Dave said:
But some don't. It would be far easier for you if you find one which can
use AA alkalines and AA rechargeables.
The Li-Ion based cameras I've seen have the charging circuit built into
the camera itself, and the mains adaptor is just a regulated supply. If
you are prepared to charge the battery in the camera, although it may be
less convenient, it would make things a lot simpler.
Here's how I might do it-
You need to find out the voltage of the mains adaptor, let's say it's 6V,
but double check your camera before plugging anything homebrew into it!.
It's essential that the camera sees a constant and well regulated 6V
throughout the charge cycle, don't power it from the dynamo on your bike
or a windmill, at least not directly. You'll at best find the battery
never charges properly and at worst you'll destroy your camera.
What I suggest is a car type arrangement. Use your bike's dynamo (these
are usually around 6V AC IIRC so you'll need to rectify to DC ) to charge
either a 6V lead-acid gel battery or 5 NiMH cells, using appropriate
charging techniques.
Build a voltage limiter to keep the battery output voltage below, say,
6.1V. A crowbar circuit to prevent catastrophies is recommended. Feed the
DC from the battery into the adaptor input on your camera. An inline fuse
would be a wise move.
The battery should ensure that the voltage stays fairly constant, and if
you choose large enough capacity cells, it should keep charging the Li-Ion
battery when you aren't pedalling, and may even be able to completely
charge the camera overnight while you sleep. IOW, the bike battery charges
during the day, then it charges your camera overnight.
You could even wire your lights into it so they stay on when you stop
pedalling! You'd need to increase the capacity for this.
So basically I'd aim to charge the camera with a battery, which in turn
would be topped up by the bike's dynamo. This is exactly what happens when
a mobile phone is charged via a cigar lighter socket on a car.
This is just a very rough idea, it would need to be well thought out
before implementing. I believe that if it's done properly, it would work
out rather well.
Dave
The above idea about using a second battery to power the camera seems likely
to work. If you want to charge the battery outside the camera then the
following information might be of use:
It looks like your battery is a single cell.
Some information on charging lithium batteries is here:
http://www.energyplus.com/articles/Panasonic_LiIon_Charging.pdf
Most lithium packs have built-in MOSFETs and protection circuitry to
disconnect the battery from the terminals if any cell is charged over some
very accurate threshold which (according to Panasonic) is 4.30V +/- 0.05V.
The safety circuit will probably also disconnect if you try to discharge
the cell to too low a voltage, i.e. it disconnects at 2.3V +/-0.1V, but you
shouldn't discharge it below 3V. Don't rely on the safety circuit to
control your charging, it is meant as a backup, and I wouldn't be surprised
if once it disconnects, it's time to buy a new battery pack.
If you are charging single cells, then the important things are:
Never exceed 4.2 Volts/cell, regardless of current or anything else. For
some cells this should even be 4.1 Volts, depending on the cell chemistry.
This needs to be an accurate regulator (1% accuracy will do).
Never exceed the current limit specified for the cell (which is usually
about 0.7C, i.e. the current you would have to draw to flatten the cell in
one hour). For your battery it would be about 0.45 Amps
Never flatten the battery below about 3V or so, nor allow it to
self-discharge below about 2.5V, the battery will undergo permanent damage
and some people say it becomes dangerous. Basically don't store them
completely flat for long periods. I have seen it suggested that optimum
life results from storing with 40% charge in the battery.
If the battery happens to have a voltage below 2.9V, the charger is supposed
to reduce the charging current to 0.1C (the amount of current that would
flatten a charged battery in 10 hours). This would be 68mA for your
battery. If you can manually verify that you haven't flattened it this far
then that ought to suffice.
So you need to limit the current to 0.45Amps and you need to limit the
voltage very accurately to 4.1 or 4.2V. If the voltage has reached 4.2V
and the current dies down to 0.1C (68mA for you) then the battery is full
and you should disconnect it for best life, though I don't think it is
dangerous to continue charging it at 4.2 Volts.
There are 'intelligent' charging chips available from several manufacturers
that will manage the whole charging cycle, but these chips would probably
expect a steady and constant supply voltage from start to finish which you
will not have unless you use the second battery route when you might as
well use the camera's internal charging circuit.
Since you require opportunistic charging, I would suggest rectifying the
generator output and filtering it with a big electrolytic capacitor, and
limiting the peak voltage with a zener diode of perhaps 8.2V, 5 Watt or
whatever power rating you find necessary. This can then be applied to a
non-intelligent charging IC such as the ADP3820.
http://www.analog.com/UploadedFiles/Data_Sheets/490002128ADP3820_a.pdf
Chris