“All Up” efficiency figures

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!

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

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?

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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

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No waste. Believe me, we've spent more time on far less worthy things. 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.

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.