Driving hints – By the numbers
Comments (0) Let me share some driving thoughts after my May 6-8 trip to Madison for the Wisconsin Clean Transportation Program Partner Vehicle Showcase. Within a 38 hour period, I drove 180 miles to Madison and back on 243% charge (with 3 recharges) at an average speed of about 28 mph. That represents an estimated 85 KWH, or about 2.1 mi / KwH, on a 5000 lb. vehicle. Each of the four legs had an expected range on 90% charge of at least 62 miles. The eLIMO performed very well, and I loved every minute of it, at least after I felt sure I had the range to get to Madison.
I drive with several (conflicting) goals, including:
Arrive safely at my destination
Maximize range
Fit in with traffic
Usability
Enjoy the trip
eLIMO has three driving settings, [Max Range], [Normal], and [Max Power]. As far as we can tell, they function only to limit the maximum current draw to about 50 amps, 110 amps, and ??? amps, respectively. I almost never use the [Max Power] setting on my test drives.
I THOUGHT I was pretty good at using the accelerator very gently. I thought that under normal cruising using [Normal], I rarely used much current. Watching the amp meter showed I was wrong. I was shocked at how often the amp meter pegged at 110 amps when I did not think I was pressing the accelerator.
On the leg from Oconomowoc to Madison (4:30 – 7:00 A.M., almost no traffic until about 6:15), I used the [Max Range] setting except for 3-4 times when traffic conditions suggested (e.g., 1/2 mile on the Beltway, hitting 58 mph). Mostly, I drove 25 – 30 mph, trying hard to avoid pegging the amp meter at 50 amps. In [Max Range], eLIMO often slows to 15 mph going up even modest hills. With no traffic, I accepted that. At 50 degrees, I drove 55 miles on 70% charge (range, 72.4 mi.). On the return trip, I used mostly the [Max Range] setting to limit current for routine cruising, usually keeping the amp meter pegged at 50 amp, mostly going as fast as the [Max Range] setting allowed (mostly 40-50 mph, higher going down hills). However, I often switched to [Normal] to accelerate in traffic or to climb hills. Accordingly, I drove quite a bit faster than the outbound trip, averaging 36 mph. At 70-75 degrees, I drove 55 miles on 78% charge (range, 62.7 mi.).
On the leg Monday from Marquette to Oconomowoc, I used the [Normal] setting, and I did my best to drive efficiently, although at least 15 of the 34 miles was in relatively heavy city traffic (mostly Bluemound Rd., 4 – 5:00 P.M.). At 70-75 degrees, I drove 34 miles on 50% charge (range, 61.9). On the return of that leg on Tuesday morning, I drove probably 90% in [Max Range], almost always going as fast as it would go. In traffic or on hills, I switched to [Normal]. I drove on Bluemound Road from Gerkes Corners to Marquette, but at about 5:40 – 6:10, so there was very little traffic, and the lights were favorable. At 45-50 degrees, I drove 34 miles in 48% charge. It seemed I drove faster, but with far fewer traffic interruptions, at 20 degrees lower temperature, and used less power by letting the [Max Range] setting limit the current draw.
Here, I am careful to give the ambient temperature. Generating electricity from a battery is a chemical process, and we know chemical reactions accelerate as temperature increases. There are too many variables and not enough data to say with much confidence, but my sense is that a 10 degree increase in temperature is good for about 5 miles in increased range, other things being equal.
If that is so, I would expect at 90 degrees, using the [Max Range] setting very cautiously, driving 25 – 30 mph, on smooth, level, dry, traffic-free country roads, I might achieve a range exceeding 90 miles. If I also assume a strong tailwind, perhaps 100 mile range? Of course, those conditions never happen, but we might hit 100 mile range if we programmed a smart controller.
Most of the time, I accelerated gently. However, twice, when there were cars behind me at a light, I accelerated harder and experience the “stalling” problem. If I let up on the accelerator, paused a second or so, and re-applied the accelerator, eLIMO accelerated just fine. I think that happened once in [Max Range] setting and once in [Normal] setting. I did not attempt to replicate the problem at will. I suspect either the motor controller of the battery controller thinks we have requested more current than some threshold and trips. We need to fix that.
I do not believe the headlights represent enough load to detect. Both morning runs used the headlights for most of the trip.
Almost all my eLIMO driving experience is with a light load. Usually with no passengers at all. Its properties loaded surely are quite different.
Oh, and I always unplug the power steering, although I have no idea how much power that saves.
Lessons learned:
The [Max Range] setting is significantly more efficient than my best efforts using the [Normal] setting, but [Max Range] does not provide enough power to fit into normal traffic, if there is any.
Use the [Max Range] setting whenever you can.
Switch to the [Normal] setting to accelerate in traffic or when approaching a hill. Switch back to [Max Range] as soon as the need is past.
If that is not enough power (e.g., loaded, steeper hills), switch to the [Max Power] setting. Switch back to [Normal] as soon as the need is past.
If that is too much effort, use [Max Power] when loaded and [Normal] when empty.
George Corliss, George.Corliss@Marquette.edu
