dynamo light cutout

james said:

I have new shimano nexus dynahub with the switch unit that
comes with it and a B&M lumotec + with standlight
(sjscycles.comitem544.htm)andOpen ↗ d toplight
+ rear (sjscycles.comitem554.htmOpen ↗). 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?

james said:

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.

Quoted message said:

(sjscycles.comitem544.htm)andOpen ↗ d toplight
+ rear (sjscycles.comitem554.htmOpen ↗). 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?

Quoted message said:

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.

Quoted message said:

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...

Quoted message said:

IRRC both the switch unit and headlamp have zener diodes.

Quoted message said:

I have never knowingly shorted any terminals.

If you had, this would probably damage the dynamo rather
than the lamp.

Quoted message said:

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.

Quoted message said:

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

james said:

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. chapmancentral.co.ukchapmancentral.co.ukOpen ↗

Just zis Guy said:

james said:

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

anonymous coward <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

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

m-gineering said:

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. chapmancentral.co.ukchapmancentral.co.ukOpen ↗

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

"Just zis Guy, you know?" <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

m-gineering said:

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

Simon Brooke said:

in message
<[email hidden]>, james

(') said:

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

Quoted message said:

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

Quoted message said:

/MArten

anonymous coward <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

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.

Quoted message said:

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

[email hidden] (Tim Henderson) wrote in message news:<[email hidden]>...

Quoted message said:

anonymous coward <[email hidden]> wrote
in message
news:<[email hidden]>...
and recovers only, after the input voltage over approx.. 1
s is reduced nearly to 0 V.

Quoted message said:

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

[email hidden] (james) wrote in message
news:<[email hidden]>... The
cutout still happens at low (10-11mph) speeds so is the

Quoted message said:

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

Quoted message said:

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.

Quoted message said:

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