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To start off, I have a couple thirdgens that have the dual electric fan setups and I know the very basics in how they operate. In an engineering class I am taking I need to create a control system and I have decided to make (hopefully) a control system that will operate the secondary fan when the coolant reaches a desired temperature and then turn back off when the engine cools down.
I am not sure if anyone is familiar with them but I will be using an Arduino Uno R3 and related components to make this system. The system will use a thermocouple to read the temp and then activate the fan through a relay of sorts.
I am here in hopes that those with knowledge of the cooling fans can answer some more basic questions about them and also I would like to know if anyone would be interested in me chronicling my build of this system that may be interested in replicating it in the future.
My first question is I need to know what current the fans draw so that I can pick the correct method and relay to control the fan circuit. Any knowledge is appreciated.
My second question is to ask again if anyone would be interested in the actual building and operation of this as an alternative (cheap one) to control the fans in the future.
That sounds pretty similar to what I am going to do. I would be interested to see it since I have a design in mind of what I will do but I am looking to find what type of relay I can use that will handle the 12V and amp requirement of the fan (which I hope someone can tell me).
This circuit only uses the Power only in “on” position ignition source located in the fuse box to trigger the relay.
The rest is independent of the stock system.
It is an adjustable temperature controlled switch that is installed on the relays low amperage ignition controlled ground wire .That way even though the switch is rated at 30amps it does not use it. Much safer for the fan switch this way.
Here's the $17.00 adjustable temp. controlled fan switch.( you do not use the diagram that comes with it ).
It is universal and you might need to enter the part # to see it. =Part # 733653 http://www.autozone.com/autozone/par...67187_69565_0_
I have two of these circuits controlling two different fans. One set at 190* and a second as back up set at 200*. With a 180* thermostat. It keeps the car within that range even in traffic. ( I painted my controllers black ).
This is just something I put together. They sell much nicer kits but...$$$$.
IMHO, the best location for the probes and I mounted the controllers where they can be seen but you could hide them.
Last edited by Ron U.S.M.C.; 02-17-2016 at 11:07 PM.
My basic idea is to use the microcontroller to "turn on" a switch/relay that allows the power to flow to the fan. This seems to be similar to what you have. Please correct me if I am wrong, I think my setup would almost be inserted between 86 and GND on the first schematic.
86 to ground would be the right spot for a low amperage 12 volt connection/placing something in line. What is happening with the ignition controlled aspect of the relay is that , I will put it this way , terminology is off but this is the basic application.
There is constant "12v pressure to the relay"(post 85) from the ignition source. When the ground wire on post 86 has the inline switch in the open position no currant can flow. When the inline switch on the ground wire closes because the temperature at the probe the currant will flow triggering the high amperage aspect in the relay. Fan runs.
When the probe senses the temperature has dropped proximately 10 degrees it will open the switch stopping flow. And back and forth it goes.
In order to set the temperature "on" with the switch I use you simply turn the dial on it all the way clock wise = highest temperature.
Then using an accurate temperature gage (best to test your gage in the car with a inferred laser temp gun to see if its right).you start the car letting it idle until it gets to the temperature you want the fan to come on at , then very slowly turn the dial on the switch counter clockwise until the fan kicks on. Done.
Last edited by Ron U.S.M.C.; 02-18-2016 at 08:28 PM.
I measured the current drawn by a stock dual fan and they pulled ~7.5 amps each motor once up to speed running on 14 v-startup surge was probably ~15-20 amps each motor for a couple seconds.
well sounds like I need to find a relay for my Arduino that will support the 20 amp draw so I dont burn anything up, I have a 10 amp but I'd hate to see the surge burn it up after a few uses.
A basic 4 or 5 post 30amp relay should do it.
You need 1 relay controlling 1 circuit = 1 fan.
2 Fans = 2 relays = two separate circuits.
( The second post on a five post relay in the # 87 spot is there to trigger a second accessory if needed as in a "set" of fog lamps for example. It is not used in this application.)
Here's a little more info.
You might know how all of this works but some reading this thread my not.
Its always nice when a thread can be used by others just learning.
I hope you don't mind.
The amperage used to trigger the relay from the ignition source is tiny compared to what the fan uses. The ignition source wiring and the fan wiring never touch. They are completely two different circuits.
The low amp ignition source is only used to trigger the relay that allows the fan power to flow.
I have a 1amp fuse on the ignition source wire going to the relay. Then that tiny bit of power passes through a coil in the relay out the other side down the little ground wire through the switch ( your Arduino or a switch like the one I used ) to ground on the frame of the car.
That little coil in the relay acts as a magnet closing a little arm that allows the fan circuit to flow.
Here's what the inside of a relay looks like and how it works.
The photo below is
what it called a "Battery Junction Block" next to the battery.
It has the thick black wire with the red stripe going to it.
The "battery junction block" is where the fan will get its power (it is the wire going to post #30 on the relay). It is "VERY" hot (very high amperage) and should only be touched when both the positive and negative terminals are disconnected from the battery.
Last edited by Ron U.S.M.C.; 02-19-2016 at 01:52 AM.
I was confused in thinking I would need to replace the factory relay
with the one going to my controller.
So ideally I can use a setup similar to the first schematic you posted and where your controlled switch is I would use a small relay on my microcontroller. When the small relay is flipped "on" by the controller it will connect the ground from the factory relay and allow the current to flow to the fan through the factory relay.
P.S. Extra info is great in the thread that may help anyone looking into this. There are too many dead-end threads on the forum with little info/final solutions.
Where on an 89 T/A would I find the factory relays for the two fans? I would like to use the secondary fan relay from the factory since it is ground "triggered" by the sensor in the passenger side head if I understand correctly and my system will do a similar method as yours (RonU.S.M.C.).
Well finally have the time for some updates on this project for those that may be interested...
As far as my understanding I have sketched a very basic and rough model of the factory control system in the car
If there are any issues with it please let me know but it is veryyyy basic.
Next is my plan for my Arduino based system
Basically the plan is to replace the cylinder head switch with the Arduino and its components. This probably won't be a "cheap" alternative but the Arduino could be added to and used for multiple other gauges to use alongside the factory gauges.
Below is a picture of some of my wiring
And then the testing of the Arduino in the 3D printed case (part of the school project)
Finished up the "school" side of this project, I linked the video i used for my presentation where the blue led on the breadboard simulates the "on" signal to the fan relay.
That looks very cool, if your wanting your fan to come on earlier you can just buy a lower temp switch, if I'm understanding you correctly. I bought a 195 for mine which cuts on my secondary fan first now, with my primary still cutting on with ac or if the temp happens to get up 220 which is hasn't even come close since I put the 195 switch on it.
That looks very cool, if your wanting your fan to come on earlier you can just buy a lower temp switch, if I'm understanding you correctly. I bought a 195 for mine which cuts on my secondary fan first now, with my primary still cutting on with ac or if the temp happens to get up 220 which is hasn't even come close since I put the 195 switch on it.
I am happy with the way the project turned out for school but I definitely think getting a lower temp switch is still the way to go. The project was interesting and I would like to see how it works in practice but I doubt I would use it as my primary controller. It is however a fun project for people who like to tinker and dabble in Arduino projects. One nice benefit would be the ability to control both fans but I know that reprogramming the PROM will give similar control.
02-17-2016, 08:11 PM
