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#11
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The last headlight you will ever need
On Tue, 25 Mar 2014 08:50:01 -0700, sms
wrote: On 3/25/2014 2:40 AM, somebody wrote: Now I have seen everything: http://www.fasttech.com/products/1/1...-3-mode-3200lm 3200 lumens is pretty lame. See http://www.aliexpress.com/item/free-shipping-5000-Lumen-2x-CREE-XM-L-T6-LED-Bike-Bicycle-Light-Headlamp-Flashlight/1492257169.html Yes, that beats it but does not have the 'wow' factor... Jeff the Cyclist would pick the 7-light version. Obligatory links for those unfamiliar... http://www.gocomics.com/pearlsbeforeswine/2013/01/13 http://www.gocomics.com/pearlsbeforeswine/2014/02/27 |
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#12
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The last headlight you will ever need
On Tue, 25 Mar 2014 08:53:15 -0700, Jeff Liebermann
wrote: On Tue, 25 Mar 2014 05:40:39 -0400, somebody wrote: Now I have seen everything: http://www.fasttech.com/products/1/1...-3-mode-3200lm Seven Cree T6 lights (10 watts or 3v @ 3A max). http://www.cree.com/~/media/files/cree/led%20components%20and%20modules/xlamp/data%20and%20binning/xlampxml.pdf I'll assume that they run it at 1A to keep the heat down. The battery pack is too small and is not going to work. The lamp data sheet shows that the 8.4v battery pack is six 18650 cells, which are running at 1A output. So, how is this thing suppose to light up LED's that can use up to 3A with only 1 watt max? I don't see an LED driver/inverter anywhere. An 8.4v @1A battery pack will deliver 8.4 watts. Yet, the lights can conceivably use 6-10 watts *EACH* or more conservatively, about 3 watts *EACH* if running at 1A. Assuming 3 watts per lamp for a total of 21 watts, an 8.4 watt battery pack can run the lights to about 25% battery capacity remaining in 18 minutes. Sounds great for very short rides. I gotta get back to work, but this was too good to ignore. Thanks. Magic. If you buy the light you receive, after the check clears, a special incarnation that causes the lights to use only a fraction of the wattage that they normally would use. -- Cheers, John B. |
#13
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The last headlight you will ever need
On Tue, 25 Mar 2014 11:04:34 -0700, sms
wrote: The actual manufacturer information doesn't claim any of that stuff http://www.trustfire.net.cn/product/1723645844-219463416/2014_newest_TrustFire_factory_D013_high_power_led_ bike_light_3200Lm_7_CREE_XM_L_2_waterproof_led_bik e_light.html Yep. He leaves out the only number of importance, the actually current drain at the various power levels. Also, I'm wondering how he converts the 8.4V to the 3.0V necessary to power the lights. Those batteries are certainly able to deliver 4A. Ok, let's do the math. (Note: I had 2 hrs sleep last night and will surely make at least one major math screwup here). The 8.4 battery pack has 6ea 18650 cells. Each cell is rated at 3.7V and optimistically 3A-hr drain. My limited imagination can't seem to conjure how to wire 6ea 3.7V batteries into something that produces 8.4 volts. My best guess is that the author of the data sheet can't add and that the voltage should really 7.4V, which is 2 cells in series, and 3 strings in parallel. Yeah, that makes more sense. That produces a 7.4V at 9A-hr battery pack. One can drain such a battery pack to about 25% of rated capacity without killing the battery, so that produces a: 7.4V * 9A-hr * 0.75 = 50 watt-hr capacity battery pack. Next, the current drain of the lights. The title says 3200 lumens, but the table in the data sheet says 2100 lumens in "hi" mode. I'll take the lower number as closer to reality. With 7 lights, that's 300 lumens per light. Diving into the Cree data sheet at: http://www.cree.com/~/media/files/cree/led%20components%20and%20modules/xlamp/data%20and%20binning/xlampxml.pdf the T6 lamp delivers a rated 280 lumens. 300 lumens would be 110% of rated power. Looking at Relative Flux vs Current graph, 110% requires 800ma current. Seven of those lights would be 5.6 Amps in high power. The power drain would be: 3.0V * 5.6A = 16.8 watts A 50 watt-hr battery capacity with a 16.8 watt load will produce: 50 / 16.8 = 3 hrs operating time. However, that assumes 100% efficiency in converting the 8.4V to 3.0V to run the lights. I don't see any evidence of a switcher, but there might be one buried inside the aluminum heat sink or battery pack. I'll give it 80% efficiency, which yields: 3 hrs * 0.80 = 2.4 hrs That's not as bad as I initially thought. The big question is whether you can power them from a hub dynamo! I can't, but maybe someone with tree trunk legs can do better. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#14
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The last headlight you will ever need
On 26/03/14 13:22, Jeff Liebermann wrote:
On Tue, 25 Mar 2014 11:04:34 -0700, sms wrote: The actual manufacturer information doesn't claim any of that stuff http://www.trustfire.net.cn/product/1723645844-219463416/2014_newest_TrustFire_factory_D013_high_power_led_ bike_light_3200Lm_7_CREE_XM_L_2_waterproof_led_bik e_light.html Yep. He leaves out the only number of importance, the actually current drain at the various power levels. Also, I'm wondering how he converts the 8.4V to the 3.0V necessary to power the lights. Those batteries are certainly able to deliver 4A. Ok, let's do the math. (Note: I had 2 hrs sleep last night and will surely make at least one major math screwup here). The 8.4 battery pack has 6ea 18650 cells. Each cell is rated at 3.7V and optimistically 3A-hr drain. My limited imagination can't seem to conjure how to wire 6ea 3.7V batteries into something that produces 8.4 volts. My best guess is that the author of the data sheet can't add and that the voltage should really 7.4V, which is 2 cells in series, and 3 strings in parallel. Yeah, that makes more sense. That produces a 7.4V at 9A-hr battery pack. One can drain such a battery pack to about 25% of rated capacity without killing the battery, so that produces a: 7.4V * 9A-hr * 0.75 = 50 watt-hr capacity battery pack. Next, the current drain of the lights. The title says 3200 lumens, but the table in the data sheet says 2100 lumens in "hi" mode. I'll take the lower number as closer to reality. With 7 lights, that's 300 lumens per light. Diving into the Cree data sheet at: http://www.cree.com/~/media/files/cree/led%20components%20and%20modules/xlamp/data%20and%20binning/xlampxml.pdf the T6 lamp delivers a rated 280 lumens. 300 lumens would be 110% of rated power. Looking at Relative Flux vs Current graph, 110% requires 800ma current. Seven of those lights would be 5.6 Amps in high power. The power drain would be: 3.0V * 5.6A = 16.8 watts A 50 watt-hr battery capacity with a 16.8 watt load will produce: 50 / 16.8 = 3 hrs operating time. However, that assumes 100% efficiency in converting the 8.4V to 3.0V to run the lights. I don't see any evidence of a switcher, but there might be one buried inside the aluminum heat sink or battery pack. I'll give it 80% efficiency, which yields: 3 hrs * 0.80 = 2.4 hrs That's not as bad as I initially thought. The big question is whether you can power them from a hub dynamo! I can't, but maybe someone with tree trunk legs can do better. I'm not even going to check your math and assumptions, because the thought of such a light is stupid to begin with. I saw 3200lm and thought "********". That said, assuming some reasonable level of dynamo efficiency, you'd need to produce something in the region of 20W mechanical to get 16.8W electrical. Considering my average power output estimate for last nights ride was a conservative 213W (conservative because with 2 water bottles and other stuff I'm a bit heavier than I told Strava), that's about 10% of my total average output. I reckon I could do it - but my 80lux IQ-TEC Premium was fine, even on the busy 80km/h arterial roads I was riding on in the darkness. -- JS |
#15
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The last headlight you will ever need
On Wed, 26 Mar 2014 14:52:26 +1100, James
wrote: That said, assuming some reasonable level of dynamo efficiency, you'd need to produce something in the region of 20W mechanical to get 16.8W electrical. That's an efficiency of 84%, which methinks is rather optimistic. Some dynamo testing he http://www.myra-simon.com/bike/dynotest.html While one went as high as 60% efficiency, most of the commodity dynamos ran about 30%. That would be 56 watts of person power needed to deliver the necessary 16.8 watts electricity to power the light. Also, I blundered into this article on using a bicycle to generate electricity. I haven't read it in detail, but basically the author suggests it's a lousy idea. http://www.lowtechmagazine.com/2011/05/bike-powered-electricity-generators.html Considering my average power output estimate for last nights ride was a conservative 213W (conservative because with 2 water bottles and other stuff I'm a bit heavier than I told Strava), that's about 10% of my total average output. With a 30% efficient dyanamo, change that to about 26% of your total average output. I reckon I could do it - but my 80lux IQ-TEC Premium was fine, even on the busy 80km/h arterial roads I was riding on in the darkness. What? You don't want 3200 lumens to scorch the paint on the cars ahead of you? Fire Phaser one, six more to go. Hmmm... I think I need to get some sleep. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#16
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The last headlight you will ever need
On 26/03/14 16:02, Jeff Liebermann wrote:
On Wed, 26 Mar 2014 14:52:26 +1100, James wrote: That said, assuming some reasonable level of dynamo efficiency, you'd need to produce something in the region of 20W mechanical to get 16.8W electrical. That's an efficiency of 84%, which methinks is rather optimistic. Some dynamo testing he http://www.myra-simon.com/bike/dynotest.html While one went as high as 60% efficiency, most of the commodity dynamos ran about 30%. That would be 56 watts of person power needed to deliver the necessary 16.8 watts electricity to power the light. SP claims 72% for theirs. This claims 67% for a SON. http://www.ctc.org.uk/file/public/fe...ub-dynamos.pdf Also, I blundered into this article on using a bicycle to generate electricity. I haven't read it in detail, but basically the author suggests it's a lousy idea. http://www.lowtechmagazine.com/2011/05/bike-powered-electricity-generators.html Considering my average power output estimate for last nights ride was a conservative 213W (conservative because with 2 water bottles and other stuff I'm a bit heavier than I told Strava), that's about 10% of my total average output. With a 30% efficient dyanamo, change that to about 26% of your total average output. I reckon I could do it - but my 80lux IQ-TEC Premium was fine, even on the busy 80km/h arterial roads I was riding on in the darkness. What? You don't want 3200 lumens to scorch the paint on the cars ahead of you? Fire Phaser one, six more to go. Hmmm... I think I need to get some sleep. Yep, you do. -- JS |
#17
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The last headlight you will ever need
On Tue, 25 Mar 2014 19:22:12 -0700, Jeff Liebermann
wrote: On Tue, 25 Mar 2014 11:04:34 -0700, sms wrote: The actual manufacturer information doesn't claim any of that stuff http://www.trustfire.net.cn/product/1723645844-219463416/2014_newest_TrustFire_factory_D013_high_power_led_ bike_light_3200Lm_7_CREE_XM_L_2_waterproof_led_bik e_light.html Yep. He leaves out the only number of importance, the actually current drain at the various power levels. Also, I'm wondering how he converts the 8.4V to the 3.0V necessary to power the lights. Those batteries are certainly able to deliver 4A. Ok, let's do the math. (Note: I had 2 hrs sleep last night and will surely make at least one major math screwup here). The 8.4 battery pack has 6ea 18650 cells. Each cell is rated at 3.7V and optimistically 3A-hr drain. My limited imagination can't seem to conjure how to wire 6ea 3.7V batteries into something that produces 8.4 volts. My best guess is that the author of the data sheet can't add and that the voltage should really 7.4V, which is 2 cells in series, and 3 strings in parallel. Yeah, that makes more sense. That produces a 7.4V at 9A-hr battery pack. One can drain such a battery pack to about 25% of rated capacity without killing the battery, so that produces a: 7.4V * 9A-hr * 0.75 = 50 watt-hr capacity battery pack. Next, the current drain of the lights. The title says 3200 lumens, but the table in the data sheet says 2100 lumens in "hi" mode. I'll take the lower number as closer to reality. With 7 lights, that's 300 lumens per light. Diving into the Cree data sheet at: http://www.cree.com/~/media/files/cree/led%20components%20and%20modules/xlamp/data%20and%20binning/xlampxml.pdf the T6 lamp delivers a rated 280 lumens. 300 lumens would be 110% of rated power. Looking at Relative Flux vs Current graph, 110% requires 800ma current. Seven of those lights would be 5.6 Amps in high power. The power drain would be: 3.0V * 5.6A = 16.8 watts A 50 watt-hr battery capacity with a 16.8 watt load will produce: 50 / 16.8 = 3 hrs operating time. However, that assumes 100% efficiency in converting the 8.4V to 3.0V to run the lights. I don't see any evidence of a switcher, but there might be one buried inside the aluminum heat sink or battery pack. I'll give it 80% efficiency, which yields: 3 hrs * 0.80 = 2.4 hrs That's not as bad as I initially thought. The big question is whether you can power them from a hub dynamo! I can't, but maybe someone with tree trunk legs can do better. I suspect that their target market doesn't do either math or electronics :-) -- Cheers, John B. |
#18
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The last headlight you will ever need
On 3/25/2014 4:57 PM, somebody wrote:
On Tue, 25 Mar 2014 09:18:57 -0400, Duane wrote: On 3/25/2014 9:02 AM, Sir Ridesalot wrote: On Tuesday, March 25, 2014 5:40:39 AM UTC-4, somebody wrote: Now I have seen everything: http://www.fasttech.com/products/1/1...-3-mode-3200lm Notice how close the light is to the beam shown? Notice the nice hot spot on that beam? Over 6.75 inches wide (172mm) and it goes on your handlebars? Sounds and looks like a bunch of flashlights mounted together but not giving a very useful beam pattern to see the road surface with. In strobe mode that light will be most annoying to anyone approaching it from in front. I'd pass on it too. Cheers I wouldn't have to turn it on to reject it. I can't imagine mounting a piece of junk like that on my bars. But I think the OP's point was to be sarcastic, no? Yes, I forgot the sarcasm header... But is there one floating out there with even more LEDs? Maybe with a bat signal? |
#19
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The last headlight you will ever need
On 3/26/2014 1:02 AM, Jeff Liebermann wrote:
Also, I blundered into this article on using a bicycle to generate electricity. I haven't read it in detail, but basically the author suggests it's a lousy idea. http://www.lowtechmagazine.com/2011/05/bike-powered-electricity-generators.html It's certainly a lousy idea if the intent is to use electricity to drive devices that can reasonably be driven mechanically. Consider what it would take to generate and store electricity to run an electric can opener, vs. just cranking a manual can opener for 15 seconds. Many years ago, we were asked to donate appliances, etc. to an impoverished immigrant family that had moved to our area. Among our donations was a manual can opener. The woman accepting donations was astonished - "Do those things still work?" etc. She'd used only an electric one for years. But earlier still, when we were given an electric one as a gift, we returned it to the store. Bicycling for transportation does have very high efficiency, but that's the result of a different factor. When a person rides a bike, they're not hauling around 3000 pounds of metal, plastic, rubber and glass. The moving mass is almost all payload. Related: http://www.bicyclinglife.com/Effecti...cacy/bacon.htm -- - Frank Krygowski |
#20
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The last headlight you will ever need
On Wednesday, March 26, 2014 11:28:00 AM UTC-4, Frank Krygowski wrote:
On 3/26/2014 1:02 AM, Jeff Liebermann wrote: Also, I blundered into this article on using a bicycle to generate electricity. I haven't read it in detail, but basically the author suggests it's a lousy idea. http://www.lowtechmagazine.com/2011/05/bike-powered-electricity-generators.html It's certainly a lousy idea if the intent is to use electricity to drive devices that can reasonably be driven mechanically. Consider what it would take to generate and store electricity to run an electric can opener, vs. just cranking a manual can opener for 15 seconds. Many years ago, we were asked to donate appliances, etc. to an impoverished immigrant family that had moved to our area. Among our donations was a manual can opener. The woman accepting donations was astonished - "Do those things still work?" etc. She'd used only an electric one for years. But earlier still, when we were given an electric one as a gift, we returned it to the store. Bicycling for transportation does have very high efficiency, but that's the result of a different factor. When a person rides a bike, they're not hauling around 3000 pounds of metal, plastic, rubber and glass. The moving mass is almost all payload. Related: http://www.bicyclinglife.com/Effecti...cacy/bacon.htm -- - Frank Krygowski In the rticle from the first link they talk about dead zones in the pedal cycle when using a bicycle to power a generator on a bicycle type trainer. I wonder if BioPace or other oval chainrings would help there? Cheers Cheers |
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