Hi,

I have one circuit ( 12V battery operated) that drives about 60 LED's.
The LED's have about 2V voltage drop, so I use 5 in series and limit the current to 20ma. That gives me a total current of 240mA.
The battery is charged by a solar panel. I must reduce the power needs, so the solar panel be as small as possible (because they are expensive). currently we use 20W panels, but I must find a solution to use 10W or less.

The Leds are on 500ms and off 500mS.

The battery and solar panel must be 12V.

Can someone give me an ideia / orientation. This 1st solution that came in mind is using a step up regulator and power the LEDs with 24V and using 10 in series (Total current will be half).

Another is using a capacitor to store energy, cut the power, discharg to the Leds and connect the power again to another cycle. (a little like a flash). Is that possible ?

Thanks for any help/advice.

JB

 

Why don't you post your entire circuit so far?

How are you regulating the battery charging current?

Are you trying to run the LEDs all day/all night?

If you double the voltage to cut the current in half, you won't have changed the power used, but the boost circuit will have (at best) around 90% efficiency. You'll wind up with a net loss.

Your power consumption in your LEDs is roughly 3 Watts. Somewhere you're losing efficiency.

 

Here is a brief description of the circuit:

Led's are controlled and must flash 24/7.

The solar panel as is own regulator and charge controller. I believe they are quite efficient.

My circuit as a micro controller that reads a light sensor, and pwm's the LEDs
so we can have automatic brightness control. The 60 Leds light at once and are switched on/off by a mosfet (connected to the micro controller). The 12 volts from the battery is connected directly to the anodes. The mosfet gives ground to the cathodes via a current limiting resistor. Power supply for the micro controller is taken from the 12V using an standard 78L05. The circuit itself takes around 10mA.

I have up to 4 sets off 60 LED's. In the worst case they light up all at once. This gets 12W from the battery. A 10W solar panel is not enough.

I must have a 5 day autonomy without sunshine. The goal is reducing the size of the panel and the batteries.

Thanks
JB

 

I must have a 5 day autonomy without sunshine.

You need 12 W * 24 hours * 5 = 1440 Watt-hours. At 12V, this is 120 AmpHours. I recommend 140 or 150 AmpHours worth of batteries to have a safety margin.

To gauge minimum panel size, one needs to know the peak sun hours where your gizmo will be used. http://www.oynot.com/solar-insolation-map.html

If this must function in winter, it would be better to use the winter numbers for peak sun hours.

I suggest a minimum panel size, in Watts, of 1.2*(rated output)*(peak sun hours)/24