Solar Battery Charger

Hi.

I have recently completed building an Arduino UNO R3 based, weather station, powered by a 240 vac > 9 vdc transformer, my next stage is to make it Battery Powered with a rechargeable battery, re charged by a Solar Panel.

The My battery is a 12 volt, AGM, Lead Acid type. My PV panel is 12 vdc - 10 Watt, which on a good day gives out around 18 vdc, therefore i have obtained a Battery Charging Controller, 12vdc - 3 amp.

My question is this, as the Arduino recommended safe voltage is 9 vdc, what is the best way, and using what equipment, parts etc; do i need to reduce the voltage on the Load side of the Charge controller to say 9 vdc. suitable for the Arduino ?

I have surfed Google for hours, and there seems to be several ways to do this, though not being an Electrical person myself, i thought i would seek guidance from someone who can put me in the right direction to achieve my aim.

Regards

Ray

You can buy a step down module that will convert 12 VDC directly to 5 VDC more efficiently than the linear voltage regulator on the Uno. Those modules are available at a very low price from the usual sites.

gresleyman: as the Arduino recommended safe voltage is 9 vdc,

The Arduino UNO operates at 5 Volts DC and the recommended input voltage is between 7 and 12 volts DC. However, this is done with a surface mount Voltage Regulator, NCP117ST50T3G in the schematic. This is done roughly by shorting to ground all voltage over 5 through a resistor. This generates more and more heat as the input gets closer to 12 volts from 7 volts or as the current drawn increases. It is also very inefficient on the solar battery. It would be better to use a DC/DC converter with 12-24 volts DC input and 7 Volts DC output.