DRV8308: Motor will not start reliably

Joseph,

Can you share details of the motor you are using? Usually when this issue presents itself there is a misalignment of the hall sensors or one of the hall sensors is switched when compared to the motor phases. For example hall sensor A is connected where phase B should be. 

Regards.

-Adam

Adam -

The motor I am using is part of a blower assembly.  I have attached the only documentation I have.

I tried every combination of connections for the hall effect sensors in case this mapping was not correct, but this did not yield any better results.

What kind of misalignment of the Hall effect sensors should I look for?

Thanks,

Joe

WM7040-Details of Blower.pdf

Joe,

Can you measure the start-up current of the system when the motor is first enabled? Maybe the blower is too big for the current limit?

Hall sensor misalignment means Hall A is connected where motor phase B is connected for example.

Please see the image.

Regards,

-Adam

Adam -

The startup current is well under 4A.  The development board as well as my board are configured with a 0.05 ohm current sense resistor and should operate to 5A.

I have eliminated the possibility of hall effect misalignment by trying every combination of connections for the hall effect sensors between the motor and eval board.

Any more thoughts?

Thanks,

Joe

Adam -

Here are some relevent scope traces.  For Hall Effect inputs and UVW outputs, U is trace 1, V is trace 2, and W is trace 4.

Thanks,

Joe

Joseph,

Do you have a second motor you can try?

Regards,

-Adam

Adam -

I have tried three already, and they all behave the same.  Are there any register settings that might be a factor?  Is there a way to determine whether the motor actually starts up?

Thanks,

Joe

Joseph check this:

 
the problem is mechanical ... of the motor...

when you test the motor without load the motor turn free like "crazy".

When you put a load in the axel  the motor stop and stay ok, if you enable the brake function they stay good.

Yes I checked the User's Guide and tuning information.

Perhaps I should give you more details.

My problem is that the motor does not aways start up.  Once it starts it operates fine.  In normal operation I want the motor to run at full speed.  The problem is the same at 20%, so I have been doing my testing at this rate.  I am running the motor at 24V and at 20% it draws about 0.2A.  On startup it looks like it briefly draws about 1A.  When it starts up properly the fault led flashes very briefly and lock asserts.  When I disable the DRV8308 the fault led does not assert.

On failure the motor does nothing when I enable the DRV8308.  The fault led flashes very briefly as before.  When I disable the DRV8308 the fault led flashes longer (about 1 sec).  While in this failure mode no current is drawn.  If I move the rotor CW or CCW while the DRV8308 is enabled it starts up fine.  

While in failure mode if I disable the DRV8308 and then reenable it the motor still does not move.  

While in failure mode if I disable the DRV8308, move the rotor, and then reenable it the motor will start up most of the time.

This seems to indicate that the position of the rotor is a factor on start up.  I have tried many combinations of DRV8308 register settings to start up the motor when it is in failure mode with no luck.  And I'm still not sure how to detect with certainty when it is in this mode. I be able to use lock for this purpose but I'd rather save it for detecting other problems.

The blower manufacturer provides a controller board that drives the motor without this problem.  I have been running my experiments with three different motors that function properly with the manufacturer's controller board.

All of my testing has been done with the entire blower assembly, not just the motor.

Joseph,

You may be experiencing a power supply issue in the cases where the startup cannot occur if the rotor is in specific positions such as far away from the initial pole pair that is trying to start the motor. This can be especially true when the motor is loaded.

Please try unloading the motor or a bigger power supply.

Do you know which faults are being caused?

Regards,

-Adam

We have noticed that the Hall effect outputs of the motor do not match up exactly with the timing diagrams in the DRV8308 specification.  I included these outputs in a previous posting.  I don't think this is an issue as I have seen various configurations described, some matching the DRV8308 specification, some matching my motor, and some others.  The Hall effect output of the motor that came with the evaluation board matches the output of my motor.  The motor that came with the evaluation board does not have the start up problem I have described.

Can you tell me what register settings might affect the ability of the motor to start up reliably?

I have taken a harder look at the state of the Hall effect outputs when the motor will not start up.  It looks like when the motor won't start the Hall effect outputs are all low or all high.  If I force the outputs to the opposite state one at a time the motor will eventually start up.

Once the motor starts up this does not seem to be problem, as can be seen in the scope traces I posted earlier.  These traces show that the Hall effect outputs from the motor can be all low or all high.

Joseph,

Did someone add the hall sensors to the motor? Something is misaligned because there should never be a time when all three halls are HIGH together or LOW together. These are states reserved for STOP and ALIGN which the driver commands, the motor should never be in this state.

My guess is that your hall sensors are misaligned (not evenly spaced on the motor housing) or this motor is unique and not compatible with conventional 3-phase 120 degree commutation.

Regards,

-Adam

This motor is part of a blower assembly we buy from Taiwan.  The Hall effect sensors are part of the assembly.  It may be that the motor/Hall effect configuration is unique, but this is out of my control.  Is it possible to use the DRV8308 in this configuration?