ideas on power source

Hey all....putting an electric fan and thermostatic switch into a previous mech. fan car. Wondering if anyone has any suggestions on best/easiest place to get power for switch that is tied to ignition (ie fan will turn off when car is turned off). Thanks

First, make sure you use a relay, not direct wiring through the switch to the fan. The relay can be up near the battery, or on the cowl / firewall area. You can spice into a wire that + at key on after the fuse box. there is likely to be one or two unused , or minimally used circuits there.

I would resist the temptation to use the actual wire to the coil for fear of draining off the volts needed by the ignition circuit.

Dave

Thanks dave.....any ideas on using the 10 amp fuse in the fuse box under hood already marked for a primary fan. what is it powering now, since there is no primary fan yet?

I used Gary's kit to do my last car and it was great, but want to go another direction here.

answered my own question....Gary's kit comes with a connecter that "splices" into this fuse. So I went ahead and went that route.

New Question.....If I am incorporating a thermostatic switch, where is the best place to incorporate it? I have done/planned to place it in the positive from relay to fan. However, I have found a diagram that has it placed on the fan relay ground. Any thoughts as to why one or the other would be best?

IF I remember my basic electronics from 45 years ago. The load in a circuit creates a voltage drop, as it is a form of resistance.  So perhaps the idea is that,  it goes after the fan motor so that it doesn't burn out as quickly, less load at that point because of the drop caused by the motor. Might want to put it on the relay said rather than the load side..

Just a guess from an old man. Maybe others have  thoughts that are more up to date or from a better level of knowledge.



Dave

The thermostatic switch should ground the relay that controls the fan. You will not have a big power draw for the relay because of the high resistance of the coil. It is also easier to supply unswitched battery voltage to the coil, and then the only time you use it is when the temperature calls for it. Remember to use a temp switch that turns off above your thermostat, or once you turn the fan on, it will not turn off. I used a thermostatic switch from JEGS that is adjustable, and set it to turn off about 1 degree above the thermostat opening temp. I hooked up my secondary fan to come on when the AC is called for. I used the AC call wire to power the relay, and grounded it to the firewall.

You should also put a second relay in parallel to the secondary fan relay, so that it turns on if the temp gets above your threshold, and the AC is not on. Since the secondary fan relay is turned on with the AC call, you can not just ground it with the thermostatic switch, because there is no voltage at the relay when the AC is not called for.

Thanks Fred.

Dave

One last note...the primary fan will not turn off until the water temp is below the threshold, even with the key turned off, unless you hook it to a switched source.

Thanks Dave and Fred....After reviewing some instructions on installing a couple aftermarket fans, I ended up installing the adjustable temp. switch on the "key on" power wire before the relay. I found a stock fan and mounted it up. The fan is working great. Thanks for the input, much appreciated.