# Electronic – Basic wattage and volt conversion when using solar panel

amperagevoltage-regulator

I have a basic electronic question or two I need to ask.

I want to use a solar panel which delivers 5.2W and is rated for "8V open voltage and 650mA short circuit". If I connect a 5V voltage regulator to lower the volts to 5V, would the amps go up to be 1A after the regulator? (W = V * A)

Another thing I'd like to know is, if I regulate the voltage to 5V and get approximately 1A out of it. How would using different components together work? I.e. I am using an arduino with a servo and a GPS unit and an XBee connected. Would these individual components' amp-usage just be added up (lets say to 850mA) and then the "extra" 150mA would just not be used?

I want to use a solar panel which delivers 5.2W and is rated for "8V open voltage and 650mA short circuit". If I connect a 5V voltage regulator to lower the volts to 5V, would the amps go up to be 1A after the regulator? (W = V * A)

The percentages used below are "out of my head" based on experience with PV panels. Your panel may vary somewhat from my assumptions.

Depending on technology used the ratio of Vmax_power to Voc will vary but using 0.8 is a good first guess. So V_max_power ~= 8V x 0.8 = 6.4V.

Imax_power will be somewhat less than Isc - probably about 90% or better, so Imax_power ~= 650 mA x 90% = 585 MA -> say 600 mA.

So actual max power in bright light will be V x I = ABOUT 6.4V x 600 mA = 3840 mW.

This will be at about 6.4V so to run with best efficiency you want to convert it to 5V with a switching regulator. A switching regulator will be typically 80% to 90% efficient if you use a good one - and rather less with lower quality designs.
3.8W x 90% =~ 3.4W
3.8W x 80% =~ 3W
3.8W x 70% =~ 2.6W

If output is at 5V then Iout = Pout/Vout =
680 mA at 90% conversion efficiency
600 mA at 80%
520 mA at 70%

Building a buck converter with an MC34063 will produce an OK result but efficiency will be lower than cxan be achieved with modern IC.
An IC with synchronous rectification is required to maximise efficincy.
The Richtek RC8286 looks ideal
Datasheet here