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MCT8316Z: MCT8316ZT used in a differential-wheel robot burnt

Bernard FROMENT
Prodigy 40 points
Part Number: MCT8316Z

Tool/software:

Hi the community,

We used two MCT8316ZT(non-programmable version) to drive two brushless motors for the propulsion of a robot.

Everything works well except when the robot is manually pushed and the MCT8316ZT are unpowered.

The problem:

The board is powered-off (a normal state for a mobile robot) and so  the 24V battery is no more connected to the MCT8316ZT power line (VM)

When the robot is manually pushed, the motors transfer energy to the supply (VM line).

But in this case both MCT8316ZT burnt !

As you can see in the schematics, there is a huge bulk capacitor (4700uf / 40V) on the power line but it seems thas this capacitor is not enough to absorb eneregy regenerated.

We measured the voltage generated by motors when robot is pushed : Approx 8VDC on the VM line.

But we measure with a multimeter. Not really accurate (may be we could have unseen voltage spikes that have burnt the MCT8316ZT)

We dont know how to cope with this problem: A resistor between VM line and ground to absorb energy, a 30V transil diode between VM line and ground ... ?

Please help us 

schematics

  • 0
    TI__Mastermind 23612 points

    Hi Bernard,

    Sorry for late reply here, our engineer is put of office.

    Let me continue this thread. Will you be able to use oscilloscope to measure the vm?

    What is the gear ration of the wheel and BEMF Constant of the motor?

    The effective voltage raise could be BEMF generated by motor and because of this device powered and PWM is switched from OUTA/B/C it will boost the voltage further due to motor inductance. There may be higher VM  raise beyond the abs max.

    We can use the suppressors to avoid Voltage raising beyond , the bulk capacitor also will absorb the energy, let me check how much it is capable of.

    Thanks and Best Regards,

    Venkatadri S

  • 0 in reply to Venkatadri Shantaram84961
    Prodigy 40 points

    HiIt is also my feeling.

    As said in  my message, we just connect a multimeter  and we get only 8VDC but may be there were spikes greater than 40V on VM!

    We can connect a suprressor on VM like a P6KE30A but I m not sure that it can absorb all the regenrated power.

    The other solution is to disconnect physically (with relays) the motors  from the MCT8316ZT

    But I begin to think that the MCT8316ZT is not adapted to our robotics application because in robotics the case where everything is powered-off and the robot is pushed by an human is a classic user case. And I think that's not a user case accepted by the the MCT8316ZT

    What 's your idea

  • 0 in reply to Bernard FROMENT
    TI__Mastermind 23612 points

    Hi Bernard,

    Can you provide motor data sheet? What is the BEMF constant, R and L of the motor.

    First let us verify how much voltage is generated by the wheel movement? What is the gear ratio between wheel and the motor?

    I am thinking if voltage generated is withing abs max and if we can stop device from operating at lower voltage then PWM will not generate which cna eliminate boost effect.

    Thanks and Best Regards

    Venkatadri S

  • 0
    Prodigy 40 points

    Hi Venkatadri

    The ratio between wheel and motor is 1/46

    Wheels can turn up to 4tr/s

    You have all info related to brushless motor here:

    https://www.nanotec.com/eu/en/products/2374-df45m024053-c2

    Thanks

  • +1 in reply to Bernard FROMENT
    TI__Mastermind 23612 points

    Hi Bernard,

    Thanks for sharing the data sheet. This looks like large inrush current via OUTx and there is a large capacitor if not charged.

    I will analyze with this information and get back to you.

    Thanks and Best Regards

    Venkatadri S