stand alone system with powercell,accu,solarcell,arduino

Hoi al,

To power up my outdoor weather station this is build up as follows, mini-pro arduino 3,3VDC XBEE for transmit data to base station temp. sensor 18ds20 wind direction via reed over resitor to ana input wind speed dig. input reedswitch count rain water counts buckets of water fals over time 6 VDC solar cell 2,5WATT LiPo accu 3,6 1200mAh ( provided the power consumption is in balance overnight ) ( intend to use the sparkfun powercell )

I have my doubts to connect the solarcell to the powercell while this is limited to 5VDC input voltage as according datasheet. The solarcell tend to raise the voltage far over 5VDC this wil harw the powercell? Can a regulated voltage be the solution? But when the voltage drops below output + reg. level? Is a zenerdiode the solution? A diode to prevent current flow back to solarcell? Any experience nown? Any help aprecieted. IlioSS :~

You should read the data sheet for the charger chip (MCP73831T) on the Spark Fun powercell carefully, available on the product page. The charger shuts down if the incoming voltage (from the solar cell) drops below a certain value, but exactly how that happens if the cell output should drop slowly past the threshold is not clear to me. It would probably not hurt to have a diode between the solar cell and the charger input (but see below, you may have to add a capacitor).

On the other hand, the absolute maximum input voltage to the charger is 6V, so if your solar cell outputs more than that under a light load, you need a regulator of some sort. A 5.5 V Zener diode would probably work but you could also consider a switching regulator. The step up-step down regulators sold by Pololu seem to be ideal for this situation. I have not tried them with solar cells, but considering that solar cells have relatively high internal impedance, you may have to add a large (1000 uF or higher) capacitor across the cell for the regulator to function properly. See

Have you conducted an "energy inventory" to determine whether the 1200 mAh battery will be sufficient for long dark or cloudy periods? If so, it would probably be of interest to others if you tell us more about the project!

Hi, Jreminton,

Thanks for your reply.
Idd it was posted twice. Unfortenutely it was not possible to delete your own post.

So if I do understand I can connect my solarcell to the powercell DC input.
Only to prevent the voltage not to rise above 7VDC max.
A zenerdiode will do this right?

I have my doubts if the system will work just to connect the solarcell which give more than 7VDC in brought daylight and will sink to zero in nighttime.


You MUST prevent the voltage from rising above about 5.5 V (which includes a safety margin) or the regulator module will be destroyed.