solar circuit

[spleen]

Hiya,

I would like to design a circuit that is powered by a battery but the
battery is charged continously by a solar cell, the circuit is
required to work 24hrs a day hence the solar cell,

i basically just need to send a few bits of information over a radio
transmitter (I can do this bit, its easy..) every couple of minutes,
this would in turn take its power from the battery.

how would I go about ensuring the battery keeps a charge and the solar
cell chargers it?

Im not sure what type of batterys to use, maybe some C type nicads or
something, but Ive got a small 1.8W solar panel, that I would like to
use.

any ideas??

thanks

Dave

 

[Andrew Holme]

spleen wrote:

Hiya,

I would like to design a circuit that is powered by a battery but the
battery is charged continously by a solar cell, the circuit is
required to work 24hrs a day hence the solar cell,

i basically just need to send a few bits of information over a radio
transmitter (I can do this bit, its easy..) every couple of minutes,
this would in turn take its power from the battery.

how would I go about ensuring the battery keeps a charge and the solar
cell chargers it?

Im not sure what type of batterys to use, maybe some C type nicads or
something, but Ive got a small 1.8W solar panel, that I would like to
use.

any ideas??

thanks

Dave

If the solar cell's nominal output voltage is greater than the battery
voltage, a very simple solution would be to connect a diode and a resistor
in series with the solar cell across the battery. The resistor limits the
maximum current. The battery manufacturer's datasheet will say what the
safe trickle charge rate is.

If the simple scheme above can't deliver enough charge, or the solar panel
voltage is significantly greater or less than the battery voltage, you need
a low-power high-efficiency switched mode converter with a current-limited
output. This will still deliver charge even when the solar panel output
voltage drops.

 

[Fred Bloggs]

I would like to design a circuit that is powered by a battery but the
battery is charged continously by a solar cell, the circuit is
required to work 24hrs a day hence the solar cell,

i basically just need to send a few bits of information over a radio
transmitter (I can do this bit, its easy..) every couple of minutes,
this would in turn take its power from the battery.

how would I go about ensuring the battery keeps a charge and the solar
cell chargers it?

Im not sure what type of batterys to use, maybe some C type nicads or
something, but Ive got a small 1.8W solar panel, that I would like to
use.

Depending on your latitude and season, the solar panel will receive a
worst case D of Joules/m^2 incident solar radiation which it converts to
electrical energy with some dismal efficiency p1 to be stored in the
battery with efficieny p2. The circuit will draw a certain energy E over
this same 24 hour period so that you will want to select a solar cell
area and battery technology so that D*p1*p2> k*E at worst case
temperature, where k is sized to reduce the chance of occurrence of
successive clouded days causing the D*p1*p2 to fall below E to some
acceptably small level. Only after this arduous study is completed can
you say things like "but Ive got a small 1.8W solar panel, that I would
like to use."

 

[Gary J. Tait]

On 30 Jan 2005 04:25:41 -0800, googlinggoogler@hotmail.com (spleen)
wrote:

Hiya,

I would like to design a circuit that is powered by a battery but the
battery is charged continously by a solar cell, the circuit is
required to work 24hrs a day hence the solar cell,

i basically just need to send a few bits of information over a radio
transmitter (I can do this bit, its easy..) every couple of minutes,
this would in turn take its power from the battery.

how would I go about ensuring the battery keeps a charge and the solar
cell chargers it?

Im not sure what type of batterys to use, maybe some C type nicads or
something, but Ive got a small 1.8W solar panel, that I would like to
use.

any ideas??

thanks

Dave

Rewire the panel to do maybe 3 volts, and set up 2 AA Nicad batteries.