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OVER CURRENT without over current?

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Oyta
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Joined: 2017-05-24 12:30
Posts: 19
OVER CURRENT without over current?

 

I got an ABS_OVER CURRENT fault code while braking:


Fault            : FAULT_CODE_ABS_OVER_CURRENT
Current          : -34.5
Current filtered : -40.4
Voltage          : 36.85
Duty             : 0.000
RPM              : 5126.7
Tacho            : 3540309
Cycles running   : 72550
TIM duty         : 0
TIM val samp     : 2
TIM current samp : 4200
TIM top          : 8400
Comm step        : 0
Temperature      : 41.51

 

I have:

  • 10s3p LG HG2 battery pack (Li-Ions)
  • Enertion R-Spec 6355 motor single drive
  • Settings:
    • Motor current max: 90
    • Motor current max brake: -60
    • Battery Current Max: 35
    • Battery Current Max Regen: -8
    • Absolute Max Current: 60
    • Max wattage: 15/-15 kW

How does a current of -34.5/-40.4 go into fault mode when the limit is -60? It doesn't look like the battery current where that high either. Are the logged values to high because the sampling rate didn't catch the lowest values? https://metr.at/r/OknDe?zoom_start=0&zoom_end=10425 -> and zoomed in to the error: https://metr.at/r/OknDe?zoom_start=6774&zoom_end=8352

arvidb
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Joined: 2018-01-16 23:09
Posts: 77

The Absolute Max current is a safety limit that the VESC uses to detect an error. I.e. if the current gets larger than that, the VESC assumes something is seriously wrong (shorted motor phases or whatever) and shuts down.

The battery and motor current limits are instead limits that are enforced: if a current gets larger than the set limit, the VESC adjusts the duty cycle to keep the current within the limit.

So you should set the Absolute Max limit a good bit wider than the other limits.

The VESC keeps track of both filtered and unfiltered (instantaneous) current, and it's possible (I don't have the firmware code on screen at the moment so I can't check for sure) that the displayed currents are the filtered ones, while the ABS_OVER_CURRENT was triggered by a single sample at >60 A.

Edit: It looks like the "Current" displayed in the error message is the field current (FOC q current) and not necessarily the total current as measured by the phase shunts. That's probably why it looks like it tripped at a lower current than the set value.

Oyta
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Last seen: 9 months 1 week ago
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Joined: 2017-05-24 12:30
Posts: 19

Thanks for a solid answer. I am not that knowledge about the VESC and FOC paramters, but I think I understood the main points. I did experience this two times after lowering the abs current max from 150A to 60A. I do have a 60A fuse on my BMS, that's why I did align them. However it seems this is the motor current, not the battery current as the duty cycle was low at the specific moment. I will increase the abs current max to, say, 100A and see if that helps. I have the fuse as security in addition if anything is too high on that side of the system.

TheFallen
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Joined: 2017-09-11 11:46
Posts: 62

The 60A fuse on your BMS will blow instantly if >120A is seen, a good value for abs current max would be 100-110A. This which would allow the VESC an opportunity to try and shut the motor down before finally blowing the BMS fuse if it cannot.