I am building a fan controller for a PWM fan for a Mercedes Benz. The fan is a 600W fan controlled by a the engines main computers. For the moment I am using a Yourdrino RoboRed which is similare to an Arduino Uno except it has a hight power 2000ma power pin on it. I have successfully got this fan to run perfectly using the PWM signals directly applied to the fan. The fan requires a 10Hz 0 to 5V PWM signal and the output has driven it directly with no further conditioning required. However I am concerned about the power being pulled directly from the PWM output pins. All my testing thus far has only been for a few minutes at most so I would like to take power from the Yourdruino's 2000ma 5V pin. I have tried several circuits with transistors and mosfets and have been successful getting them to work but all seem to have the same problem and I am not sure it it will cause a relaibility issue if this thing were to run daily for sometimes extended trips of 5 to 10 hr or so.
In any case today I tried a new device called a PC817 Opticoupler. The results appear to be the same in that the signal is shifting. Presented below is a wiring diagram of what I have tried.
1) If I remove the opticoupler and and just reconnect the two blue wires together the fan works perfect and reading the voltage with a scope in the blue wire to ground gives me a very desirable 0 to 5V PWM signal.
2) With the opticoupler installed but the blue wire to the fan control module disconnected I once again get the desired 0 - 5V PWM signal between pin4, the collector and ground.
3) once the blue wire to the fan control module is connected to the pin 4 colector of the opticoupler, the fan will not work and the voltage readings between pin 4 and ground shift to 7.28 to 13.6. So I am getting a shift of ~ 7.28V. And the 13.6V is about the same as the large power going into the power side of the motor controller and the voltage feeding the RoboRed.
I prefer the opticoupler idea in that it separates the circuits but no mater what I use stuff is moving around. Does anyone know how I can beat that signal back into place.
In any case today I tried a new device called a PC817 Opticoupler. The results appear to be the same in that the signal is shifting. Presented below is a wiring diagram of what I have tried.
1) If I remove the opticoupler and and just reconnect the two blue wires together the fan works perfect and reading the voltage with a scope in the blue wire to ground gives me a very desirable 0 to 5V PWM signal.
2) With the opticoupler installed but the blue wire to the fan control module disconnected I once again get the desired 0 - 5V PWM signal between pin4, the collector and ground.
3) once the blue wire to the fan control module is connected to the pin 4 colector of the opticoupler, the fan will not work and the voltage readings between pin 4 and ground shift to 7.28 to 13.6. So I am getting a shift of ~ 7.28V. And the 13.6V is about the same as the large power going into the power side of the motor controller and the voltage feeding the RoboRed.
I prefer the opticoupler idea in that it separates the circuits but no mater what I use stuff is moving around. Does anyone know how I can beat that signal back into place.