electric fan, chevy pickup

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ca18de

Member - Posts: 5

Joined: August 05, 2006

Location: United States

Posted: December 14, 2006 at 2:03 PM / IP Logged

Hello all, I didnt see anywhere to ask general questions about other automotive wiring. If there is a section please let me know.

I needed some help working out a wiring issue with an electric fan in an old chevy pickup.

I have a relay wired up with #85 12v, #86 goes to the fan, #30 12v, and #87 goes to a temperature switch. The temo switch is a common negative coefficient thermistor, and shows zero resistance at the maximum temperature. One side of the thermistor is grounded, and the other is wired to #87 on the relay.

The problem is that the temp switch does not complete the circuit to ground early enough. This keeps the fan from coming on, and obviously causing the engine to reach unsafe temperatures.

What i was wondering, if i were to ground #87 on the relay and run voltage through the thermistor to #30 on the relay would I be able to trip the relay at a sooner time in order to turn the fan on. Would this be unsafe to run voltage through the therm.

Any other advice on a better way to wire this would be greatly appreciated. I am trying to keep from going to buy new parts for the sake of keeping cost low, so i'm trying to make due with what I have

Again, I apologize for posting this here... But i was unsure as to where to post.

Thanks in advance, Stephen

geepherder

Platinum - Posts: 3,668

This member consistently provides reliable information

Joined: October 27, 2003

Posted: December 14, 2006 at 7:34 PM / IP Logged

I think you actually mean 86 goes to the thermistor, and 87 to the fan. You need to use a transistor to trigger the relay.

Go to www.bcae1.com and on the right side, scroll down to 65- cooling fans. That will give you a diagram that you (or a friend) can probably modify to meet your needs.

My ex once told me I have a perfect face for radio.

ca18de

Member - Posts: 5

Joined: August 05, 2006

Location: United States

Posted: December 15, 2006 at 10:58 AM / IP Logged

Great info there...

I've just never delt with op amps or transistors... any advice?

geepherder

Platinum - Posts: 3,668

Joined: October 27, 2003

Posted: December 15, 2006 at 6:49 PM / IP Logged

Read up online and have a friend help you. I'm not all that good designing, but whenever I need to make something, I usually do most of my research with Google until I somewhat have an understanding.

Here's a good place to help learn about transistors: http://www.williamson-labs.com/480_xtor.htm.

Here's a good website to help learn about op amps (just scroll down until you see it on the left): http://www.talkingelectronics.com/te_interactive_index.html.

My ex once told me I have a perfect face for radio.

ca18de

Member - Posts: 5

Joined: August 05, 2006

Location: United States

Posted: December 30, 2006 at 11:39 AM / IP Logged

bUMp for more help....

I tried putting 12 volts through one side of the sensor, and measuring the voltage coming out of the other side. At 185 degrees (the point that i want the fan to come on) there was a sold 6 volts. Is there some way that i could actuate the coil side of the relay at 6v? I;m sure they make relays for that, but they arent always a sold voltage. Some relays come on early, some late. This has to be very exact so that i can protect the motor.

Thanks again

geepherder

Platinum - Posts: 3,668

Joined: October 27, 2003

Posted: December 31, 2006 at 12:28 PM / IP Logged

I was just thinking- if you wired it up like the diagram on www.bcae1.com, you may be able to just set it at 6 volts rather than 5. Go back to that website, and play with the interactive parts of that diagram. You can get a feel for what will happen if either the temperature rises/falls, or you adjust the voltage at which the op amp switches. It's a pretty ingenious design with many safetys to prevent frying something, and it's accurate, too.

The only thing is, depending upon the resistance value (at room temperature) of your thermistor, you may need to interchange some of the components/values. I'm no engineer, so I can't offer much assistance there.

My ex once told me I have a perfect face for radio.

transam355

Member - Posts: 2

Joined: January 01, 2007

Location: Canada

Posted: January 01, 2007 at 6:02 PM / IP Logged

If I was you I would just wire the relay up normal and change the temp switch to a naturally open two prong temp switch that closes at the desired temp 185 as you said.Wire one side of the two prong switch to ground the other side to the relay.This temp switches are available at most parts store in different heat ranges.This how I wired my coolant system and have not had a problem yet over 2 years now. HAPPY HOLIDAYS GOOD LUCK !!!!!

Got Boost ??

ca18de

Member - Posts: 5

Joined: August 05, 2006

Location: United States

Posted: January 02, 2007 at 8:01 AM / IP Logged

do you have a part number or a specific store you go to ? Everytime i go to a parts store around here they just play dumb. They dont seem to know what they have. That was my original intentions, but like i said they dont know they have it... so how will I

transam355

Member - Posts: 2

Joined: January 01, 2007

Location: Canada

Posted: January 02, 2007 at 4:44 PM / IP Logged

I got my switch from the local Napa store I swing by there and try to get a part # for you I don't know if the part # in CANADA and the USA will the same or not but I will give it a try.

Got Boost ??

ca18de

Member - Posts: 5

Joined: August 05, 2006

Location: United States

Posted: January 02, 2007 at 7:38 PM / IP Logged

thanks alot man

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electric fan, chevy pickup

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