SON dynamo, bulbs keep blowing

I've got a SON hub dynamo on the Brompton together with a B&M toplight
plus on the rear and lumotec round plus on the front (although the
standlight on the front no longer works)

But the 2.4W bulbs on the front keep blowing (I typically seem to get
about 30-60 hours of use out of a bulb) and because this is Central
London I don't necessarily notice straight away that the bulb has blown
(which is how the standlight got destroyed)

I've wired two 8v6 zeners across the dynamo. That seems to have saved
the rear light but didn't save the standlight.

My average cycling speed is probably around 20mph (hard to be certain
because of all the stops at traffic lights) with a peak speed of about
30mph. Would this be tending to overvolt the bulbs (the zeners should
start to clamp as the voltage reaches 6V RMS but obviously I'll be
getting about 9V RMS if the output becomes a square wave)

Are there any other light options (LED?) that won't have this problem?
I use the front luggage so there isn't a lot of room and I don't think
"Busch and Muller DLumotec Oval, the new LED front lamp" will fit.

Or should I be using 3W bulbs even though I've got a rear light? (Off
to buy some bulbs now and I'll get a 3W bulb to give it a try as I've
run out of 2W4 bulbs except for the one that is now in the light)

Tim.

wrote:
I've got a SON hub dynamo on the Brompton together with a B&M toplight
plus on the rear and lumotec round plus on the front (although the
standlight on the front no longer works)

But the 2.4W bulbs on the front keep blowing (I typically seem to get
about 30-60 hours of use out of a bulb) and because this is Central
London I don't necessarily notice straight away that the bulb has blown
(which is how the standlight got destroyed)

I've wired two 8v6 zeners across the dynamo. That seems to have saved
the rear light but didn't save the standlight.

My average cycling speed is probably around 20mph (hard to be certain
because of all the stops at traffic lights) with a peak speed of about
30mph. Would this be tending to overvolt the bulbs (the zeners should
start to clamp as the voltage reaches 6V RMS but obviously I'll be
getting about 9V RMS if the output becomes a square wave)

Are there any other light options (LED?) that won't have this problem?
I use the front luggage so there isn't a lot of room and I don't think
"Busch and Muller DLumotec Oval, the new LED front lamp" will fit.

Or should I be using 3W bulbs even though I've got a rear light? (Off
to buy some bulbs now and I'll get a 3W bulb to give it a try as I've
run out of 2W4 bulbs except for the one that is now in the light)

Tim.


a 3 w bulb might help, but the main problem is probably vibrations.
Check that the bracket is strong enough so that it doesn't amplify the
raod buzz.

Average rated bulblife is only 100 hrs, but vibrations and some
overvolting will reduce this obviously

--
---
Marten Gerritsen

INFOapestaartjeM-GINEERINGpuntNL
www.m-gineering.nl

wrote:
I've got a SON hub dynamo on the Brompton together with a B&M toplight
plus on the rear and lumotec round plus on the front (although the
standlight on the front no longer works)

Which SON have you got? If it's not an XS or the small wheel version
you might be putting out rather more oomph than you want, perhaps?

My average cycling speed is probably around 20mph (hard to be certain
because of all the stops at traffic lights) with a peak speed of about
30mph.

That's pretty impressive on a Brom, and if you have got the "standard"
SON it may well be compounding things. Even if it's the small wheel
one, Brom wheels are smaller than average small wheels and 20 mph
average is pretty quick.

Are there any other light options (LED?) that won't have this problem?
I use the front luggage so there isn't a lot of room and I don't think
"Busch and Muller DLumotec Oval, the new LED front lamp" will fit.

I don't think it will either, and I have a couple to experiment with
directly to be on the sure side :-(

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net http://www.dundee.ac.uk/~pjclinch/

wrote:
But the 2.4W bulbs on the front keep blowing (I typically seem to get
about 30-60 hours of use out of a bulb) and because this is Central
London I don't necessarily notice straight away that the bulb has blown
(which is how the standlight got destroyed)

Someone who uses a Lumotec can probably give a more authoritative answer,
but I suspect that kind of lifetime isn't out completely of the ordinary
for fast riding, especially if you're riding a small wheeled bike on poorly
maintained surfaces. Presumably you have the correct SON for the Brompton
wheel size?

Are there any other light options (LED?) that won't have this problem?
I use the front luggage so there isn't a lot of room and I don't think
"Busch and Muller DLumotec Oval, the new LED front lamp" will fit.

Solidlights?

Or should I be using 3W bulbs even though I've got a rear light? (Off
to buy some bulbs now and I'll get a 3W bulb to give it a try as I've
run out of 2W4 bulbs except for the one that is now in the light)

If I understand correctly, the front and rear lights are wired in parallel,
and the SON approximates to a constant current source, so I think if you
put a 3W bulb at the front you'll just overload the rear. I may be wrong
about this though.

You might want to try asking these questions on the 'bikecurrent' list:

http://www.topica.com/lists/bikecurrent/

Anthony

Anthony Jones wrote:

If I understand correctly, the front and rear lights are wired in parallel,

correct

and the SON approximates to a constant current source,

correct

so I think if you
put a 3W bulb at the front you'll just overload the rear.

No:


I may be wrong about this though.

correct
---
Marten Gerritsen

INFOapestaartjeM-GINEERINGpuntNL
www.m-gineering.nl

Peter Clinch wrote:
wrote:
I've got a SON hub dynamo on the Brompton together with a B&M toplight
plus on the rear and lumotec round plus on the front (although the
standlight on the front no longer works)

Which SON have you got? If it's not an XS or the small wheel version
you might be putting out rather more oomph than you want, perhaps?

It's the 16"-20" version.

My average cycling speed is probably around 20mph (hard to be certain
because of all the stops at traffic lights) with a peak speed of about
30mph.

That's pretty impressive on a Brom, and if you have got the "standard"
SON it may well be compounding things. Even if it's the small wheel
one, Brom wheels are smaller than average small wheels and 20 mph
average is pretty quick.

When the bulb blew yesterday it was shortly after the 30mph section
that I noticed. It definitely was working at Euston, had blown by the
time I turned into Dingley Road from City Road and it's the downhill
bit at the start of City Road immediately after Pentonville Road that I
usually reach 30mph (46-50kph depending on wind and traffic). I try to
keep my speed above 28kph on my entire commute (although just recently
I've been struggling up Pentonville road and slowing to 24kph - I can't
believe that it's the dark mornings and the extra drag from the dynamo
but I can't imagine what else it could be)

Are there any other light options (LED?) that won't have this problem?
I use the front luggage so there isn't a lot of room and I don't think
"Busch and Muller DLumotec Oval, the new LED front lamp" will fit.

I don't think it will either, and I have a couple to experiment with
directly to be on the sure side :-(

Are there any options to mount it on the handlebars instead of on the
brake calliper? (And if so and one of yours is surplus to requirements
I might find a way to swap it for some beer tokens)

Tim.

M-gineering wrote:
wrote:
I've got a SON hub dynamo on the Brompton together with a B&M toplight
plus on the rear and lumotec round plus on the front (although the
standlight on the front no longer works)

But the 2.4W bulbs on the front keep blowing (I typically seem to get
about 30-60 hours of use out of a bulb) and because this is Central
London I don't necessarily notice straight away that the bulb has blown
(which is how the standlight got destroyed)

I've wired two 8v6 zeners across the dynamo. That seems to have saved
the rear light but didn't save the standlight.



a 3 w bulb might help, but the main problem is probably vibrations.
Check that the bracket is strong enough so that it doesn't amplify the
raod buzz.

Average rated bulblife is only 100 hrs, but vibrations and some
overvolting will reduce this obviously

:-(

Vibration is probably pretty bad, both because I ride quite fast and
because the light touches the luggage block on the front.

But it's not so much the bulb life as the fact that its destroying the
standlight that is the problem. Initially I had a Lumotec without
standlight and a rear light with battery powered standlight (forget the
make now). Front bulb blew and within 3 miles the rear light was dead
never to work again - light was definitely working at work and had
blown by the time I got to Euston. So then I bought the B&M rear and
also got the Lumotec with standlight. Also put in the two zeners.
Another light blew, same journey, and the standlight on the front has
never worked since. 9 times out of 10 I've caught the bulb going
without any damage but that one time in 10 is costing me a new
standlight each year which is making the hub dynamo less reliable and
more expensive than battery lights. (especially as, when it was the
back light that failed I couldn't do anything until I'd bought a new
light. At least with bulbs you can carry a spare)

http://www.bikeplus.co.uk/cgi-bin/qu...&affiliate_id=
is a dynamo regulator. But I don't know if it will protect the
standlight if the bulb blows.

Tim.

said the following on 17/10/2006 10:02:

I've wired two 8v6 zeners across the dynamo. That seems to have saved
the rear light but didn't save the standlight.

Would this be tending to overvolt the bulbs (the zeners should
start to clamp as the voltage reaches 6V RMS but obviously I'll be
getting about 9V RMS if the output becomes a square wave)

There's the problem. Have you tried lower voltage zeners? Also, how
have you wired them? They should be cathode to cathode in series with
each other, and in parallel with the bulb.

I don't know what voltage zeners the manufacturers use, but as they're
cheap enough perhaps you could just try various voltages and see what
happens.

--
Paul Boyd
http://www.paul-boyd.co.uk/

Paul Boyd wrote:
said the following on 17/10/2006 10:02:

I've wired two 8v6 zeners across the dynamo. That seems to have saved
the rear light but didn't save the standlight.

Would this be tending to overvolt the bulbs (the zeners should
start to clamp as the voltage reaches 6V RMS but obviously I'll be
getting about 9V RMS if the output becomes a square wave)

There's the problem. Have you tried lower voltage zeners? Also, how
have you wired them? They should be cathode to cathode in series with
each other, and in parallel with the bulb.

I don't know what voltage zeners the manufacturers use, but as they're
cheap enough perhaps you could just try various voltages and see what
happens.

But if I use, say, 5v6 then I will start clamping the voltage before
the bulb gets up to full brightness. (I've actually used 8v2 zeners, I
was getting confused with 6v8)

I've thought about a triac to short the dynamo whenever the voltage
reaches a certain level (for the rest of that half cycle) but I still
have the problem that either it will turn on too early at low speeds or
too late at high speeds.

My electronic skills are not good enough to design something that has
negligible forward voltage drop and yet can turn a (fairly poor)
constant current source into a constant voltage source for AC. (Infact,
if I wanted to do this I'd rectify the AC but I don't know if the rear
light would like this and I'd be giving up about a quarter of a watt in
the process)

(I also don't know how close the waveform gets to a square wave while
the bulb is working - it's not far off an ideal squarewave under no
load conditions - I can spin the front wheel fast enough by hand while
having the oscilloscope connected but I can only reach about 20kph like
that)

Tim.

wrote:

Are there any options to mount it on the handlebars instead of on the
brake calliper?

It'll be a relative PITA to organise the fold and the wiring such that
the fold doesn't do naughty things to it, but no deal-breaking reasons
you can't spring to mind, assuming you can find a suitable bracket.

(And if so and one of yours is surplus to requirements
I might find a way to swap it for some beer tokens)

They're variously attached to other bikes which quite like them just
where they are, I'm afraid! ;-/

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net http://www.dundee.ac.uk/~pjclinch/