TSDZ2 failed in odd way, suspecting the controller?

[stratohunter]

I know I have been posting so many TSDZ2 related questions but...

My 52V TSDZ2 with 860C and OSF 1.1.0 failed again today, at a 2500km mileage. I left home with a full battery at 58.8v and things started to go wrong after riding for 20 minutes, when power delivery started to pause for short (<1s) gaps. Over the next 15km trip this worsened quickly and the output became intermittent, like sharply off and on once per 1 second or so. It was not the brake/shift sensor because the monitor would indicate a "brake" sign if it was, which was not the case. Probably not the torque sensor since it would have caused the power to rise and drop in a ramp, but the assist went off and on rapidly as if the brake sensor was frequently triggered, and full throttle won't help. I also don't suspect the speed sensor because speed reading was fine. Oh yeah, I hooked up a temperature meter to the stator of the inside motor and kept its reading under 99 degC.

After resting for half an hour without turning off the monitor, I started riding home. In the first half mile it was at least still giving intermittent power. Note that in the short periods when it was giving power, the power magnitude was usual. Yeah it was really jerky with me pedaling hard in that situation. Till this point the monitor was good.

Until all of a sudden it gave way completely. No power at all. Monitor blacked out. At this moment the battery was 50.9V. If I hit power key shortly after it was dead, the monitor blinks and blacks out again. I could wait for several minutes and then would be able to start it successfully. But after working for a short while (depending on how long I had waited since its last failure) it's dead again. After sitting for hours it can power up now and idle on throttle, but I'm sure it'll fail again if I ride it.

Did anyone experience similar issues, and could someone help me troubleshooting? Any advice is appreciated.

 

[amberwolf]

Until all of a sudden it gave way completely. No power at all. Monitor blacked out. At this moment the battery was 50.9V. If I hit power key shortly after it was dead, the monitor blinks and blacks out again.

When a system powers off completely, it almost always means the battery has shut off to protect itself, so that cells do not get damaged and become a fire risk.

This can be from a low cell, or overcurrent, or any other condition the BMS is designed to protect the cells against.

If a cell or cell group drops below LVC under load, then the BMS would shut off power, and then the system would go dead. Restarting the system while in this state might blink the display momentarily, but there is insufficient capacity left in the battery (at least in the low cell(s) to power it, so the BMS then cuts power off again. Sometimes a cell may recover just a bit over time (a few minutes to an hour, etc), and allow the BMS to power the system back on, until a load is placed on it (attempting to operate the motor, for instance), then the cell drops and the BMS shuts off again to protect it.

Before it reaches the shutoff point, the controller will usually stop working (but not turn off), sometimes repeatedly as the battery level crosses the controller's LVC under load and then recovers; eventually failing to recover enough to allow the ocntroller to operate the motor further.

Your symptoms match this scenario, so most likely you need to troubleshoot the battery, find the problematic cell group (it will be lowest in voltage; all the good cell groups will match each other in voltage), and replace those cells with new ones, to fix the problem with the battery.


Note that a temporary fix is to leave the battery on it's charger for at least overnight, and potentially for days (or weeks if the cell group is very far off from the others), but this doesn't fix the problem, it just masks it by making the cells all the same voltage. They still aren't the same capacity or performance, so the problem will recur every time the cell drops far enough.

 

[stratohunter]

When a system powers off completely, it almost always means the battery has shut off to protect itself, so that cells do not get damaged and become a fire risk.

Thanks for your detailed explanation. The battery did bump off from its base and smash to the ground while I'm at 20+ mph several times due to poorly designed securing. Perhaps they got damaged from these and worsened enough in my last ride? I will go for some test rides with half and fully charged battery to see what happens, then check inside it.

 

[amberwolf]

Thanks for your detailed explanation. The battery did bump off from its base and smash to the ground while I'm at 20+ mph several times due to poorly designed securing. Perhaps they got damaged from these and worsened enough in my last ride? I will go for some test rides with half and fully charged battery to see what happens, then check inside it.

I would check inside it first, whenever physical damage is suspected.

If there is damage that has disconnected some cells in some groups, causing lower capability and capacity in those, then the remaining cells in each of those groups is being run a lot harder than they're designed for, and may be being damaged by this, or being overheated by excessive current draw (since less cells would be providing the same amount of current within any group that has disconnected cells).

It is also possible that some cells are physically damaged from the impacts themselves, and not just disconnected by interconnect failure.

If cells are sufficiently damaged or overheated, a fire could result. It isn't that likely, but under the wrong circumstances, it can happen.

 

[stratohunter]

I would check inside it first, whenever physical damage is suspected.

If there is damage that has disconnected some cells in some groups, causing lower capability and capacity in those, then the remaining cells in each of those groups is being run a lot harder than they're designed for, and may be being damaged by this, or being overheated by excessive current draw (since less cells would be providing the same amount of current within any group that has disconnected cells).

It is also possible that some cells are physically damaged from the impacts themselves, and not just disconnected by interconnect failure.

If cells are sufficiently damaged or overheated, a fire could result. It isn't that likely, but under the wrong circumstances, it can happen.

Thanks a lot you really saved me a whole lot of hassle messing up with the motor! It was a loose connection in the base rack of the battery, and motor was perfectly fine.