It’s a brushless 3 wire fan in the seat ventilation system. I recognize that an ECU can provide this, but I’m looking for a solution using a PMU and/or an H-bridge. Any suggestions?
thanks!
I suppose the fan has an internal controller for BLDC motor, just like a simple PC cooling fan. In such a situation it would have 3 wires for GND, 12 V and a tachometer. You can control it by PWM from PMU.
If it doesn’t have controller and the wires are connected to the motor windings, then you need an external BLDC controller (or a different fan).
I’m pretty sure it’s a BLDC motor. I can get the motor to work using an oscilloscope generated square wave form. However the PMU PWM waveform doesn’t work – the scope shows the wave only dropping to 7.6V. I assume then, that I need a digital “signal-based” square wave, not a “12v power-based” square wave. Admittedly, I’m on the edge of my knowledge… hence the question.
You need a square wave that goes from low to high state.
PMU outputs are either floating (unconnected) or connected to a battery supply. To create a low state on the output, add a pull-down resistor to ground, which will pull the output to 0 V when the output transistor is switched off.
There is also a question of whether it’s safe to provide battery voltage on the control signal for the motor controller. It might be designed to work with a 5 V signal. You either have to measure the OEM signal to confirm, or you can measure the current flowing into the motor controller input when battery voltage is applied. If it’s below 20 mA, it should be safe.
Yes, I’m using a pull-down resistor. Using a 1k pulldown, I get a nice 0-12V square wave from the PMU when driving something simple (like an LED). However, when I connect this to the control signal wire, the wave becomes 7.6V to 12V.
An ordinary measurement of the control wire (without connecting it to the PMU) shows 12V, so I assume it has a 12V pullup on it.
Then there must be some resistors inside the motor controller that created a voltage divider.
In that case, it would be easier to use a low-side output.
Do you have any other Ecumaster devices in the car?
Is this the normal or the Autosport version of the PMU?
You can also try using a lower resistance pull resistor to minimize the effects of the voltage divider. Remember to consider the resistor power rating. With a 100 ohm resistor and a 15 V supply, the resistor dissipates 2.25 W when the output is switched on constantly.
I have H-bridges available in this car. It’s the normal PMU-16 (non-DL)
Today’s experiment was to generate a 5V square wave using this PWM signal generator I picked up from Amazon: DROK Signal Generator, DC 3.3-30V Function Generator 5-30mA LCD Display PWM Pulse Frequency Duty Cycle Rectangular Wave Square Wave Signal Generator: Amazon.com: Industrial & Scientific
I’m playing around with frequencies and duty cycle, but the net result is that this works. Now the question is: what ECUMaster devices can provide this? I have an ECU (OEM GM), and I’m using a PMU-16 and a PMU-16 DL. I also have dual H-bridges here in the shop.
Any suggestions welcome!