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[electrictwowheeler]

I just sold my 2013 Brammo Empulse standard model with 27,000 miles on it. It also charged to 4.15 per cell and max discharge voltage was 3.4v. It had a 9.3 KW nominal pack and based on the range compared to the range people were getting when they were new I estimated the actual capacity at around 7 KWH so that is 75% after 8 years and 27,000 miles. So it seems possible that the Zero battery with proper care could still be close to 80% after 10 years depending on mileage. That is what I'm hoping with my SR/S. In 10 years I'll be 80 yo and need to get a trike anyway, ha ha

Back to the subject. It appears from enaefs data that at the higher charge rate the time from when the SOC read 100% till the charge ended was 27 minutes but at the lower rate at home was only 14 minutes. When I charge at 5.8 KW it is about 10 minutes so it looks like the SOC while charging is less accurate with higher charge rates. So it would be more of a concern for him than me. Do you suppose the bike just shows 100% SOC while charging when the voltage first reaches 116.4? That is how it has always appeared to me but I have no way to check the actual voltage. That would be a normal CC/CV charge. That would mean that it is more accurate when charging at lower rates and less accurate at higher rates.

[enaef]

Thanks a lot Morgan and DonTom for your explanations.

Morgan, you wrote that the basic Farasis cell characteristics (without capping) are 32Ah cells.

When you use the term 'cell' here, I guess you actually meant 32Ah 'short brick' (a term you used later in the post), consisting of 28 smaller cells?

Do I understand correctly, that the battery consists of 4 short bricks, each one with 28 cells. In total therefore 112 cells?

Any idea on which ground Zero gives a nominal capacity of 12.6 kWh in their information?

[MVetter]

Thanks a lot Morgan and DonTom for your explanations.

Morgan, you wrote that the basic Farasis cell characteristics (without capping) are 32Ah cells.

When you use the term 'cell' here, I guess you actually meant 32Ah 'short brick' (a term you used later in the post), consisting of 28 smaller cells?

Do I understand correctly, that the battery consists of 4 short bricks, each one with 28 cells. In total therefore 112 cells?

Any idea on which ground Zero gives a nominal capacity of 12.6 kWh in their information?

Each cell is 32Ah. When you series cells together the voltage goes up but the Ah capacity remains the same. A single cell has a nominal voltage of 3.65vdc with a 32Ah capacity. 3.65 x 32 = 116.8Wh

If you had two cells and ran them together in parallel it would be a pack that is 3.65vdc with a 64Ah capacity. 3.65 x 64 = 233.6Wh

If you had two cells and ran them together IN SERIES it would be a pack that is 7.3vdc with a 32Ah capacity. 7.3 x 32 = 233.6Wh. The exact same amount of energy.

Therefore each pack of 28 cells in series gives you a nominal voltage of 102.2vdc with a capacity of 32Ah. The capacity number doesn't change until you start adding parallel packs. As to the answer of why Zero's numbers are listed the way they are, here's some light reading.

[enaef]

Thanks, Morgan !!! 

So much when a nurse starts thinking about EV-Batteries ... 

[electrictwowheeler]

enaef
Now that we know the actual usable capacity is 11.6 KWH if we add up the bits from when the dash indicates 100% SOC to the charger shutdown I get 1.41 KWH. Knowing that you actually must put in a little more power to charge the battery than you can get out if we assume a charge efficiency of 90% that would be 1.41X0.9=1.27. If we subtract that from the actual KWH of 11.6 we get 11.6-1.27=10.33. That would be the actual capacity in KWH when the indicated SOC reads 100% according to your data. To make that a percentage we figure 10.33 divided by 11.6 and come up with .89 or 89% so your data is showing 88.8% at that point. Pretty close!

I did the same calculation for my SR/S with 6K charger. It ends the charge 6 minutes after the indicated SOC reaches 100% and adds approximately 0.3 KWH in that last 6 minutes so the actual available capacity would be 97%. So if I unplug at an indicated 100% SOC I am 3% short of the full available capacity but you would be 11% short. Certainly something to consider when making long runs without intermediate charge points available.

[MVetter]

At some point you need to factor in cell balancing which is often done by burning off excess juice with resistance. If you were fairly out of balance and you let it do a full charge you may show some extra power consumed in the balancing process.

[electrictwowheeler]

That is true, balancing can use a little power but if everything is working right the cells will need very little balancing. I've run my Vectrix on Chevy Volt cells for 4,000 miles without a BMS or any kind of cell balancing at all, just checking the voltage once in a while and they are still balanced. We don't need much accuracy to get a rough idea of how accurate the displayed SOC is while charging. If we were doing a scientific test in a lab we would certainly have to factor that in. If we were just unplugging the bike at an SOC below where balancing takes place then we could disregard it.
I had another thought though. Rather than trying to figure out the relationship between indicated and actual SOC we could set the charge target to the SOC we need and just let the bike do the math for us.(Yes I am lazy) I'm pretty sure the charge goes through the constant voltage stage when you do that so it would be accurate. I don't know that there is any balancing happening when we charge to an SOC less than 100%. Anyone know ? The Constant Voltage stage is not really a balancing stage as such, even though that is when the balancing might be happening. Even with no balancers at all the charger will still have to taper down the power so that the cell voltages don't go above the max charge voltage. If you cut off the charge at 116.4v the pack will not be charged fully. If you just keep pumping in the amps you will ruin your battery.

[Richard230]

I have mentioned this before, but when I watch my Kill A Watt meter, after my 2018 Zero S with PT reaches 100% SOC, the charger is sucking up just under 13 amps from my 120V wall outlet. Then it will shut down without any tapering and with no indication of balancing the cells. When I check cell balance with the Zero app, they are all balanced at around 2 or 3 mV at 100% SOC.  So I guess the cells somehow become balanced while being bulk charged. I might also add that when the charger shuts off voltage shows as being 115V on the Zero app.

[DonTom]

Anyone know ?

I read somewhere that balancing usually starts at around 97% SOC and ends when it is done charging.  I am not sure if that was for Zero or something else, but I assume it is usually the same 97%.


-Don-  Auburn, CA

[Crissa]

In an earlier firmware, it was observed that one of the reasons that target mode in the Gen 3 bikes was going long was because it went into balancing mode as it approached the target.

-Crissa

[electrictwowheeler]

97 % seems reasonable because at least on level 2 charging that is about the time when the charge starts to taper so that would be when the voltage reaches its max.
I watched my bike finish charging to 100% today on 120v and like Richard says it did not taper off. Well maybe a tiny bit from 13.4 amps to 13 amps AC from my WattsUp meter but essentially flat. The KW reading on the dash went from 1.3KW to 1.2KW. I did notice that the charge ended well after 100% SOC was reached. I didn't time it but would guess 20 minutes. I don't think there would be any actual indication of when cell balancing starts. On level 2 charging the amps on the dash goes from like 55 to 16 at which time the charger shuts off. Maybe 13 amps on 120v is so low that no tapering is needed.
If the cells balanced at target SOCs of less than 100% that would mean that for each different SOC the balancing would have to start at a different voltage. The choices are every 5 percentage points starting with 5 and going to 100 so I think that is 19 different settings. I don't know that the balancing circuitry is that sophisticated but it could be. The next time I have occasion to speak with a tech rep I'll try to remember to ask .

[Auriga]

FST bikes do taper, but not really if you're charging at 1.3kW. Charging at 3, 6, or 12kW should make it more obvious.

As I understand it, it tapers based on battery temp and pack/cell voltage. The BMS constantly sets a max input current, and the chargers respect it. Charging at higher powers should taper earlier, and if the temp is higher it'll taper harder. 

[Mooseman]

FST bikes do taper, but not really if you're charging at 1.3kW. Chargint at 3, 6, or 12kW should make it more obvious.

^ That. I can see the effect when I charge at 6 kW. It starts somehwere north of 95%. Bikes with 12 kW charging capability probably start to taper earlier.

[enaef]

I can confirm, that my SR/F tapers towards reaching the charging goal.
My dealer confirmed it is cell balancing. I guess he got the answer from Zero.

At the moment my SR/F anyway also has a separate problem with showing the correct SoC when I set a target.
Just did it a few minutes ago: Goal set to 75%, after automatically finishing the charge  (including balancing) SoC shows 95%. Tomorrow it will show 76 or 75% according to my experience the last times ....

So, at the moment my confindence in the indicated SoC is not that good ...
- Magic Charging
- Seemingly overshooting charging goals (which in the end probably is not, but it seems)
- Incorrect indicated SoC (too high) while charging


May be, second and third problems are related. Or all three are.

The dealer asked me to show up in order to download 'things' from the bike ...
This will probably happen at Friday.

I'm happy with how the bike runs. I'm not so happy about the things mentioned above and about the App however ...
At least: propper running of the bike counts most, ofcourse. But there is room for improvement for FW and App ...

[electrictwowheeler]

Interesting. I usually set the charge target to 80% and charge overnight at my shop which is a couple of miles from my home so I never see it just after it has shut off. The next day it's 80 or 81%. I'll try to do it while I can watch. Big difference from 75% to 95%! What happens if you ride the bike right after it shuts off reading 95%. Would the SOC drop quickly back to where it is supposed to be at 75%?