Re: Help me build a bicycle phone charger

On Feb 20, 7:02 am, ehsjr <eh...@xxxxxxxxxxxxxxxx> wrote:
goo...@xxxxxxxxxxxxx wrote:


Don't want much, do you? Let's see, 100% efficiency,
0 weight ... I give up. Those things are available
in the Twlight Zone ... or not. :-)

OK. But assuming I'm understanding the examples given they're likely
to get worse than 40% efficiency for a single 500mA supply.


To play the game, the specs have to be properly stated.
The voltages alone don't suffice, we need to know the
current that will be drawn from your supplies. You
did not say anything about the *second* 6V supply,
you only mentioned a first and third 6V supply. And you
did not specify the current to be drawn from the two
6V supplies. We also need to know what input power
is available, at what speeds.

Maybe there's a typo above that I can't see. But the first supply is
to drive the lights (500mA at 6V). The second supply is to drive a
standlight (50mA at 3V). And the third supply is any power left.


The best we can do at this point is a pre-regulator feeding
a DC-DC converter or linear regulator. Bob gave you a shunt
pre-regulator (which would benefit from an added dropping
resistor to protect the shunt transistor) which is nice, I
gave you a pass pre-regulator, which would also benefit from
a dropping resistor (since you insist on 500 ma CC) to protect
the diodes and the source. The dropping resistor will waste
power, as will the linear that follows. A wide input range
DC-DC converter would avoid at least some of that waste.

Maybe I don't understand the circuits well enough (very probably) but
the hub will quite happily supply 6V at 500mA or 12V at 500mA. We have
5V at 500mA of useful power. If the hub is supplying 6V then we've got
an acceptable 80% efficiency. If the hub is supplying 12V then we've
got an unacceptable 40% efficiency. I don't understand why any of the
circuits will keep things in that 80% efficiency zone.

But playing the game of finding a "wide input range" DC-DC
converter without knowing the range is not something many
people want to do. You'll just come back with "what about x" .


http://www.baldurdash.org/OtherStuff/www.nabendynamo.de/12vinfo.htm

Has some graphs showing output voltage under no load, a 6V 3W bulb and
a 6V3W bulb in series with a 6V2W4 bulb.


So I'm gonna stick with my offering of a pre-regulator
followed by linears, and whatever warts it carries with
it. :-)


Just driving my lights, what I need is overvoltage protection.
Currently I'm using two 8V2 zeners to clamp the p-p voltage at about
9V. In normal usage they should (approximately) not conduct at all so
100% efficient. If the front bulb goes open circuit then I get a 9V
square wave driving the rear light which, so far, has meant that I've
not destroyed a rear light in about 2 years after having gone through
three in a year. I still have a problem with the front light
standlight (which has it's own overvoltage protection but is only
designed to be enough for you to stop and change the bulb - I suspect
that the front light overvoltage protection is doing all of the work
and the front standlight electronics are destroyed before I notice the
bulb has gone)



This is the front light:
http://www.sjscycles.co.uk/product-Busch-and-Muller-Busch-and-Muller-Lumotec-Plus-(Standlight)-Round-Halogen-Dynamo-Headlamp-with-Standlight-544.htm
Rear light:
http://www.sjscycles.co.uk/product-Busch-and-Muller-Busch-and-Muller-D-Toplight-Plus-(50mm-or-80mm-bolt-centres)-Rear-Dynamo-Light-with-Standlight-for-carrier-(excl-cable)-11849.htm


And the weight thing is a bit of a joke - but I've just ordered a new
bike and spent an extra 400GBP to have titanium parts that will save
me 915g.

Tim.
.

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