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Unread 07-08-2013, 09:15 PM   #1
papitt
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1995 ZJ 
 
Join Date: Dec 2008
Location: Stephenville Texas 76401, Texas
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Digram for the thermal temp fan sensor.

.. I'll give you guys a shot on this question .. I have a 4BT Cummins .. I have electric fan on the motor side of the radiator. At this time I've been running the fans from a Toggle Switch. Fan grounded. and other wire from fan goes to the toggle for it's power.
.. Now Question... I have added a 185 normally open switch into the head . It has 2 terminals out the top of it. Give me a digram on how to wire it off the positive side . I like my ground so I'd rather break the positive side. I'd also like to keep the toggle incab . So I TURN IT on & off to over ride it.
..........
... Does it really have to have a relay.
.. can you explain why the relay. With out 40 pages.

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Unread 07-08-2013, 10:18 PM   #2
MeanGreenZJ
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Sounds like you're out of your element with this issue. You can't draw that much current via temp switch and you should never run a positive into one either.
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Unread 07-09-2013, 05:08 AM   #3
ZeeJay1997
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yep, at minimum use a relay designed for the current the fan draws. use the sensor to control ground to the relay coil. if you want to keep the switch, use it to break the other side (hot) of the relay coil. be sure to put a fuse rated for the relay near the source of the hot side.
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Unread 07-09-2013, 07:40 PM   #4
papitt
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Mean Green, So your say brake the ground side in the thermal switch. And keep the Hot side going straight to the fan.
... And how much current am I putting into the fan. To me it's 12V. How much do you say I'm putting into it.
................
... Thanks for the answers Keep um coming.
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Unread 07-09-2013, 10:27 PM   #5
kachink
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I think meangreen's right, you are out of your element - but that's how you learn things. An engine fire can be a very educational experience!

I have a basic understanding of this, but I'm sure someone will correct me if I mis-speak.

Current and voltage are 2 different things.
Voltage is like electrical pressure, measured in volts.
Current is the actual flow of electrons, measured in amps.

The little idiot light on your dash is 12 volts, just like your headlights, but the headlights use much more current - to produce more light.

These numbers aren't right, but say your efan uses 30 amps. That's while it's running. It probably takes twice that to get it started and up to speed. That fan is going to try and suck that much current through your circuit, so you need wires and a switch that will move 60 amps without overheating and burning up. The shorter those wires are, the less resistance, less heat they build up. That's why you want to use a relay. It keeps your high amp wiring to a minimum and lets you buy other components (like the temp switch) that are rated for a lower amperage.

A relay is just an electrically operated switch. You put your relay (rated for the max current that you expect) in your high amp circuit, then run a smaller wire (because it doesn't take much current to operate the relay) to the temp switch and/or manual switch. Here is a circuit diagram for a two speed efan setup with two temp sensors and two relays. If you google "efan circuit diagram" you'll find a lot more.
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Unread 07-09-2013, 11:34 PM   #6
MeanGreenZJ
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Voltage and current (amperage) are two different things. But to answer your question, your fan can draw 30-40 amps on start up. You will need to use a relay. The thermal switch can't handle the much current draw. Learning things is great and all, but an error can spell an overheated engine or a fire.



Quote:
Originally Posted by papitt View Post
Mean Green, So your say brake the ground side in the thermal switch. And keep the Hot side going straight to the fan.
... And how much current am I putting into the fan. To me it's 12V. How much do you say I'm putting into it.
................
... Thanks for the answers Keep um coming.
MeanGreenZJ is offline   Reply With Quote




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