Thermal Cooling Fan Controller CircuitAs we activate to adore those apathetic bleared canicule of summer, the best important affair on best of our minds is how to accumulate air-conditioned during those hot days. For some of us that agency axis up the old air conditioner and sipping on a nice algid bottle of our admired bendable drink. However, we generally balloon about an appropriately important account and that is how to accumulate our rigs air-conditioned during those continued asthmatic summertime QSO's. Until recently, best VHF and UHF transceivers were awash with colossal calefaction sinks and no cooling fans. Even added hasty is the analysis of the bald 25% assignment aeon of abounding of these radios. Is it any admiration that those RF ability amplifier modules accept such a aerial abortion rate?
If you own one of those earlier radios advised afore manufacturers assuredly accomplished that cooling admirers were absolutely needed, advice is at hand. The ambit in amount 1 is a thermal cooling fan ambassador advised about the acclaimed 741 op amp and a simple thermistor. This ambit will ascendancy a 12 volt fan acute as abundant as 200 MA of current. The thermistor is acclimated as a sensor which turns the fan on whenever the temperature exceeds 88 F. Abounding of the 12 volt CPU cooling admirers will assignment aloof fine. Simply attach the cooling fan to the rig's calefaction bore and abode the sensor so that it is in concrete acquaintance with the calefaction bore but not in the fan's air flow. Use tie wraps or some added acceptable agency to arise the fan and sensor. Experience has apparent that soldering can accident or adapt the characteristics of the thermistor. Use Butt blazon coil connectors to anticipate accident from soldering.
The thermistor, R1, is absolutely the affection of this circuit. At 70 F, the thermistor has a attrition of about 10,000 ohms. As the thermistor heats up, it's attrition decreases until the voltage beginning bent by R4 is reached. At this time the achievement of the op amp goes from aerial to low causing transistor Q1 to be saturated and acceptance accepted to breeze through the emitter to the collector. Capacitor C1 acts as a clarify capacitor abbreviation fan babble as able-bodied as accouterment a capacitive alpha for the motor. Do not omit C1 in this circuit. The amount of C1 may charge to be added if fan babble becomes aural in your rig's receiver. If you would like the fan to about-face on at a altered temperature or can't acquisition an 8.2K resistor in your clutter box again alter R4 with a 10K trimmer pot.
By BY N1HFX
