Battery Cutoff Start/Stop Failure

General topics and discussions about the VESC and its development.
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable
vaziri
Posts: 7
Joined: 18 Feb 2016, 17:59
Location: San Jose, CA
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Battery Cutoff Start/Stop Failure

Postby vaziri » 18 Sep 2016, 06:14

I have had the following settings on my VESC:

Minimum input voltage: 8V
Maximum Input voltage: 57V
Battery Cutoff Start: 25.6V
Battery Cutoff End: 24V

I was very alarmed to see that my 8S battery had gotten as low as 9.5V (measure with no load) after my latest run. I have confirmed that my VESC truly had the above settings. Are there some modes in which the battery cutoff does not work? What could I have done wrong?

My understanding is that the motor should have slowed down once the battery dipped below 25.6V (3.2V/cell) and entirely stopped at 24V (3V/cell). Is that the wrong interpretation?

pf26
Posts: 310
Joined: 28 Mar 2016, 14:37
Location: FR Valence
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: Battery Cutoff Start/Stop Failure

Postby pf26 » 18 Sep 2016, 08:45

There is a function called "update_override_limits" in mc_interface.c that checks the battery voltage and VESC temperature every millisecond, and sets the max current to a reduced value below Battery Cutoff down to 0 upon Battery Cutoff End.
There may be an issue with highly impendant batteries, that reducing current might increase battery voltage and create some oscillations in this process.
I think it would be good to add some delays in this function, before allowing full current after cutoff reduction.
But at lest you should feel you get much less power than usual on the wheel...
Possibly, there are some other bug that prevent this function to be operational in your case.

Also beware that when batteries cells are not well balanced, even if the sum of the voltage is "protected", you may well empty the cell with least charge (and destroy it).

vaziri
Posts: 7
Joined: 18 Feb 2016, 17:59
Location: San Jose, CA
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: Battery Cutoff Start/Stop Failure

Postby vaziri » 18 Sep 2016, 17:23


rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: Battery Cutoff Start/Stop Failure

Postby rew » 19 Sep 2016, 09:03

I agree with vaziri: The intention is to "not work" below the low cutoff.

If you have an 8S setup, I would pull in the batt max and min a bit more. In theory you should not charge beyond 33.6, but you don't want to end up without brakes the first few meters, so I would set the batt max at 35V. Then batt_min at 25.6: Near the bottom, the cells often diverge a bit. So while the average would be 3.2V, some might already be hitting the 3.0V... (even more so after this "event")

So that would mean that battery cutoff start should start around 26.5 or 27 volts.

The disadvantage of taking big margins is that you might start getting reduced power with still say 40% of the battery capacity remaining. This is due to the internal resistance causing the voltage to drop into the reduced power zone when under load. For example, I'm now charging my bike to only 4.0V/cell and the reduced power kicks in quite fast. :-(

vaziri
Posts: 7
Joined: 18 Feb 2016, 17:59
Location: San Jose, CA
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: Battery Cutoff Start/Stop Failure

Postby vaziri » 20 Sep 2016, 06:46

After further troubleshooting it seems the root cause of this problem is that the VESC was able to revert to some sort of default configuration. In that configuration the battery thresholds were much lower. I am not sure how that is possible, but it seems to be the case. Unfortunately before I could try to reproduce the error I had an electrical failure in one of my VESCs.

benjamin
Site Admin
Posts: 280
Joined: 15 Dec 2015, 08:38
Location: Sweden
Contact:

Re: Battery Cutoff Start/Stop Failure

Postby benjamin » 20 Sep 2016, 07:19

The battery cutoff should work and I have tested it coutless times. Also, braking should work regardless of what the battery voltage is. How long did you leave things connected after finishing your ride until you measured the battery voltage? It could be that the battery was more or less completely out of energy, and then it does not take too long until the logic drains the rest of the voltage that is left.

subodh.malgonde
Posts: 4
Joined: 17 Sep 2018, 13:17
Location: India
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: Battery Cutoff Start/Stop Failure

Postby subodh.malgonde » 19 Sep 2018, 06:11

@benjamin: Is there a lower limit for the minimum input voltage and battery cutoff end voltage? Can I set these to 7V? My VESC hardware version is 4.12.


[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Return to “General”

Who is online

Users browsing this forum: Bing [Bot] and 2 guests