Ford Mustang Forums banner

1 - 20 of 29 Posts

·
Registered
Joined
·
1,189 Posts
Discussion Starter · #1 ·
do i really need to use a relay or can i just use a switch..what kind of switch do i use also?...are there any downsides to not useing the relay?..thanks
 

·
Registered
Joined
·
1,157 Posts
You shoudl realy use a relay. If you plan on using something like the mark viii or taurus fans, theres really no way around it.
 

·
Registered
Joined
·
5,236 Posts
yes using the relay is a really good idea. there is a lot of voltage that goes through the wires. I have seen switches get burned up from not being able to handle the load. Can it be done with out a relay, of course it can if you get a relay that can handle the full load. but using a relay is a very nice cheap bit of safety. I eprsonally always use a relay. I am sure some other peopel will chime in with a better explination or even some other reasons.
 

·
Registered
Joined
·
1,973 Posts
The reason for the relay is the current draw. Most switches you get from an auto parts store are limited to about 10 amps. The Mark VIII fan can peak at 80 amps on startup and pull about 20 amps running or there abouts. I am not familiar with the current draw of the Tarus fan but it will be more than 10 amps. The Bosch relay or equivalent is the current carrier. You use a manual switch in the car or a temperature switch or both to trigger the coil in the relay. Typically the coil only needs about 0.3 amps to engage the contacts in the relay to allow the path for the current to pass to the fan.

Go to Matt's website if you have not already and read up on this.

http://svo73mm.cjb.net/

Darren
 

·
Registered
Joined
·
2,548 Posts

·
Registered
Joined
·
254 Posts
If your controlling the fan via a computer you need a relay (duh).
If your turning the fan on/off manually via a switch your better off without the relay, just make sure your switch can handle the amps.

Your best bet is to skip the auto store and go to a hardware store and look for a high voltage toggle switch in the electrical department.
 

·
Registered
Joined
·
1,247 Posts
blown302ho said:
If your controlling the fan via a computer you need a relay (duh). If your turning the fan on/off manually via a switch your better off without the relay, just make sure your switch can handle the amps.
Good luck finding a switch like that!

blown302ho said:
Your best bet is to skip the auto store and go to a hardware store and look for a high voltage toggle switch in the electrical department.
It's the amperage, not the voltage, that is the issue.

The only way you will successfully be able to use ONLY a switch to power an electric fan is if you use a small fan that does not draw much amperage.

Of course, using such a fan will be futile as it will not move the amount of air necessary to cool a 5.0.

Use the relay.
 

·
Registered
Joined
·
254 Posts
If the fan you are using draws more than 20A (dual fan setup), then use a relay.
IF the draw is less than (the Black Magic fan draws 13.9 A) 20A, its easier (faster installation and less complexity) to use a 20A rated switch as there are many available.
 

·
Registered
Joined
·
621 Posts
You should really be using a good quality relay. You can find quite a few different Bosh relays at Waytekwire.com
The even have 75A Bosh relays. They are awesome. Very heavy duty contacts and mounting tabs. If you use a switch even rated at 20A, it will most likely be a heavy duty switch which isn't very fun to be switching all the time (if you manually control your fan(s), or it will eventually suffer from carbon build up on the contacts from the initial current draw which even on a modest fan is more than 20 amps. Do it right the first time. This is one area where overkill is never overkill. Put a wimpy switch in and couple it with smallish gauge wire and you have a recipe for a meltdown and possibly a fire somewhere down the road.
There is no excuse not to run a relay. The are easy as beans to wire. There are plenty of places to mount them with a million holes in the fenderwell and such.

A nice trick for those not running foglights. It costs a few bucks but I did this years ago and absolutely love it. Get a new headlight switch assembly with functional foglight switch. Tap into the tan wire with blue stripe (I believe for Fox bodies). If anyone needs to know how to correctly wire this you can pm me. I can go look at my wiring as I have it all apart now to hide wires. This tan wire with blue stripe has power coming from the foglight switch. It will go to the positive switch side of the relay.
Here is a neat little diagram of a typical Bosh relay and how to wire the contacts.



The foglight switch is very nice and easy to use when controlling your fan manually. It is in a handy spot for both in car and out of car operation. (I often leave the fan on when I get back to the pits and later have to shut it off. This way I don't have to reach in to an awkward spot to shut it off. It's right inside the window.

Paul
 

·
Registered
Joined
·
831 Posts
sum87mustang said:
do i really need to use a relay or can i just use a switch..what kind of switch do i use also?...are there any downsides to not useing the relay?..thanks
A relay is definitly nessasary. So is a fuse, (or breaker), on both sides of the circuit.
The relay acts as a switch. The relay controlls the high amperage draw of the fan with a safe, low amperage draw of the switch.
This is nessasary to prevent overloading and fire.
If you do a search, you'll find that there are a million diferent ways to wire in a fan. At first, it appears easiest to just wire in a switch to the dash. This is also the worst way to do it.
To have it PCM controlled is best, but not cheap.
To use a separate temperature sensor, breaker, relay- is the next best way. And cheap too!
Summit sells a nice setup with a temperature probe that pokes thru the Radiator fins near the inlet hose. Its cheap and easily adjusted, AND easily installed.
Trust me, its better to set a fan up properly and have it come on automatically, than to have to 'turn' it on manually. Because gaunteed youll forget to switch it on and you'll overheat.

In the past I have used the OneWire temp sensors from Pontiac 6000's and Chryslers to turn my fans on. These type of sensors thread into the block or head and provide a ground when a certain temperature is reached. Its a cheap and easy way to have an automatic fan. If I recall correctly, the pontiac sensor opens at 205* and the Chrysler at 212*. Use it on the ground side of the relay, (low amp). Works great!!!

Heres a pic of the breaker I used instead of a fuse on my fan, it prevents the initial 50 -plus amps the fan draws at startup.


 

·
Registered
Joined
·
979 Posts
Not going to go against everyone here and say not to use a relay but I've been using a switch only setup with my mark fan ever since I bought it and theres been not a single hickup...YET! I bought my toggle switch from radio shack, not sure of the amps or whatever but I remember telling the sales guy I needed the baddest one he had. good luck.
 

·
Registered
Joined
·
1,247 Posts
DsuperA,

I hope your power lead is fused. If not, keep a fire extinguisher at the ready! :)
 

·
Registered
Joined
·
1,973 Posts
Adam,

Yep, pasted the wrong URL!! I meant to put Blown88GT's site up, thanks for the catch.

I think by all the replies that a relay, fuse, and power wire that can handle the load required are a must.

Darren
 

·
Registered
Joined
·
952 Posts
Don't forget!!!! The short distance btwn the relay and fan motor including the large wire size, prevents the wire from heating up and a serious voltage drop.

The much longer run FROM the battery TO the switch and back TO the fan requires LARGE wire.

Believe it or not.
 

·
Registered
Joined
·
1,189 Posts
Discussion Starter · #15 ·
hey ..thanks for the replies on my Relay question...

would this summit part help me...

http://store.summitracing.com/partdetail.asp?part=DER-16759&view=257#largerimage

do you think that would handle just about any factory dual fan setup. im not sure where my fans came off of but i know that the whole thing mesures about 30" across (15" each fan)...? that would basically help me eliminate the switch right...

i would then just hook up the two fans to run on the temp.relay...right ..?

thanks in advance
-jes
 

·
Registered
Joined
·
1,189 Posts
Discussion Starter · #17 ·
so i guess its a no to the part number from summit??
 

·
Registered
Joined
·
1,247 Posts
What fan setup do you have? If the assembly is 30" across, I doubt the fans are 15" each....

In any case, the controller from dccontrol.com is very good and WILL handle any OEM setup, including the powerhungry Mark VIII fan.

I just noticed this at their website:
http://www.dccontrol.com/kitsr1.htm

They offer a kit that looks an awful lot like a 3.8 Taurus fan. I use a 3.8 Taurus fan (but don't have their controller yet).

If you use the SEARCH feature, you will find more info than you ever wanted to know on the electric fan subject. :)
 

·
Registered
Joined
·
1,189 Posts
Discussion Starter · #20 ·
i think i will..
 
1 - 20 of 29 Posts
Top