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Old 06-06-2010, 09:25 AM
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electrical switch to fan

Is there a way to run the an electrical fan directly to a on/off switch. I've heard about relay kits but I would like to know the purpose and efficiency of buying a kit vs building it from scratch. Will it cause my alternator to die? I'm a junk yard hot rodder so if you have an ideas about cars I can rip it off at the pick a part, let me know!

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Old 06-07-2010, 06:23 AM
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You need a relay big enough to handle the load of the fan. This often means a 70 amp or bigger relay, which is bigger than what you find in the parts stores. However, many cars now have electric fans, and you should be able to get a suitable relay from one in the junkyard.

Then use a standard toggle switch to turn the relay (and fan) on and off. If you power the switch from an ignition-on source, it will only have power when the car is running.

Running the fan all the time will probably hurt the fan more than it does the alternator. However, some alternators are not sized to handle the load of an electric fan, so you you might have low voltage at idle. That will also reduce the cooling ability of the fan.

Bruce
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Old 06-07-2010, 07:12 AM
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Quote:
Originally Posted by 67MercCat
Is there a way to run the an electrical fan directly to a on/off switch. I've heard about relay kits but I would like to know the purpose and efficiency of buying a kit vs building it from scratch. Will it cause my alternator to die? I'm a junk yard hot rodder so if you have an ideas about cars I can rip it off at the pick a part, let me know!
Much better to run a relay. If you choose to just use a toggle, it has to be rated for the draw of the fan- some fans will pull 40 plus amps.

Below is a couple diagrams that show how to wire up an electric fan. The Taurus fan on the bottom is a popular swap, BTW, and readily available in the 'yards.




WIRING FORD TAURUS FAN
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Old 06-08-2010, 09:07 PM
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A relay's main purpose is to turn small voltage into high voltage.So in order to make it work,you need two sources of voltage.And the other reply from one of the quotes is right.Just make sure you get a relay big enough to handle the fan.Switching off and on is not really a good idea,you never know when you might over look it,and it will prematurely wear components out.
Paisano
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Old 06-09-2010, 01:04 AM
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You may want to check this out: www.fordmuscle.com click on technical,click on cooling to the left,then look for "installing a junkyard fan" this shows the Taurus fan installation with pictures.Do not use a toggle switch! the majority of the ones available are "Chinese Junk" check the labels!They are not capable of handling the amps required for an electric fan and will short out fast

Last edited by JeffB; 06-09-2010 at 01:09 AM. Reason: add info
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Old 06-09-2010, 01:51 AM
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I have dual fans each with itīs relay, one fan I can switch on from the dash, just spliced into the fan switch connection and earthed it with a switch.
That way the relay is still switching on the main high voltage feed.
I did that but have never used it, best to let the thermal switch do the job.
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Old 06-09-2010, 09:40 AM
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no problem...

been on my bucket for 8 yrs now and NO problems.. need to know the amps of the fan.. auto parts store or radio shack has them.. i'm running a sw that takes 20 amps so i don't need a relay.. my volt meter reads a steady 14v so i don't have alot of drain..
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Old 06-09-2010, 10:16 AM
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Just To Eliminate Confusion

"A relay's main purpose is to turn small voltage into high voltage"(The Flyin Wop)

This should read; The relay's main purpose in this circuit is to turn low CURRENT into high CURRENT.

No offense intended, just to eliminate confusion. olnolan
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Old 06-09-2010, 11:45 AM
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Quote:
Originally Posted by OLNOLAN
"A relay's main purpose is to turn small voltage into high voltage"(The Flyin Wop)

This should read; The relay's main purpose in this circuit is to turn low CURRENT into high CURRENT.

No offense intended, just to eliminate confusion. olnolan
Sorry,Brain Fart,comes with my age.It comes with my age.And I often repeat myself.
Paisano
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Old 06-09-2010, 01:21 PM
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Beg to differ, it does not turn low current into high, the relay is a switch activated by low current.
The fans are then "driven" directly from battery or alternator not through any switch at the dash which may not be able to handle the high current needed.
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Old 06-09-2010, 02:02 PM
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Yep

Quote:
Originally Posted by malc
Beg to differ, it does not turn low current into high, the relay is a switch activated by low current.
The fans are then "driven" directly from battery or alternator not through any switch at the dash which may not be able to handle the high current needed.
Haa Haa, Yes Malc, both the OP and myself know how a relay works. The correction I made was in reference to the word VOLTAGE instead of CURRENT. I got a kick out of you post too, folks across the ocean use the term EARTH or EARTHING instead of our term GROUND or GROUNDING here in the U.S. The intent here was to try and keep the electrical terms correct for the folks that are still learning about electrical things. olnolan
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Old 06-09-2010, 02:12 PM
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Iīm from "across the ocean" and up until I started to read Hot Rod etc., used the term "earth".
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Old 06-09-2010, 02:18 PM
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Country?

Quote:
Originally Posted by malc
Iīm from "across the ocean" and up until I started to read Hot Rod etc., used the term "earth".
I like the jokes you post! But I don't want to guess the country because if I guess wrong, well you know! So, Where? across the ocean?
olnolan
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Old 06-09-2010, 02:43 PM
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Quote:
Originally Posted by OLNOLAN
So, Where? across the ocean?
olnolan
I'm guessing Australia.
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Old 06-09-2010, 03:03 PM
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Haa Haa

Quote:
Originally Posted by The Flyin Wop
Sorry,Brain Fart,comes with my age.It comes with my age.And I often repeat myself.
Paisano
Hey Paisano, Don't feel like like the Lone Ranger, I'm getting the CRS thing pretty bad. Some times I go to say someones name or something and all a sudden clunk, ca-clunk, clunck, CRS. I have to continue what I was gonna say and think of the persons name later. I ain't no spring chicken either. olnolan
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