Hey Guys,

I am looking to add a small 7" fan to my hood so that when closed it will help vent the area of the intake for my supercharger.

Where would a good place be to make an ignition activated power connection?

Thanks,

Sean

 

Use a relay, then you can tap into any hot-in-run wire under the hood. It takes very little to activate a relay, then you can use direct battery power to run the fan.



85 = any hot-in-run wire source - small gauge wire fine, only need 200 milliamps draw
86 = ground - small gauge wire fine
87a = not used
87 = 12v+ out to fan - use larger gauge wire like 10 gauge
30 = 12v+ from battery - larger gauge 10 gauge - connect to battery pos, or power distribution block between battery and radiator, or to the terminal on your starter where the pos battery cable connects.

When you turn on key, 85 gets voltage which activates the relay, connecting 30 to 87, thus running 12v+ directly from battery to fan - totally safe method of using a small hot-in-run wire tap to activate a large amp draw item such as a fan. Any 30amp relay $8 at parts store.

 

Mount the fan wherever you wish and run the power wires to the cabin through the firewall. Add one of these:

http://www.google.com/products/catalog?q=automotive+fuse+tap&hl=en&client=firefox-a&hs=0Vz&rls=org.mozilla:en-USfficial&prmd=ivns&resnum=1&biw=1350&bih=571&bav=on.2,or.r_gc.r_pw.&um=1&ie=UTF-8&cid=1132966779626101549&sa=X&ei=twqGTc_sLM6y0QGRlPTHCA&ved=0CHUQ8wIwAw#

to a fuse that's on the ignition circuit and you are good to go.

 

Not good to run high amperage wires to the interior - better to have them all under the hood - that's why I recomend the relay. I really hate that everyone wants to run a gazillion wires to the fuse panel, that's NOT what it was designed for.

You've already got umpteen hot-in-run wires under the hood, as well as the battery - why get battery power from the interior when the battery is already under the hood?

Always best to keep wiring short, you gain resistance (ie heat that melts wires) the farther you run a wire. Plus, why tax the fuse block anymore than what it already is? Add enough power devices to the fuse block and you'll be blowing the fusible link to the interior knocking everything out.

Always get high amperage juice from the source, the battery, which is under the hood.

 

Thanks Camaronewbie,

Which wire would you suggest for my application.

The fan will be mounted on the hood near the brake master cylinder (driver's side rear).

Sean

 

That is certainly the professional way to go... don't forget to fuse the battery side.

No need to go nuts with the wire length. 18GA wire has a resistance of ~.00751 ohms per foot. Not exactly an alarming amount if you go from bumper to bumper (~.12ohms).

 

So what would be a good wire to tap into for ignition power?

Sean

 

It takes very little to activate a relay (as little a 200 milliamps), so any wire that is hot-in-run would be fine.