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[SOLVED] Detection Circuit for motor connection/disconnection or short/break

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Hi
I'm operating a DC motor at 7.4v using a motor driver
The motor connection to the driver isn't constant - it can be disconnected mechanically by the user
I need to detect this disconnection using MCU interrupt (don't want to wake & sense but to get interrupt when disconnection happend)
Some ideas ?
 

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Hi,

There are intelligent motor driver ICs, high side drivers, low side drivers with open circuit / short circuit detection.

Consult distributirs or IC manufacturers internet pages.

Klaus
 

Hi
Thanks for the reply
I want to design an external detection circuit (and use DRV i'm already using...)
 

Hi,

Without knowing what your DRV is and how it works ... it will be hard to give an adequate circuit.

--> Give complete circuit informations.
What current range?
Linear, ON/OFF, PWM'd - what frequency, one or both directions.....

Klaus
 

Hi
DRV8833 connected to BLDC motor with Approx 2A RMS & can reach to 4A at peaks
The DRV8833 controlled by MCU bu PWM when needed to operate the motor
In idle state (no motor, MCU in sleep) i need to detect the motor disconnection
 

Hi,

I'd test the common driver power DC input current.

I assume there is short current detection inside the driver.

If you need an external test circuit for "disconnected" during motor OFF, then maybe use a 2k pulldown on one phase and two individual 10k pullups on the other phases.
Two comparators at the pullup'd phases with threshold at VCC/2 need to show "LOW" in case of a properly connected motor.
If one or both comparators show HIGH, then the motor is not connected properly.

Klaus
 

Hi
In idle state (motor connected but not rotating) it's connected in parallel to the DRV & to the detection circuit
Motor's impedance is Approx 3-4ohm
In rotating mode - same thing but now there is 7.4v PWM to the motor and following to the detection circuit i want to design (so i need to prepare for that & be protected)
 

Hi,

In post#1: you talk about a DC motor
In post#2: you talk about a BLDC motor

????
It´s all too confusing.
I will come back after you posted your real circuit.

Klaus
 

It's BLDC motor sorry for the confusion
The detection circuit i'm asking about should be connected to motor's 2 contacts in parrallel with the DRV output (as in picture above)
The detection circuit should detect when motor is disconnected from the DRV
But it also shold be protected/isolated from 7.4v PWM when motor is operating
Many thanks and again sorry for the confusion
 

Hi,

So BLDC...
Now there are BLDC motors with built in controller (usually two power wires)
And there are BLDC without controller (usually three power wires).

From your picture it looks like two wires --> controller built in.
You should consider to add some kind of filter (LPF) in the power lines from DRV to motor.
You need to find out how your motor reacts when you use a 10k resistor in series with the motor. What's tthe voktage across the motor?

On the other hand you talk about 3-4 Ohms of motor impedance...as if it was a motor without built in controller.

Please clarify ... and maybe give a corrected/improved picture.

Klaus
 

Hi
Again sorry for the confusion
I'm very new in to this and i though brushed DC is BLDC.. but i guess its just DC...
 

Hi,

BLDC = BrushLess DC

So with a brushed DC motor:
* detect overcurrent with the DRV feature
* detect a not connected motor in idle state with a pullup resistor and a comparator.

Klaus
 

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