Jump to content
HybridZ
jacob80

Megasquirt fan control using the fast idle relay on relay board

Recommended Posts

Look on the Megasquirt site - that's where I found it when I did it.

 

Can't seem to find it. I did find this:

 

http://www.diyautotune.com/tech_articles/common_megasquirt_modifications.htm

 

But for some reason, i just can't follow what they're saying. Can you help me out zmanco? Perhaps put it in dummy terms? :D

Share this post


Link to post
Share on other sites

Found this:

 

http://forums.hybridz.org/index.php?/topic/82336-fan-control-ms2/

 

Looks like pin 30/PM2 will control the fan without any modification. Does this translate to the fidle port on the relay board? Do i simply run a wire from this output to my external relay? Of course, it will only be the signal wire for my external relay, not primary power.

Share this post


Link to post
Share on other sites

jabob80, I'm afraid I don't have time to look all this up to check it out. I rarely remember pin numbers, rather I follow the wiring on the schematics to see what pins on the MS board lead to the DB connectors and relay board. Use these two schematics I'm attaching (I saved them from the MS site) to trace the wires and I'm sure you'll be able to answer the question yourself.

megasquirt_ShemV3.00.pdf

mspower_ShemV1.2.pdf

Share this post


Link to post
Share on other sites

FIdle WILL power your relay. I believe it's one of the few (if not the only) port that doesn't require a transistor to directly control a relay.

 

Note that the LEDs, FIdle and IAC1,2 outputs already have transistors capable of conducting considerable current (check the transistor datasheets to be sure they are sufficient for your application). The LED(s) can be removed and the LED holes on the PCB can be connected to a spare DB37 port. If you use the LED connections, note that you will bypass the current limiting resistor. Be SURE your device limits current itself (i.e., that it has a resistance of 50 or more Ohms). If it doesn't, you will have to add a resistor in series with the device. You connect the device (relay, etc.) to the LED hole closest the DB9 connector (which you can jumper to a spare pin on the DB37 to route it externally).

 

yadda yadda yadda

 

Note that the FIdle circuit on the relay board is limited to 1.1 Amps by the polyfuse. The relay is capable of handling much more current, but the traces on the relay board are NOT. If you wish to use the FIdle relay, do not use it to drive a device that requires more than 1.1 Amps (though you can use it to drive a second relay and control much more current - like an electric fan relay)

 

Electric Cooling Fan Control Another example is electric electric cooling fan control. We will turn it on 180°F and off at 170°F, using the relay board FIdle output to control a separate cooling fan relay (the traces on the relay board may not have enough current capacity to control your fan directly):

 

* FIdle (PM2)

o Port PM2, FIdle enabled

o variable = coolant > threshold = 180, hysteresis = 10,

o AND

o variable = rpm > threshold = 450, hysteresis = 10, (fan will not run while cranking - you can add any second condition that works for you, of course)

o Power-on value = 0

o Trigger value = 1

 

Of course you can change the conditions to suit your vehicle.

 

Note that changing the FIdle port settings (PM2) does not affect the operation of the stepper IAC settings and ports. You can still use the IAC stepper functions for controlling idle speed during warm-up (just select one of the stepper options for idle control).

 

Note that the settings will depend on whether you have an NC (normally closed) or NO (normally open) relay, so you must check that the fan works as you think it should.

 

Other conditions could be used to drive a nitrous solenoid, a shift light, or a water injection system, for example.

 

This won't cover every condition people can think of, but it should be easy for people to add more code for custom applications.

 

And yes, it's pin 30.

Edited by e_racer1999

Share this post


Link to post
Share on other sites

e_racer's write up is for MS2. MS1 can only use this for a fast idle output. However, if you use a 5 pin relay, you could set up the relay so that it turns the fan on when the fast idle relay output is off. The one thing I don't like about this is there is no hysteresis, so it will pulse the fan off and on if you're right at the fast idle temperature.

Share this post


Link to post
Share on other sites

Wait wait wait...I just ran a wire from a relay to the Fidle output thinking its going to switch my fan on/off...now this won't work?

 

Ugh, I need help, and more detailed instructions as to how to approach this. It is a 5 pin relay, how do I make this work?

Share this post


Link to post
Share on other sites

There are many possible ways to go about doing it, but for simplicity sake, why not just signal a relay via megasquirt? Before I began re-wiring my EFI, it was run off a stock trigger box via the radiator hose, but I had to pinch a metal wire between the radiator input neck and hose, causing A) a small leak and B) a nasty metal wire had to be run down to the box, and in the end looked fugly as hell and janky at that. All I need is some output to trigger 12v when the temp is at 180 and turn off 12v when the temp is at 190...seems easy but maybe not. Feel free to chime in, Matt. Thanks!!

Share this post


Link to post
Share on other sites

The best way to control the fan with MS1 is to add a mod for an extra relay control output. This link shows how it's done.

 

http://www.msextra.com/doc/ms1extra/MS_Extra_Hardware_Manual.htm#outputs

 

Matt,

 

I went ahead and ordered the parts from Digikey. I'm assuming I'll be wiring my fan output "setup" according to this diagram:

 

RelayOutput.JPG

 

Then, once I've wired this (which I haven't figured out completely), it looks like I'll want to use "OUTPUT 2 (X5) source" (correct me if I'm wrong). Also, the temperature also looks close to what I want it to be except I would like to have it come on at 190 and turn off at 180.

 

outputs1-2.JPG

 

Looking back at the wiring to use Megasquirt outputs:

 

It looks as though I will need to use "JS3" due to the fact that it is equivalent to output 2 in this photo:

 

V3PCB_Pinout.JPG

 

Then, on the MS wesbite part numbers needed, it listed a relay. I ordered this, but can't I just use my plain jane 5 polse SPDT 30 amp relay instead? I'm also a little confused as to how this will all come together considering I'm using a relay board. IIRC, I thought I saw an output for JS3 on the relay board. I'll have to take some photos when I get home and eventually draw a final wiring diagram. I'd like to keep things as simple as possible. Thanks for your help!

Edited by jacob80

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...