DRV8871 power supply issue

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SRAKER123
 
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DRV8871 power supply issue

Post by SRAKER123 »

Can I power DRV8871 with 12V DC 500 mA power supply to drive a 3V brushed dc motor with starting current of 70 mA?? Also would I still need to connect the ground pin to the MCU or is it grounded like the Vm is to power +?

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Re: DRV8871 power supply issue

Post by adafruit_support_bill »

Can I power DRV8871 with 12V DC 500 mA power supply to drive a 3V brushed dc motor
12v into a 3v motor would likely be a problem - unless you configure the DRV8871 to limit the current to a safe level for the motor.
a 3V brushed dc motor with starting current of 70 mA?
70mA seems rather low for a starting current. Starting current is the same as the stall current - at least until the rotor starts moving. The maximum efficiency point for a loaded motor is usually about 50%-70% of the stall current.

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Re: DRV8871 power supply issue

Post by SRAKER123 »

12v into a 3v motor would likely be a problem - unless you configure the DRV8871 to limit the current to a safe level for the motor.
Would adding a 500K Ohm resistor help with that? 64/500 = 128 mA current going to motor.
70mA seems rather low for a starting current.
It's a small 4mm x 8mm motor that's used in pagers and cell phones.

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Re: DRV8871 power supply issue

Post by adafruit_support_bill »

128 mA is still nearly twice the rated start current. The motor might survive that in intermittent operation. But it is likely to overheat if you are not careful.

What voltage is the motor rated to run at?

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Re: DRV8871 power supply issue

Post by SRAKER123 »

What voltage is the motor rated to run at?
It's for 2.5V - 4V

I can put two 500K ohm resistors in series so the current to the motor will be 64 mA. Would that work?

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Re: DRV8871 power supply issue

Post by adafruit_support_bill »

This is probably a better solution: https://www.adafruit.com/product/2745
It will bring the supply voltage down to the motor's normal rated operating range. And you can control it via the EN pin.

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Re: DRV8871 power supply issue

Post by SRAKER123 »

Would I still need the DRV8871? For driving the motor in both directions

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Re: DRV8871 power supply issue

Post by adafruit_support_bill »

In general ERM pager/vibration motors do not need direction control. They vibrate the same in either direction. But if you have other reasons to reverse the motor, then you would need a driver with a full H-bridge. The DRV8833 would be a better match than the DRV8871. It works well with lower voltage motors.
https://www.adafruit.com/product/3297

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