Run a 2 speed fan w/ temp switch

shotsy · Apr 27, 2005

I grabbed a fan for my coupe at the junk yard and realized that it had 2 speeds when I got it home. Here's a wiring diagram that I made up to let you utilize both speeds without frying the motor and tick tock between slow and fast depending on the temp, good for stop and go I'd think.

ron67fb · Apr 28, 2005

How about just getting two temp sensors? I don't see why you'd need the fan on all the time anyway, even on "low". "Low" is usually triggered by the A/C circuit on cars that use a two stage fan.

351LX · Apr 28, 2005

I picked up a Taurus 3.8 fan from the wreckers and tested it out with an amp gauge.On the high setting,the fan would peg my 60 amp gauge on start-up so I couldn't get an accurate measurement of what it took but I noticed that even if the fan was turning slightly it required a lot less amps on start-up.Once it settled down it needed about 30 amps on high.I know some people get the two stage fans and just use the high setting but it would seem that it would require a lot less current to start if you go from low to high instead of just using the high setting.

shotsy · Apr 28, 2005

351LX said:
I picked up a Taurus 3.8 fan from the wreckers and tested it out with an amp gauge.On the high setting,the fan would peg my 60 amp gauge on start-up so I couldn't get an accurate measurement of what it took but I noticed that even if the fan was turning slightly it required a lot less amps on start-up.Once it settled down it needed about 30 amps on high.I know some people get the two stage fans and just use the high setting but it would seem that it would require a lot less current to start if you go from low to high instead of just using the high setting.

Not sure what the current draw is on the low side on start but it's got to be way less than the high side. I built the above this morning with some relays I had on hand and it worked as advertised, I'll be installing the motor in my car when the rest of my parts come in from jegs, and I'll let ya know how it works out. Not sure what the donor fan came out of but it's 16 inches across and the shroud is almost perfect.

jaredgoodwin · Apr 28, 2005

http://www.dccontrol.com/

351LX · Apr 28, 2005

For my application(86 Mustang with a 351c) I decided to use a Audi dual 11" fan I picked up at the wreckers a while back as it only needed about 12 amps to keep it running and seems to cool the motor just fine.I am using a foglight wiring kit I picked up in the clearance section of the tool store that cost me $4.99 and came with a 30 amp relay,a switch, an inline fuse for each of the two relay power leads and an assortment of wiring.My temp switch came from a 2.3 motor with an electric fan and I also added a switch in the negative circuit connected to ground so I have the option of turning on the fan manually.

ForceFed70 · Apr 28, 2005

ron67fb said:
How about just getting two temp sensors? I don't see why you'd need the fan on all the time anyway, even on "low". "Low" is usually triggered by the A/C circuit on cars that use a two stage fan.

Becasue dual temp sensors would end up turning both the low and high speeds on at the same time and could result in burning out the motor. Unless more relays are used...then the wiring starts to get complicated.

shotsy · Apr 28, 2005

70_Nitrous_Eater said:
Becasue dual temp sensors would end up turning both the low and high speeds on at the same time and could result in burning out the motor. Unless more relays are used...then the wiring starts to get complicated.

Exactly!!! My setup keeps one circut off while the other is on, no crispy fans!!

shotsy · Apr 28, 2005

jaredgoodwin said:
http://www.dccontrol.com/

Thats a nice unit for $350.00!!! bucks mine cost less than $15.00 to build!!

ron67fb · Apr 28, 2005

So what's more important to you, having the fan use less amps while switching from low to high vs. off to high, or your starter having less amps available to it because your fan's on even before the car is started? Regardless of how you wire it up, I don't see the point of an electric fan running all the time. Millions of other cars on the road with single speed fans, including mine, don't seem to mind starting the fan from zero.

I'm not saying you're nuts, since I did play with the idea at one point. I was hoping I could save some underhood components from the heat if I could keep the fan on low at certain times, but decided it wasn't worth the trouble.

70_Nitrous_Eater said:
Becasue dual temp sensors would end up turning both the low and high speeds on at the same time and could result in burning out the motor. Unless more relays are used...then the wiring starts to get complicated.

My VW POSsat does not turn off the low-speed circuit when high comes on. I guess it depends on the fan. As a side note, it has dual fans but one motor. The second fan is driven off the first one with a belt!

Jester67 · Apr 28, 2005

351LX said:
I picked up a Taurus 3.8 fan from the wreckers and tested it out with an amp gauge.On the high setting,the fan would peg my 60 amp gauge on start-up so I couldn't get an accurate measurement of what it took but I noticed that even if the fan was turning slightly it required a lot less amps on start-up.Once it settled down it needed about 30 amps on high.I know some people get the two stage fans and just use the high setting but it would seem that it would require a lot less current to start if you go from low to high instead of just using the high setting.

This is a DC motor and the inrush current “the starting current spike” should be about the same no matter if it is set to the high or the low speed setting. The initial inertia is the same. Once it starts to rotate the current will drop and will stabilize at its operating current very fast.

351LX · Apr 29, 2005

You are correct.On the low setting there is an instantaneous spike which pegs the amp meter but it quickly drops to about 30 amps and then settles after a couple of seconds down at about 12-15 amps.On the high setting it pegs the amp meter as well but then it drops to 30 amps.I noticed that by putting a resistor in the circuit the start-up spike is greatly reduced but I don't know what the long term effect on the fan motor would be.

ForceFed70 · Apr 29, 2005

ron67fb said:
So what's more important to you, having the fan use less amps while switching from low to high vs. off to high, or your starter having less amps available to it because your fan's on even before the car is started? Regardless of how you wire it up, I don't see the point of an electric fan running all the time. Millions of other cars on the road with single speed fans, including mine, don't seem to mind starting the fan from zero.

Your correct.. not all fans are designed the same. Some are ment to have the low and high circuits on at the same time...like your VW.

If wired properly, you can have the fan on low all the time EXCEPT for when cranking. Much like alot of other circuits in the vehicle.

And personally, I think the 2 speed fan is a good choice. Fans are much more efficient and quiet when ran at a lower speed. But at the same time, I wouldn't hesitate to throw in a single speed fan and only have it turn on when radiator temps get high.

You also have the option of putting in a low/high switch. Then you could leave it on low unless your stuck in traffic on a hot day or something.

Run a 2 speed fan w/ temp switch

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