Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[benswing]

Here is some data I collected over 650mi of riding a ZF9 in the NYC metro area during the fall of 2012.  As we ride the motorcycles more, the performance characteristics are getting clearer and I welcome data from anyone else who has measured your electricity usage.

Most of my riding is done 50/50 highway/city between Montclair, NJ and NYC in Sport mode for a distance of 40-50miles.  Temps this fall have been mostly 40-50's Fahrenheit. 

 - 8.27mi/kWh resulting in 2.0556 cents/mile cost to ride (electricity here is $0.17/kWh).

 - $6.94 - cost per month of electricity (about 340 miles/month)

 - 74.41 miles is the overall predicted average range.

 - 6.6 miles/bar - A "bar" in this case indicates one of the 11 indicator bars for battery capacity

 - Temperature effect on range seems to be significant below 40 degrees.
Above 40 degrees, average range is about 75 miles for (40's, 50's, 60's, 70's, 80's)
Riding in 30 degree weather makes range closer to 65mi.


I'm a physics teacher, therefore I measure things.  Here is some insight into my data collection and calculations.

 - I measure the electricity being drawn at the outlet using an Enerati energy monitor (www.enerati.com).
 - Predicted range is calculated based on the proportion of electricity needed to recharge after a ride compared to 9kWh of ideal battery capacity.  (This is a prediction and there are uncertainties inherent in extrapolating data, but I am pretty confident in the results.)
 - There are few data points (between 2-6) for temperature data, but it's a start.
 - My total riding distance is 2,700mi in 8 months.

[protomech]

Keep in mind the 9 kWh "maximum capacity" specification is derived by calculating the peak-of-charge 4.2 volts per cell * 18 cell banks in series * 120 Ah (6 cells in parallel per bank) = 9072 Wh. This is at best a quick-and-dirty capacity specification. Real world capacity will be significantly lower.

Take a look at the rate capability graph at the bottom left of this image:
http://www.eigbattery.com/eng/product/3.jpg

As the battery is depleted voltage drops, though it isn't exactly linear for any significant length of time. EIG uses 3.65V as nominal voltage for the pack, which is what Zero uses to calculate their nominal capacity @ 3.65V * 18 * 120Ah = 7884 Wh.

It's, uh, been a bit since my last calculus course, but we can do a bit better with numerical integration. I get the following with some coarse sampling:

Under city riding and light discharge conditions - say 0.5C for the ZF9 bike - there's around 7.8 kWh of available capacity. The cell averages 3.70V from 10% to 90% DOD.

Under suburban riding conditions and moderate discharge rates - say 1C for the ZF9 bike - there's around 7.5 kWh of available capacity. The cell averages 3.65V from 10% to 90% DOD.

Under freeway operation or aggressive riding - say 2C for the ZF9 bike - there's as little as 7.2 kWh of available capacity. The cell averages 3.58V from 10% to 90% DOD.

The voltage drop under load affects the available capacity in two ways: you get less energy from each Ah of battery, and you hit the lower voltage cutoff more quickly (before 100% DOD). I believe Zero uses 3.2V per cell as a cutoff voltage, which means with a balanced pack you should see the bike disconnect the battery at 93% (2C) and 96% (1C) DOD respectively.

Note that the battery will have a higher internal resistance as the temperature drops, dropping the voltage output and causing it to hit the lower voltage cutoff more quickly. This is slightly offset by the motor and motor controller being slightly more efficient in cooler temperatures.

[benswing]

Thanks for the insight, protomech.

I just recharged after a 114mi trip and the electricity monitor reported that it took 9.24kWh of electricity.  I know there are some inefficiencies in charging and I am measuring the electricity used to charge the battery, not the actual charge used by the battery. 

Also, it would be great to get a list of how many miles/bar one can ride in order to communicate range differences more effectively.  Here are some stats I recall from the long ride yesterday:

9mi/bar - 40mi/hr
10mi/bar - 35mi/hr
11mi/bar - 30mi/hr

I don't expect the mi/bar to increase in a linear fashion due to wind resistance, and these measurements came on rolling hills so there is some variability.  However, after some time I found myself accurately predicting how many miles each bar would last at different speeds.

[protomech]

Total charging efficiency seems to be around 85% efficiency for me. Balancing will use a little more power.

A full charge after using 11.0 bars takes 8.83 kWh for me. There's a small amount of charge left below 0 bars, equivalent to 1-1.5 bars. Use at your own caution of course : )

This is what I recorded on June 4th, temps in the 90s iirc:
6.5 mi/bar - 50 mi/hr
7.5 mi/bar - 45 mi/hr
8.1 mi/bar - 40 mi/hr

Note that I am not running a windscreen, and I'm around 200 pounds fully geared.

Should replicate that test in the winter at various temps.

See scatter plot of charge energy vs bars consumed.

Linear regression on my charging data on 110V AC shows 0.102 Wh + 0.752 kWh/bar. Each bar represents approximately 9.5 Ah on the ZF9 bike, or 632 Wh at 3.7V nominal.

So my charging efficiency is around 84%, including balancing.

[ColoPaul]

Linear regression on my charging data on 110V AC shows 0.102 Wh + 0.752 kWh/bar.

Interesting data protomech, thanks!

Over the last 3 months my ZF6 BMS had been misconfigured into thinking it's a ZF9 (Long story).   After taking alot of data, I observed almost exactly what you have:  0.74 kWh/bar (to charge) and for my ZF6 (before it got messed up and now that it's corrected) 0.49 kWh/bar (to charge).

Because of the mis-configuration, I was able to observe something else:   I would start from a full charge, and run for a period of time, watching the bars erroneously drop at the ZF9 rate (so I would lose fewer bars than I should have) then I would stop, turn the bike off/on and 'bang', suddenly the bars would were they should be for the ZF6.   

I think that the way the BMS decides to display bars is:  (A) if the bike is 'off' and there's little power draw, it measures the voltage and when powered on sets the bars based on that voltage.   (B) while running (with variable power draw which makes voltage unusable) it just measures current and drops bars accordingly.

Now that it's winter and I'm riding in 25-40 degF temps; I see the following:  If I ride 10 miles on a set route, it takes 1 kWh to charge, and I lose 2 bars.  If I ride the same exact route, but stop at the 2 mile mark and power cycle, it still takes 1 kWh to charge, but I lose 3 bars.  A bar disappears during the power cycle.   I am assuming this is because it's cold and the battery loses voltage faster than it does at summer temps;  and when I power cycle at the 2 mile mark, the BMS reads the voltage and drops the bar (prematurely).

[Joseph]

Thanks, PROTOMECH and BENSWING for the most valuable informations you gave.

kind regards form Germany, Munich
Joseph