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Author Topic: Overestimate Battery Capacity  (Read 1245 times)

Doctorbass

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Overestimate Battery Capacity
« on: July 31, 2013, 09:04:56 PM »

Well This might not be the case of everyone but from now i had two different Zero and ther eis a common fact with both: The rated Battery Energy and REAL measured energy is very different!

Usually people will use the 11 bar gauge to have an idea of their "fuel" left, but when it come with more precision instrument like the install of the great Cycle Analyst EV monitoring device, you get more details abot the battery energy.

DS2011
I had a brand new DS 2011 last year ( in 2012) and when i have installed the cycle Analyst with Fluke calibrated shunt to measure the capacity and to measure the voltage of teh battery, i discovered that the battery was giving me only about 3000Wh or 60Ah before the battery cut . The rated energy of that battery is 3.9kWh ( 3900Wh or 70Ah) wich is a HUGE difference!!

That's 23% less energy !!

S 2012
When I had a brand new S 2012 FZ9 recently  and when i have also installed the cycle Analyst with Fluke calibrated shunt to measure the capacity and to measure the voltage of teh battery, i discovered that the battery was giving me only about 6600Wh or 95Ah before the battery cut. The rated energy of that battery is 7.9kWh ( 7900Wh or 120Ah) wich is a HUGE difference too!!

That's 17% less energy !!

I had installed a cell bank voltage monitoring device i installed made with multiple RC gadget like the Celllog8.

The 2011 and 2012 battery have cut when the cells average voltage was  about 3.3V (The BMS cut when one or more cells reach as low as 3.0V wich is the minimum  allowable, but between 3.3V and 3.0V there is very low capacity left. i had probably cells between  3.3-3.4V to  3.0V.

The 2012 battery have 2700km on it


IMAGINARY BATTERY ENERGY to RATED ENERGY to REAL ENERGY

So my conclusion is that the what is called ZF9 should be called ZF6.6 or .. at least ZF7.9 wich is the rated cenergy.

I know that zero have two way to call the battery energy. One is to accomodate for the rebate $$$ that depend on the battery capacity of the vehicule so to maximize their chance to have customers Zero to be  elligible to these rebate they simply used the Max voltage ( battery full) x capacity to get the Wh ( energy) .

The second way is :
The real practice is to use the NOMINAL voltage of the battery x Capacity to get the energy.


Some theory:

2011 DS
The cells maximal voltage of the 2011 is 4.20 ( according to EMOLI IMR26700 spec)
The cells Nominal  voltage of the 2011 is 3.8 ( according to EMOLI IMR26700 spec)

The "imaginary"energy(4.4kWh) of the 2011 DS battery is 4.20 x 14 x 70Ah = 4.116 kWh
The RATED energy (3.9kWh) of the 2011 DS battery is 3.8 x 14 x 70Ah = 3.724 kWh
The REAL masured energy (3.0kWh) of the 2011 DS battery is 3.7 x 14 x 59Ah = 3.056 kWh


2012 ZF9
The cells maximal voltage of the 2012 ZF9 is 4.15
The cells Nominal  voltage of the 2012 ZF9  is 3.7

The "imaginary"energy(9.0kWh) of the 2012 FZ9 battery is 4.20 x 18 x 120Ah = 9.072 kWh
The RATED energy (7.9kWh) of the 2012 FZ9 battery is 3.7 x 18 x 120Ah = 7.992 kWh
The REAL masured energy (3.0kWh) of the 2011 DS battery is 3.7 x 14 x 59Ah = 6.6 kWh




SUMMARY:

There is a difference between the what i call "Imaginary" energy and RATED energy of :
9.5% for the 2011 DS
12% for the 2012 ZF9

There is a difference between the RATED energy and REAL energy of :
18% for the 2011 DS
17.5% for the 2012 ZF9


I dont think it could be due to the C rate of use vs capacity drift because the average  C rate the 2012 and 2011 are used is about 0.5 to 1C wich would not derate the nominal capacity of the cells alot...



Just... curious....

Doc







« Last Edit: July 31, 2013, 09:09:23 PM by Doctorbass »
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protomech

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Re: Overestimate Battery Capacity
« Reply #1 on: July 31, 2013, 09:44:05 PM »

So my conclusion is that the what is called ZF9 should be called ZF6.6 or .. at least ZF7.9 wich is the rated cenergy.

I know that zero have two way to call the battery energy. One is to accomodate for the rebate $$$ that depend on the battery capacity of the vehicule so to maximize their chance to have customers Zero to be  elligible to these rebate they simply used the Max voltage ( battery full) x capacity to get the Wh ( energy) .

I agree 100% with your conclusions, Doc.

None of the US rebates depend upon the capacity of the battery. I don't think they use the maximum rating for this purpose .. I think it's partly a historical artifact (Zero has always rated their batteries with max capacity) and partly what they view as a "good enough" metric. As you explain above, even the nominal capacity rating is not reached with a "full" discharge of the battery.

Partly the discrepancy can be explained by not allowing the battery to fully charge or discharge. Zero sets a lower cutoff voltage a fair bit above EIG's recommended cutoff voltage, though there's not much energy available below that point.

Partly it appears to be degradation of the battery. See attached below the median energy used to charge my bike overnight, per bar. A rough guess shows about 20% energy less used to charge each bar; assuming conditions are roughly similar, this means that the bars represent roughly 20% less energy than at purchase.

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Doctorbass

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Re: Overestimate Battery Capacity
« Reply #2 on: July 31, 2013, 10:12:05 PM »

Here in Canada there is a rebate that a gouvernment program allow future EV buyer to have.

There is a 5000$ rebate for any 100% electric vehicule with 4kWh battery or more!!.. but they added recently in the requirement that the vehicule must be 4 wheels  ::) >:(  DAMN !!!!

Curiously these rebate are to promote the efficient green transportation!... they appear to not understand that a 300 pounds motorcycle that consume about 60Wh/km is MORE efficient and GREEN than a 4 wheels car with 250Wh/km! ::)

That's why i tought that these uncommon battery energy calculation could be used since in canada the minimum was 4kWh and that the 2011 zero had 3.9kWh nominal and 4.4 listed..... These rebate started to be availlable in 2011...

I see you are using the bar to quantify the energy use. are you using a killa watt meter and measure the input power in the charger? and make some efficiency calculation to extrapole the consumed energy bu the zero?

btw I remember that on my DS 2011, i was able to select CAPACITY or VOLTAGE based fuel gauge bar meter in the option. I guess that the bar was correponding to a programmed calibration graph with voltage to bar level, and that the capacity based bar are a coulomb count from the current sensor in the battery.


For my measured data i have used a precision calibrated 600A shut directly connected before the controller B-

But as well in these conditions the shunt dont take account of the DC-Dc converter consumption that take maybe 1-2% of the power of the controller for the light and Mbb and contactor etc..

But this is a very small effect that can not justify the 10-20% difference in battery energy

For the 2012, there might be something that affect a little bit the measured value. THE REGEN ! 

My Ah count goes in reverse when regen is activated. but with the current firmware version i have with my cycle anlayst it dont display the forward Ah (regen Ah)

So for my 2012, the 95Ah i have measured might be a bit off since the regen Ah are substracted form the real Ah draw value.  I will update the firmware and will mesure that again. My guess is that i could measure maybe 100-105Ah if not taking account of the regen Ah substracted.

 

Doc
« Last Edit: July 31, 2013, 10:17:54 PM by Doctorbass »
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protomech

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Re: Overestimate Battery Capacity
« Reply #3 on: July 31, 2013, 11:53:07 PM »

Doc,

The energy listed is AC energy consumed to charge the bike divided by the approximate number of bars used.

For example, if I discharge approximately 4.8 bars and consume 4 kWh to recharge, then I say the bike consumed 0.83 kWh/bar.

There are some problems with this metric: the first bar seems to represent a smaller amount of energy, and of course it's also measuring the efficiency of the charging system which could change over time. Also, my measurements of the bars consumed are not terribly precise.

However, by using a sliding window - the red line is the 9 day median consumption - it should be enough to make some small observations.
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Doctorbass

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Re: Overestimate Battery Capacity
« Reply #4 on: August 01, 2013, 12:25:02 AM »

Doc,

The energy listed is AC energy consumed to charge the bike divided by the approximate number of bars used.

For example, if I discharge approximately 4.8 bars and consume 4 kWh to recharge, then I say the bike consumed 0.83 kWh/bar.

There are some problems with this metric: the first bar seems to represent a smaller amount of energy, and of course it's also measuring the efficiency of the charging system which could change over time. Also, my measurements of the bars consumed are not terribly precise.

However, by using a sliding window - the red line is the 9 day median consumption - it should be enough to make some small observations.

Ok i see.

On my side i use the true motorcycle energy consumption at the battery, not at the AC cahrging system. I did a couples of run with my ZF9 and  i can now state that:


at 70kmh average i get 11km per bar
at 90km/h constant speed i get 9.5km per bar
at 110-120km/h speed i get  6km per bar

On my zero, the first top bar range is equal to the rest 8 next bars below and all these 9 bar are pretty equal, but the two last flashing bar seem to be only like 10km total. but i still not have tested precisely them.

I would really love to know whre i sthe calibration fo rthese bar!! i already know how to calibrate the speed on these KOSO display gauge that zero use, but fo rthe fuel bar it seem somewhere else. I did not see anything in the MBB settings,  maybe thru another level of security in the Can Bus.

Doc

Doc
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BSDThw

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Re: Overestimate Battery Capacity
« Reply #5 on: August 04, 2013, 06:34:22 PM »

Hi Doc,

I personally just use the Bars and my experience of the last 10000km riding it, because I have to know if I can reach the next charging point or not.

Reducing the air drag / speed will help you much in this situation.

What I think most people don't realize is the tolerance of the tachometer, mine is 52-53 km/h at real 50km/h so if I ride 105 km is is only 100km real, so there is most 5-10% wrong calculation at a lot of other vehicles :'(

I really like your effort to make correct calculation and data logging 8)

I know you are very in the technical details but I really like my 2012 DS having a XU front fender and the summer screen I could really extend my drive distance I don't care so much of the figures I care what comes out and how I can use it. This Fr+Sa I did a 240km ride with 5 colleagues riding there ICE bikes. Fist stop was at my Dealer 80km away and all of them test rode the 2013 S.

All have been totally impressed and we talked a lot about it when having your beers at night ;D 
   
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WindRider

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Re: Overestimate Battery Capacity
« Reply #6 on: August 05, 2013, 12:39:44 AM »

Doc,

I think that you discovered a couple of universal truths here:

1.   Marketing departments always inflate the numbers. 

2.   Government programs to promote some idea generally fail for lack of understanding. 

I would also add the Zero engineers seem to be very protective of the battery pack and this the BMS is conservative in it's battery protection logic.   I think that this is a good thing as I am hoping for long battery life.   
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Lipo423

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Re: Overestimate Battery Capacity
« Reply #7 on: August 07, 2013, 03:31:05 AM »

Agreed with all the above.
IMHO the main reason (besides marketing  ;D) is to extend/guarantee battery charging cycles...as you all know by now, there are a few elements which would challenge battery life-span -or cycles, being a couple of them:
- Reaching max capacity (cell voltage)
- Reaching lowest capacity (cell voltage)
When you are "dancing" in the middle -leaving aside other further factors- your battery pack will live longer
Obviously, our Zero friends want to make sure the battery pack (in the event someone in the forum is able to charge/discharge 100% the battery twice a day * 365) will last longer than the warranty period or the advertised committed Km/life
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Doctorbass

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Re: Overestimate Battery Capacity
« Reply #8 on: August 07, 2013, 07:21:51 AM »

event someone in the forum is able to charge/discharge 100% the battery twice a day * 365

Hey, that's funny :)  charge and dishcarge twice a day a ZF9 mean 8h + 8h +about 3h ride = 19h of Zero time in a 24h

it's like you wakeup, jump on it, ride, charge, ride, charge, sleep 5h, redo.... for 2 years     8) ;)

that would certainly be a Zero Maniac !!! lol

Doc
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BSDThw

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Re: Overestimate Battery Capacity
« Reply #9 on: August 07, 2013, 09:41:07 PM »

Hi Doc I would count you as a person to do this ;D

But I know some people use the Zero for commuting ~100km charge at work 8-9h and back home 100km and over knight charging. It is not too far away of this.

And when your fast charger works you will do 200-300km a day 8)
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grindz145

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Re: Overestimate Battery Capacity
« Reply #10 on: August 09, 2013, 03:25:48 AM »

Terry Hershner is actually pretty close to doing that... He rides like crazy.  40k in a year and a half!

CliC

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Re: Re: Overestimate Battery Capacity
« Reply #11 on: August 09, 2013, 09:07:24 PM »

Quote from: Doctorbass
Hey, that's funny :)  charge and dishcarge twice a day a ZF9 mean 8h + 8h +about 3h ride = 19h of Zero time in a 24h

it's like you wakeup, jump on it, ride, charge, ride, charge, sleep 5h, redo.... for 2 years     8) ;)

that would certainly be a Zero Maniac !!! lol

Doc

His name is Terry :)
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