relay

[monte70car]

In my new harness I have a wire for elec fans which is tied to a fuse in the fuse box, I also have a 12v battery and a 12v ing feed wire. Can I use a 30 amp relay and tie it into the control box for the elec fans? I know the fused elec fan wire is used for a relay and I'm not sure if I'll need the add 12v power feeds(haven't wire in a relay and want to make sure I get it right).

[wallaby]

I'm trying to figure exactly what you are asking.

If you have a 30amp fuse that is being used to run your fan power through, you might find it blows easily...there is a big draw of current as the fans start up that subsides as they get up to speed. A motor rated at 30amp draw can pull much more when starting. I used a length of fusible link wire instead of the usual glass or ATO fuse. The fusible link wire can tolerate overloading for a brief period, whre glass fuses blow imediately. I wired my link wire like a jumper between two terminals, and made several extras as spares.

 

A relay acts as a remote switch. You can use light gauge wire to your thermal switch, and your on/off switch, and the relay does the real work by turning on the main large-gauge power supply. This avoids having to use big wires and big switches and having them run all the way from the battery to the inside of the car and back out again to the engine compartment. I used the buss bar on the original voltage regulator as my point of supply for the main fan power...this lets the alternator "see" the power draw and compensate, without all the line signal loss of going through the ignition switch and fuse block etc. and is even better than hooking to the battery direct.

 

So basically, you want a big wire going from your buss bar, through your fuse, then to the fan; and the relay gets spliced into that line somewhere. When the relay gets a low-current signal from your thermal switch or in-car toggle, it closes and sends the big power to the fan motor.

 

Imagine the inside of the relay looks like this:

And the extra wires of the relay control if the switch is open or closed. They use an electromagnet to move the switch and the magnet requires only a small current, like a lightbulb might. So now you have a way to remotely turn on/off a big switch, without having to run big power all the way to where you are.

 

maybe this is all to basic, and not what you're asking. Anyway, I figured if you could visualize what's going on inside that relay box, it would help you out.

[Mo's70MCs]

Weren't you supplied with a wiring schematic? I'd would have to ask a couple of questions first? (1) Are you going to wire the fans independent of each other,like #1 & #2? in a basic circuit, one would control both fans independent of each other, with an (off), (on) and an (auto) position being the thermostat. (2) Any warning lights? Fan..off, fan running. Though I would imagine the 30A (fused) feed goes straight to the auxiliary relay to a N/O contact. The ign + would go to the, thermostat contact via a possibly 2PDT toggle switch. I'd say there are many variables, but this method is the simplest..cause you can go the extra mile and add a derangement warning light, of course I'd say that would be foolish. The reason for the first question.. some people wire them lead & lag.. where one fan runs and only when the temp goes far beyond a certain point will #2 kick in. Make sense?

[wallaby]

Here is a basic schematic for ya.