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dynamo light cutout



 
 
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  #1  
Old June 23rd 04, 09:09 PM
james
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Default 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
Ads
  #2  
Old June 23rd 04, 09:30 PM
Zog The Undeniable
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Default 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  
Old June 23rd 04, 10:35 PM
anonymous coward
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Default 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  
Old June 24th 04, 09:25 AM
Just zis Guy, you know?
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Posts: n/a
Default 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


  #5  
Old June 24th 04, 09:46 AM
m-gineering
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Default 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
  #6  
Old June 24th 04, 01:09 PM
Rory
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Posts: n/a
Default 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
  #7  
Old June 24th 04, 04:48 PM
Just zis Guy, you know?
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Posts: n/a
Default 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  
Old June 24th 04, 09:03 PM
james
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Posts: n/a
Default 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
  #9  
Old June 25th 04, 10:13 AM
james
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Posts: n/a
Default 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
  #10  
Old June 25th 04, 12:35 PM
Simon Brooke
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Default 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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