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Author Topic: Can someone check my math?  (Read 1659 times)

lolachampcar

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Can someone check my math?
« on: January 16, 2015, 01:25:00 AM »

I was driving my 2015 SR today with range on one display and W Hr / mile on the other.  I was averaging around 100 W Hr / mile and noticed my range mirrored my % remaining capacity.

If the display are accurate, there seems to be 10 KW Hr of useful battery in Zero's 12.1 KW Hr battery.  Does this sound consistent with other's experience?  Does Zero really charge to less than 100% and discharge to way more than zero for safety?  Giving up 2.1 KW Hr of a 12. KW Hr battery sure seems like a lot of insurance.
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frodus

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Re: Can someone check my math?
« Reply #1 on: January 16, 2015, 02:08:07 AM »

Your math sounds right, but you have to realize that you don't get all of the energy out of the battery at anything higher than 1C, but it should be pretty close. i.e. the higher the current draw, the less total energy you get out). So you have a 12.1kWh pack, which can discharge 12.1kW for one hour and you should see most of that energy back out (you'll never see all of the energy into the battery come back out).

So you were averaging 100Wh/mi, which would be about 10,000W for one hour, or 10kWh discharged, so you're right there. The issue is, that the kW usage of the motor and the rest of the Aux components is never constant, the load changes. Also, I'm not sure that the onboard current measurement is on the battery side (versus what the Controller is reporting), so its hard to know how much goes in, versus how much came out, as all you have is a SOC meter. The Zero and Brammo estimate the SOC based on a long string of variables like Temperature, current draw, voltage of the battery, battery internal resistance, etc to get that %.

I bet if you got an Wh meter and actually calculated the energy in, versus the energy out of the batteries, you'd get close to 12.1kWh.
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Travis

Doug S

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Re: Can someone check my math?
« Reply #2 on: January 16, 2015, 02:35:59 AM »

My understanding is that the battery pack on my 2014 SR (no PT), rated at 11.4kWh, really provides no more than 10kWh real-world. It makes sense: There are four 25Ah cells in parallel, with however many in series, so that means the pack as a whole is rated for 100Ah of capacity. The cell voltage, which is the sum of however many cells it has in series (I want to say 28 but I'm not sure I remember correctly), I do remember as being 103V nominal. When the charger finishes the charge cycle, the cell voltage peaks a bit to 114V, which when multiplied by the 100Ah capacity, gives the 11.4kWh rating. This is the "salesman's number"; it's the highest number you can reasonably claim. But in reality, the battery voltage quickly drops from it's peaked value down to near the nominal value, which it stays near for most of the discharge cycle, drooping a bit more as the battery ends its discharge cycle. So a much more realistic number for the "11.4kWh" battery is 10kWh, which all my reading says is pretty close to the actual value. Zero can't use that number, however, because nobody else rates their battery packs that way -- one guys overstates their numbers, then everybody else has to do it or look like they're underperforming.

The solar panel people have the same problem, but even worse. A solar panel may provide 3.5A into a dead short, and 18V open circuit, so the sales people multiply those two numbers together and call it a "60W" panel. But the reality is it won't provide anywhere near 60W in real life, no matter how bright the sun is, because it can't provide 3.5A and 18V AT THE SAME TIME. In reality, it's more like a 40W panel, 45 at the most. But once the first person did it that way, everybody has to do it that way, or the customers would just buy the "higher-power" panel without digging into the real situation. Specsmanship, pure and simple, but everybody has to play the same game.
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ultrarnr

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Re: Can someone check my math?
« Reply #3 on: January 16, 2015, 03:52:28 AM »

I have a 2014 SR with Power Tank. The max capacity I see is 13.01 kw. But useable power is only around 10kw. Again, like you did multiply wh/mile times the mileage. It is also possible that Zero is allowing the 2015's to use more of the available battery capacity. We could potentially have similar max range despite you not having the PT.
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Richard230

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Re: Can someone check my math?
« Reply #4 on: January 16, 2015, 04:31:02 AM »

I have a 2014 SR with Power Tank. The max capacity I see is 13.01 kw. But useable power is only around 10kw. Again, like you did multiply wh/mile times the mileage. It is also possible that Zero is allowing the 2015's to use more of the available battery capacity. We could potentially have similar max range despite you not having the PT.

My 2014 Zero S with Power Tank shows 13.34 kWh when fully charged.  The power meter seems to be very accurate.  I once ran it down to Absolute Zero and (after 15 hours of charging) it returned to 13.34 kWh on the Zero app.  I might add that when exhausted the various battery modules were showing something like 170 mV difference in balance, but when fully charged all of the modules are balanced to within 2 mV.  Again, per the Zero app.  That seems like pretty good cell performance to me.   :)

Any differences in battery capacity might be the result of the computer programming used to determine the battery capacity and power usage.
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Richard's motorcycle collection:  2018 16.6 kWh Zero S, 2009 BMW F650GS, 2020 KTM 390 Duke, 2002 Yamaha FZ1 (FZS1000N) and a 1978 Honda Kick 'N Go Senior.

KrazyEd

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Re: Can someone check my math?
« Reply #5 on: January 16, 2015, 11:44:57 AM »

We should be happy with this amount. Chevrolet only let me access 10K of my 16K pack on my 2012 Volt.
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Burton

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Re: Can someone check my math?
« Reply #6 on: January 16, 2015, 07:00:38 PM »

About 15 minutes before your trip unplug the bike, wait for it to "really" turn off, then plug it back in. If I do this I see a temporary increase in my total kW available. If I let the bike sit in ideal conditions I get 10.556, with this trick I get 10.672 if I recall. Not too much more but that is at least a mile for me at highway speeds. This with the 11.4 pack.

Also keep in mind when you cycle the battery the pack size should go up some with time. On a side note I have a 2013 and don't have the w/hour display yet (since I haven't installed a cycle meter yet) but I do see the kW left after a trip and can figure out my something closer to my "real" w/mile.
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trikester

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Re: Can someone check my math?
« Reply #7 on: January 16, 2015, 10:50:58 PM »

On a 2013 you can see the wh/mi if you use the Bluetooth connection to a mobile device.

I have also noticed the little extra charge i get if I unplug for a bit and then re-connect until it shuts off the charge. I use this trick if I know that I'm going to be pushing the mileage on the ride I'm about to start. Even if it only gains a mile or so, that is better than pushing that last mile.  :'(

Trikester
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Richard230

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Re: Can someone check my math?
« Reply #8 on: January 17, 2015, 04:06:31 AM »

On a 2013 you can see the wh/mi if you use the Bluetooth connection to a mobile device.

I have also noticed the little extra charge i get if I unplug for a bit and then re-connect until it shuts off the charge. I use this trick if I know that I'm going to be pushing the mileage on the ride I'm about to start. Even if it only gains a mile or so, that is better than pushing that last mile.  :'(

Trikester

That trick also worked on my 2012 S.
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Richard's motorcycle collection:  2018 16.6 kWh Zero S, 2009 BMW F650GS, 2020 KTM 390 Duke, 2002 Yamaha FZ1 (FZS1000N) and a 1978 Honda Kick 'N Go Senior.

Burton

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Re: Can someone check my math?
« Reply #9 on: January 17, 2015, 09:42:40 PM »

On a 2013 you can see the wh/mi if you use the Bluetooth connection to a mobile device.

You can see this real time on the drive screen with the S/DS? I see the average watt/hour on other screens but it is hardly accurate when I compare it to the kW battery pack numbers before / after a ride vs real distance (since my bike hasn't been set for the high speed gearing yet and maintains the ~500/3000 setting in DVT ) the 500 might be another number but I don't have DVT open to check.

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KrazyEd

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Re: Can someone check my math?
« Reply #10 on: January 18, 2015, 01:11:07 PM »

I noticed this on my 2013 FX 5.7. It seems to charge to 95% ( as shown by the app ).
If I unplug it ( or, turn the key on, then, off ) it goes to 97%, then, to 100% if done
a second or third time. The last 5% as noticed by others offers only a fraction more
range, so, not something I do unless the bike hasn't been ridden in a while.
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lolachampcar

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Re: Can someone check my math?
« Reply #11 on: January 18, 2015, 07:15:59 PM »

So it seems like Zero's 12.1 KW-hr battery has a useful capacity of 10 KW-hr.  I suspect this was needed to meet the 5 year warranty.
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aaronzeromoto

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Re: Can someone check my math?
« Reply #12 on: January 19, 2015, 05:30:12 AM »

For some additional details on this topic, check out our Specs page for the motorcycles on our website.  You'll find specifications for max capacity and nominal capacity.  If you hover over the "?" on the left, we provide definitions explaining the difference.

Since most of the posts were about the Zero SR, you'll find those specs for the 2015 here:

http://www.zeromotorcycles.com/zero-s/specs.php?model=sr

Regards,
aaronzeromoto
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Zero Motorcycles
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2018 Zero DSR + 6kW Charge Tank
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2007 Yamaha V Star

protomech

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Re: Can someone check my math?
« Reply #13 on: January 21, 2015, 08:32:38 PM »

It's relatively easy to measure energy in and energy out as it's being used. It's very hard to accurately predict available energy with any kind of precision.

I suspect that any SOC differences on things like restarts are due simply to slightly different inputs feeding the estimation logic. Cell module temperatures and voltage drift.
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