Wednesday, January 20, 2010

Fourth drive, and charging stats

So, we took the 120V Civic out for its fourth and longest run so far, driving 9.6 miles by going twice around the 5.1 mile course my wife would usually take to work and home. We shaved a few corners here and there, which accounts for the total drive being 9.6 miles instead of 10.2 miles.

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. :-)

Monday, January 18, 2010

Third Drive of 120V System

Well, I don't know why we put it off more than a week, but we finally gave the new & improved 120V Civic a 3rd test drive. Mostly I guess I was afraid something else would go wrong.

But finally, tonight Alisa and I drove a closed 1.7 mile course starting from our house, three times around for a grand total of 5.1 miles, with an elevation change of about 140 feet from the lowest point on the route to the highest. That's 420 feet of rise & 420 feet of fall in 5.1 miles, or an average slope of 3.1%. Of course, most of the uphill occurs in about 0.5 mile of the course, and the rest of the course is level or downhill (it's a closed course!), so actually it is more like an average of 5.3% incline over 1.5 miles and 2.2% decline over the remaining 3.6 miles.

The KDH14500B did pretty well, IMO. Yes, it is dog-slow off the line, but if you have it in first gear and really step into it, it does alright. Not as good as a golf cart off the line, but then it gets up to 20-ish in first gear pretty easily, and subsequently up to 35 mph in 2nd quite easily. Haven't taken it over 40 mph yet.

But coming up the steepest part of the hill, which is from the low point on the course up the one block to our driveway, we couldn't keep it in 2nd gear. The old 72V controller would hold about 18 mph in 2nd gear. But the 14500B really wants you to shift down into first, and then it will also hold about 18 mph up the hill. Now, we did add 300 pounds of batteries and chargers that weren't there before, and it is still a 500A controller. Probably if we'd added 300 pounds into the Civic with the 72V controller, it would have had more problem with the hill then, too.

Afterwards I went around and felt the connections and battery temps and etc., and measured voltages, and everything seemed pretty copacetic. The controller and the motor were both very warm, enough that if they were any warmer at all I would have said they were hot. The starting voltage while still on float charge was 133.0V, and the ending voltage was 127.1V at rest before plugging back in. The six (92Ah) C&D Tech batteries were between 12.60 and 12.65 at the end of the drive, and the four (115Ah) Discover batteries were between 12.90 and 12.94.

And that's my report on drive #3.

Saturday, January 9, 2010

Up and Running again!

The story with the Kelly KDH14500B controller ended about 400 feet after it started. I took my first test drive the day or two after Thanksgiving, and the car sluggishly rolled about 400 feet then stopped with a low voltage error flashing on its front panel. The voltage at the controller was 128V.

People at Kelly Controller were helpful in doing some debugging, but in the end they concluded that all the measurements I made were at nominal values, so if the controller still wasn't working then I should send it back. It took me a while to get it out of the car, boxed up and shipped, but I eventually did, and then things slowed down for Christmas. I finally received a replacement controller on Tuesday (Jan 5th), and I found time to reinstall it this evening. The controller booted up just fine, so I took it out for a couple short test drives around the neighborhood streets, sticking to streets above my house where I knew I could roll the car home if it quit again. Overall, things seem positive at this point.

Performance-wise, this controller is much slower off the line than the 72V unit was (it was a KD72500). In fact, when starting on any sort of a grade, 2nd gear is absolutely anemic and seems like a bad idea... First gear may actually be required to get the car moving. But once rolling in 2nd gear, the KDH14500B seems pretty good, and I got it up to 30 mph (on a slight downgrade) quickly with what seemed like less effort than the 72V system required. Further observations will be forthcoming as I venture out on longer trips.

Finally, some stats on the battery heaters. The car has been sitting here without moving for the last 5 weeks while the controller was out of it, and I had the batteries plugged in on float charge that whole time... which means the heaters were running too, keeping the batteries warmed to about 95'F. In that time, the Kill-A-Watt meter measured 198 KWh. That's about 40 KWh / week, or about 240 W average power consumption. 90 W of that is the chargers floating the batteries, which means the heaters are drawing about 150 W on average, or 1.25 Amps. Given that the ten 35W heaters would draw 350W if they were running continuously, I surmise that they are running about 40% of the time. In 5 weeks, 200 KWh @ $0.09/KWh costs about $18 for 35 days, or about $15.50 for a 30-day month. That's $15.50/mo. to keep the batteries float-charging and the heaters running in average 38'F weather (avg temp from NOAA for Dec. 2009 in Seattle). Seems like the heaters are running a lot, so I might have to look at tightening up my insulated boxes a bit.