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[motorrad36]

Does anyone have an idea of the actual parameters for the BMS to start limiting discharge? A couple weeks ago I had longer rides than normal and rolled into my garage with <1%. It was a pretty chilly night, and I felt no response at all from the throttle over 25ish mph (this moment I still had about 4-5% left). Could barely make it over a nearby overpass! I thought I had just poorly planned the trip, and coupled with the temp, maybe it made sense to limit. Yesterday, I had 31% left at the start of a trip. I left it in sport mode, did not push it very hard, and it was a normal 55* daytime temp. It felt like it was having trouble keeping it at 65mph. The whole trip was 11 miles home, and I went from 31% to 11%! I looked at the logs, I don't see any errors, just a battery discharge limited log. Should I be taking it to a dealer at this point or Zero?

[BrianTRice@gmail.com]

So, those events reflect normal operation of the bikes at low SoC, BUT your battery could be experiencing particular circumstances that exacerbate it.

Here's the overview (which is a good time for me to figure out how to write this for the unofficial manual):
- Power draw from the motor is grossly a measure of a kW load.
- Power is current times voltage, and at low SoC, battery terminal voltage gets quite low especially under load, so the current required for a given power demand gets really high.
- This combines to effectively limit current substantially even in normal situations.

The current limit is driven by the size of the cabling from the battery to the controller (and then to the motor), so it's a hard physical kind of limit to prevent overheating and deterioration of those cables.

Anyway, the exacerbation typically comes directly from cell imbalance and internal resistance variance.
- Cel imbalance means the lowest cell voltage is driving the current limit more than it would normally, and can be affected by ambient temperature but also the cells do drift if they don't get a rebalancing by the BMS when charging regularly.
- Internal resistance varies very much by ambient temperature, and goes up quite a bit in the cold, which is the source of a lot of performance and range frustration.

Anyway, this is all to say that you can try looking at battery temperature and cell imbalance for your bike when those cutoffs happen to see if they're driving it. I wish Zero's software would communicate that directly, on the mobile app and definitely on the SRF which has a much richer display.

[BrianTRice@gmail.com]

FWIW if it's cold temperatures that are impacting your battery, which I suspect, I have in the past recommended securely wrapping the battery to keep cold air and moisture off the battery case as you ride.

I even was trying to develop this into a product, but ran into a number of issues that stalled the project, so I haven't really followed through fully. BUT I can say that 3mm or 1/8" thick Neoprene foam sheeting is sufficient for the purpose, and doesn't risk battery overheating the weather happens to warm up and you forget to take it off. (or overheating in the case of charging above say 6kW).

[motorrad36]

There seem to be many factors that would/could combine to make it more pronounced. Would the ambient temp reading in the logs inform whether colder temps are affecting it?

as to Neoprene, I would be open to doing that, but how do you get the sheeting in between the battery and frame? take the battery out or??

[BrianTRice@gmail.com]

The logs will never imply causality. You'll need to look for a trend or something. I would focus more on cell imbalance, since that is more directly indicated.

The neoprene is best fitted behind the lower and front plastics, outside the frame. It's better to have it there, off the surface of the battery casing, because its role is just to ablate air and moisture from the case, not to insulate the case per se.

[SebfromBE]

I think you can also look at it in the way that there is that generally cutoff happen as to prevent the cell voltage to drop below a preset minimal voltage that would start deteriorating the battery.
Keep in mind that applying load (turn the trottle) wil lcreate a voltage sag compared to the cell rest voltage. With that in mind:
- High SoC : even with full throttle, voltage sag does not lead to reaching the low voltage limit => You get the full power
- Mid SoC (starting at 50ish on my MY20017): you may experience enough sag at very high power that limits reaching for instance top speed of >150km/h
- low SoC: voltage limits clearly kicks in stronger and stronger, leading to limp mode

Factor that affect this: as explained above, in low temperature conditions, the internal resistance of the cell wiil increase, which will automatically increase the voltage sag under load, leading to earlier cutoffs than at normal temperature.

Brian: I am wondering about this cable current limitation item. If that is also the case then it is quite silly, because it is clearly a drawback of the Zeros that this limitation quicks in. Also I actually don't really believe this because what creates torque is current (not voltage), which means that if you can apply a given current (to a given motor), the input voltage should not matter (from basic physics and magnetic field generation laws).

[domingo3]

Couldn't find from your posts which battery you have.  The lower capacity batteries are much more impacted with current limiting at low SOC than the higher capacity batteries.  As others have said, your experience is pretty normal.  I've found that the conditions (weather, SOC, speed) that I experience limiting is pretty unpredictable while riding.  Of course cold, low SOC and high power are all significant factors, but I've had nearly identical conditions with different results.  As Mr. Trice puts it, the cell balance is probably the key, but I don't know a way to get that info real-time while riding.

[BrianTRice@gmail.com]

Brian: I am wondering about this cable current limitation item. If that is also the case then it is quite silly, because it is clearly a drawback of the Zeros that this limitation quicks in. Also I actually don't really believe this because what creates torque is current (not voltage), which means that if you can apply a given current (to a given motor), the input voltage should not matter (from basic physics and magnetic field generation laws).

Please do not take my comment as more than a general explanatory note.

The cables are sized and rated for the controller, which has its own limits. The controller limit is the primary concern.

Perhaps the motor/stator windings have similar issues, but this is all academic - the fact is, the current is the limiting factor in the powertrain delivery, and lower pack voltage makes power demands reach current limits sooner.

[BrianTRice@gmail.com]

Couldn't find from your posts which battery you have.  The lower capacity batteries are much more impacted with current limiting at low SOC than the higher capacity batteries.  As others have said, your experience is pretty normal.  I've found that the conditions (weather, SOC, speed) that I experience limiting is pretty unpredictable while riding.  Of course cold, low SOC and high power are all significant factors, but I've had nearly identical conditions with different results.  As Mr. Trice puts it, the cell balance is probably the key, but I don't know a way to get that info real-time while riding.

Yes, the smaller (longbrick 7.2 or older 3-brick monolith) pack has a smaller current limit, and will trigger this condition at higher SoC/voltage.

FYI it's "Brian T. Rice", just so I don't get quoted wrong elsewhere (spam email with "trice" in it is one reason I picked this handle).

[TheRan]

Yes, the smaller (longbrick 7.2 or older 3-brick monolith) pack has a smaller current limit, and will trigger this condition at higher SoC/voltage.

Is the limit based on the controller? In America you only have the lower powered 7.2 and the R models which are all 14.4 (550 and 775 amp controllers respectively), however in Europe (and perhaps other markets) we also have a non-R 14.4 model that has the same 550 amp controller as the 7.2 (well, perhaps not exactly the same but the description is identical on Zero's site). The 14.4 does have more peak power however at 44kW versus 33kW for the 7.2, and then the R models are 52kW.

[BrianTRice@gmail.com]

Yes, the smaller (longbrick 7.2 or older 3-brick monolith) pack has a smaller current limit, and will trigger this condition at higher SoC/voltage.

Is the limit based on the controller?

No, that's a smaller battery, by virtue of having fewer bricks. Each brick is in parallel and a full monolith has 4 bricks, so a longbrick 7.2 has 2 bricks in parallel.

Fewer batteries in parallel means lower output current capacity. The cells have current limits, too, and each brick is just 28 cells in series, electrically.

[domingo3]

FYI it's "Brian T. Rice", just so I don't get quoted wrong elsewhere (spam email with "trice" in it is one reason I picked this handle).

Off topic, I was kidding with the name. Quite some time ago, you had posted something about being misrepresented as Mr. Trice, which I found humorous. It's been long enough that the reference is probably lost, no harm intended.

[TheRan]

Yes, the smaller (longbrick 7.2 or older 3-brick monolith) pack has a smaller current limit, and will trigger this condition at higher SoC/voltage.

Is the limit based on the controller?

No, that's a smaller battery, by virtue of having fewer bricks. Each brick is in parallel and a full monolith has 4 bricks, so a longbrick 7.2 has 2 bricks in parallel.

Fewer batteries in parallel means lower output current capacity. The cells have current limits, too, and each brick is just 28 cells in series, electrically.

I see. Do we have any numbers for the current limit of the battery, which we could then use to calculate at what voltage (and thus SoC) the limit could actually be reached based on the peak power? Seb said around 50%, but I don't know if he has a 7.2 or a 14.4 and if he's just going by "feel".

Also, do you happen to know when the current limit on the controller would come into play, if at all? Doing the math for the 550 amp controller on the 33kW bike would mean it's good down to 60 volts which would never actually happen. Even on a 44kW bike that's 80 volts, 94 volts on a 52kW R model. According to the manual 0% SoC is 95.2 volts. So, unless I'm thinking about it all wrong (wouldn't surprise me) the current limit on the controller wouldn't be a factor even if you stuck the one from the low power model in an R model and went WOT with a dead battery.

[Crissa]

Since wattage is current x voltage, when you have a lower available voltage, that necessarily implies less energy across the device.  Whenever current is being drawn from a battery, available voltage drops - and vice versa, when there's less apparent voltae,there's lower amount of current available.  Voltage is easier to measure, so it's used as a shorthand here.

Different methods of storing energy and different electronics will have different respnse curves (see also diodes that have lower resistance at specific voltage, or capacitors which have more frequency response at higher voltage.)

-Crissa

[BrianTRice@gmail.com]

The voltage of the pack under load will be much lower than the voltage stated for a given SoC which is at rest. This is called “sag” and results from the effective circuit element of internal resistance within the pack. So the current will be quite a bit higher.

None of this really matters. Zero engineers implemented this to protect their systems. It’s academic to wonder which system hits a current limit first, only really touching on how they picked components to put in the bikes.

I wish my reward for answering questions weren’t simply more questions sometimes. It makes me want to ignore more of this forum.