PWM Mercedes fan signal. Help ?? [SOLVED]

[TheMonkey]

Brand new fan from late model S class. https://www.amazon.com/gp/product/B06X3 ... UTF8&psc=1

Has it's own fan controller on board. 4 wires. 2 heavy gauge power wires, an ignition signal (black/red 22awg), and pwm signal in (green/blue 22awg). See pic below.

Supposedly requires 100Hz frequency at 10% duty cycle for 'off', 15%-90% duty cycles variable fan speed from low to full blast. In the event that it does not receive PWM and it has ignition signal, it has a fail safe mode to go full blast.

Just trying to get the fan to work right now on PWM signal and understand this. I built a simple PWM from an Arduino Nano with a potentiometer to adjust duty cycle, frequency is fixed at 100Hz. But it seems whatever I try, it just goes into fail safe as if it cannot see the PWM. It soft starts and gently ramps up to 100% so the fan controller has a brain.

At duty cycles from 10% to 90%, I have tried and confirmed good signals on scope:
- 0v-5v signal direct from PWM out pin
- 0v-3.3v signal through a voltage divider

And then I discovered most fans want an 'open collector' PWM signal such that it grounds the duty cycle and floats when off. So I put PWM out pin through 10k resistor to base of 2N2222a, emitter to ground, and collector direct to fan unit without any resistors. I confirmed on scope the transistor is switching okay, it floats when off and grounds when on.

Tried:
- float/ground signal switching through an open collector

When I put the scope on that 'open collector' signal to the fan unit when wired up and connected to fan, I can see a good signal and the fan unit is pulling it up to 12v. So the scope shows 0v-12v square wave going to fan unit. This is both when ignition signal is not connected (fan off), or when ignition signal is connected (goes into fail safe).

Any help with any nuances or what I'm doing wrong? When MS3 gets wired in, does the fan PWM signal get pulled up or is it open collector? Someone here can confirm configuration and signal to a Mercedes fan?

Thx - Scott

[SwedCharger-67]

I don't know anything about the Mercedes fan, but it does look very similar to the Volvo V70 fan I'm using.

The Volvo fan has a 4-pin connector as well, 2 fat wires for power, 2 thin ones for control. I'm using the MS3X output FIDLE to pwm-control the fan speed. The second low power pin is left unconnected, in fact I don't know what function it has.

Since it all worked as planned from the very beginning, I haven't looked into any specific details, but I might be able to dig out some info if needed.

[TheMonkey]

MODS - I meant to put this in the general forum rather than new purchasing questions. Please move if appropriate.

Hi Martin -

Thanks for that. From all my clicking, I’m nearly certain that the required frequency and dc are as I expect.

Saw a few Mercedes fan installs here, but I’d like to know someone got this exact model fan working? Others are close but haven’t seen exact.

what I really would like:
- scope on the trigger of a working unit (even stock install) that will confirm:
- frequency and duty cycle
- sequence of signals (Mercedes seems to care that pwm comes before ignition, maybe this model is even more particular about time of introduction).
- confirm pull-up to 12v (can’t imagine why not if that’s what I’m seeing)
- signal inverted or not (assume ground signal grows w DC)
- any nuances to the circuit feeding the PWM. Does your pin 30 FIDL have the TIP resistor upgrade? I figured logic level feeding pwm to another board is not necessary but I think I’ll try that today.

I have a sneaky suspicion that this fan requires a particular sequence of timing of Introduction at startup between between the ignition power and pwm signal. If so, that’s rather Applesque lol. I’d love to molest someone’s S class for 10 mins

[DaveEFI]

Must admit to not being sure why it would need both power 12v, and switched 12v from the ignition? They normally run independent of the ignition to cool after switch off. Could it be a kill circuit to stop it when cranking?

[TheMonkey]

SOLVED !!!

I found this page and changed the frequency to match 95ms cycles (10.53Hz) at it works so smooth. Such a powerful fan and absolute drop in to a 3rd gen 4runner.

open collector through 2N2222a transistor at 10.53Hz. 10% off. 15% low to 90% full blast.

Duty cycle is on the high (pull up side). The ground signal shrinks as duty cycle goes up.


Thanks for any consideration and help. Surprised the frequency is that slow. Can the PWM from MS3x go down to 10Hz? I had to change the prescaler register on the chip timer.

Hope this info helps others.

- Scott

[TheMonkey]

Must admit to not being sure why it would need both power 12v, and switched 12v from the ignition? They normally run independent of the ignition to cool after switch off. Could it be a kill circuit to stop it when cranking?

It has a huge 8awg power wire that always has power even when car is off. No need to send through a giant relay to trigger when ignition is on. The AMZN listing says its 850w (!!!). I have an 80amp fuse in that.

It's possible that it would only take in a PWM signal after that, and a lot of PWM fans only have one trigger wire for PWM. Mercedes put in a fail safe so if it has ignition signal which says car is on, and IF the ECU sends no PWM or funky signal, the fan fail safes into turning on strong. Actually I think this S class has another separate unit after ECU but before embedded fan controller that sends this signal. Perhaps the ignition also wakes up the embedded fan controller from sleep mode when car is parked.

I also need to figure out some logic to ensure that the ignition trigger wire only gets power after the PWM signal is sent otherwise the fan fail safes full blast if it gets ignition first and PWM after. It won't operate until power cycled on ign trigger with PWM first.

[DulcePinel]

Hi...Is this unit set for AC operation ? At how many speeds (%) ?Can the unit be set to keep the engine at a desired temperature ?Does the unit have input(s) for to activate via torque converter temp, air intake temp, and AC high pressure switch signal ?

pcba prototype

[Earl1]

@TheMonkey,
I am currently on the same train and going to modify my Jeep JK from clutch controlled fan to a MB electrical fan.
Want to start with the simple way as You did and then hack into the OBD2 can bus to get the information of the actual temperature. Could You provide me with any further details? Where did You store the Arduino nano board? Inside the car or in the motor bay?
Any hints or help is appreciated so far.

Earl1 aka Helmut from Germany