Can a dynamo be used to reharge a small lead acid battery?

I have dynamo lights (6v) which I am thinking of boosting with a 10W lamp
powered by a 6v lead acid battery for cummuting. as my journey to work is in
daylight... could the dynamo be used in daylight to charge the lead-acid
battery?

nick

"Clarks" wrote in message
...
I have dynamo lights (6v) which I am thinking of boosting with a 10W lamp
powered by a 6v lead acid battery for cummuting. as my journey to work is
in
daylight... could the dynamo be used in daylight to charge the lead-acid
battery?

nick


Sheldon Brown has a bit on his web site about charging batteries and
rectification.
http://www.sheldonbrown.com/dynohubs.html
Paul.

(PS Remove junk to reply)

In theory yes with a suitable converter.

Of course what you really need is it linked to the brakes to shift the
hundreds of joules of available energy from you at speed into the
battery when you squeeze.

Jon

"Clarks" wrote in message
...

I have dynamo lights (6v) which I am thinking of boosting with a 10W lamp
powered by a 6v lead acid battery for cummuting. as my journey to work is
in
daylight... could the dynamo be used in daylight to charge the lead-acid
battery?


What the others said: it *can* be done, but it is difficult and rather
unsatisfactory. I use the SON in 12V mode and a headtorch with a four C
cells in a belt pack - the batteries last about a year because the headtorch
only gets used in the really dark bits.

--
Guy
===

WARNING: may contain traces of irony. Contents may settle after posting.
http://chapmancentral.demon.co.uk

Tony W must be edykated coz e writed:


"Clarks" wrote in message
...
I have dynamo lights (6v) which I am thinking of boosting with a 10W lamp
powered by a 6v lead acid battery for cummuting. as my journey to work is
in
daylight... could the dynamo be used in daylight to charge the lead-acid
battery?

You will gather from others that is possible but tricky.

Remember, to charge a battery you will need more volts than the battery has
to drive the charging current in. You will lose about 1.4V across any
rectifier. So you will need more than, say 7.5V to even start.

Two things are going for you. The dynamo produces an ac voltage with an RMS
average of 6V -- so during parts of the cycle it will be above the magic 7.5
V

And, the dynamo -- unless 'clamped' will produce more volts the faster your
little legs pedal.

So, without some fancy chopper circuits its unlikely that you would get much
power into your battery -- unless you go for a 12 V dynamo.

But, frankly, why? As a home electronics project it might be fun but as
practical engineering there are better solutions.

T


Er with a bridge rectifier you can obtain 10v dc from a 6v ac generator.
--
Ian

http://www.catrike.co.uk

"Tony W" wrote in message
...
Remember, to charge a battery you will need more volts than the battery
has
to drive the charging current in. You will lose about 1.4V across any
rectifier. So you will need more than, say 7.5V to even start.

A bridge rectifier will multiply the AC by 1.42 giving 8.52 VDC with a
capacitor across the output to smooth it (which the battery effectively is).
You then need to limit the voltage to, say, 7 volts. A voltage regulator is
one way of achieving this but I don't know if you'll get one for exactly
that value, another crude way is by using a zener diode.

But your biggest problem will be producing enough power from a dynamo to
charge a SLA sufficently for your return journey in the dark.
Put simply the dynamo will top up the battery at less than a third of the
rate your 10w lamp will consume power, assuming no other losses.

Pete

Clarks wrote:

I have dynamo lights (6v) which I am thinking of boosting with a 10W lamp
powered by a 6v lead acid battery for cummuting. as my journey to work is in
daylight... could the dynamo be used in daylight to charge the lead-acid
battery?

nick


It can be done, most texts describing this will be German, as a SON hub
is probably mandatory. A good start is www.enhydralutis.de, but only if
you read german.
But a good 12v Setup (Bisy FL/E6 etc) is probably superior to messing
about with a poorly designed 10w light, and will run without batteries
straight from the dynamo

--
Marten Gerritsen
cycle-imports & framebuilding

Quoth Nick Clark:

I have dynamo lights (6v) which I am thinking of boosting with a 10W lamp
powered by a 6v lead acid battery for cummuting. as my journey to work is in
daylight... could the dynamo be used in daylight to charge the lead-acid
battery?

Thanks to stupid German regulations, cycle dynamos put out only 3
watts of power.

This means that even if the charge/discharge cycle were 100%
efficient, you'd need to ride 2 hours by daylight to store enough
juice to run your 10 watt lamp for one hour of darkness (with the
dynamo helping.) Thus, this is not practical on the scale you
describe.

Battery/dynamo systems can work if the light is low enough wattage to
be powered by the dynamo alone. In such setups, a small battery can
serve to keep the light going whilst you're stopped for traffic
signals and the like.

I used to have a setup like this with an old Sturmey-Archer Dynohub,
30 years ago. I used a full-wave bridge rectifier and nickel-cadmium
batteries. It worked pretty well. In addition to keeping the light
lit when I was stopped, the low internal resistance of the NiCd
batteries kept the voltage from getting too high and burning out the
bulbs whilst descending (this was on a tandem, and I commonly would
hit speeds that would have toasted standard bulbs if connected
normally to the Dynohub.)

Sheldon "These Days I Use A Lumotec 'Standlicht' Headlamp With My
Shimano Dynamo Hubs" Brown
Newtonville, Massachusetts
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M-Gineering import & framebouw must be edykated coz e writed:

Sheldon Brown wrote:

Quoth Nick Clark:

I have dynamo lights (6v) which I am thinking of boosting with a 10W lamp
powered by a 6v lead acid battery for cummuting. as my journey to work is in
daylight... could the dynamo be used in daylight to charge the lead-acid
battery?

Thanks to stupid German regulations, cycle dynamos put out only 3
watts of power.


Whoa.... Most dynamo's put out 0.5 amps. With the official bulbs this
translates to 3 watts. Change the bulbs and you can get quite a bit more
power.

--
Marten
What about the Dymotech S12 from Busch and Muller, it has a 12v, 6w output?
--
Ian

http://www.catrike.co.uk

Sheldon Brown wrote:

Quoth Nick Clark:

I have dynamo lights (6v) which I am thinking of boosting with a 10W lamp
powered by a 6v lead acid battery for cummuting. as my journey to work is in
daylight... could the dynamo be used in daylight to charge the lead-acid
battery?

Thanks to stupid German regulations, cycle dynamos put out only 3
watts of power.


Whoa.... Most dynamo's put out 0.5 amps. With the official bulbs this
translates to 3 watts. Change the bulbs and you can get quite a bit more
power.

--
Marten