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Discussion Starter #1
I am trying to measure “All Up” efficiency figures on my recent 180Ah SE Li-Ion pack upgrade and would be interested to find out what other people are currently getting in real life.

I am under the impression I should be getting, in the perfect world, an overall “All Up” efficiency around 74% to 83% (max) - Maybe 90 to 92 % on the charger and maybe 80% on the Li-Ion round trip discharge/charge cycle. Could be my measurement technique but I have used two different power meters on the input of the charger giving pretty much the same poorish result of less than 70% (in the order of 68%)? I use a calibrated Cycle Analyston the EV side and believe it's readings to be fine. The Ah taken from the pack certainly seems to agree with the Cycle Analyst.

I am totally impressed with the new batteries but disappointed in a 65% to 70% efficiency figure.

All the details on this EV are at my website http://www.mightyboyev.com and the current data is here http://www.mightyboyev.com/Li-Ion%20Upgrade%20On%20Road%20Data%20Results%20final%20set%20Dec%204%202010.htm

So what are others achieving for “All Up” efficiency figures? The Elcon charger seems great, happy with the BMS setup and all the cells balanced etc – perfect in all other ways.

I must be overlooking something simple here? Or maybe this is the real world??

Any views appreciated…

Cheers
Bruce
 

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How are you calculating the "all up" efficiency? Edit: found it on your website. I took a random 46.3 mile (77 km) run from my logbook and get 85% approximately. Calculated from assuming an average pack voltage of 115V (36 CALB cells). This run used 75.0Ah according to my TBS ExpertPro gauge, so about 8625Wh or about 186Wh/mile (111.6Wh/km). My EKM meter on the AC input to the charger recorded 10,000.01Wh during recharge after this run, so about 85%. Another run of 57.8 miles at average speed of about 50-55 mph (83-92km/hr) gives 101.9Ah*115V = 11719Wh, or about 203 Wh/mile (122Wh/km). EKM: 12970Wh, so 90%. Average pack voltage estimate should be within +/-2%.

But this is just based on the difference in energy into the charger and pack during charge, and energy out of the pack during discharge, so only effected by power dissipation in the pack during charge/discharge, and charger during charging, correct? So it is some combined efficiency of the charger and cells, and does not include motor/controller it seems to me.

I would expect at best around 80% combined efficiency of motor and controller (0.9*0.9), and I've previously measured my Manzanita charger efficiency at about 94% for a typical range of charge currents, so I would expect about 75% at best overall.

Very clean conversion btw!
 

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One way to estimate overall efficiency would be to datalog motor rpm during a run, estimate motor torque from the motor's torque-speed curve, use these to calculate the motor shaft power at each rpm sample point, multiply that by the sample interval time to get an "average" energy output over each interval, and sum these all up to get total energy output of the motor over the run. Sample time should be like 0.5 sec or so since current and torque are varying rapidly during accel/decel. Then take the ratio of this to the AC power from the wall. Not sure what the magnitude of error would be due to the torque estimate.
 

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Discussion Starter #4
Thanks for that information….

I’m now thinking my trusted Cycle Analyst readings (I used the Ah, w-h and wh/km data from that in my calculations) could be incorrect? All these figures seem low compared to other 700kg or less EV on EVAlbum. It has the correct shunt values and wheel measurements but will put in a new large format version I have and double check in the near future.

Your values are what I would have expected….

Thanks

Bruce
 

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Discussion Starter #5
I think I found my problem…..

In checking the CA against a known Ammeter I found the CA was reading 20 to 25% low – feel a bit stupid here for overlooking this issue! Certainly convinced myself over and over that the CA was 100%. I have now calibrated the “Rsense” value on the CA accordingly. Will do the road tests again soon but feel things will start to make sense now. Worst thing is I think it has always been out of calibration (for the past two years of driving). So my amazing w-h per km figures now looks like everyone else’s and I don’t have the most efficient EV in the world!

Re your other point tomofreno, comparing the energy taken out of the pack with the energy need to replenish the pack for a given distance travelled ….. Would that not be an overall EV efficiency figure on its own? IE the energy needed to accelerate and sustain the vehicle at speed is directly reflected in the w-h value?? What have I missed (maybe again!) ?

Anyway, sorry for wasting time on the forum for something so obvious in the end….

Regards
Bruce
 

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Re your other point tomofreno, comparing the energy taken out of the pack with the energy need to replenish the pack for a given distance travelled ….. Would that not be an overall EV efficiency figure on its own?
Well, when charging the pack, energy/time, or power, goes from the wall outlet to the charger. Most of this goes to the pack as DC power, but some is dissipated in the charger (neglect losses in the lines to/from the charger). Some of this energy is dissipated in the pack due to some internal resistance, and most is stored as charge at some potential. During discharge, charge/time at some potential, or power, leaves the pack and flows through the controller and motor. Some of this power is dissipated in the controller and motor, and most does useful work per time applying torque at some angular velocity to the drive train, the motor shaft power.

Measuring the total energy output from the pack, does not tell you how much of that energy was dissipated in the controller and motor, and how much was useful work. Taking the ratio of shaft power to the power from the wall outlet would include those two efficiencies. I left out the fact that the motor turns the drive train, and the drive train also has losses. These would not be accounted for in the above ratio. You would need the ratio of power delivered to the wheels to the AC power from the wall outlet. I think Bob Brant says drive train efficiency can roughly be approximated at 90%, so I would expect about 65% or less efficiency overall, assuming about 90% motor, 90% controller, 90% drive train, 90-95% charger, and maybe 98% pack efficiencies.

Maybe that isn't what you meant though. Maybe you just want to know how much of the energy that came out of the wall was stored in the batteries and used in operating the vehicle. Your ratio does of course tell you that.

Anyway, sorry for wasting time on the forum for something so obvious in the end
No waste. Believe me, we've spent more time on far less worthy things. :D It was well worth the time spent viewing your website. Very nice job! I think Coulomb mentioned others having problems with Cycle Analyst accuracy some time ago, but I don't recall the details.
 

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Discussion Starter #7
Thanks again,

Yes it was only a question about the efficiency of “how much of the energy that came out of the wall was stored in the batteries and used in operating the vehicle”.

I fully understand the other points raised but only wanted to look at how much better the Li-Ion technology was compared to the old SLA AGMs I had in the vehicle originally. And I am totally impressed with the CALB 180Ah LiFePo4 cells. In my case the 180Ah cells are overkill but I wanted to operate around (or below) the continuous .3C rating given. I still can’t believe the improved performance over the full range…. Highly recommended if you are serious about driving a nice quick urban EV.

Tomofreno any details about your EV or EV project? I would be interested to see what you are doing…. I don’t follow many of the EV forums - this one has been good because it has guys that actually have built and drive them – That’s what going to make it happen one day….. Hopefully.

Regards
Bruce
 

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I absolutely love that Mighty Boy and I'm happy to see you've gone lithium. I couldn't find the new performance figures on you site besides an estimated range of 120 km.

Do you have a known top speed and 0 - 100 km/h time yet?
 

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Discussion Starter #9
Thanks, I will do some updated performance figures this month.

Re Acceleration: I have limited the acceleration for 0 to 60 kph to about 8 secs via the controller. Mainly to allow better range but I seem to have more than needed for my job anyway. The controller is rated for 450 Amps and I have seen it get past 420 Amps (pack side current) so that’s cranked back a bit now. Only 4th gear and reverse are used. Things seem always a compromise in the end....

Re Top Speed: I live in a small city of about 1 million people (Adelaide, South Australia) and am limited in my daily travels to city speeds (50 and 60kph) with a few 80 km zones. This EV is only a 72 volt system so lots of things do suffer - mainly top end performance and top speed. The car is a Japanese ‘K-class' or Kei Jidosha car and only designed for urban transport anyway. The ICE version does well over the 100kmh given enough time and road! As an EV it does the 80 km zones with absolutely no problem and I have had it up to 90 with maybe a bit left. But this thing is fun to drive and keeps up very well in any city traffic – much better now than the standard ICE version.
 

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Yes it was only a question about the efficiency of “how much of the energy that came out of the wall was stored in the batteries and used in operating the vehicle”.
Ahh, ok, I misunderstood. I also am using CALB 180 Ah. I chose that size so I would pull less than 1C at 60 mph (100 kph) and less than 3C during max acceleration (controller max is 540A), sounds like you were even more conservative than that - yours should last "forever"! Sounds like your conversion is a perfect match for your needs.

Tomofreno any details about your EV or EV project?
I have a build thread here on the "All builds and conversions" forum under "SwiftE", but it is long...the car is also on evalbum at http://www.evalbum.com/3060. I've been driving it about 1 year now, very happy with it.
 

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Discussion Starter #11
Thanks for that link(s).... some great information on your EV! Good to read others experiences.

Maybe I should have purchased the TBS E-xpert Pro gauge as well! Picked up a calibrated clip-on ammeter this afternoon from a friend. It’s an ISO-TECH ICM30R clamp meter 300A ac/dc (Dual Hall sensor with 1.0% basic dc/ac current accuracy) – nice little instrument. So will recalibrate my CA “Rsense” value soon and check the main dash amp meter as well. Will put up the results in the next week hopefully…..

Bruce
 

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Maybe I should have purchased the TBS E-xpert Pro gauge as well!
I purchased it from evworks in your country! Now it and a version made for Xantrex are available at several dealers in the U.S. Will be nice to see the difference in energy from the wall between your former lead acid and new Li cells - especially if you get much cold weather. I've not seen a quantitative comparison.
 
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