Now, this course doesn't have any 5% slopes in it (except the hill to our house, which was one of the corners we shaved), so it was interesting to compare the energy use of trips 3 and 4. After each trip I put the car on the charger and let it sit for 24 hours, then looked at the Kill-A-Watt meter.

Trip 3 of 5.1 miles, showed 5.83 KWh on the meter after 23 hr 41 min.

Trip 4 of 9.6 miles, showed 7.90 KWh on the meter after 24 hr 19 min.

In my post on Jan. 9th, I estimated that the chargers and heaters pull about 240W on float charge. I'm going to shade that down because the weather has been warmer, and guess that 225W is probably closer. Let's assume that the batteries reach float stage after 6 hours on trip 3, and after 8 hours on trip 4. Total guesstimates, but let's just follow the line of thought.

That means that after trip 3, the chargers were floating for 17 hr 41 min @ 225W, accounting for 3979 Whr (4.0 KWh), making the total charge only 1.83 KWh. During active charging, the Kill-A-Watt meter shows a power factor of about 0.82, so I figure that means the chargers are about 80% efficient, which means 1.5KWh reached the batteries. Over 5.1 miles, that gives a Wh/mi measurement of 300 Wh/mi. Typical speeds on this trip were in the 20-30 mph range.

After trip 4, the chargers were floating for 16 hr 19 min @ 225W, accounting for 3671Whr or 3.7 KWh. That means the total charge was 4.2 KWh. 3.4KWh actually reached the battery at 80% efficiency. Over 9.6 miles, that gives 350 Wh/mi. This is probably reasonable, considering I "drove the car harder" being out on real city streets (not my little neighborhood streets) and at higher average speeds--typical speeds being more in the 30-40 mph range on trip 4.

Neither of those numbers demonstrate stunning efficiency for this vehicle, but they do seem to be inline with numbers posted by other people for Kelly controllers in similar small cars (look at Brian Blocher's blog about his Honda S2000 EV @ http://s2kev.blogspot.com).

Now the grand projection. The car has six 92 Ah batteries and four 115 Ah batteries (20 hr rating). That means the nominal pack capacity is 12.1 KWh. If the car consumes 350 Wh/mi in city driving, it implies a range of over 30 miles! Whoa. Of course, I would be wise to use a 1-hr rating instead of a 20-hr rating, if I knew it, but I don't. So let's assume that we actually get 60% of the published 20-hr capacity. That means the usable pack capacity is more like 7.3 KWh, and the range is more like 21 miles on city streets. I could believe that pretty readily.

I worked the numbers a couple different ways, making different assumptions for number of hours charging and watts drawn during float, and get similar results varying between 250 Wh/mi on the neighborhood streets and 480 WH/mi on city streets. In all cases, range was between 15 miles and 26 miles, depending where and how I drive. 21 is right in the middle, so gives me something to shoot for. :-)