Quote:
Originally Posted by Chris D.
When your driving on the freeway and the fans free spinning,
doesn't that cause the led to light up a little?  |
Good question, but no it doesn't.
As important as the rad fan is, I'm very glad to know when it's running.
In my design the LED is driven off the fan relay's trip circuit, so the LED never sees any voltage generated by a wind-driven fan. OTOH, if the fan power side of the circuit ever fails, the LED won't tell me.
If you run a bulb or LED off the fan's power circuit it might well light up if the fan spins due to air flow through the grill. I never tried it.
If you're an electrical noob and lost as far as relays, here are the basics:
A basic relay has four terminals. One pair controls the switch within the relay and the other pair receives and sends out power to the fan, through that internal switch. The first pair powers a coil/magnet which operates a switch. When the relay's coil gets power it closes the switch to allow power to the fan. One of the leads to two coil terminals has a temperature switch so the coil only gets current when the temperature switch permits.
Long story short, the two circuits are entirely separate and will have no interference. You can run a light or LED off either one. I decided to not tamper with the very thick and well sealed power leads and connectors to the fan, and instead just tap into the wiring to the temp switch. The last thing I want is corrosion in the fan's power leads.
I added a second switch to the trip circuit so the fan runs on low speed when I use the brake. This provides a moderate air flow when the car is still, mimicking the behavior of a clutch fan. If it ever truly gets hot the temp switch kicks in and the fan then runs on high speed.