Information concerning my Davis Vantage Pro 2 weather station and any other weather-related news in the nearby Midland MI area.
By: mactoot , 4:14 PM GMT on December 31, 2010
Last week I suddenly started losing outdoor weather data after sunset, only to have it return at sunrise (provided it wasn't cloudy). My research on the web strongly suggests that the super capacitor ("super cap") has failed and is leaking power, thus draining the battery.
If you are not aware of how the wireless solar-powered system works, here is a quick primer: the power generated by the solar panel is stored in a high-capacity capacitor - NOT in the battery. The battery is a normal, everyday Li non-rechargable cell easily obtained at your local store (CR123A, 3V). Do not make the mistake of using a rechargable Li battery because apparently they have a higher voltage and might damage your system (I never read of any clear evidence of this however). Besides they are unnecessary and more expensive. The normal Li battery should last 6-8 months (?) even if there was no power from the solar cell. Its job is to provide energy if the capacitor runs low (consecutive cloudy days in winter, etc.). Therefore, in theory a battery should not need replacing unless it or another component fails.
The reason I suspect the capacitor is that there is a known problem with these (pre 2007 I believe - I bought mine in 2007) and the station starts transmitting instantly when the sunlight hits the panel and stops very shortly after sunset. If the battery were bad, the capacitor would normally keep the station powered all night, depending on the day's radiation. If the solar panel were bad, well, we wouldn't have power during the day.
The problem is not that the capacitor fails but rather how it tends to fail. It often leaks electricity and drains the battery. If it just failed to hold charge, the station would work fine up to the lifetime of the battery (at least a year if solar is available because it would only be needed at night).
Today I took advantage of the thaw and carefully climbed up my steep roof, removed the old battery and inserted a new one. I could not see much else in the unit because it is 6' above the roof peak and I was shaking too badly to dare to take a glimpse. I did take an equally shaky picture but it revealed nothing about the condition of the capacitor (I believe it is hidden under another cover anyway). I climbed down and checked the receiver - it is now transmitting perfectly! If the capacitor is NOT leaking, the battery should last into summer. If it IS leaking, it will probably die in a few days. Check back in a few days and see if the station is still transmitting.
Meanwhile I ordered another capacitor (from Digikey 589-1002-ND for $3.54). If the battery fails quickly I will remove the unit from the roof and replace the capacitor. The alternative is to buy a replacement transmitter from Davis but they quoted $82 (part 7345.976). I'll try the cheap route first.
My bet is the battery will fail by Jan 2, 2012 and I will be scaling the icy roof two more times to correct the problem. Time will tell. Why couldn't this happen in summer?
Happy New Year to everyone!
Comments will take a few seconds to appear.