Hey guys, getting sick of having to replace my switch to turn my dual fans on. I have 8 gauge wire running from the positive bundle by battery/radiator and another 8 gauge from the ground. Have two alligator clips to put together when I need fans on, sometimes they don't get warm at all and other times they burn the Crap out of my fingers. Any ideas how to get a reliable solution to this situation so I can run a switch with no issues? Thanks.

 

You need to run the power through a 12V relay to the fans, and a second circuit to a 12V rated switch that triggers the relay. The problem you are having is excessive current through the switches, which aren't rated for it, hence the heat you're feeling. The wire to the switch doesn't need to be heavy gauge for the relay trigger, but make sure to use heavy gauge for the power supply to the fans through the relay.

 

Right on buddy, I greatly appreciate that. So wire the relay back up and mount a switch to trigger it. Makes sense now.

 

Is there a specific relay you have in mind cause I just have two atm for my blower motor and fuel pump I believe..

 

Just go to the junkyard and chop a few off of a camaro, S10, etc just find the ones with 12 ga wire hooked to them.

 

Any 12V rated relay will work. Auto parts stores carry them in the electrical section, usually near the driving lights. You can re-use factory relays, but they're a little more interesting to figure out how to wire up sometimes. The basic operation is style the same.

The side of the relay will have a diagram showing the interior circuit, such as this;

Run your fused 12V heavy gauge wire to pin 30. From pin 87 connect the 12V heavy gauge feed to your fans. This is the relay switched power feed. You can run the trigger for the relay either of two ways; Either run a 12V fused source to your switch, then to pin 85 of the relay, with pin 86 of the relay connected to chassis ground - Or - Connect a 12V fused source to pin 85 of the relay, then run the output from pin 86 to your switch and connect the output of the switch to chassis ground. The only difference between these two methods is the second will not allow you to use a lighted style 12V switch. The benefit of the 2nd style is that the wire to the switch is essentially just a long ground wire, reducing the chance of a 12V short to ground if it becomes damaged over time. Either method will work.

 

Great information, that's all I need! Thanks.

 

Just a quick note:

You'll notice I said to use both a 12V rated relay and a 12V rated switch. So you may wonder, "If they're both rated for 12V, and the car's system is 12V, then why was it burning up my switches?". The problem isn't the voltage, it's the amperage, or current flow. The relay is rated for much higher current than the switch. So while both are using only 12V, the amount of current, or the flow of the voltage, is going to encounter much more resistance in the switch which translates directly into heat. This is why high current items like starters, alternators, fans, etc, use much larger gauge wire. Electrons travel along the surface of a wire, so the greater the surface area, the more electrons can safely travel along it. This is also why stranded wire can carry more current than solid wire - greater surface area. When the surface area is insufficient, resistance to current flow increases, which manifests as heat. The relay allows a workaround by providing a circuit path for the high current item with an internal switch triggered by an inductor - basically a tiny electromagnet - so that by using a low current circuit controlled by a switch, the inductor's magnetic field activates and closes the contacts in the relay completing the high voltage circuit safely.

People always confuse voltage and current. Voltage is the potential in a circuit, but current (amperage) is the flow. A person can take touching 50,000 volts...it'll hurt, but if there's no current, that's all it will do. However, even 12 volts can be deadly if the current is high enough, or the flow path goes across the heart. As little as 11 milliamps is considered life threatening.

 

Here ya' go: