I noticed the megasquirt provides efan shut off at WOT. So I got to thinking about installing a capacitor in there so the fan continues to run after power has been cut.
Then I researched a bit, and found capacitors really run down in voltage as they run out of juice. So I figured using a miniature battery will work much better than a capacitor.

So I came up with using either a 5 pound, 8 amp/hour, 115 CCA battery or a lighter 3 pound 5 amp/hour battery. Both batteries are 12v AGM's and around $15-$20.

A 5 amp hour battery can power 12 amps for one minute before being considered fully discharged. Or run 24 amps for 30 seconds before being fully discharged. (I think)

The biggest things I'm worried about besides sizing the battery...

Is all of this worth it? Complexity, replacing of the battery, even power gain vs the weight of the battery?

Will I damage the alternator from possible repeated draining and charging of the little battery?

Any one think this is a good idea?

 

Why do you want your fan running at WOT? Are you running an very undersized radiator?

I would think that megasquirt cuts the fan when you open the throttle like that is because the natural airflow over the radiator would/should supercede the airflow of the fan.

Neither of those batteries would give the 15-40amp fan enough power to run on for long.

Doubtfully on it being worth it, and you won't pick up any power either from this modification.

 

Nah radiator is good. I may or may not be ok without the fan at WOT, but really I want it to run during WOT. As it stands I come out of a 40 second autocross lap about 3-4 degree's over my normal temp.

The autocross is all low speed stuff, its all 2nd gear WOT. So not as much airflow as you'd think with the intercooler there.

Supposedly, based on manufacturers claims, the smaller of the two batteries up there will run my 24 amp fan for 30 seconds. Or breeze through say 13 seconds of WOT. You could do an entire 1-4 gear run in less than 30 seconds, and the fan never see any difference.

And you will defiantly gain power from not running the Efan. It will just be very marginal, below 4 HP for sure. Maybe even below 1 HP.

 

Ah AutoX + front mount makes sense now.

Why not make an emergency switch to just keep the fan running when you want.
One that grounds out the same pin on the relay that the megasquirt grounds out to control the fan. So you can have your fan running when you want, or you can leave the switch off and megasquirt will control it as per usual?

Would save a ton of weight and complexity.

-M

 

Hmm, that's not too bad of an idea. Maybe even have it temperature based, instead of a switch, use say another megasquirt output to trigger it above say a few degrees above operating temp.

Seems like a nice feature to be in the fan control menu, the option to not have the fan shut off at WOT if you are at temperature ___ (blank) or above.

Also, just after starting this thread I noticed my fan wasn't working, (relay burnt out) but I was forced to drive for a bit, and was shocked the car didn't overheat too bad. I usually have 196 F rock solid, but during my 10 minute drive I only had a few spikes to 198 at stops then temps dropped back to 196. Was around dawn though. Probably 75-80 F ambient temperature.
Then I went out in the day time. It was probably 90-95 F ambient, I was feeling confident, same 10 minute drive, same amount of stopping, but I flew in the driveway at 207 F....

 

You do realize all the electrics, including the fan, will continue to run off the battery that is already in the car when the alternator is shut down by the ECU? You're trying to answer a question that is not being asked.

 

Or, you know, just set the MegaSquirt to NOT shut down the fan at WOT.

Yes, you could just use a relay to swap the fan to a smaller battery (such as a 12V 7AH AGM, commonly found in alarms, UPSs, etc.), then use another output to connect that battery to the car 12V at non WOT so that it maintains a charge. Really though, it seems like a lot of unnecessary complexity. Personally at autox I set my fan to run 100% during my runs as the speeds are slow but engine load is high. Autox is pretty brutal on cooling systems.

 

What?

My alternator is not being shut down by my ECU. The ECU will only shut off the cooling fan.

Most newer cars do control the amount of power the alternator creates by varying the voltage signal. Which I would love to see the megasquirt do.

Lol. Good point. It's just my alternator is soooo hottt lol..