I am building a solar swamp cooler for burning man (hot dry desert environment).
Purchased a 15w solar panel that outputs 0.9a at 20V in full sun (verified as true with my voltmeter). The solar panel apparently provides 0.8a at 17V under load.
I applied the output to power a 12V fan rated at 0.4a, and it seemed to work fine, although a little slow.
THEN, I applied my PC power supply output to the fan, and it hummed along superfast, providing an awesome air current.
What's the story here? If the fan draws 0.4a, what is the solar panel lacking?!
Thanks for any insights!
Best Answer
A solar panels current rating is based on short circuit current (short the wires together) and it's voltage is open circuit.
When you attach a fan (an inductive load, relatively heavy load too), the voltage of the panel will drop and is probably less than 12V. However, because there is some current flowing through the fan coils, it will spin, albeit slowly.
Your solar panel CAN'T provide 800mA @ 17 V. It can provide up to 800 mA current and up to 17 V. Give or take.
The plug in power supply can deliver however many A @ 12 V. It will maintain 12 V. A solar panel won't.
You should use a battery and solar regulator to supply the power to the fan. As long as there is more power going into the battery than the fan is consuming over a long period, you should be ok. Remember the battery won't charge during the night so the panel needs to deliver enough power during the day that will be used in a 24 hour period. That assumes a sunny day every day too...