Recently I built a PWM fan controller for a 50 Amp automotive radiator cooling fan. You can probably find several of my versions of this in this sight. It worked great for 5 years but I decided to add some upgrades recently and one of the things I added was 2 zener diodes on the input power to clamp voltage spikes. It also worked great up until yesterday when I had a transient on the output that took the board out. The way this fan works is 12V power is available at the fan motor at all tomes feed by large 6 ga wires. The fan will not run until it gets a signal from the controller. The controller signals are low current milliamp signals which tell the fan to run and how fast. One of the signals is a straight 12V which is present whenever the key is on. The other is a PWM signal that controls the fans speed. The straight 12 signal provides power in an emergency mode, where if the PWM signal is lost the fan will run at full speed. In any case the 4 conductors come through the same connector, Power, Ground, 12V with key on and PWM. In this case there was a leaking radiator that got into the connector, despite the connector being a weather pack sealed connector. The only way the fan could run would have been if the power from the large power wires got into the smaller signal wires. I had already removed the fan controller from the car when the fan suddenly started to run at full speed with the fan controller removed and the key off. I had to pull the connector to shut it off and break a 50 amp circuit to do so. So in this case, I believe the 12V signal or the PWM signal were seeing intermittent power from the large cables that are directly connected to the battery.
The first picture shows the burn connector. There were originally 2 large pins and 2 signal pins in there. Now the large positive pin is burnt away.
Second picture shows the board as made for reference.
Third picture shows the full schematic. In that schematic pins A4 of the J1 connector is the pin that supplies a PWM signal to one of the small pins in the 4 pin connector. Pin B4 supplies the constant 12V with the key on to the other small pin. These can be better seen in the 4th picture
Pictures 5 and 6 are of the board layout with the full size and the blown up section of connector J1
So the question is what can be done to protect this system from such and event of antifreeze getting into the connector. I was thinking of putting the same zener diodes on pins A4 and B4 as I have on the input shown as D1 and D2. I believe that will work for at least the straight 12 signal but I'm not sure what it would do to the PWM signal.
What load resistors did you add for each of the zener diodes? And when the spike exceeds the voltage limit for the diode, it becomes and open circuit. Zener diodes are designed for DC, not voltage spikes.
Normally with Zeners you add a fuse. When the Zener voltage is exceeded, excess current flows through the Zerner (and the fuse), blowing the fuse before the diode gets burned-up.
Without a fuse, the diode might short completely before it burns-open or before a trace burns-open, etc. ...Usually semiconductors short when they die and then sometimes they kill something else.
But of course that's only for rare or catastrophic voltage spikes/surges because you don't want to be replacing fuses every day or even every few months.
So maybe you need a different solution, or maybe no "solution" since it worked for 5 years.
So the question is what can be done to protect this system from such and event of antifreeze getting into the connector.
Maybe move the connector (longer wires?) but you can't protect against every possibility.
No resistors are used. The way I understand it when voltage exceeds about 18 volts in this case the diode will just shunt it to ground. Of course it cant do this for hours on end but the wires on the diodes are of very large gauge.
After looking at the circuit I realized that only the PMW circuit is not protected and that is the only one that seems to have failed.
It is true that fixing my radiator will fix the problem and thats #1 in the works. But it did open my eyes to potential pit falls and gives an opportunity for improvement. There are no fuses involved at this point and the Zener diodes I selected can handle substantial current but certainly not unlimited. They are just there to handle stray transients like starting the car. I only put them on because I was told this circuit would never survive the automotive environment without them. But as it turns out it ran 5 years without them. It turns out if you look at the circuit the 12V signal is also protected by the zenor diode D1. And that circuit did survive. Only the PWM circuit which is totally unprotected failed.
Protection to the PWM circuit can be done with an opticoupler. I have tried that solution and it does work but opted against it due to it low MTBF. I calculated the MTBF of an opticoupler to be low enough to require replacement every so often in a car that is driven daily. But for this type of application its pretty much limited to hot rods and show cars, it would probably be fine. So that is an option. So I am open to the opticoulper and any other ideas.
There are transient suppression devices specifically made to do that. I have a bag full of 42 volt device that Digikey sent that were ordered by someone else. Never used them.
Have you tested your zener diodes to see if they are still diodes?
As far as other transient suppression sachems. I did look into it but only elected to do as far as I could understand. Essentially the first basic pass of protection.
I tested all passive components on the board and replaced the two transistors. All components are good including the diodes, so I assume the Arduino Nano 33 BLE is not working.
They don’t publish it as a zener wattage rating but they do offertest current of 1A and peak pulse currents of 19A. Diode is a Vishay model SA16AHE3/54
That was a big decision at the time, I actually started with 15V because cars don’t normally run that high but as I read more about it heat can develop if it does go above the the standoff voltage. An automotive engineer told me the industry uses 16V as maximum in there specs. So I brought it up to 16V. But that brings the clamping voltage up high which is already operating above the Arduino max input voltage of 20.
Sounds like you are not powering your Arduino project from the car’s auxiliary power, which is off while the starter is engaged.
Where is your project ground return connected? If you are using the car frame as ground, then there will also be transient voltages on that ground when the starter solenoid opens up while flowing 100 amps to the starter motor.
The Arduino is powered by two sources. If you look at the schematic in the first post you will see a C30. C30 is battery power on at all times. That is used to run the Arduino for about 30 seconds after the car is shut off. C15 is power with the key in the run position. They are both somewhere along the line tied into the starter. I’m not aware of an Aux power source not connected somehow to the battery in cars with 1 battery.
I have heard that a lot, but so far I have proved everyone wrong. And why should the Nano’s 5V (3.3V in my case Nanao 33 BLE) be any worse than an external 5V or 3.3V converter?
But we are getting off topic hear. Good discussion on TVS diodes and stuff and I’m no expert on them for sure, but so far they are working fine where they are.
The issue here is the PWM circuit which has no protection at all.
I fave3nt measured the C15 voltage in the car at the fan or controller. Ive only done that on the bench. But the C15 circuit was not effected in the event that burnt up the connector. That still works. Only the PWM circuit is malfunctioning.
