drscottsmith

Can the factory twin cooling fan setup be turned into a variable speed unit with slow ramp up by simply using a PWM module to control it?

T&T Racing

I believe so but why?

drscottsmith

Changing over to MS which will also run the fans based on coolant temp. I can use CAN BUS from MS to send PWM signal to fan controller and map fan speeds based on engine load and coolant temp to be more efficient.

Zirconocene

I don't know if you've seen post #19 from this thread: https://rennlist.com/forums/928-foru...l#post18339287

It may not make a difference if you're moving to a PWM anyway and have what you need, but this is an idea that I have bookmarked for my 928s and may be useful to you.

Cheers

drscottsmith

Hey Zirc -

I’ll take a look in more detail but it looks like that setup will require two different outputs from the microsquirt which I might not have. Sure is much easier if so.

Gasngo

That's a neat idea. I have no intention on MSQ but the thought of it is good. They are noisy for sure.

V2Rocket

should be able to.
years ago i took a Volvo fan that was originally PWM controller and just chopped off the PWM box - the motor still just had +- wires going into it from that box. worked fine.

drscottsmith

Here's a mockup of the circuit....open to comments!

87944turbo

I think it's an interesting idea. I realize this is not a direct comparison, but the setup I have on my LS swap is what I would consider a middle ground between the stock setup and what you're suggesting.


It's based on two inputs (Hi and Lo) and either splits the 12V across the two fans (low speed) or sends 12V to each fan (high speed). One other thing that is possible (I am using the LS PCM) is disabling the fans above a specific speed (I have it set to 35mph) which is measured via a speed sensor on the DS axle. This is b/c fan operation above this speed acts more as impediment to cooling than it helps.

FWIW I lost the operation of both fans almost immediately after starting home from the 944 Fest. One the highway, it held a steady ~190F, but as soon as I pulled off for gas it quickly rose to 220F. So I guess my point is fans are really only necessary in low speed scenarios if the rest of your cooling system is doing its job. So I don't really see the need to have variable control from say 0 - 35mph. It's a cool project though, looking forward to seeing how it turns out!

Tiger03447

What is a PWM?

drscottsmith

Pulse Width Modulation controller. Allows you to use continuously variable speed inputs to control fans for an infinitely adjustable speed. Also allows for a slow ramp up to ease the eletrical system as fans kick in. With a computer like MS, you can have more than one variable sent out over CANBUS for control, for instance, not just coolant temp but also, say, AC being on or off to control when and how much the fans come on.