My downfall is automotive electric. I have hated it since I was a teen. Now that I am running an electric fan, I have read that I should have a ralay. I don't know how to install one or even what they are for. After driving my car for 15 minutes, my car doesn't want to start. I still have the stock alternator as well. I know I need at least a 100 amp alternator. Please educate me on what a relay is for and why it is needed. Thanks in advance.
The relay is used to "switch" power directly from the battery to the component vs the power running through a factory switch that cannot handle the load and might fail. How is your fan currently connected? Is it wired straight to the battery with a toggle switch or a temp switch? Depending on the load of your fan and what the specs of your switch are, you may not need a realy. Of course there are a dozen different ways to wire it and what you are running the power from, so we'll need to know how it is currently wired before it is known if you'll need a relay.
I'll try to explain how a relay operates first: The thing mounted on your inner fender (that a lot of people keep calling starter selonoid) is a relay. If you check on that there's a HUGE cable going from battery to the relay and another HUGE cable going from there to starter. The starter sucks up a LOT power (amps), hence the thick cable. So basically if you turn the starter key it puts 12v+ on one of the small connectors on the starter relay, which causes the relay to internally connect those 2 huge cables. This way the starter gets power directly from the battery. If we hadn't got this starter-relay, then we would need to run the HUGE cable from battery to ignition switch and from there to the starter. Needless to say it's going to be a more expensive cabling and the last thing you want is that huge amperage somewhere in the dash. This might well warm up your ignition key while starting. This is the purpose of a relay. Hope that makes sense.
Analog with your setup. The fan takes quite a bit of power to run as well as it has to push all the air. So in your current setup all that power has to go through your switch.
Do you know anyone with car electronics experience? he might have a relay lying around. And I'm quite sure if you'd ask in a car parts store they could sort you out with the relay you'll need for that. Maybe someone else here on the forums has a better idea or did that before
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1964 1/2 289 2bbl (autolite 2100) with holley headers and flowmaster 40s new: Quick Performance Racing 9" rear, Moser axles, 3.5:1 trac loc from FRPP and T5. CSRP disc brakes front and FRPP discs back. New wheels and tyres
Posts: 2031
Joined: 9/5/2006 From: Barossa Valley, South Australia Status: offline
Piece of cake Valley...I hate electrics and even i can do this one.
take a look at the diagram.
1) Battery to fuse to 30tab. 2) 87 tab to the fan +. Then fan - to earth. Under a radiator support bolt should do.
3) Power feed from the Ignition On side of your fuse box to switch on dash.
4) Dash switch to 86 tab 5) 30 tab to earth.
all the relay is doing is taking a "message" from your dash switch (running from fuse box to switch to ground 85) to "tell" the relay to open up the bigger power line from main power into 30 across to your fans via 87.
a good parts shop should be able to supply everything you need for around $20.
Main thing is to use a relay, fuse and cable that is bigger than the rated amps of the fan. But not ridiculously bigger! So, for example, if the fan is 20amp, use around 25 - 30 amp cable, relay and fuse.
good luck
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A 2007 study found on average Australians walk 900 miles a year. We drink 26 gallons of beer. That means, on average, Australians get about 34 miles per gallon. Not bad hey!
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