Fan control working backwards (off=on, on=off)

[Bev]

Ok, posted a question about this the other day, but managed to work it out myself. Thought I would post my solution to help people who may come across the same issue.

The problem:
I rigged the fidle pin of my megasquirt v3 board to the ground side of my cars OEM cooling fan relay. However, the fan was working the opposite to what megasquirt was commanding it to do. When the megasquirt was commanding the fan off, it was turning on. When it was commanding it off, it was turning on.

I could have fixed this by not using the "fan control" window of megasquirt. I could have programmed it through the "programmable on/off outputs" section, using coolant temperature and rpm settings to define when the fan came on and off, and if it would allow fan operation when the engine was shut down. I didn't want to do this though, because the fan indication on my megasquirt dashboard wouldn't work then, and I couldn't use the "fan on when A/C on" selection of the fan control window, which is pretty useful if a car happens to have A/C.

The reason my fan was working opposite to my megasquirts commands, was because my original Toyota relay was a normally closed relay - applying a ground to the relay coil did not close the contacts - it opened them, thus turning the fan off! From what I understand, some mazdas use a normally closed relay for their fan control also. Either way, the opposite of the type of relay that megasquirt's fan control is designed to work with.

Anyhow... my solution. I removed R19, and ran two wires from the board holes to the proto area, then made the following circuit using a 2N2222 transistor, and two 1k resistors. This could be fixed from code with a MS2, but from what I understand, there has still been no source code released for the MS3 (boohoo...).

Anyhow, this is the circuit that I made to reverse the fidle output. I hope someone finds it useful. It's working great for me.

Bevan

[zeion]

I am using MS3 1.4.1 on a 3.57 board and FIdle as my Fan output to a standard Toyota Fan relay, and would like to see this as a software setting.
Simple the possibility to reverse the Fan output.

/Lasse

[jsmcortina]

but from what I understand, there has still been no source code released for the MS3 (boohoo...).

Take a look at the Downloads page.

James

[zeion]

Hi James..

I believe that at the time Bev wrote his post, that is might not have been available.

Even though that i am a software developer, i am not that familiar with C, and i don't want to mess around with a custom firmware.
But James - are there any reason ( other than yet another feature request vs time ) that this is not possible ?

[whittlebeast]

Feature creep is something we always fight in the MS world. Any new feature must have a fairly large group of people that can use the new feature or it gets hard to justify adding it.

Is solving your logic issue simply a matter of moving the control wire at the relay?

[zeion]

I understand your point very well, and i know that users have a tendency to think "me first"

So to justify the request, this is the behaviour of all Toyota models with electric fan, that i am aware of ( i am 80-90's kind of guy )
And the fan relay is not part of the engine harness only the control wire for the relay.
Cutting and re routeing a part of the chassis harness, spoils the beautiful plug'n'play solutions that can be made with a MS installation.

So please consider making this an option

[Six_Shooter]

Wouldn't a "Plug and Play" solution for the Toyota already have a circuit built in to correct this? If not, it's not really "Plug and Play", is it? The few market available Plug and Play adapters I've seen usually include adapting circuits for such conditions such as this.

[zeion]

Normally the fan relay is controlled by a thermal switch on the thermostat housing. But if you use a newer enigen that has the fan controlled by the ecu or you want the ecu to control the fan, your are left with the options of doing what Bevan described, using programble output switched by the clt or modify the chassic harness.
But a simple possibility to reverse the fan output, would make it a mod free soulution.

[billr]

Do I understand correctly, that Toyota fan system in question must be powered (drawing current) whenever the car is sitting unused? That seems like a rather poor system to me, modify it to eliminate that auto-battery-kill "feature".

[zeion]

Fan control relay only powers on when ignition on.

[herron_mac1]

is it too obvious to just change the relay to a n/o one? just a question...

[Boosted393]

Can you post that circuit ? I still don't believe there's that option and my car has a factory control rely box that operates backwards of the mega squirt. Thanks