PWM Motor Drive via PIC

[Docara]

Hello All,

Some pointers if you please its been years since I dabbled with electronics (bit rusty!!) and I just don't know enough about motor control electronics / good practice to allow me to complete a little project I'm working on.

I have a 12vDC 'sensor' water pump in which the electronic control has failed. I can gain enough access to bridge the thyristor's legs to allow (in principle) full speed operation of the motor. I'd like to try and sort out my own control with what I have in the workshop.
A secondary requirement is that is that I would like to be able to find out at what pressure the pressure relief valve is opening.

I have a 0-60psi pressure transducer (0.5-4.5v), various PICs with PWMs and ADC and a few Op-Amps available the pump is rated at approx 5A max (8A fuse)

I need to be able to alter the speed (linearly ish) of the motor based on the pressure so that the flow from the taps is a constant stream and not pulsed as was my initial design consideration if using a comparator

So here are my questions:-

1)Would the basic PWM output from a PIC via a suitable driver be suitable for this application, considering the start-up loads etc.

2)What would be a suitable drive chip / circuit to achieve the above

3) as I'm here... can a comparator be used as a voltage follower and if so is it considered good practice?

Thanks
Matt

- - - Updated - - -

Oops forgot to mention it is a conventional brushed motor

 

[chuckey]

What you need is a current amplifier as you micro can only deliver 10 mA and you need 5A (or more). So you need a FET or a darlington power transistor. Make sure to put a diode across the motor to suppress back EMF.
I think you need a PI controller ( https://en.wikipedia.org/wiki/PID_controller#PI_controller ). A good test would be to see what DC the pump needs to deliver a reasonable flow rate. Either do this with resistors or manually alter the on/off of the PWM. this will give you a "end" position. It could be that if you inserted some resistance or drove your motor from a constant current source, that on powering up, the pressure would not increase so rapidly.
Frank