Quick Spal fan wiring question

[z31maniac]

Let's say I don't care about using the A/C switch (which I don't) and just want to wire the fan to a switch inside the car that will work with or without a switched lead/temp sensor etc, just "ON/OFF".

I can just bypass all the relay bullshit and give it a power and ground, and ground the signal when the switch "closes" correct?

If yes, would you still use the big stock power lead, or grab a power source from say the block the starter wire hooks to on the passenger side?

[Tchao]

If you are dead set on using a stwich (even though the factory provides you with a very nice thermo setup) then yes.

Make SURE to fuse it somewhere.

Best bet is to use the stock wires, get a M42 thermo-switch, and wire the low/high together. Change the low-speed fuse to 30amp. Done. No switches, no bullshit.

[z31maniac]

Yup, I am dead set on using a switch. The kit came with a fuse and wiring for such a setup.

I mainly wanted to make sure that hooking up to the power block/starter block on the passenger side was going to be OK since that's where my E30 fuse box will be getting it's power as well.

[StereoInstaller1]

Don't even think about running a fan without a relay.

Switches are like 10A max. Your fan will draw way more than that.

That is what relays are for!

Luke

[z31maniac]

^So basically find a heavy duty switch?

I'm going to slowly eliminate all unnecessary wiring from the car as it progresses.

[E30Idea]

^So basically find a heavy duty switch?

Yes, but dont expect a wiring professional like Luke, to agree.

The only "correct" way to do it is with a relay. But a big ass switch will also "work"

[z31maniac]

Lucas, edumacate me. Explain the importance of a relay (or how the relay helps prevent overdraw/etc) for the amperage that the fan will pull. That's not a smartass question, that's an honest question, I want to learn something.

(it was provided with a fuse holder and 30 amp fuse.)

[StereoInstaller1]

OK, I will see what I can do.

Basically, a relay is an electro-mechanical toggle switch.

This allows several uses, but the primary usage is to allow a small amount of current to control a larger current- like a tiny switch (the fan switch on your radiator) to run something that is basically a HUGE load, like an electric fan.

Current capacity of ANY switch is limited to the mass of the contact itself, and the shunt holding the contact.

What this means is that the big burly switches than can handle 30A of continuous draw (versus the varied draw of say, an audio amplifier) are gonna be WAY bulkier and far more "clunky" in their operation.

So, yeah, you can use a simple switch to run your fan...but think of the length of wire (load on wire increases with length, logically) so the chance of the wire getting hotter increases exponentailly as you move the switch farther from the load (fan) and voltage will drop more (less RPM is what would happen).

Personally, I think a single wire from a main distribution point to a fan relay on the firewall or core support, then either a single wire from a switch in the dashboard or a radiator fan switch (or both, which is best IMO) is the easiest, most reliable and cleanest method of handling the fan needs.

I feel dumb as hell trying to explain this shit to a guy who is a professional technical writer, so I hope I am making some kind of sense...

Luke

[z31maniac]

Hahaha, you did a great job explaining it.

So basically still use the relay to supply power and "switching" for on/off, but instead of "grounding" the relay to thermostat, I would "ground" the relay to the switch to complete the circuit? Is that correct?

[SamE30e]

Theres a perfect setup in the a/c setup. Literally took me 10 minutes to hook it up. And it turns on when you hit the a/c button.

[StereoInstaller1]

You can pow4er the coil of the relay with either +12V or ground, as long as the other is on the other side

[Jean]

+1. Plus I wouldn't want to run thick wires to my dash with 15 amps of current going through it. Use a relay ;)