dynamo headlamp brightness

Quoted message said:

I am running a B&M round lumotech with standlight directly wired to
HX30 hub dyamno (still waiting for warranty replacement of switch...).
Recently I have noticed that the headlamp sometimes flickers between
standlight and main bulb, or the main bulb doesn't reach full
brightness until speeds up to 12mph. It has a 2.4w bulb and teh system
also powers B&MD toplight on the back.

Something's up, whatever: the standlight should only come on if there's
no real power going into the lamp which is down at slow walking pace
(literally, my lamps behave like this wheeling the bikes up my garden path).

Mine (I've got a round B&M powered from a B&M 6 bottle on the 8 Freight,
a round B&M from a SON on the Brom and an oval B&M from a SON on the
'bent) are up to good brightness at what I'd guess would be 6-7 mph.
Maybe better faster than that, but we're certainly well under way with
acceptable illumination at anything past a brisk walk on any of them.

Whether Mystery Problem X is with the dynamo, lamp or wiring I don't
know. If you can put a meter on the wiring and see what the output is
as the light changes state that may well give you a clue.

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 [email hidden] http://www.dundee.ac.uk/~pjclinch/

Quoted message said:

I am running a B&M round lumotech with standlight directly wired to
HX30 hub dyamno (still waiting for warranty replacement of switch...).
Recently I have noticed that the headlamp sometimes flickers between
standlight and main bulb, or the main bulb doesn't reach full
brightness until speeds up to 12mph. It has a 2.4w bulb and teh system
also powers B&MD toplight on the back.

I am not really /certain/ but I have the impression that performance
improves once the lamp has warmed up a bit. Past performance (and best
case nowadays) has the light cutting over to proper bulb at around
5-6mph and reaching full brightness (or good as) by 7-8 mph.

Does anyone have any opinions on what could be happening? Is the bulb
nearing end-of-life? Is the zener diode degrading? Could there be a
problem with the dynamo?

Have you tried cleaning the plugs at the dynamo and the lamp?

Zog The Undeniable said:

Quoted message said:

[headlamp performance problem]

Quoted message said:

Have you tried cleaning the plugs at the dynamo and the lamp?

I'll give that a go but the performance seems to vary in quite a
predictable way over my commute (eg it is poor on startup and when I
come out of the greenwich foot tunnel but better after some of the
quicker sections of the ride) which is what made me think of a problem
with electronics. My mum has the same setup so I guess I can try
swapping wheels/lamps sometime

best wishes
james

email hidden said:

I am running a B&M round lumotech with standlight directly wired to
HX30 hub dyamno (still waiting for warranty replacement of switch...).
Recently I have noticed that the headlamp sometimes flickers between
standlight and main bulb, or the main bulb doesn't reach full
brightness until speeds up to 12mph.

The round Lumotec has given me a lot of trouble over the years, so I
would suspect that.

Quoted message said:

It has a 2.4w bulb and teh system also powers B&MD toplight on the back.

^^^

You are Ian SMith & ICMFP :-D

Quoted message said:

Does anyone have any opinions on what could be happening? Is the bulb
nearing end-of-life? Is the zener diode degrading? Could there be a
problem with the dynamo?

More likely the lamp IME; you might want to contact B&M about it.

Guy
--
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

88% of helmet statistics are made up, 65% of them at Washington University

Just zis Guy said:

email hidden said:

I am running a B&M round lumotech with standlight ...
Recently I have noticed that the headlamp sometimes flickers between
standlight and main bulb, or the main bulb doesn't reach full
brightness until speeds up to 12mph.

Quoted message said:

The round Lumotec has given me a lot of trouble over the years, so I
would suspect that.

I replaced the bulb (because the old one had a tiny bit of brown
deposit on it) and checked, reconnected all of the wiring which all
looked fine (it is all soldered or large spade-jointed with good
insulation and heavy gauge cable). I gently bent out the connection
terminal for the back of the bulb (just in case) then I noticed what I
think could be the problem. I never really understoof exactly what Guy
claimed to be the problem he has experienced with the lamps so
apologies if I am rediscovering the wheel here:

The one of the two electrical contacts in the reflector seemed poorly
supported and so may not have been making a good connection with the
contact on the lamp body. I inserted a fragment of plastic behind it
to push it back against the contact. The other side seemed firmer
anyway. I could not see if something had fallen off or cracked (ie was
this a design flaw or a failure in use) but it looked like it might be
a systemic problem. I have scrawled a picture here to illustrate the
point. The lamp is shown from the rear with the two halves split.
<url: http://pog.org.uk/bm.gif >
--
best wishes
james