I have a fan I'm trying to control using a Arduino RoboRed. The fan is a 600W radiator fan from a Mercedes Benz. The fan has 4 wires two large cables are connected to the battery at all times. It has a smaller wire that is connected to +12V with the key on to activate the high power fan controller. And finally a PWM signal wire. I have successfully been able to control the fan with a wave form generator as shown in the video below. I have also been able to control it with the Arduino with the exception that when I turn the fan off the Arduino will not reset itself unless I momentarily disconnect and the PWM signal wire from the Aurdrino. This appears to be cause by voltage leaking from the high power module into the PWM circuit. Measuring the voltage on the PWM signal I find it to be ~2.5V with the Arduino connected. It measures 12V at the wire on the wire on the High Power module when the PWM wire is disconnected from the Arduino.
So I have two questions.
Is this leakage normal.
Can I stop this voltage from getting back into the Arduino with a diode. And if so how do I size the diode. I know the PMW circuit runs at 5V PWM at 10 Hz. While in operation I measured 75mA of current. The PMW wire is the blue wire in the schematic below. In the video it is the white wire.
I need a better description of where the 75 ma is measured. And what the blue wire is driving. And if you have a 5V or 3.3V arduino.
As a minimum I would add a 5k or 10k resistor in series with the Pin A0-S. This will limit any fault current if the 10k pot is at 0 and the Arduino has no power.
You have a rather unconventional way of connecting your 10K pot, it works.
But usually the two outside terminals of the pot are connected to 5V and gnd and the centre wiper connects to the A0 input, the 10K fixed resistor is not needed..
My Audrino is a RoboRed its basically a clone of the UNO but can drive to 2000Ma It can run in 3.3V or 5V. I am running it in 5V. the 75ma is measured with a clamp around the blue wire in the wire diagram coming out of PMW pin 9 on the Arduino. The blue wire in the wiring diagram is connected to the fan PWM input signal. If you look at the video attached in the original post it is the white wire that goes into that big finned motor controller on the corner of the fan shroud.
The fault can occur no mater where the 10K pot is. I'm turning the fan off with the ignition switch as it would be turned off in the vehicle, except the 10K pot will ultimately be a thermister.
The diode is what I was thinking. But how do I size the diode. With the ignition key off the diode will see 12V-15V at all times, so I believe I need a diode that will be 25% to 50% above that and pass 75ma. I also need a diode that will not allow the voltage to drop too much as the fan wont work below 3.8V and I would like some margin. I came up with the diode in the attached file. But its not in stock anywhere and has minimum quantities of 5000. Do you have a recommendation on a diode that is available in small quantities.
The Arduino and fan both take power and ground from the same power supply using the 5.5mm x2.1mm pin connection. Basically the Arduino power wires are connected to the two big wires at the top of the diagram.
As far as the pot its connected the way you say. Its just a bad drawing representation.
Any generic small-signal Schottky diode will do fine. I use MBR0520 for this but it's an SMD part. BAT46 is also available as a through-hole component I believe and would also be suitable. As would a few thousand other types
If you have any of the kind that @TomGeorge mentions lying around, I'd start with those; if that works, it saves you the hassle of going online and buying new ones.
Thanks I ordered the 1N4001 and 1N4003 as well as the 1N4148. They are all in stock and available in quantities of 1. These are 50V, 200V and 100V diodes. Any disadvantage to going with higher voltage than required. I assumed 20V was all I needed.
The MBR0520 is available and its 20V. But is it important to get my voltage down to 20V or from what I'm reading anything over 20V is fine. I can't use it for the moment because its not through hole. But the final product will not be on an Arduino.
I had not realized the link was the video you referenced.
Now I'm not going to try to tell you what you have, but I've worked on similar parts for a GM controlled HVAC fan. So my response mixes some of what I learned on that system.
What I see is:
on your bench the blue wire seems to be connected to +12V (the black supply?)
The white wire is going to your function generator. It is more likely the function generator is grounding the white wire at a PWM rate rather than supplying voltage to the white wire.
Can your function generator really supply 75 ma? My recollection the PWM control was in the order of 10 to 20 ma. Not 100% sure of this but I'm sure it was much less than 75 ma.
Just a note: the "standard" automotive PWM is 10 to 90% PWM for 0 to 100% fan voltage.
If your system is similar to what I am used to, the diode suggested will not allow the fan to function.
Could you verify your wire functions? Or maybe I'm missing something.
You have the wiring understood correctly except the PWM signal is not grounding. Its getting the signal directly from the Arduino board.
75ma is a good question. I don't have a good ammeter for those low currents. Its a digital clamp that apparently has lost its zeroing capability. With it not clamped to anything, it reads about ~250ma. When I clamp it it reads ~325ma. That's where the 75ma comes from but both those readings are fluctuating ~ +/- 25ma. But at ~15 amps it is consistent with the ammeter on the power supply.
Mercedes operation of this fan is:
20% to 90% PWM is the operational range.
10% PWM is fan off.
0% PWM is fan in emergency mode running full speed.
In testing I found the fan will operate from 15% up but I cant test over 60% due to my small power supply.
Fan will be off in the range of 6% to 14%
Fan will be in emergency mode full speed from 0 to 5%
The fan will also operate a frequencies between 10 and 15Hz.
It can still be a sink signal instead of source. The fact that it connects directly to an Arduino can still be perfectly consistent with this. You'll notice if you try to plug in the diode; the setup will stop functioning.
Ok, so let's ignore the 75mA as it's very suspect I think it's unlikely that the PWM signal will either have to source or sink that much.
You may be onto something here. Just because I got it to work doesn't mean its working correctly or as designed. I have heard several reference to pulling down the voltage. And maybe the 12V I read with the PWM wire disconnected needs to be pulled down to zero rather than be pushed back up to 5V.
I have tried zener diodes which are the only ones I have around at the moment and the system did stop working completely no matter what way I installed the diode. The diodes I tried were both 1 w zener 12V and 5.1V.
I have also tried a MOSFET to switch 5V from the power bus on the Arduino to the fan signal. That did not work but it sounds like possibly switching to ground might work. I don't know if the MOSFET that came with the Arduino kit is appropriate for this. It is a RFP30N06LE.
Sorry I didn't know you were looking for the Arduino in the videos. Hope this helps
This is a different fan with the motor controller integrated into the motor but they both work with the same signal. Wire colors change on the fans from model to model. On this fan the PWM wire is Blue and Green and the Ignition on wire is Black and white.
Of course this time when I took the video everything worked perfectly and the voltage at the PWM wire read ~ 0.8 volts. I couldn't even get it to fail for about 5 on off cycles after the video was complete. Then it suddenly started doing its old tricks. Would not reset when turning it off and it was back to ~2.5V at the PWM signal. I think this video link should work. I have it shared as private so anyone with the video link should be able to see it according to youtube. Please let me know otherwise.
I would but a 1N4148 in series with the Arduino PWM output. The polarity that works will tell you if the Arduino is sinking or sourcing the PWM.
If the Arduino is sourcing the PWM then the diode will protect when the Arduino is off. If the PWM is sinking current then I suggest you but a small MosFet at the arduino PWM output and in vert your PWM dutycycle.
From my experience 75ma is excessive (I understand your current measurement is not happy at these low currents)
I have the 1N4148 on order but it will take a few days. I also tried the MOSFET that came with the kit but so far no luck. The one that came with the kit is RFP30N06LE. That is an N channel MOSFET. I think depending on what you are saying about sinking or sourcing I may need a P channel. I'm not sure about how to size these MOSFETS so it you have something you could recommend, I would appreciate it. As far as my ammeter, I did find out how to zero it. Press the zero button for 2 seconds. (I red the directions). It now seams to work and still ~75ma +/- ~25ma. It probably works as good as its supposed to but its a $20 ammeter. I will keep playing thanks for the help.
