I have a pc fan controlled by this circuit http://img4.imageshack.us/img4/5034/circui18.gif The problem that i have is when the sun hides behind clouds the relay starts chatter.I must say that my electronic knowledge is very limited.
Thank you for your answer.As i have said i am a newbie to electronics so i want to ask you if it is possible to sketch it.Here's the schematic:
The problem is that there is no hysteresis in the control loop.
Hysteresis definitions: http://en.wikipedia.org/wiki/Hysteresis
Scroll about 2/3 of the way down under Electronics.
To add hysteresis, feedback (in the form of a resistor) needs to exist between the output of the opamp (used as a comparator) pin 6, and the noninverting input pin 3.
Without making any extensive analysis, try connecting a 47k resistor in series with a 500k potentiometer wired as a rheostat (just one "end" terminal and the middle terminal used) across pins 3 and 6. Adjust the pot until the relay stops clattering, but it does switch when the sunlight level changes significantly.
[eta]
Also, a large capacitor (1,000uF to 3,300uF) should be added across the supply of the relay, and a small cap (0.1uF) across the supply of the comparator
Thank you again.I will try it.OK, here's an edited version:
I missed the fact that there already is a capacitor present; C1, 100uF. That is rather small, considering that a relay is being driven in the same circuit. I would increase it to the range I wrote in my prior post.
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