PWM Controlled Electric Water Pump

[cdphx4]

I'm having some trouble setting up a water pump that is controlled by PWM. I'm using a MOSFET to amplify the PWM signal from the M600. The GATE of the transistor is connected to the AUX1 pin of the M600, the SOURCE is connected to the negative terminal of a 12v source, and the DRAIN is connected the negative terminal of the water pump. I've attached a simple drawing for clarity.

The issue that I am running into is that I am unable to vary the speed of the water pump. When I increase the minimum duty cycle from zero the water pump stays off until the duty cycle reaches 51, then the water pump turns full on. Increasing the duty cycle past 51 has no affect on the speed of the water pump. I've attempted using 2 different MoTec functions and I've received the same result using both. Below are the parameters I used for each function.

Function #132: Thermo Pump Function Parameters
Hi Temp: 80
Lo Temp: 0
Timeout: 0
Frequency: 100
Polarity: 1
Output Mode: 2
Min Duty: Varied from 0 to 100 (Water Pump turns on at 51)

Function #3: Aux Table
PWM/Switched: 0
Output Mode: 2
Polarity: 1
Frequency: 100
Minimum Duty Cycle: Varied from 0 to 100 ( Water Pump turns on at 51)
Maximum Duty Cycle: 100
Hysteresis: 0


If I can provide anymore information please let me know!

[SprinterTRD]

Does your circuit work as expected with a resistive load rather than the motor?

Also does the gate connect directly to the ECU output or do you have a resistor there as well?

[cdphx4]

I have not tried replacing the pump with a resistive load to see if it would function as expected. I fear that won't fix the problem though because I connected an oscilloscope to the AUX1 pin and the GROUND to see if that would help diagnosis the issue. The oscilloscope showed a 0% duty cycle (a flat line) when the minimum duty cycle was less than or equal to 50 and the oscilloscope showed a 100% duty cycle (still a flat line) when the minimum duty cycle was greater than 50. I was never able to get a square wave. Just in case, I will give that a try it with a resistive load and let you know what happens.

The gate is connected directly to the ECU. There is no resistor.

[cdphx4]

Are all of the AUX outputs for the MoTeC M600 able to do PWM?

[cdphx4]

After pouring through the forums, I found a solution.

The AUX2 pin (and I think all AUX pins, I can't confirm that though) is unable to do high-side PWM. On the circuit side of things, I had to add a pull-up resistor that went from the gate of the FET to the 12v source to invert the signal. On the MoTeC side of things, I had to change the polarity to 0 and the output mode to 0. I also bumped up the frequency to around 1000, but that's just because it made the pump run a little smoother.

I hope this helps someone out!

[mfalah]

I have discovered that bmw water pump will fit almost anywhere and not only that, it has high flow to 30 litres a minute. It uses a kostal 4 pin connector, and I came to know this when buying for my brothers car. I assume at least 1 pin will go to positive and 1 pin will go to ground or perhaps 2. Anyway not a way of knowing till I connect a multimeter. The BMws need removal of undertray for that as its really cramped down there.

Will give it a try myself.

[Blu302]

Did you fit a bypass diode across the motor? The current will still try to flow through the motor when the FET is off.