Home built FARS

[Gina]

Had a look at the mechanics of changing fans but it wasn't really on so I'm feeding it from a cable. Bell wire, in fact. I see no harm in running the fan continuously at low speed. In fact that would stop any problem of the bearings getting sticky in frosty weather, plus extract any heat generated by the transmitter circuit.

Here's an up-to-date diagram.

Screen-4.png

[beteljuice]

Looks good to me

[malc-c]

Gina,

Most PC cooler fans are brushless, which might be the reason it stops at low voltage. Being brushless each overlapping coil is energised in sequence to either attract or repel the core magnet. If the voltage is on the threshold you often see a sort of stepping / cogging effect.

Hope this helps

[Super-T]

Gina
Is your airflow up?

[Gina]

Gina,

Most PC cooler fans are brushless, which might be the reason it stops at low voltage. Being brushless each overlapping coil is energised in sequence to either attract or repel the core magnet. If the voltage is on the threshold you often see a sort of stepping / cogging effect.

Hope this helps

Yes, I've noticed that. And at a lower voltage it makes a high pitched whine. This is probably not harmful but I think I would prefer the fan motor to either be running normally or not at all.

Gina
Is your airflow up?

Yes, the fan draws the air upwards.

[malc-c]

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?

[mike]

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

[RCE]

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.

[Gina]

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.

[Gina]

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.