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Motor driver selection
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Motor driver selection

by Learnplayfun on Wed Aug 14, 2019 1:33 pm

Hi all I'm trying to figure out which controller is suitable to control a 24vdc (18w) pump. The pump i have have already got an controller (speed and stop). But I want to integrate this into my raspberry pi and it seem like it will be easier to find a separate controller, then find an way to integrate this into work with pi. From searching around people been saying this company pump control the speed via 0-5v signal. I open the controller box and does seem an 78Mos 5v regulator inside along with an stc15w204s ic for speed setting. The controller have 8 speed setting trigger via the on board bottoms and a bottom for stop. I have took measurement of the signal line of each speed setting as below. I'm trying to make sense of all this and see if anyone have suggest on motor driver i can use. Oh one thing the pump is hard wires in the signal line so 3 line 24V+, 24V-(gnd),control wire.

Voltage measurement as follow
Setting 1: Gnd - Signal = 3.51v
Setting 2: Gnd - Signal = 3.68v
Setting 3: Gnd - Signal = 3.86v
Setting 4: Gnd - Signal = 4.04v
Setting 5: Gnd - Signal = 4.22v
Setting 6: Gnd - Signal = 4.41v
Setting 7: Gnd - Signal = 4.58v
Setting 8: Gnd - Signal = 4.98v

So my question is will the DRV8871 motor driver work? From spec there is enough power to run it however how does the build in pwm work in this case? Or should i just use it to run the motor and get another 0-5v signal line off raspberry.
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Learnplayfun
 
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Re: Motor driver selection

by adafruit_support_bill on Wed Aug 14, 2019 4:06 pm

The stc15w204s is a generic clone of an 8051 microcontroller. There must be some sort of power transistor or MOSFET that does the actual switching of current to the motor.

If you have a manual or spec sheet for that controller board, you could probably come up with a way to interface it to the Pi. If it is a simple 0-5v interface, something like a DAC and a level shifter would probably work:

https://www.adafruit.com/product/935
https://www.adafruit.com/product/757

The other approach is to just use a power MOSFET and drive it directly with PWM from the Pi:

https://www.adafruit.com/product/355

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Re: Motor driver selection

by Learnplayfun on Wed Aug 14, 2019 6:03 pm

Driving it motor directly without an motor driver?

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Re: Motor driver selection

by adafruit_support_bill on Wed Aug 14, 2019 7:04 pm

Unless you need to reverse your pump, a pwer mosfet and pwm are all you need.

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Re: Motor driver selection

by Learnplayfun on Wed Aug 14, 2019 7:58 pm

I see thank what about flyback diode and capacitor for protective circuits? Bu the way I also purchase an automation hat, If direct powering can just use one of the on board 24v relay output.

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Re: Motor driver selection

by adafruit_support_bill on Wed Aug 14, 2019 8:08 pm

You'll need a flyback diode to protect the MOSFET. No other components are necessary.

Image

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Re: Motor driver selection

by Learnplayfun on Wed Aug 14, 2019 8:55 pm

Thank so much I'll try running it directly without the original motor driver pcb. Just future reference all these motor driver module got capacitor on board is it because there used for bi directional movement or to smooth out the transition during speed up and down? I notice the original controller of this pump also got two small capacitor on board but the pump is unidirectional only.

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Re: Motor driver selection

by adafruit_support_bill on Thu Aug 15, 2019 5:41 am

Just future reference all these motor driver module got capacitor on board is it because there used for bi directional movement or to smooth out the transition during speed up and down?

Hard to say what they are for without a full schematic. To reverse a motor, you would need 4 transistors or MOSFETs in an H-Bridge configuration. http://www.modularcircuits.com/blog/art ... he-basics/
It is possible they are simply bypass capacitors to help filter noise on the power/ground buses. The microcontroller on the board would need some fairly clean power.

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