DRV8871 power supply issue
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- SRAKER123
- Posts: 4
- Joined: Thu Jul 14, 2022 12:32 pm
DRV8871 power supply issue
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 +?
- adafruit_support_bill
- Posts: 88136
- Joined: Sat Feb 07, 2009 10:11 am
Re: DRV8871 power supply issue
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.Can I power DRV8871 with 12V DC 500 mA power supply to drive a 3V brushed dc motor
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.a 3V brushed dc motor with starting current of 70 mA?
- SRAKER123
- Posts: 4
- Joined: Thu Jul 14, 2022 12:32 pm
Re: DRV8871 power supply issue
Would adding a 500K Ohm resistor help with that? 64/500 = 128 mA current going to 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.
It's a small 4mm x 8mm motor that's used in pagers and cell phones.70mA seems rather low for a starting current.
- adafruit_support_bill
- Posts: 88136
- Joined: Sat Feb 07, 2009 10:11 am
Re: DRV8871 power supply issue
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?
What voltage is the motor rated to run at?
- SRAKER123
- Posts: 4
- Joined: Thu Jul 14, 2022 12:32 pm
Re: DRV8871 power supply issue
It's for 2.5V - 4VWhat voltage is the motor rated to run at?
I can put two 500K ohm resistors in series so the current to the motor will be 64 mA. Would that work?
- adafruit_support_bill
- Posts: 88136
- Joined: Sat Feb 07, 2009 10:11 am
Re: DRV8871 power supply issue
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.
It will bring the supply voltage down to the motor's normal rated operating range. And you can control it via the EN pin.
- SRAKER123
- Posts: 4
- Joined: Thu Jul 14, 2022 12:32 pm
Re: DRV8871 power supply issue
Would I still need the DRV8871? For driving the motor in both directions
- adafruit_support_bill
- Posts: 88136
- Joined: Sat Feb 07, 2009 10:11 am
Re: DRV8871 power supply issue
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
https://www.adafruit.com/product/3297
Please be positive and constructive with your questions and comments.