Quote:
Originally Posted by sixto
Thanks for the responses.
To be clear, I'm not trying to alter the PWM output of the blower controller/porcupine to the blower motor, I'm trying to alter the voltage signal output of the PBU to the blower controller. It's a signal that varies between 2V and 7V. I don't know what current DC signals typically generate but I imagine it's a tenth or an amp or less.
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The "controller/porcupine" is nothing more than a high current semiconductor. it is dumb it has no intellegence function. To use a water analogy it's simply a large valve. The CCU in dash controller sends it a smaller lower voltage/amp control signal, the controller/porcupine essentially amplifies that signal. The CCU signal does not vary in voltage it is a Pulse Width Modulated signal, the pulse widths vary and as a result the greater the pulse's width the greater amount of time the controller/porcupine is turned on and the greater amount of power the blower motor receives and the faster it turns. Pulse width determines the percentage of time the current flows, greater percentage faster blower speed.
If your goal is to control the speed of the blower motor the only way is to vary the percentage of the pulse's width. The controller/porcupine is only on or off, it will require a threshold voltage and a nominal current to turn it on, if you try to reduce the voltage you will get below the threshold and it will not turn on. Too high a signal voltage can damage the controller/porcupine, although in this automotive syste the Vin control voltage and the Vmax of the semiconductor are probably the same. I'm not sure what the semiconductor exactly is, could be a MOSFET, SCR, Thyristor or something else.
I'm going to presume you have not looked at the control signal from the CCU to the controller/porcupine with any type of oscilloscope? That is what you need to see what the signal actually is, if you attempt to measure the CCU signal with an analog meter or digital VOM you will only see the averaged power of the signal represented as an unsteady voltage value.
If you hadn't already seen this, here's an old write-up done by Steve Brotherton which shows what the PWM signal to the monovalve looks like. The signal from the CCU to the controller/porcupine will be similar. The output of the controller/porcupine will have the same frequency and pulse width but will likely have an amplitude of +12 volts and you can't see it but it will be flowing a much larger current. The blower motor uses a 30 amp fuse if I'm not mistaken, so that means the motor can pull up to 360 watts of power at full speed. The electrics and electronics used to control the ACC stuff are high frequency digital On-Off rather than the old fashioned linear ramped style of doing things.
http://www.peachparts.com/Wikka/AcDiags