Sandaysoft

Gina, that's interesting, this would suggest that the chip on the controller inside the fan uses PWM to control and monitor the speed. Not sure why the frequency increases when the lower voltage is applied?

Here is my new fars. It has a cd player motor running off
a garden solar panel. Works great.

Just a note to the wise, always make sure any fan you use is moving the air away from the temperature sensor. If you use the fan to blow onto the sensor the heat from the fan motor could influence (even if only slightly) your readings.

Yes, my fan draws air upwards away from the sensor.

This morning we are getting alternate sunny spells and cloud and I can see the result on the recorded temperature. With the fan running at a low speed I'm getting just under one degree Celcius rise in the sunny spells. I've just turned the fan speed up a bit and will see if it makes any difference. Previously I was getting 2 or 3 C rise due to sunshine.

Now appear to be getting just below 1 degree C rise due to solar radiation so the difference due to increased airflow is marginal. But the difference from no aspiration is significant. There is also a significant improvement in the humidity readings. Previously the readings were almost always 90% and above but now they look much more realistic. Both day and night RH readings have improved by the constant aspiration.