by
pointing a pedal-powered fan at the sail. ;-)
- Frank Krygowski
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Date: 13 Sep 2006 08:00:02
From: peter
Subject: Re: Wind powered bike light
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chuck wrote:
> How long would a typical dynamo take to charge a 6V battery pack?
Depends on the charge capacity of the battery pack.
> Too me
> a 6 watt bulb seems to be the minimal needed for my purposes. It'd be
> nice knowing that on a 5 hour ride the last 3 in the dark will be
> lighted.
When riding at reasonable speeds (say over about 10 mph) you can get 6W
directly from most dynamos just by giving them the right load. Some
riders attach two 3W headlights in parallel and have a switch so only
one operates at very low speeds but both can be turned on at cruising
speed when desired. That would provide you with the 6W you want and
would be much simpler than combining a charging circuit with a dynamo.
The latter requires that the AC output of the dynamo be rectified to DC
and then further regulated to avoid damage to the battery pack. That's
not very convenient to do with the way dynamos are generally wired,
typically using the bike frame as part of the current path.
We used to have a cheap 12V, 6W dynamo on our tandem that provided a
very bright light but I haven't seen those units for sale anymore.
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Date: 13 Sep 2006 05:48:41
From: Earl Bollinger
Subject: Re: Wind powered bike light
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"Gooserider" <Gooserider@mouse-potato.com > wrote in message
news:7zJNg.42069$JO5.29948@tornado.tampabay.rr.com...
> Hmm. Wonder how it compares to a hub dynamo?
>
> http://www.treehugger.com/files/2006/07/a_double_whammy.php
>
Well it puts out a max of 3.5v at 70millamps so it can only power one single
LED light.
A typical LED uses about 20milliamps to 50 milliamps in order to light up.
Smaller LEDs can use 20ma, wheras the brighter ones use about 40-50ma (not
the big 1w LEDs).
I suppose they could build the white LED light into the unit itself, making
it self contained.
Hummm, if the white LED light and the red LED rear light are blinking, you
might be able to run two, if they alternate.
at 70milliamps, you are talking the high intensity small LED's. These are
regular LEDs that are brighter than normal.
These are not the new high power 1 watt LEDs either.
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Date: 12 Sep 2006 22:43:03
From: peter
Subject: Re: Wind powered bike light
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chuck wrote:
> On 2006-09-13, Mike Kruger <MikeKr@mouse-potato.com> wrote:
> > One of the commenters indicates that 3.5V*0.07A gives ~0.25W
> I wonder how long it would take to trickle charge a battery? If
> something like this worked, I could have a battery mounted somewhere and
> not worry about putting it on the charger all the time.
"Trickle" is certainly the appropriate term. Let's say you're using
this to charge a small bike light powered by 4 NiMH AA cells. The
energy of typical NiMH cells is now about 1.2V x 2.5 A-hr = 3 W-hr and
you have 4 of them for a total of 12 W-hr. Dividing by the power
output of this device gives 12 W-hr / 0.25 W = 48 hours for a recharge.
And that's assuming perfect efficiency in charging - more realistic
would be about 60 hours per recharge.
Depending on how much riding you do, the NiMH cells might be losing
charge due to self-discharge about as fast as this device would be
recharging them. A conventional dynamo seems far more practical to
provide a useful level of electrical power.
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Date: 13 Sep 2006 11:53:14
From: chuck
Subject: Re: Wind powered bike light
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On 2006-09-13, peter <prathman@comcast.net > wrote:
> chuck wrote:
>> On 2006-09-13, Mike Kruger <MikeKr@mouse-potato.com> wrote:
>
>> > One of the commenters indicates that 3.5V*0.07A gives ~0.25W
>
>> I wonder how long it would take to trickle charge a battery? If
>> something like this worked, I could have a battery mounted somewhere and
>> not worry about putting it on the charger all the time.
>
> "Trickle" is certainly the appropriate term. Let's say you're using
> this to charge a small bike light powered by 4 NiMH AA cells. The
> energy of typical NiMH cells is now about 1.2V x 2.5 A-hr = 3 W-hr and
> you have 4 of them for a total of 12 W-hr. Dividing by the power
> output of this device gives 12 W-hr / 0.25 W = 48 hours for a recharge.
> And that's assuming perfect efficiency in charging - more realistic
> would be about 60 hours per recharge.
>
> Depending on how much riding you do, the NiMH cells might be losing
> charge due to self-discharge about as fast as this device would be
> recharging them. A conventional dynamo seems far more practical to
> provide a useful level of electrical power.
>
How long would a typical dynamo take to charge a 6V battery pack? Too me
a 6 watt bulb seems to be the minimal needed for my purposes. It'd be
nice knowing that on a 5 hour ride the last 3 in the dark will be
lighted.
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Date: 13 Sep 2006 05:19:20
From: Werehatrack
Subject: Re: Wind powered bike light
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On Wed, 13 Sep 2006 01:56:19 GMT, "Gooserider"
<Gooserider@mouse-potato.com > wrote:
>Hmm. Wonder how it compares to a hub dynamo?
It doesn't.
Wind generation is fine if you're standing still in a spot where
there's lots of wind. Trying to convert forward velocity through air
back into electricity is far less efficient than simply engaging a
mechanical connection between the wheel and a good generating device.
The cited device is a toy, by any reasonable measure.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.
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Date: 13 Sep 2006 03:34:19
From: Mike Kruger
Subject: Re: Wind powered bike light
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"Gooserider" <Gooserider@mouse-potato.com > wrote in message
news:7zJNg.42069$JO5.29948@tornado.tampabay.rr.com...
> Hmm. Wonder how it compares to a hub dynamo?
>
> http://www.treehugger.com/files/2006/07/a_double_whammy.php
A Dynotec model 6 (tire generator) provides 3W.
One of the commenters indicates that 3.5V*0.07A gives ~0.25W
Even a tail light on a typical generator scheme is 0.6W, so this definitely
wouldn't be much help to see by; more of a "be seen" light.
I am slightly confused, though, and need an engineer to help.
On the one hand, any power this generates is from increased wind drag /
making you less aerodynamic.
On the other hand, it sits in front of you on the handlebars, so you'd be
blocking that wind anyway.
I'm guessing it's the former, but anybody else want to weigh in?
--
Mike Kruger
Blog: http://journals.aol.com/mikekr/ZbicyclistsZlog/
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Date: 13 Sep 2006 00:29:31
From: Paul Hobson
Subject: Re: Wind powered bike light
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> "Gooserider" <Gooserider@mouse-potato.com> wrote in message
> news:7zJNg.42069$JO5.29948@tornado.tampabay.rr.com...
>> Hmm. Wonder how it compares to a hub dynamo?
>>
>> http://www.treehugger.com/files/2006/07/a_double_whammy.php
Mike Kruger wrote:
<snip >
> I am slightly confused, though, and need an engineer to help.
> On the one hand, any power this generates is from increased wind drag /
> making you less aerodynamic.
> On the other hand, it sits in front of you on the handlebars, so you'd be
> blocking that wind anyway.
> I'm guessing it's the former, but anybody else want to weigh in?
My off the cuff guess:
The drag that would come from the corresponding portion of your frontal
area tries to tip the light over (but it's mounting hardware prevents).
The extra drag comes from moving the blades. Kind of like wearing a
form fitting jersey vs. a snug t-shirt that still flaps in the wind.
--
Paul M. Hobson
Georgia Institute of Technology
.:change the f to ph to reply:.
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Date: 13 Sep 2006 03:48:08
From: chuck
Subject: Re: Wind powered bike light
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On 2006-09-13, Mike Kruger <MikeKr@mouse-potato.com > wrote:
> "Gooserider" <Gooserider@mouse-potato.com> wrote in message
> news:7zJNg.42069$JO5.29948@tornado.tampabay.rr.com...
>> Hmm. Wonder how it compares to a hub dynamo?
>>
>> http://www.treehugger.com/files/2006/07/a_double_whammy.php
> A Dynotec model 6 (tire generator) provides 3W.
> One of the commenters indicates that 3.5V*0.07A gives ~0.25W
> Even a tail light on a typical generator scheme is 0.6W, so this definitely
> wouldn't be much help to see by; more of a "be seen" light.
>
I wonder how long it would take to trickle charge a battery? If
something like this worked, I could have a battery mounted somewhere and
not worry about putting it on the charger all the time.
> I am slightly confused, though, and need an engineer to help.
> On the one hand, any power this generates is from increased wind drag /
> making you less aerodynamic.
> On the other hand, it sits in front of you on the handlebars, so you'd be
> blocking that wind anyway.
> I'm guessing it's the former, but anybody else want to weigh in?
>
>
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Date: 12 Sep 2006 19:46:43
From: Dane Buson
Subject: Re: Wind powered bike light
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Gooserider <Gooserider@mouse-potato.com > wrote:
> Hmm. Wonder how it compares to a hub dynamo?
>
> http://www.treehugger.com/files/2006/07/a_double_whammy.php
Err, what about when you have a tailwind canceling out your wind? Aside
from that, it's also increasing your drag whether you need the light or
not. Plus at 0.25 watt it is not what I would call a worthwhile light.
Cute in terms of blueskying, but nothing I would bother buying.
--
Dane Buson - sigdane@unixbigots.org
"Well, that was a piece of cake, eh K-9?"
"Piece of cake, Master? Radial slice of baked confection ... coefficient of
relevance to Key of Time: zero." -- Dr. Who
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Date: 13 Sep 2006 15:28:44
From: Chris Z The Wheelman
Subject: Re: Wind powered bike light
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more efficient than that sloo-oow loading web page, I would hope.
But I wouldn't put my money into it. Wind is just not as effective as a
rolling wheel when it comes to turning something, especially anything
with any resistance.
- -
Comments and opinions compliments of,
"Your Friendly Neighborhood Wheelman"
My web Site:
http://geocities.com/czcorner
To E-mail me:
ChrisZCorner "at" webtv "dot" net
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Date: 13 Sep 2006 02:36:15
From: Kristian M Zoerhoff
Subject: Re: Wind powered bike light
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In article <7zJNg.42069$JO5.29948@tornado.tampabay.rr.com >, Gooserider@mouse-
potato.com says...
> Hmm. Wonder how it compares to a hub dynamo?
>
> http://www.treehugger.com/files/2006/07/a_double_whammy.php
Very interesting idea; the installation would be easier than a dynamo, and you
could take them from bike to bike with relative ease.
I also like the self-lighted pedals, but don't see options for toe clips or
clipless cleats for them (though they claim to be working on it).
--
__o Kristian Zoerhoff
_'\(,_ kristian.zoerhoff@gmail.com
(_)/ (_)
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