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Old 01-12-2006, 09:46 AM
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Electric Fan - relay or not?

Hey I don't know much about wiring so I wanted to ask everyone here for some help.

I just ordered an electric fan for my 69 Nova. I'm not going to use the thermastat for activation, I want to just wire it up to a switch on my dash. Here is a link to the fan i bought:


Can I wire it straight to the switch or do I need to use a relay? Anything else I need to know... For some reason I have a weird feeling that it is going to cook my switch... but I know pretty much nothing about wiring.

Thanks in advance for any help!

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Old 01-12-2006, 10:15 AM
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I would certainly use a relay and certainly use a thermostat control. I would get a thermostat/relay kit from Summit, like this one:

$25 well spent and free shipping if you buy it with the $120 fan you chose.
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Old 01-12-2006, 10:16 AM
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Best to use a relay for full power to the fan, without going through a switch.
Just use the switch to turn the relay on.

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Old 01-12-2006, 04:05 PM
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Doc here,

You'd be hard pressed to find a switch that will handle 17 amps ... Most Consumer type switch gear is 250/125Vac/5 amps max at the contacts ..AND If you Do find one It'll Cost MORE than relay's Will for sure.

You need to use a relay on any high draw component..Especially Fan motors, and TWO in parallel are preferred as a Safety Issue.

A Relay Coil (Or Set of coils) Will only draw an amp to an amp in a half, Whereas The motor will draw 17 amps and Spike on startup, or If you Suffer a rotor lock on the motor.. (A plastic bag kicked up and caught in the blades.)

The Contact Ratings on the relay are rated at about 250/125/Vac At 30 or so amps This will deliver The current to your fan motor directly from your Current source.

Wire your relay(s) Coil To a Properly Fused 12 volt switched source. The ground side of your coil will go to the switch in your dash, through the switch contact to ground.

Your Contacts will be as follows, The Normally Open Contact (NO) will go Via a properly sized wire To a Fuse link at the battery or at the main cable terminal on the starter solenoid. The Center Wiper (CW) , or movable contact will go to your fan power Terminal on the Fan plug. I always keep power on the NO contact where ever possible so you don't have a NC (normally Closed Contact ) Heated up all the time to drop a tool on and short..

If you plan to use a Thermo or Automatic switching, you are already set for that by using the ground for switching the relay..(Most senders are referenced to ground) So you just need to tap in there at the switch, OR put in a 3 position Switch (Off/On/Automatic) where the standard one was.

The use of Two relays in parallel is a preferred method of wiring, to avoid harness heating and plug/contact meltdown..I had a drawing for that, (that I didn't draw, or check!) but it turns out it was in error, otherwise I'd post you the schematic here.

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Old 01-12-2006, 11:18 PM
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Look a little further down to a thread "SPAL fan rotation change", I posted a wiring schematic for dual SPAL fans the shows a bypass for an optional switch. I wired mine to the thermo switch and made another circuit for manual activation, simply grounding the thermo switch, and it still utilizes the relays.

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Old 01-14-2006, 06:07 PM
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Always use a relay

Trust me you always wnat to run a relay on something like that. You don't have to have the thermatic switch, thats not a problem. But do use a relay, I have heard stories of vehicles buring up just from not putting a relay on a fan control. Plus it will save you from buying alot of switches.
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