dynamo light cutout

Simon Brooke wrote:
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.


From the bible on dynamo's (beleuchtung.pdf @ enhydralutris.de):

An einem gebrauchten SW-NX30 gemessen ergeben sich folgende Erkenntnisse:
• An einem Frequenzgenerator mit Verstärker (kein Fahrraddynamo!) bricht
ab einer Eingangsspannung von 6,99 Veff (bei 50–1000 Hz) die
Ausgangsspannung, dann 6,22 Veff an 12 , zusammen und erholt sich erst,
nachdem die Eingangsspannung über ca. 1 s fast auf 0 V reduziert wird.

ie after an overvoltagesituation you have to stop for a second before
power can be resumed
/MArten

From the bible on dynamo's (beleuchtung.pdf @ enhydralutris.de):

An einem gebrauchten SW-NX30 gemessen ergeben sich folgende Erkenntnisse:
An einem Frequenzgenerator mit Verstarker (kein Fahrraddynamo!)
bricht ab einer Eingangsspannung von 6,99 Veff (bei 50–1000 Hz) die
Ausgangsspannung, dann 6,22 Veff an 12 , zusammen und erholt sich erst,
nachdem die Eingangsspannung uber ca. 1 s fast auf 0 V reduziert wird.

ie after an overvoltage situation you have to stop for a second before
power can be resumed

I've been pretending to myself I can make sense of that, but who am I
kidding?

Why should this be?

AC

/MArten

anonymous coward wrote in message e...

I've been pretending to myself I can make sense of that, but who am I
kidding?


Me too - but Babelfish did its best with :

Based on a used SW-NX30 the following realizations result: ? At a
frequency generator with amplifier (no bicycle direct current
generator!) if the output voltage breaks starting from an input
voltage of 6,99 Veff (with 50-1000 cycles per second), then 6.22 Veff
at 12, together and recovers only, after the input voltage over
approx.. 1 s is reduced nearly to 0 V.

Why should this be?


'Cos the cunning people at Shimano designed it so !

I run my Lumotec from the NX30 without the switch (and this means the
light is on all the time.) It also means that when the bulb goes I
probably put rather large amounts of power through the poor little
Zener diode that is really only there to stop me overvolting the bulb
at high speeds - and if I do it too long the diode is fried.

I guess that the Shimano people try to cope with this situation by
putting in circuitry/software so that the generator won't do anything
if abused !

I'd welcome a better explanation .

Tim

(Tim Henderson) wrote in message om...
anonymous coward wrote in message e...
and recovers only, after the input voltage over
approx.. 1 s is reduced nearly to 0 V.

Why should this be?


'Cos the cunning people at Shimano designed it so !

That makes sense then because I determined that I could "recover" from
the (presumed) overvoltage event by slowing down almost to a
standstill but without actually stopping.

Fiddling the contacts in the front lamp turned out to make no
difference. Swapping the front lamp out also made no difference.
Bypassing the switch unit altogether seems to resolve the issue. So I
suppose the question is does that mean that I am risking frying the
bulb? The cutout still happens at low (10-11mph) speeds so is the
switch circuitry being bit previous or is the generator outputting to
high a voltage? I haven't worked out how to get a multimeter
attached, rotate the wheel fast enough for long enough and still be
able to monitor values without something getting eaten by the spokes.
Since the unit is fairly new I guess I will try talking to sjsc and
see how they feel about a swapout of the switch. I would be happy to
move a to a h'bar mounted dumb switch but I quite like the idea of
more sophisticated overvoltage protection (provided it actually
works...)

best wishes
james

(james) wrote in message om...
The cutout still happens at low (10-11mph) speeds so is the
switch circuitry being bit previous or is the generator outputting to
high a voltage?

As I understand it, the voltage is just a function of the speed and
the load attached to it. I would be surprised if the generator
malfunctions to produce a greater voltage than design. But if you put
two 6v 3W bulbs in series , at a decent pedalling speed loads of
people seem to get 12v to power both up satisfactorily.
If you were getting overvoltage at low speeds, are you sure that you
have the right bulb in your lamp ? Have you tried another ?



I haven't worked out how to get a multimeter
attached, rotate the wheel fast enough for long enough and still be
able to monitor values without something getting eaten by the spokes.

I was recommended to use a power drill and gently bring the chuck in
contact with the tyre to spin it.

Since the unit is fairly new I guess I will try talking to sjsc and
see how they feel about a swapout of the switch. I would be happy to
move a to a h'bar mounted dumb switch but I quite like the idea of
more sophisticated overvoltage protection (provided it actually
works...)

Unsophisticated beefy back to back Zeners should do - though I
splashed out on the Reflectalite packaged dynamo regulator (which is
just the same thing in a little resin filled box). Unfortunately when
I swapped from bottle dynamo to NX30, I didn't put it back in the
circuit - so when the bulb went I suspect the little Zener in the
Lumotec did not like it .

Regards,
Tim