Battery chargers for solar panel help

 I'm interesting in finding a product that I can charge AAA, AA, and D size
batteries off of my uni solar flexible 10 watt cell preferably without
overcharging them please. Anything available for this task? Thanks in
advance.

  drehus27@yahoo.com wrote:

Walmart has some nice 12vdc input chargers for aaa and aa
batteries.Radio shack may have one for D size.


--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html

 Thank you

 Just grab any two old bridge rectifier diodes (1n4004's for instance) and
turn them with the gate toward the output of the positive terminal in
series.  This will give you about  7 tenths of a volt each or about  1.4
volts output.

Mitch

 
drehus27@yahoo.com wrote:

This seems simple, but in fact it can be more complicated than it
looks. Most wallplug battery chargers supply a constant current to the
batteries, and terminate charging either when the battery voltage peaks
and then starts to drop (minus delta V) or when the battery temperature
rises either above some predetermined value (maxT) or when the
temperature rises a few degrees Celcius in one minute (deltaT/t). This
all works great as long as there is enough power available to provide
the constant current, which is not always the case with solar charging.


If the solar module cannot provide enough current to the battery (too
small, partly cloudy, etc.) then the charger may either quit charging
altogether or terminate before it should.

A second problem is that solar modules produce their maximum power at a
single voltage, which varies somewhat with module temperature. This is
the reason that the better inverters use MPPT (maximum power point
tracking). An ideal solar charger will use some similar method to
assure the batteries are being charged as quickly as possible under the
conditions.

Unless you have the skills and want to develop your own charger, your
best bet is to buy an inexpensive charger and try it to see what
happens. It is a good idea to check the maximum input voltage if it is
listed to make sure it can survive the high open circuit voltage (Voc)
of your 10 Watt module. This should be listed on the label, and will
probably be 20 to 30 Volts. Sometimes this Voc will damage either a
capacitor or a semiconductor inside the charger.

The method suggested by Mitchell Dickinson should work fairly well,
although his description may be a little vague. As I understand what he
is saying, connect two diodes in series across each cell you are trying
to charge, with the cathode (stripe or bar on diode symbol) connected
to the negative terminal on the battery. This places the diodes in a
forward bias condtion resulting in approximately 0.7 volts across each
diode, thereby limiting the voltage on each cell of the battery to 1.4
volts. This is a form of shunt regulator which will conduct excess
current through the diodes preventing the battery from exceeding about
1.4 volts. You may not achieve the ultimate full charge, and it will
not be very efficient unless you are charging 8-10 cells in series at a
time, but it should prevent overcharge.

If you need more details send me a message with your e-mail address and
I will respond with what I can provide.