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dynamo light cutout
I have new shimano nexus dynahub with the switch unit that comes with
it and a B&M lumotec + with standlight (http://www.sjscycles.com/store/item544.htm)and d toplight + rear (http://www.sjscycles.com/store/item554.htm). The lights are wired in parallel using heavier-than-usual-for-dynamos speaker wire with proper soldered ends and spades etc. The light cuts out after anything from a few seconds to a few minutes. The standlights remain on (if they had time to charge up). If I stop the front wheel for a few seconds and then set off again the lights work again. I cannot determine if the length of time they work for correlates with anything (such as length of time that the dynamo stops for) or is random. The dynamo needs to stop for several seconds (eg braking and lifting the front wheel whilst in motion doesn't do it) It seems as though slowing to below the speed required to fire the light up (ie 2mph) does the same thing but I cannot be certain of this. Switching the switch off and on (without stopping the front wheel doesn't seem to do anything. I *think* the key is stopping the elctrical output from the dynamo (as opposed to some sort of mehanical effect from stoppingthe wheel) which leads me to suspect something to do with the zener diode protection or somesuch. IRRC both the switch unit and headlamp have zener diodes. I have never knowingly shorted any terminals. I have had the unit up to 40mph (although not with lights on) but dont often go much above 25 mph (peak speeds). Can anyone suggest a likely hypothesis for these syptoms or has anyone had similar eperiences. ISTR Guy has bad words for B&M lamps but that was mostly to do with terminal connections and I don't *think* that is the issue here best wishes james |
#2
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dynamo light cutout
james wrote:
I have new shimano nexus dynahub with the switch unit that comes with it and a B&M lumotec + with standlight (http://www.sjscycles.com/store/item544.htm)and d toplight + rear (http://www.sjscycles.com/store/item554.htm). The lights are wired in parallel using heavier-than-usual-for-dynamos speaker wire with proper soldered ends and spades etc. The light cuts out after anything from a few seconds to a few minutes. The standlights remain on (if they had time to charge up). If I stop the front wheel for a few seconds and then set off again the lights work again. I cannot determine if the length of time they work for correlates with anything (such as length of time that the dynamo stops for) or is random. The dynamo needs to stop for several seconds (eg braking and lifting the front wheel whilst in motion doesn't do it) It seems as though slowing to below the speed required to fire the light up (ie 2mph) does the same thing but I cannot be certain of this. Switching the switch off and on (without stopping the front wheel doesn't seem to do anything. I *think* the key is stopping the elctrical output from the dynamo (as opposed to some sort of mehanical effect from stoppingthe wheel) which leads me to suspect something to do with the zener diode protection or somesuch. IRRC both the switch unit and headlamp have zener diodes. I have never knowingly shorted any terminals. I have had the unit up to 40mph (although not with lights on) but dont often go much above 25 mph (peak speeds). Can anyone suggest a likely hypothesis for these syptoms or has anyone had similar eperiences. ISTR Guy has bad words for B&M lamps but that was mostly to do with terminal connections and I don't *think* that is the issue here I wonder if the xener diode has a bad connection. They get hot in use and the connection could be breaking. Could you try another lamp? |
#3
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dynamo light cutout
On Wed, 23 Jun 2004 13:09:31 -0700, james wrote:
I have new shimano nexus dynahub with the switch unit that comes with it and a B&M lumotec + with standlight I have the version of the light without a standlight. (http://www.sjscycles.com/store/item544.htm)and d toplight + rear (http://www.sjscycles.com/store/item554.htm). The lights are wired in parallel using heavier-than-usual-for-dynamos speaker wire with proper soldered ends and spades etc. The light cuts out after anything from a few seconds to a few minutes. Could the effect be related to heating? For example, if the light went out after you were going fast and you only stop for a short time, it may only work for 2 seconds. But if the light goes out whilst you are going slowly, then you stop for several minutes - it will work for several more minutes before going out again? The standlights remain on (if they had time to charge up). They are probably a separate circuit (powered by the dynamo, of course) so I doubt they can tell us that much about how the rest of the light works. If I stop the front wheel for a few seconds and then set off again the lights work again. I cannot determine if the length of time they work for correlates with anything (such as length of time that the dynamo stops for) or is random. The dynamo needs to stop for several seconds (eg braking and lifting the front wheel whilst in motion doesn't do it) It seems as though slowing to below the speed required to fire the light up (ie 2mph) does the same thing but I cannot be certain of this. Switching the switch off and on (without stopping the front wheel doesn't seem to do anything. I *think* the key is stopping the elctrical output from the dynamo (as opposed to some sort of mehanical effect from stoppingthe wheel) which leads me to suspect something to do with the zener diode protection or somesuch. Could be... IRRC both the switch unit and headlamp have zener diodes. I have never knowingly shorted any terminals. If you had, this would probably damage the dynamo rather than the lamp. I have had the unit up to 40mph (although not with lights on) but dont often go much above 25 mph (peak speeds). At least one dynamo - the expensive and sophisticated Lightspin - is destroyed whenever the rider exceeds a certain, rather low speed (3X mph IIRAC). Those continentals don't have steep hills like we do, so their bike lights aren't always designed to withstand the speeds that we can attain. Open-circuit dynamos can produce quite high voltages at these speeds, and I wouldn't be surprised if they could roast a small varistor or zener diode placed accross its output. You might put such a component in front of the switch (i.e. not turned off when the light is turned off) in order to protect it from the sparks the dynamo would otherwise make if you tried to switch off the lamp whilst you were moving. Can anyone suggest a likely hypothesis for these syptoms or has anyone had similar eperiences. If I short out my Schmidt dynohub, it starts to produce a moderate amount of resistance as I try to turn the wheel - it's a small recumbent wheel so this may be easier to detect. On the other hand, if it's open circuit then it just keeps spinning. I would suggest you put your bike upside down, and spin the wheel until the lamp goes out. If the wheel suddenly starts to slow down rapidly, this would suggest that the problem was a closed-circuit fault - perhaps a failed Zener diode. On the other hand, if the wheel just keeps spinning then you probably have a good old fashioned loose connection. AC |
#4
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dynamo light cutout
anonymous coward wrote in message e...
At least one dynamo - the expensive and sophisticated Lightspin - is destroyed whenever the rider exceeds a certain, rather low speed (3X mph IIRAC). Those continentals don't have steep hills like we do, so their bike lights aren't always designed to withstand the speeds that we can attain. I bug to defer: I max'd out last week at 81kph going down a continontil hill, with Nexus + BuM (mit Standlicht) blazing away happily - my commute in Luxembourg has 1000m of ups&downs, and the dynamo is always on, I've changed the bulb once in the last year. - Rory |
#5
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dynamo light cutout
james wrote:
I have new shimano nexus dynahub with the switch unit that comes with it and a B&M lumotec + with standlight [...] The light cuts out after anything from a few seconds to a few minutes. The standlights remain on (if they had time to charge up). If I stop the front wheel for a few seconds and then set off again the lights work again. Round Lumotec? This is normal :-( You need to spring the internal contacts a bit, and make sure you don't adjust the light up and down by pushing on the reflector. The oval Lumotec is somewhat better, but will still do this. The SON E6 does not do this, but has no standlight. -- Guy -- May contain traces of irony. Contents liable to settle after posting. http://www.chapmancentral.co.uk |
#6
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dynamo light cutout
"Just zis Guy, you know?" wrote:
james wrote: I have new shimano nexus dynahub with the switch unit that comes with it and a B&M lumotec + with standlight [...] The light cuts out after anything from a few seconds to a few minutes. The standlights remain on (if they had time to charge up). If I stop the front wheel for a few seconds and then set off again the lights work again. Round Lumotec? This is normal :-( You need to spring the internal contacts a bit, and make sure you don't adjust the light up and down by pushing on the reflector. The oval Lumotec is somewhat better, but will still do this. The SON E6 does not do this, but has no standlight. The switching off is caused by the shimano switch which is brimm filled with clever electronics you could do without. It probably detects a loose contact and manages to turn this into a real problem, hiding the cause in the process -- --- Marten Gerritsen INFOapestaartjeM-GINEERINGpuntNL www.m-gineering.nl |
#7
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dynamo light cutout
m-gineering wrote:
The switching off is caused by the shimano switch which is brimm filled with clever electronics you could do without. It probably detects a loose contact and manages to turn this into a real problem, hiding the cause in the process It also happens on my SON-equipped recumbent. Honest. Either way, the problem is in the lamp -or at least it is if my experience is anything to go by. -- Guy -- May contain traces of irony. Contents liable to settle after posting. http://www.chapmancentral.co.uk |
#8
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dynamo light cutout
"Just zis Guy, you know?" wrote in message ...
m-gineering wrote: The switching off is caused by the shimano switch which is brimm filled with clever electronics you could do without It also happens on my SON-equipped recumbent. Honest. Either way, the problem is in the lamp... [in my] ...experience I sprung the centre contact forwards this morning and managed 12 laps of the garage without a cutout. It isn't conclusive (I will run the light home tonight) but it looks hopefull although I am still puzzled by the apparent pattern I identified earlier best wishes james |
#9
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dynamo light cutout
various people wrote various things...
I don't think theissue is overheating as there doesn't seem to be any correlation between speed, time to cutout, time paused (as long as it is longer than about a second) and time to next cutout following the pause. After spinning teh front wheel by hand until the light cut out the resistance to turning *seemed* to reduce suggesting an open circuit (I say seemed, becuase the difference in resistance is most easily observed as the wheel stops but this is also about the time that the light comes back to life. I will investigate the contacts in the front lamp and try swapping it out (although my other lamp has a light sensitive switch in the lamp head so that might comlicate things). MG, do you have experience of teh switch unit being a common failure point with shimano units? I might also see if I can bypass the switch altogether thanks everyone james |
#10
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dynamo light cutout
in message , james
') wrote: various people wrote various things... I don't think theissue is overheating as there doesn't seem to be any correlation between speed, time to cutout, time paused (as long as it is longer than about a second) and time to next cutout following the pause. After spinning teh front wheel by hand until the light cut out the resistance to turning *seemed* to reduce suggesting an open circuit (I say seemed, becuase the difference in resistance is most easily observed as the wheel stops but this is also about the time that the light comes back to life. I will investigate the contacts in the front lamp and try swapping it out (although my other lamp has a light sensitive switch in the lamp head so that might comlicate things). MG, do you have experience of teh switch unit being a common failure point with shimano units? I might also see if I can bypass the switch altogether I know this is awfully scientific, but have you put a multimeter across the bulb? What happened to the voltage? What happened to the resistance? FWIW mys experience of the Shimano magic switch is very good. -- (Simon Brooke) http://www.jasmine.org.uk/~simon/ ;; Perl ... is the Brittney Spears of programming - easily accessible ;; but, in the final analysis, empty of any significant thought ;; Frank Adrian on Slashdot, 21st July 2003 |
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