On 12/08/13 16:43, Trent W. Buck wrote:
James writes:

On 06/08/13 18:41, Trent W. Buck wrote:
I suspect the responses are all gonna be "I hate dynamos! Batteries are
not that hard, just HTFU" so I haven't bothered to dig up hub specs &c,
but I'll do so if there's interest. The bulb claims to be a Philips
HPR60, 3.6V 2.4W.

Interesting that the bulb is rated for such low voltage.

What is the rating of the hub dynamo you have?

Most dynamos and the required bulb are rated something like 6V, 3W.

Now you've got me freaked out, because I tried a "HPR53 4V0.85A JAPAN"
in it, and it didn't light up *at all*. (A replacement bulb finally
arrived from LBS, and that's working, hooray.)

Ah, well that's good. Perhaps the light housing has a voltage limiting
zener diode or similar, to protect the 3.6V bulb from the full 6V. Or
perhaps the original lighting circuit had the front and rear bulbs wired
in series, so that the 6V was shared across two bulbs. I can't tell
from here.

The hub has written on it "SHIMANO DH-3R30-N 6V 3W 646-716mm".

After looking at the PDF from
http://www.shimano.com.au/media/techdocs/content/cycle/SI/HubDynamo/DH3R30_DH3R35/SI_2ZL0A_001/SI-2ZL0A-001-ENG_v1_m56577569830658011.pdf
it seems the head lamp and tail lamp bulbs should be 6V each, indicating
that they should be wired in parallel. If your head lamp bulb is really
3.6V, there must be some electronics in the housing to protect it, and
it's not the original head lamp by the looks.

It's also powering an LED taillight, but it seems a bit wonky that
that'd be using up half the volts...

Indeed.

PS: hm, I looked at the 4V bulb even closer and now I see the filament
is broken, so that'd be why it didn't light up.

;-)

--
JS