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Originally Posted by ItsJustMe
(Post 11357215)
Well, they're full of **** on the specs if nothing else. If the first one is really 17 watts, and it uses 3 AAA cells, which is 4.5 volts, that means it's drawing 17/4.5 = 3.7 amps from the AAA cells.
First off, AAA cells won't even deliver ONE amp. But even if they did, that would give you about a 10 minute runtime. They may be trying to imply that it puts out as much light as a 17 watt incandescent lamp. But they'd need at least a 2 or 3 watt LED to do that, and even that is problematic with AAA cells. Same analysis holds for the other one. If you do decide to get these, be sure to let us know how it works out. I suspect that you'll go down the road a bunch of us did (including myself) - I spent $20 to $35 each on about 5 lights before finally giving up and spending the money to get a real light. I blew more money on crappy lights in the end than if I'd just bought a good light to start with. I think a lot of us have a shoebox full of crappy useless $20 lights that we'd be happy to mail to you. I don't see how anyone can claim a 17w draw from 3 AAA. Heck, some 18650 have issue providing 2+ amps, and that's from a Lithium cell. Don't be misled from that article with 17w from 3AAA. |
In electronics and lights exggeration is all too common. I agree that no way can 3 AA batteries put out 17 watts. With NIMH batteries that would require 4.7 amps. Very possibly explode the batteries if you tried to draw that many amps and almost certainly damage them.
I bet if pinnned down the advertiser would claim they mean a light output equivalent to a 17 watt incandescent light bulb and even that may be exaggerated. I like lots of light even for road riding and have the Supernova E3 triple dynamo light on one bike. A nice unit but IMO not for the average dirt rider. It is used for MTB endurance racing in Europe per some Supernova advertising but IMO probably not for slow technical riding. I also have the Magicshine and to me that is near minimum lighting wanted for MTB riding under most conditions. Actual output as measured by a competitor is about 550 Lumens. That still makes it a best buy in bike headlights. The center beam is also a bit wider than on the Fenix and Olight flashlights I have, a definite advantage for a MTB headlight. |
Originally Posted by crazzywolfie
(Post 11358951)
i think i might try the 17 watt one.
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Originally Posted by cyccommute
(Post 11357707)
Sorry but for riding trails, you want a steady light output that is independent of speed. That cuts dynamo lights out of the equation.
BUT.... Off the dyno I get 250lm at 5mph and over 600lm at 15mph. Plenty in both situations. |
Originally Posted by cyccommute
(Post 11357707)
The operative phase being at high speed. What speed is "high speed"? 5mph, 10mph, 20mph? Might work well for downhill mountain biking but won't work at all for uphill. I can point you to any number of climbs around Colorado that would impossible for even a strong rider to maintain 5mph. And what happens when you stop? If you are in the middle of the woods on a bike that you can only generate light by turning the wheel at 5mph, you could be stumbling around in the dark a whole lot. There are any number of places where it's prudent...even in full daylight...to walk a section. What then?
Sorry but for riding trails, you want a steady light output that is independent of speed. That cuts dynamo lights out of the equation. However, good dynamo LED lights put out 25% of they max power at only 3 mph, and reach max output around 10 mph. See the graph (5 kph = 3 mph, 15 kph = 10 mph): http://www.peterwhitecycles.com/edel...PWC08-02-4.pdf At low speed you don't need as much light, since you are going slow and have plenty of time to stop for an obstacle only a few yards ahead; when you are going fast downhill you do need to see 100 or 200 yards ahead. At 2 mph and below LED dynamo lights become less useful, but I can walk 3 mph even uphill, so I don't see that being a huge problem. The good ones include a capacitor which provides dim light for up to 5 minutes after stopping, even. But for MTB trails you might want a small AAA battery powered headlamp as an additional light source, for emergencies and when stopped. I would think that would be a good addition to an external-battery headlight as well. |
Originally Posted by znomit
(Post 11361327)
Generally people run a helmet light too(battery) which helps on the technical stuff.
BUT.... Off the dyno I get 250lm at 5mph and over 600lm at 15mph. Plenty in both situations.
Originally Posted by jeisenbe
(Post 11361508)
Oh, I assumed "riding trails" referred to bike trails in flat-ish areas, like parks. I wasn't thinking of (uphill) mountain biking.
However, good dynamo LED lights put out 25% of they max power at only 3 mph, and reach max output around 10 mph. See the graph (5 kph = 3 mph, 15 kph = 10 mph): http://www.peterwhitecycles.com/edel...PWC08-02-4.pdf At low speed you don't need as much light, since you are going slow and have plenty of time to stop for an obstacle only a few yards ahead; when you are going fast downhill you do need to see 100 or 200 yards ahead. At 2 mph and below LED dynamo lights become less useful, but I can walk 3 mph even uphill, so I don't see that being a huge problem. The good ones include a capacitor which provides dim light for up to 5 minutes after stopping, even. But for MTB trails you might want a small AAA battery powered headlamp as an additional light source, for emergencies and when stopped. I would think that would be a good addition to an external-battery headlight as well. http://i144.photobucket.com/albums/r...e/52900001.jpg you could easily come to a dead stop if you happen to hit a rock or lose traction on the rear wheel. Look at the lower left of the picture. That is a step that the rider has to go up and over to hit a flat spot. She may be at near zero as she goes up and over that step. She'll need high torque but low speed to maintain forward momentum. A stopped dyno is a dead light in most cases. And, because the trails aren't graded, maintaining any kind of steady speed...even 3 mph...can be nearly impossible. The rider needs to concentrate on the ground in front of her and not on a light that is varying in intensity depending on her speed. I've been on plenty of stuff that I couldn't walk up at 3 mph at a steady rate. And there's the problem of dealing with the light being off while you dismount and get started walking. Now you are standing in the dark, night blind, on a hill that you are going to walk up because you can't ride up it. Not a recipe for a happy ending. If you are going to wear a battery powered helmet light, why not just use all batteries so that you don't have to deal with the dyno issues? Even on downhills off-road, the rider may have to come to a near stop as they pick their line or go around switch backs. Having the intensity of your light vary would hardly be an asset to the rider. And you may want to scout the route before you commit to riding it. A dyno light isn't going to be of much help there. |
8aa's=12volts.
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Originally Posted by trx1
(Post 11516249)
8aa's=12volts.
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true dat :)
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LED lighting and battery recommendations please
Hello, Bike Forum, new member here.
I would like some advice please on LED lights, where I might source 12V rechargeable battery pack? Need to find a rechargeable battery which will run 60" of LED for 4 hours. Really prefer some small, roundish battery for mounting at seat tube / bottom bracket area. The Bike is a 3-speed, 1970 Schwinn Racer. I am planning on using LED tape strip for a total of 60" of lights, in two separate runs, inside of the frame, utilizing the same power source for both runs. Does anyone know if the LED operational range is 9~14.8 VDC would an 8.4VDC battery pack turn on the diodes? Any help or resource links appreciated CS |
I've figured out what I am doing on my lights. Someone, please double check me on the numbers.
Total wattage of LED lights - 5.6 @ 12VDC Output of dynamo - 12 VAC @ 6 watts Converter - 12VAC to 12VDC @ 3 amp max output Anticipated Amp draw .5 (A=W/V) (.5=5.6/12) So based on my calculations everything should run well and leave 2.5 amps available from the converter. My concern is the 6-watt output of the generator compared to the 5.6-watt draw of the lights. The converter should contain a capacitor and diode rectifier bridge to make the conversion, I believe a .4 watt buffer will be fine. Also, the dynamo use 12VAC and the bike frame as its neutral (one wire to light one wire to the tail light). Was planning on using same wire path and connections for 12VDC LED application (using bike frame as DC ground & grounding LED to frame) Was planning on using bike ground for AC neutral and DC ground - any thoughts? Thanks |
I've figured out what I am doing, double check me on the numbers, please.
Total wattage of LED lights - 5.6 @ 12VDC Output of dynamo - 12 VAC @ 6 watts Converter - 12VAC to 12VDC @ 3 amp max output Anticipated Amp draw .5 (A=W/V) (.5=5.6/12) So based on my calculations everything should run well and leave 2.5 amps available from the converter. My concern is the 6-watt output of the generator compared to the 5.6-watt draw of the lights. The converter should contain a capacitor and diode rectifier bridge to make the conversion, I believe a .4 watt buffer will be fine. Also, the dynamo use 12VAC and the bike frame as its neutral (one wire to light one wire to the tail light). Was planning on using same wire path and connections for 12VDC LED application (using bike frame as DC ground & grounding LED to frame) Was planning on using bike ground for AC neutral and DC ground - any thoughts? Thanks |
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