electric fan

[hjewell2]

Sooo instead of running a relay to my fan I have run 10awg wire to the positive lead on my batt cable, and ran 10 awg ground wire to a switch inside to turn on after starting and leave it running til I shut motor off. Is it good or bad by shutting fan off by killing ground? switch is rated for 20 amp AC

[87Skier]

It won't hurt the fan. switch might be undersized since DC ratings are generally lower than AC.

[hjewell2]

Originally Posted by 87Skier

It won't hurt the fan. switch might be undersized since DC ratings are generally lower than AC.

Thank you for the quick response.

[dave`12]

I've heard it's not good to hook stuff straight up to the battery, DMJLambert advised me in a post:

1. connect accessories that are a heavy draw directly to the alternator output or to the place where the alternator wire connects to the junction near the driver's side headlight where the big wires and the fused ammeter wire come together.
2. don't connect anything other than the battery, fused ammeter wire, and the wire that goes across the top of the radiator towards the alternator, at the passenger side fender terminal.

I know those fans suck a lot of amps. Mine are hooked up to a terminal strip that I installed on the firewall. If you have an ammeter, as I do, hooking up stuff straight to the battery will also take it out of the loop.

Just something to consider.

[SunSoaked]

My dual Spal fans, Vintage Air a/c and Holley fuel injection system ALL say (several times) to connect DIRECTLY to the battery. Between all thier engineers and lawyers it can't be that bad?

[dmjlambert]

I don't think it's "bad." It may be better to connect to the alternator output if you want the factory ammeter to show accurate charge/discharge current. If you connect something that draws current directly from the battery, it will draw current along the alternator-to-battery 12 gauge wire that acts as a shunt for the ammeter. Normally, that wire does not have significant current running in it very often. It only has current during a short while after starting when the battery charge is being topped off, or when accessories are being run when the engine is off.

If you have something that draws directly from the battery when the truck is off, the ammeter will not show the discharge is happening.

And finally, in a properly wired truck, except when the battery is being charged to recover from the energy used to start the truck, the battery is not actually being used and is pretty much out of the picture. 100% of the electric energy needed is being supplied by an adequate sized alternator (which in turn gets energy from the engine and gasoline). So, connecting things as close to the alternator as possible would be most efficient.

[Andy4639]

This is my opinion and it's just good practice.

Always run high amp loads off of a relay always. In rush of a fan can be 50-60 amps depending on the size of the motor fan.

Running it like you have it is well it will work! I hope you put a in line fuse in it as well.

A 20 amp switch isn't enough for a good fan. Not knowing the size and amp draw of the fan it's hard to know what kind of switch you need. 20 amp's is low side for a good fan.

Another note. When directions say run directly off the battery that doesn't mean you can't run a relay.
Relays are directly from the battery.

[VetteVet]

If you run your wires off the starter solenoid at the battery post connection you will be pulling directly off the battery and it should show the draw on the ammeter.
A relay is just a switch if you think about it. It just allows a smaller wire to control a larger
current so if the switch will handle the 40 amp load it will be fine. But like Andy said, you should use a fuse or fusible link compatible to the amp draw and the wire size.

My recommendation is always use a terminal block powered by the alternator with a battery backup wire that the alternator can use to charge the battery. If you plan on using the battery with the engine off you should run a larger feed wire from the battery post or the solenoid in addition to the charging wire. You don't need that for a cooling fan if the engine isn't running.
Also why would you not use a temp sensor and a relay to control the fan automatically? What if you were driving along and your GF's or your wifes hand was in your lap, your engine could overheat right along with you, LOL.

Here's a simplistic diagram showing what I mean.





If you connect the ammeter wire for the alternator to the junction box and the one for the battery to the fender junction the ammeter should work as advertised. VV