When fan bearing/bushings fail they seize, on the units I have seen this blows the fuse.
To detect a blown fuse you only need to detect a lack of voltage on the fused side of the circuit.
The fans may open circuit which would cause them to fail without blowing the fuse. RODALCO's current detection using the reed relay would work to detect the lack of current through the fan. The fan should be thermostatically controlled so you need to only light the error LED if the thermostat is on and the fan is not running.
Light RED LED when ( (FAN_ON) AND (NOT(FAN_RUNNING)) )
which would be thermostat is on but the reed switch is not powered/active.
Run the fan hot lead through a
normally closed reed switch (SPDT wired to open when active).
If the fan is on and the fan is running the led will not light.
If the fan is on and the fan is not running the led will light.
If the fan is off the led will not light.
With a bit of work you can light the same LED when the fuse blows.
It would be easier to add a second LED to indicate a good or blown fuse.
Good fuse is easy, a green LED and current limiting resistor on the fused side of the fan prior to the thermostat. For a bad fuse you need to invert the logic and light the led when the fuse is blown, no voltage on fused side.
I am in the process of (slowly) building a custom fan control system. I plan to have heat sensors on the engine and radiator. Since I will be switching the fan(s) I already know when they are on/off. I like your idea of using a tach even if it is overkill. It would give advance warning of bearing failure as indicated by a decrease in fan speed. But this is not a simple sensor.
ferez said:
hi ya'all,
i want to design a circuit which will tell me in real-time what is the status of the radiator fan in my car (alive or dead).
i thought of placing a led in parallel to the fan but the problem with that is that the fan could be actually burned out while the led will still be on (it will still recieve 12v).
any suggestions?
mabe some kind of tachometer or any other simple sensor?
thanks for the replies