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Photos Supplied
In Melbourne the rainfall interests me because it's been borderline drought conditions these last few years. But the trouble is every 2, 3 or 4 weeks depending on the type of batteries used in the transmitter they retire without warning and I lose my accumulated rain fall. Bugger! Then I have to mess about with new batteries and resets. I checked on several forums to discover that the Thermor Weather Station is very heavy on batteries. So I thought I'd try to use a solar charger from a cheap garden light to fix my problem. I headed straight to Bunnings at the corner of Cheltenham & Springvale Roads Braeside. Lucky for me there was nobody to help, so I was able to unpack a light in my price range ($13.00) and examine the gizzards at the business end of things. Ok, this was the one I wanted, it even came with 2 x AA rechargeable batteries.
At home the multimeter told me the solar cell was producing a healthy 3.2 volts. It told me that the cell kept generating, even with the light switch off. The switch allows the batteries to cop a full charge over several days without lighting up the little light emitting diode {LED} which illuminates for the night time effect once the built in photo electric cell detects night and tells the LED that it's showtime. That was ideal because I didn't want the LED to be pinching any of the power from the batteries at night time or I would have had to snip it off.
It took only a few minutes to solder wires to the solar light, battery terminals (the batteries stay out) and thread it through to the transmitter terminals. Nothing came apart and the neatly soldered wire ends tucked securely under the transmitter battery terminals so that with the RECHARGABLE batteries in place there was adequate tension to eliminate any connection problems.
With pre-charged, rechargable batteries in the transmitter and a quick poke around with the multimeter all seemed well. This was 5pm when there was still a little bit of late autumn daylight. I popped my head in frequently to check the display. All seemed well until the 9pm check yielded the flat transmitter batteries problem... You know, no: wind speed, wind direction or outdoor temperature.
I guessed that the solar cell might be drawing current back out of the batteries because it was directly coupled to them. Maybe the garden light circuit (which I'd by passed) had a diode in play to allow the current to flow in only one direction. Anyway an old 'talking electronics' project board was hoarding a nice juicy diode so I de-soldered it and put it in the middle of the positive wire between the solar cell and the weather station transmitter, making sure the solar cell could send current to the batteries but it couldn't sneak back to the cell. I have used 2 x 2100mAh batteries, but a couple of 500mAh batteries seemed to work well too.
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