30 August 2009

Big Ears?

I have been experimenting with a lot of different routes to commute to work. While I have managed to cut a couple miles from my trip, I have also gotten some evidence about how much quieter an electric car is.

Not that much from the outside at speed.

I often I take back roads to work through Bucks county in Pennsylvania. There are a fair number of people out walking their dogs, jogging, or just walking. And guess what?

They all hear me coming. Probably from just as far away as if I were in a piston powered car.

Don’t get me wrong, the Mini E is much quieter, especially on the inside, especially if the windows are closed, and especially when accelerating or when moving really slowly (which does not make much tire noise).

But a lot of modern cars are fairly quiet these days when cruising at light throttle. And tire noise at speed is not going to change much based on the motive power source. I suspect that people who are facing away from me are hearing my tire noise when they walk to the edge of the road long before I get close. These are not high speed roads, usually 35 to 40 mph. Maybe 45 tops, some 25.

And the Mini E is not completely quiet at very low speed either, there is a whirring sound when under power even at a fraction of one mile per hour. I suspect it might be the cooling fan, maybe someone more familiar with AC Propulsion’s system can comment. I wonder if this fan noise (or whatever it is) is audible to the average pedestrian. On the other hand, if you don’t touch the throttle, there is no whirring noise below one mph. Although the battery cooling fan always seems to run, though more quietly in the cooler weather now.

22 August 2009

Constant speed versus constant fuel?

Accelerator pedal position in the Mini E is very nearly constant when cruising. It might be close to what engineers would call a constant speed control. By contrast, my foot moves a lot when driving a piston powered car in the hills at steady speed. Perhaps the accelerator pedal in a piston car is closer to a constant fuel rate per stroke, and then the vehicle speed varies widely with engine speed, terrain, gear selection, wind, etc. if the pedal does not move.

I have commented to friends about how easy the Mini E is to drive because of the nearly stationary position of my right foot, but I had not mentioned it in this blog until now. Well, last week when my wife was driving she observed that the Mini E brought to mind that old Irish verse "May the road rise to meet you". It never really made any sense to her and maybe it is a bad literal translation but that fact that the car goes up hills so easily without the driver even having to press the pedal any harder brought the verse to mind.

(I'm starting to get slightly worried that my wife likes this car more than she likes me. The law of unintended consequences is always lurking. Perhaps I am not as easy to get along with as the Mini E. Ha ha. Maybe I should learn from my car.)

I have paid very close attention and when I hold my foot as steady as I can, the Mini E does slow slightly on up hills and speed up slightly on down hills. But only slightly and much less than any other car. I missed not having cruise control at first, but figured it was one of those features that they just did not get to in time. Every prototype project has some features that don't get done in time. But with this car, you hardly miss cruise control.

14 August 2009

There is a bounce at the bottom of the charge gauge

Since a Mini E engineer encouraged me not to hesitate to run the batteries all the way down, I have been watching for an opportunity to do so. The charge estimation algorithms have been very reliable and my range awareness has become quite comfortable. A couple days ago I had the chance to go for zero.

On the way home from work, the charge gauge hit zero at about 5 miles from home. No sweat, everything kept moving right along. I was not on the freeway (I rarely am) and I was expecting some sort of limited road speed but nope, I was driving as usual. Then the fun part: I came to a stop light and while waiting, the gauge crept up a few %. Drive on, it goes back to zero, a downhill, and it creeps up a couple %. This kept going all the way home. It never went negative and when I parked at home and started scribbling down all the numbers from the display that you can find in my logs, it crept up to 3% before I plugged in.

This reminds me a bit of the absolute value of the SINC function, for any of you math geeks out there.  Of course at some point the charge gauge will droop into the negative range but I'll have to push it harder to get there. And I don't care for fast driving, so we'll have to wait until the next time that I'm late for a 7 AM meeting and HAVE to take the freeway to work.  The freeway only saves me a few minutes, but it is many more miles and leaves me at low charge on the way home.

The bottom line is that the Mini E range is probably better than most of us drivers of it realize. And it is not at all like the sudden death overtime of driving a piston car burning "Satan's saliva" (petroleum that is). When you get too low on liquid fuel, your car suddenly stops. The Mini E might slow down, but not at all suddenly. Maybe it is more like a horse when it gets tired. But Mini E 458 didn't even slow down, it just bounced off the trampoline at the bottom of the charge gauge.

If I may digress, I am very suspicious of the talk about the "A" word regarding range in electric cars, and I would really like to see us proponents stop repeating it. Keep in mind that there is always a propaganda machine at work trying to undermine any alternatives to petroleum. Economics 101 says that without alternatives, there is no downward pressure on prices. Petroleum has had a monopoly in transport fuels for a long time, and they will say anything to keep it. So don't repeat the "A" word. Nissan was very smart to use the term range awareness, which I have chosen to follow.

You can probably remember a time when you were young and ran out of gas, right? (Maybe not so young.) Most of use have not done that since. Well, you probably had some anxiety when that happened and ever since you paid attention to the gauges and gas stations and you have been sanguine about your range. There is not much different with an electric car except that if you do run out of charge, you get warning and you slow down gradually. And there are literally about a billion places you can plug in your car if you have the social skills to ask. I have plugged in at a super market, a small local grocery, at work every day, and I have spotted lots of retail locations with outdoor outlets where I could ask if I ran short. Sure it charges slowly at 120 volts. But lets drop the "A" word, OK? Don't play into the hands of the petroleum monopoly.

11 August 2009

80% charging efficiency at highest rate, 60% at lowest

Today I turned off every circuit breaker except for the smoke detectors and the clock radio, then recorded the power company watt hour meter. I read 14% charge remaining when I plugged in the car, and took another reading when the charge rate slowed down at 98% and we really wanted to turn on the central AC again.

I read total power used as 29.3 kilowatt hours for adding 84% charge. By the way this took 2 hours 32 minutes at 50 amps. Sorry, I did not get a precise voltage reading. So:

29.3 / 0.84 = 34.88 KwHr needed to charge from 0% to 100% by extrapolation.

The Mini E spec sheet says usable battery capacity is about 28 KwHr. If we define charging efficiency as usable energy available after charging divided by energy input while charging, I get:

28 / 34.88 = 0.8 or 80% efficiency.

This is very good. I did a similar measurement long ago with the 120 volt charging cable when that was all I had and got a number closer to 60%, presumably due to the fans running just as hard but being a higher fraction of the available charging power.

The 2.9 hour charge time given for the highest charge rate seems to be quite accurate for 0% to 100% charge. However, the 23.6 hour charge time given for the low rate 120 volt charger seems to correspond to charging from 30% (when the first low battery alarm comes on) to 100% by my measurements. I extrapolate to about 37.5 hours for charging from 0% to 100% with the 120 volt box. Of course, this would depend on ambient temperature since that can affect fan speed. I'll meaasure again when it cools down in the autumn. The high rate charge time might be less affected by temperature between 40 and 100 F.

The real point of all this is trying to estimate how much of an effect terrain and start stop driving have on range versus the effect of speed. Assuming that regenerative braking is as or more efficient than the high rate charger, I am guessing that 80% efficiency goes a long way towards removing the effect of hills and start stop driving. High speed might be the bigger cost to range.

And by the way, I once figured the max regen rate works out to about 20 Kw, which is much higher than the 12 Kw max charge rate for the wall box. So efficiency might be above 80% for regenerative braking.

I had thought I should strive not to go below 30% battery charge since that is where the low battery warnings start. But one of the Mini engineers at a Mini E social event encouraged me to run it as low as I want, even into the negative area. He insisted the battery was fully protected and I would only lose speed at very low charge levels. I usually get home in the 20% vicinity. You can see the details in my trip logs. (Click on the title line of the oldest posting.) I have noticed limited acceleration when passing when I am below 20% but never any sense of a speed limit yet. Some day I'll get the nerve to get down to 'zero' charge or below. Not this week.

10 August 2009

Minor EMC issue

At 3600 miles, I finally found a complaint, however minor.

The rear window defogger can wipe out radio reception. Specifically, driving from Princeton to Hopewell NJ and listening to 88.1 or 90.9 works only when the rear window defogger is off.

I have not run into this in other cars, although a colleague with long automotive experience has.

If this is the worst of the problems, it only reinforces what an excellent job they have done on this prototype vehicle.

And Electro Magnetic Compatibility issues like this can be pretty easy to fix. Or not. I have seen issues that take down the entire CAN communication bus, now that was serious. But there was a very simple fix.

I have other comments about the radio but I want to limit this blog to observations that are specific to the electric only version, and I suspect the radio is common with the piston versions of the Mini. Plus, I have not read the manual for the radio yet and I don't want to make a fool out of myself. Yet.

UPDATE:  It seems the EMI from the defroster is intermittent, maybe there is a loose wire and not a design issue.  This is not worth a trip to the dealer, certainly not in warm weather.  The occassional fog lately is something I can live with without using the defroster.  When we go on vacation I'll drop it off for them to look into.

08 August 2009

Qualitative Comments

I have to digress from the theme of this blog and move from the quantitative to the qualitative.

The reason this car is such a wonderful ride is the gestalt of less noise, less vibration, less smell, less heat, and less guilt about the fuel source.  Being someone who occasionally falls into the trap of 'road rage', I can testify that driving this electric car has a salutary effect that mollifies the tendency towards aggression and makes it easy to take one's time.

I do not expect those that have to drive in NYC or LA to experience this effect, with the over riding pressure of those environments.  But combined with the opportunity to drive on county roads with low traffic, this car has convinced me that I am never going back to piston power if I can avoid it.  Do not misunderstand, I loved driving on biodiesel for years and in the short term it might even be better environmentally than the nuclear based electric power here in New Jersey.  But it does not have the multidimensional luxury of electric power.  And of course electric power can move to solar and wind, I just don't have those options immediately.  Soon maybe.

I have heard that when the first flush toilet was installed in the White House, it was a novelty.  Most people had outhouses, which got the job done but they were uncomfortable, stinky, not so healthy and not so good for the environment.

Today, electric cars are a novelty.  Piston cars cars get the job done but they are uncomfortable, stinky, not so healthy and not so good for the environment nor for geopolitical stability.

OK, to take the metaphor to the limit, I would be in a hurry if I were still driving around in the automotive equivalent of an outhouse.  But I'm not.  I'm driving a Mini E.  And I love it.  I admit that in the best of all possible worlds we would not need cars.  At the moment I do need a car, and I'll take the metaphorical equivalent of a flush toilet over an outhouse, even if it is more expensive.

My wife was skeptical about this car at first, mostly due to the cost.  But she realized that with my ridiculously long commute, there was value in reducing my driving stress.  She is hooked now too.  Though my wife NEVER liked to drive, now she grabs the key fob and heads for the driver's door of the Mini E, while I follow to the passenger's door.  And she has started to complain about her car.

The second time we came home from church in the Mini E, my wife said "When the lease runs out on this car, it is going to be very sad".  I knew she was hooked.

I have to get a windows sticker made, saying "Pistons?  We don't need no stinking pistons!"

07 August 2009

Battery temperature

I do not drive much on the freeway, but I had to yesterday. After charging the Mini E all day at work as usual, the battery temperature was 104 degrees F when I left. I have sun shades in the windshield and on one side window, but it is still fairly warm in the car even with the fan running while the batteries charge.

On the freeway I was driving rather aggressively, and saw the battery temperature peak at 109 degrees F about three quarters of the way through my 68 mile trip. Now this is fine, the car ran perfectly, the AC is very strong, range is great. But 109 degrees is close to what I recall as the limit for regenerative braking to function.

So I question the wisdom in the owners manual of recommending that the windows always be fully closed when the car is parked. If I did not have the car plugged in and charging, it would be much hotter in there without the fan. Has anyone else gotten into a high enough temperature that they lost regen? The only blog I have read about loss of regen was related to problem that was repaired.

So I leave the windows slightly open if there is no rain in the forecast. And if rain is expected, it is usually cloudy enough that the car stays cooler even with the windows closed fully.

But I would like to know from Mini if the fan always exhausts interior air to the outside to cool the batteries? Would it work better to reverse the fan when the inside of the car is hotter than the outside? Can the battery fan reverse in winter to heat the cabin when the batteries get hot? (Maybe the batteries don't get that hot in winter.)

It is rare for me to drive aggressively, so I don't think I'll see these high battery temperatures again. I suspect that Mini or BMW will go to a liquid cooled battery when they come out with a production electric car. But they seem to have done a very nice job for a prototype.

And I love the fact that the car stays as cool as it does parked in the sun when it is plugged in. Too bad the AC won't run when it is charging but it is hardly needed in my experience. Maybe I should get in interior thermometer and put some more numbers in this post...

05 August 2009

Portable charger not completely water proof

Several weeks back there was a heavy rain at work before I left for home. The 120 volt charger was lying flat on the concrete, face up and the car was still charging when I unplugged it. When I got home, the 120 volt charger would not start, both red LEDs were blinking which means an internal fault. (This was before the wall mounted charger was installed.) 
Knowing what happened, I unplugged the charger, carefully opened the case, and poured out the water. I dried it with a hair dryer set on low for about ten minutes and it was fine. 

The gasket and grommets look perfect, I don't know where the leak is. Normally I hang the charger from the strap when it looks like rain, but this day I did not.

One of the GFI outlets at work that I use to charge the car started tripping a few weeks ago. I thought at first that one of the guys was pulling a practical joke by pressing the 'test" button on the GFI, since I had charged at that outlet many times with no trouble. But now I suspect that moisture in the yellow box caused the external GFI to trip before it got so bad that the yellow box decided it had an internal problem. That outlet seems to be working again now that I dried out the yellow box. 

In the photo you can also see the meter I use. I have to pay for the electricity I consume at work. The extension cord is 12 gauge, with screw terminal connectors. It does not get warm. The owner's manual warns not to use extension cords, but this one is sufficiently over rated. Most molded connectors on extension cords from the hardware store will over heat after a few hours at 12 amps, so I agree in principal with the owner's manual. But the outdoor outlets at work have spring loaded covers and I cannot get the power meter in directly, so I use this heavy extension cord.

02 August 2009

Detailed trip logs

Central New Jersey might be the last location to get wall chargers installed for the Mini E. Something about the inspectors being fussy here. For various reasons I delayed blogging about Mini E #458 until my 50 amp charger was installed, which happened two days ago.

So far I have been driving my 120 mile round trip commute only 3 days a week due to the long charge time at 120 volts. We also drive on the weekend but usually less than 100 miles total. With the big charger I should be putting 3000 miles per month on the car.

I had my first problem last weekend when the car refused to charge. I still had only the "baby" charger at the time. It still drove fine, so I dropped it at the dealer on Monday night where it also refused to charge with their "adult" 50 amp charger. They checked it in Tuesday morning, sounds like the "flying doctor" checked it out on Wednesday, Thursday it was fixed and Friday we picked it up.

The dealer says I was the first to take delivery in Princeton, and the first to bring it in for the 3000 mile check up. If I had not had the charging problem, I would have been over 3000 when I went in for service, instead of just under 3000 miles on the odometer.

I have never seen a car as anything more than a mobile appliance. Much the same for my wife. We used biodiesel in an old Mercedes for 4 years before now, and that was interesting and a little annoying. The Mini E is the first car either of us has been impressed with. Of course it is mostly about the fuel, but the car is well executed in most respects. This is the future.

My trip log is linked, click on the title of this post "Detailed Trip Logs" above.  It will open a Google Spreadsheet.  You can see that I don't always get a range over 140 miles, but I get a very dependable 120 mile range when I'm not in a hurry. Analysis and summary to come in later posts.