powering old B&M dynamo lights with 6v lead acid

When I moved my old Busch und Mueller dynamo lights from one bike to
another, I decided to try powering them from a 6v sealed lead-acid
battery instead of messing around trying to mount the dynamo (Dymotech
6). The lights are both 'stand-light' models (Lumotech plus and Toplight
plus). The problem is that the rear bulb is blowing very quickly
(sometimes within minutes) - it is rated at 6V, 0.1A. Assuming that the
bulb is blowing as a result of excessive voltage, is there anything
obviously wrong with my set-up? e.g. stand-light circuitry causing
voltage surge at switch-on. Any suggestions as to how to fix this would
be gratefully received. At the moment I'm considering getting some
better quality bulbs, maybe rated at 7.2V.
Thanks,
Chris

Chris said the following on 07/12/2006 14:32:
Assuming that the
bulb is blowing as a result of excessive voltage, is there anything
obviously wrong with my set-up? e.g. stand-light circuitry causing
voltage surge at switch-on. Any suggestions as to how to fix this would
be gratefully received. At the moment I'm considering getting some
better quality bulbs, maybe rated at 7.2V.

A possibility is that with dynamo lighting of any sort, the voltage
increases gradually (unless you flip the switch on a dynohub at speed).
It may be just a problem with 6V being applied instantaneously,
although I really can't see why that should be a problem - that's how
old-fashioned bike lights work. The standlight circuit if anything will
slow the voltage rise, but I suspect the effect will be so negligible as
to be not worthy of note. Just a thought - have you actually measured
the battery voltage to make sure it really is 6V or thereabouts?

One suggestion - replace your rear bulb with an LED rear lamp. Not only
are these more indestructible, they are far more efficient and will make
your battery last longer.

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

On Thu, 07 Dec 2006, Chris wrote:

When I moved my old Busch und Mueller dynamo lights from one bike to
another, I decided to try powering them from a 6v sealed lead-acid

[... but the bulbs blow]

Odd. I have used (for years - maybe 10?) dynamo lights with a central
battery. Sometimes lead acid, but more normally a six-cell NiCd pack.
The latter is nominally 7.2V. I've had fewer bulbs blow with a
battery than with a real dynamo, even at the higher-than-spec voltage.

None of my lights have ever been standlight models, however.

regards, Ian SMith
--
|\ /| no .sig
|o o|
|/ \|

Chris wrote:
When I moved my old Busch und Mueller dynamo lights from one bike to
another, I decided to try powering them from a 6v sealed lead-acid
battery instead of messing around trying to mount the dynamo (Dymotech
6). The lights are both 'stand-light' models (Lumotech plus and
Toplight plus). The problem is that the rear bulb is blowing very
quickly (sometimes within minutes) - it is rated at 6V, 0.1A.
Assuming that the bulb is blowing as a result of excessive voltage,
is there anything obviously wrong with my set-up? e.g. stand-light
circuitry causing voltage surge at switch-on. Any suggestions as to
how to fix this would be gratefully received. At the moment I'm
considering getting some better quality bulbs, maybe rated at 7.2V.

Voltage regulator on the battery output ? (ie. one transistor with
suitable heatsink).


- Nigel


--
Nigel Cliffe,
Webmaster at http://www.2mm.org.uk/

"Chris" wrote in message
.. .
When I moved my old Busch und Mueller dynamo lights from one bike to
another, I decided to try powering them from a 6v sealed lead-acid battery
instead of messing around trying to mount the dynamo (Dymotech 6). The
lights are both 'stand-light' models (Lumotech plus and Toplight plus).
The problem is that the rear bulb is blowing very quickly (sometimes
within minutes) - it is rated at 6V, 0.1A. Assuming that the bulb is
blowing as a result of excessive voltage, is there anything obviously
wrong with my set-up? e.g. stand-light circuitry causing voltage surge at
switch-on. Any suggestions as to how to fix this would be gratefully
received. At the moment I'm considering getting some better quality bulbs,
maybe rated at 7.2V.
Thanks,
Chris

Try putting an iron-cored inductor in series with the lamp/ The current
change will be damped when switched on, and a (low!) DC resistance in the
inductor will give a slightly lower voltage across the lamp.