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[ultrarnr]

I made a trip to the mall yesterday and returned with 13% SOC on my 2014 SR. I didn't think an additional 6 mile trip to get some groceries was a big deal at all considering all but a few hundred yards was at 25-35 MPH. When I turned on the final 200 yards to the store which was a 45 MPH zone the SR could not get up to 45, couldn't get to 30MPH even. I was at 11% SOC and power had been severely cut. On the way home it was the same way, could not get the bike up to 35 MPH despite SOC showing 10%. When I was about 100 feet from my driveway I heard a click and the SOC dropped from 9% to 0%!

The SR has been erratic below 10% SOC before. I have had power cut at 9% where I could not maintain 45% and have had full power at 6% SOC. But this is the worst I have ever seen.

This also showed that I have just over 9kWh of usable battery capacity. When fully charged the app shows 13.1 kWh total capacity.

Bottom line here is be careful when you are planning trips that will take you close to the maximum range of the battery. Especially if it requires a 55-60 MPH speed.

[odedmaz]

Similar experience, although not that drastic with my FX
http://www.electricmotorcycleforum.com/boards/index.php?topic=4802.0

[rayivers]

I've noticed many times that switching off and on again at low SOC brings up a lower SOC number, sometimes much lower.  I think that during a ride the SOC may be an ongoing calculation involving actual power use / expected regen / 'miles remaining' etc. while the turn-on SOC is more of a simple battery measurement, but who knows.

Ray

[grmarks]

It is my understanding that SOC on lithium batteries must be calculated by monitoring the current draw. But age and out side temp. makes a difference too. If it is cold then range is less (easily 10% less) depending on how cold. Possibly the Zero electronics is not monitoring temp. or the calculation is not that sophisticated. If you partially recharge a lot then the pack could be out of balance and the SOC calc. is not reset to 100%, and it will drift out. Its a calculation so its not perfect.
If its 1% out then thats pretty close, but if you don't fully charge it could be 1% out on the way down and 1% out on the way up = 2%. Do this 5 times and you are 10% out.   
   

[Doctorbass]

Cell imbalance, low temp ( make  voltage sag)  have huge effect also on the last % SOC.

On my modified 2012 S ZF15 i have 13400Wh usable ( 200Ah at 66V) and i can get all the 13400Wh and reach 2%soc no prob everytime. The cells are perfectly balanced.

Doc

[Kocho]

I read somewhere that one can't expect perfectly balanced cells at both top and bottom end of the SoC. And that cells can be perfectly balanced at a particular SoC, but will become disbalanced at other SoC. They can br rebalanced at that new SoC, but that will cause them to be disbalanced at other SoC-es. The reason is that cells in the pack have slightly different capacities and internal resistances and sometimes temperatures from each other. Resulting in slightly different charge/discharge curves for the different cells. On top of that, you got the BMS that introduces disbalances by monitoring the cells and drawing unevenly from each cell. The result is that, suppose you start with top-balanced cells, as they discharge, they end-up slightly disbalanced. At that point, the BMS hopefully detects this condition and tries to protect the weakest (emptiest) cells, even though the overall SoC of the pack may indeed be way above "empty". So it cuts power.

On my Vectrix with Nissan Leaf cells,  I do not have a BMS. My cells are top-balanced to within a few 1/1000 of a Volt. But as I drain the battery, towards the lower SoC, they get differences as big as 1/10 of a Volt, a 100 times more than where they started when fully charged. However, since they were all drained by the same amount, as I charge them back and as their SoC reaches back towards "fully" charged (somewhere 10-20% below max. rated capacity actually is where my "full charge" is), they again become almost perfectly balanced. Over about 2,000 miles, charging every 40-60 miles, they still remain top-balanced. The lack of BMS (and the good quality of the Nissan cells) really helps keep the cells top-balanced.

The better BMS systems actively balance cells when in use, not just during charging. Does anyone know what type the BMS in the Zero is? I.e., does it just top-balance during charging or does it also actively balance while riding?   

Cell imbalance, low temp ( make  voltage sag)  have huge effect also on the last % SOC.

On my modified 2012 S ZF15 i have 13400Wh usable ( 200Ah at 66V) and i can get all the 13400Wh and reach 2%soc no prob everytime. The cells are perfectly balanced.

Doc

[Justin Andrews]

At 13% SoC you have about 4% usable SoC. At 8% to 10% you can easily have the batteries go into "safe mode"

[xmjsilverx]

So besides temp monitoring how would this differ on a leaf battery?  I have had it down below 6% and never had any issues on the leaf.  I have had the SR down to 11% before with no issues but I've never pushed it further than that.

[Richard230]

My 2014 S doesn't have this problem. While it will drop 1% at times upon turning the bike off and then back on, I have ridden it down to completely empty, without significant power loss until it reached less than 5% and it didn't stop moving until the moment the display said 0%. Maybe the 2015 models are a little more conservative in calculating the power remaining?  My cells all balance out at 2 mA on top and when the system was completely drained I was getting a 160 mA difference between the 5 modules.

[Kocho]

I don't think it would differ. But since I don't have a BMS, there is nothing to disbalance the cells, other than differences on the cells themselves - and so far they seem to be staying top balanced exactly as good as the day I got them in over a year and 2,000 miles ago. I monitor their voltage manually every now and then to make sure they are OK. And because the Vectrix uses considerably less max current than the Zeros, the pack doesn't heat-up either.

So besides temp monitoring how would this differ on a leaf battery?  I have had it down below 6% and never had any issues on the leaf.  I have had the SR down to 11% before with no issues but I've never pushed it further than that.

[grmarks]

Kocho the manual says to leave the bike plugged into the charger if you won't be riding it for more than a month. It says that every 72 hours it does a cell balance so that would mean its top balanced. I.e. if its plugged in the first thing it does is a full charge.

[Kocho]

I've read about that (and really don't like it, to be honest) - based on some research I've found, if that topping-off happens too often, it will decrease the life/capacity of the Li cells. Once every 72 hours might not be a big deal, especially if one is riding it in-between that. But over a whole winter season for instance, I'd be concerned. Every guidance I've seen suggests that Li batteries be stored at half-charge, not full charge (and BMS topping-up the pack is keeping it at full charge when it is not used).

That said, if there is no way to fully turn off the bike, it might be even worse to leave the bike in storage unplugged for extended periods of time, as the BMS itself (plus some other active electrical components) might drain the battery and drain its cells unevenly. I don't know if that's the case with the Zeros either, unfortunately.

Regardless, that does not seem to provide information about whether the BMS actively balances the cells while riding (e.g., while discharging the batteries in use). Probably it doesn't, which means that it is possible to have disbalances near the low end of the SoC, which the BMS will detect and shut down the bike even though the rest of the pack might have plenty of juice in it.

Kocho the manual says to leave the bike plugged into the charger if you won't be riding it for more than a month. It says that every 72 hours it does a cell balance so that would mean its top balanced. I.e. if its plugged in the first thing it does is a full charge.

[kensiko]

9kWh usable energy with a power tank, that is pretty low.

[Richard230]

9kWh usable energy with a power tank, that is pretty low.

I agree.  My 2014 S with power tank shows 13.34 kWh usable energy when fully charged.

[ultrarnr]

Richard230,

My SR shows 13.1 KWh when fully charged so close to what you are seeing. But when you multiply the Wh/Mi times the total mileage when the battery is showing 0% SOC I get just over 9kWh.