You are here

VESC 100/250 won't go full duty cycle

6 posts / 0 new
Last post
TheBennis
Offline
Last seen: 6 days 38 min ago
VESC Free
Joined: 2018-07-08 05:55
Posts: 3
VESC 100/250 won't go full duty cycle

Hello vesc team,

I'm building an ebike with the 100/250 esc. I have an issue where at about 82% duty cycle will start to lose sync with the motor and if pushed beyond 82% will current fault. This testing is done with the motor freewheeling.

The Setup:

    20s battery pack
    GMAC hub motor
    FOC mode running at 30Khz
    5A motor current and 20A max current for testing

Things I've tried:

    Switching to 13s battery (rpm decreases, duty stays the same)
    Doubling or Quadrupling observer gain (no discernable change)
    Halving or Quartering time constant (no discernable change)
    Decreasing frequency from 30 to 25Khz (gain a few percent before becoming unstable)

My temporary solution to this issue was to limit duty cycle to 80% and go riding. When incrementally increasing current I hit another fault, if I go to about 50 amps or over on the motor it will fault out with an unbalanced current fault. I really wonder if this is related to the motor sync issue.

Another data point that may be useful is that I also have a vesc6 mkv and with the 13s battery am able to freewheel to the default 95% duty cycle and run 90 motor amps with no faults.

Any suggestions on what I could do to make this work?

electricfox
electricfox's picture
Offline
Last seen: 4 hours 17 min ago
VESC Original
Joined: 2019-01-01 17:11
Posts: 53

Suggestions: Try playing with Duty Cycle Current Limit Start to lower value like 70-90%. Time constant even lower and higher. You can also try using beta firmware. 

frank
Offline
Last seen: 23 hours 48 min ago
VESC BronzeVESC FreeVESC GoldVESC OriginalVESC Silver
Joined: 2016-12-27 20:19
Posts: 725

You can try to increase the switching frequency to 40Khz and pay with the time constant. If tracking is not good, you will get current spikes and they can kill the controller. So better tune the motor properly.

Have a look at Vedder latest Youtube videos. He runs a Youtube Channel.

TheBennis
Offline
Last seen: 6 days 38 min ago
VESC Free
Joined: 2018-07-08 05:55
Posts: 3

I increased the frequency to 40khz and the top speed before losing tracking decreased. It's just weird to me because the vesc 6 mkv doesn't get the overcurrent fault and doesn't lose tracking.

Also do you have any idea what could be causing the FAULT_CODE_UNBALANCED_CURRENT on the 100/250? I initially thought it was a crappy connection or a crappy motor but again the VESC 6 mkv doesn't get this fault under the same conditions and I have redone the connectors on the 100/250 with no change in symptoms.

I could be wrong but I would expect these two escs to act nearly identically with the same motor and same configuration.

frank
Offline
Last seen: 23 hours 48 min ago
VESC BronzeVESC FreeVESC GoldVESC OriginalVESC Silver
Joined: 2016-12-27 20:19
Posts: 725

The 100/250 is a low side shunt design and the MKV a phase shunt design. So there might be a difference...

Did you already try the BETA version of VESC-Tool?

TheBennis
Offline
Last seen: 6 days 38 min ago
VESC Free
Joined: 2018-07-08 05:55
Posts: 3

Okay got some time to play around with the setup. Running the beta firmware on default settings did not help the problem.

After playing around I found a setting that would allow me to reach full speed, the high current sampling mode. The caveat is that in this mode it will fault out at anything above ~15 amps. One other thing I noticed, when measuring hall sensor offset @20amps with the high current sensing mode there is a very noticeable cogging of the motor while running hall detection that does not exist when high current sensing mode is off.

Also looking at sampled data there seems to be a current offset (phase a and b slightly positive, phase c slightly negative).

Is it possible that one of my current shunts is outside of tolerable limits and that is what is causing my problems? Is there a good way to verify that the current shunts are working properly?