Metrics Musings

As the owner of a number of EVs I've long ago come to grips with a conservative number for the miles I can drive without recharging. Just as a prudent ICE driver doesn't get down to empty, neither do we, and the term "range anxiety" (promulgated by GM http://www.wired.com/autopia/2010/08/gm-wants-to-trademark-range-anxiety/) is simply not in our vocabulary. We do, however, have a significant advantage over the ICE driver: we have a fueling station at home and can start off every day on a full tank... it's the ICE driver late to work and running low on gas that has the range anxiety!

Which brings me to the metrics of the iMiEV.

If we go with the EPA number for range of 62 miles and seeing that our fuel gauge has sixteen bars, we can say that roughly we can travel 4 miles/bar.

Our significant metric, while on the road, is how far we can go for the amount of time we plug into a socket.

Using Mitsubishi's advertized 7 hours for a full recharge and the EPA's 62 miles we get about 9 miles/hourcharging, or a little over two bars/hour using a Level 2 EVSE.

Sanity check for that 7-hour number: using our 240v 3.3KW charger to charge our 16kWhr battery, assuming 80% efficiency and ignoring Peukert and decreasing power draw as the batteries top up, that's about 6 hours to recharge, giving us closer to 10 miles/hourcharging... so the 7 hour recharge time is about right.

I still can't believe Mitsubishi derated their 120v EVSE to allow only 8A draw. Using Mitsubishi's figure of 22 hours means only about 2.8 miles/hourcharging using 120vac. Boy, someone sure wants us to buy a Level 2 EVSE! Incidentally, I'm still using 120vac for my EVs.

I just bought an SPX J1772 EVSE which covers 95vac-264vac, allows the selection of either 12A-16A current draw, and will thus allow me to tailor to whatever's available when on the road... there are many 120vac 20A outlets in commercial buildings, so cranking the EVSE up to 16A at 120vac will give about 5.6 miles/hour recharging ... not bad if you're a commuter and can plug in at work into 120vac without having to rely on 240v or a J1772 station. Still need to validate that the iMiEV's charger will accept 12A or 16A at 120vac.

Hypermiling I would think we should be able to easily increase the range by at least 20% above that 62-mile figure. Time will tell...

Curious how the miles-to-go anxiety meter is working out for you new iMiEV owners and how it correlates to the fuel bars and your own experience?

Now, has any iMiEV owner measured their EVSE input energy and come up with a grid-to-wheels number for either Whr/mile or miles/KWhr?

Interesting point about the ICE drivers not being able to fill up at home and how that causes range anxiety. That's a comment I haven't heard before, I like it!

For us novices, please help me out and tell me what an ICE driver is. I'm sure that it doesn't have anything to do with "Ice Road Truckers" on the History Channel. Thanks in advance Dan O

ICE = Internal Combustion Engine.

http://en.wikipedia.org/wiki/Internal_combustion_engine

Yep, the 'conservative' rate of charge is somewhat frustrating. I only pulled 2865 Watts from a Level II ChargePoint station (starting at 50% SOC) when I was hoping for something much closer to the stated 3.3 kW. This measurement is 'at the plug' and not discounted for charging loses. A smallish pack coupled with a slowish charger makes for less effective range. I should be receiving a 240V meter any day now that will allow precise measurement of at-home charging sessions.

jray3 said:

... I only pulled 2865 Watts from a Level II ChargePoint station (starting at 50% SOC) when I was hoping for something much closer to the stated 3.3 kW. This measurement is 'at the plug' and not discounted for charging loses.

Click to expand...

Wow, that's disturbing, as at that SOC I would be expecting full power draw. Perhaps the BMS is still trying to fine-tune the balance of the cells, or perhaps the ChargePoint EVSE was somehow limiting the amount of current available?

I have a set of TED 5000 CTs (current transformers) dedicated to measuring my EV power draw. Awfully curious how the iMiEV fares.

When I first got my iMiEV a little over a month and 1300miles ago, I started two logbooks - one for charging and one for discharging, trying to keep track of Fuel Bars, Range Remaining, miles driven, and kWHr consumed, with notes as to the type of driving and driving conditions encountered. From this I was hoping to pin down the correlation between Range Remaining (RR) and actual miles driven/remaining, similar to the chart JohnQ put together (http://myimiev.com/forum/viewtopic.php?p=744#p744), and also try to get a handle on our iMiEV's energy consumption under various conditions.

I installed a TED5000 energy monitor, with one MTU/CT set dedicated to my iMiEV charging ports (picking up both 120vac and 240vac).

I've quickly come to the realization that Range Remaining after the vehicle is fully charged is very dependent on who was driving and how they were driving just prior to the vehicle being fully charged. I've seen the starting (fully charged) RR number range from a high of 94 miles to a low of 55 miles. I consider the Range Remaining display to be quite useful once we start driving, but I think it is somewhat meaningless before that.

Now, I've abandoned the above detailed datakeeping for a number of reasons:

1. Our Mitsi gets used a lot - with opportunity charging when not at home and random hour-or-two charging at home throughout the day. It quickly became a pain to record before/after every trip and charging session.

2. In order to get a handle on energy consumed, the only stable reference is when we "fill-up" our battery pack - something I rarely do. There were enough lapses in datataking that it was not possible to add up all the intermediate charging events prior to fillup.

3. My TED 5000 monthly tally blows up when I have guest EVs using my charging station(s) unless I really pay attention and subtract out their consumption.

Anyone who hypermiles will tell you that, for a given vehicle, fuel-economy figures are primarily dependent on who is driving and HOW they're driving. Except for the EPA, I take all mpg or mi/kWh numbers with a grain of salt unless they're built into a vehicle's display - and, even then, they should reflect wall-to-wheels consumption and not just some intermediate calculated figure such as on the Leaf or the Great Misrepresenter, the Volt. I personally also wonder if even the EPA figures (which try to take the driver out of the equation and employ no hypermiling tricks) adequately reflect the effects of aerodynamics and regeneration.

Which brings me to the iMiEV Range Chart http://myimiev.com/forum/viewtopic.php?f=9&t=208. I think it's great to attempt to quantify the effect of all the variables on our iMiEVs range in order to give us a feel for the magnitude of each variable on the overall picture. Whoever pursues this, I wish them luck...

My own Range rule of thumb is to readily undertake freeway trips of up to 50 miles with no concerns at all (knowing that I can easily kick in to hypermiling mode to achieve this), but to venture carefully into the 50-80 mile trips and to have a pre-planned backup charging scheme if needed. Since I don't subscribe to Range Anxiety nor Battery Abuse, I don't think I'd undertake any primarily freeway-driving trips much over 60 miles without a planned recharge. Happily, the SF Bay Area now has a proliferation of charging stations so reliance on friends' garage outlets is diminishing - unlike my previous EV excursions, I haven't had to impose on anyone with the iMiEV yet.

For myself, I've changed my own datataking format as follows: whenever I fully fill-up my iMiEV (e.g., just before a long trip), I reset Trip A and note the date/time of this event. Now, since I know my home charging data is being stored in my computer, all I need to keep track of is off-site charging: the Coulomb ChargePoint network tells me what I used there, and for charging elsewhere I have the Kill-A-Watt to track 120vac energy consumed or for unmetered 240vac charging I note the EXACT plug-in and disconnect times (in my case using 3.06kW/hr charge rate) to identify that figure. I keep track of those numbers until the next time I fully fill-up and then simply tally all the intermediate chargings from both the computer and my datasheet and then simply use the Trip A reading to end up with an overall miles/kWHr or kWhr/mile or kWhr/100miles number. At least I'll be able to point to hard data for our own iMiEV. My last such tally was 42.163kWh over 212miles = 5.03miles/kWhr (wall-to-wheels!), mostly driven by my featherfoot wife but also contaminated by myself with a few leadfoot excursions. Thank you for listening.

Thought y'all might be interested in seeing exactly how the iMiEV charger tapers off as it approaches full charge. The following series of screenshots off my TED5000 display (taken on the evening of March 22) show the following:




The red line represents line voltage and is the nominal 120vac off one of the two power input legs.
The green line (kW) is the day's tail end of my solar generation, showing it decaying to zero as it got dark.
The orange line (kW) represents my other EV charging and is showing zero as nothing was charging.
The blue line (kW) represents my iMiEV. You can see that about an hour into the charging process the charger paused for a few minutes by itself before starting back up. This is not unusual, and I surmise that this is may be part of the BMS recalibrating itself. At the end of charge you can see that from the point the power draw starts to decay to the actual cut off by the charger the time is about an hour.

Incidentally, I thought I had set my timer to turn off at around 14 bars, but somehow I got it wrong and she charged fully. As soon as I realized this I actually drove a few miles so as not to leave her fully fully charged overnight (can't hurt, might help).

Anyway, this full charge gave me another datapoint to calculate and by adding up all the charging of the past few days shows, for a mixture of maybe 30% highway and 70% city (guestimate), that driving 199.2 miles consumed 48.194kWh from the wall, yielding a respectable 0.242kWh/mi or 4.13miles/kWh wall-to-wheels. The usual caveats regarding instrumentation calibration apply.

For those who don't know, the iMiEV is my second EV, the first being a custom Karmann Ghia conversion that's documented at www.karmanneclectric.blogspot.com
For the first time since buying the i, I ran both cars over the same course back-to-back for a performance comparison. Here's a cross-posting that I wrote for the nicad battery users group I'm also a part of.
Bottom Line- the uber-efficient i did not compare favorably to the efficiency of my homebuilt drag racer with similar weight but 360% the power of an iMiEV!

So after wishing I could throw in the towel on this bb600 pack aftermultiple incidents of spewage, ground and interpack shorts that melted holes through a dozen cells, and apparent loss of capacity down to about 16 Ah, Karmann Eclectric didn't get a lot of use after a fall recommissioning of the pack, but I cycled it a few times over the winter, took a few short drives, and got the Onan range extending genset trailer working, due largely to a lack of confidence in the pack. The car seemed to be sulking, especially when I added a 2012 Mitsubishi iMiEV to the fleet! Well, it seems that the pack was actually ready for prime time once again! Tonight, with a pack temp of 50 deg and outside temps a few degrees lower, I topped off the charge and took the car for a diciplined 45 minute drive, covering a 27 mile loop with only 4 stops at intersections, for an average speed of 34.8 mph and a peak speed of 68 mph (climbed up and coasted down a 127 foot incline twice at speed, with many other smaller climbs). The 200 cell pack came off a peak charge of 333V and rested at 305V after about 15 minutes, with 0.1 Ah of parasitic consumption before takeoff. I set off with headlights blazing and pulled into the garage 45 minutes and 27 miles later, having consumed a total of 31.1 Ah, or 6.82 kwh. That's 1.148 Ah per mile, or at an estimated average V of 230, a battery-to-wheels efficiency figure of 264 Wh per mile. Next time I'll reset the EMeter to report kWh instead of Ah, and then it'll be time for some data collection with the range trailer hooked up!

Not bad, considering that this was at night in a car with a very heavy-duty transaxle and series motor, while my iMiEV consumed 257 Wh/mile during a 51 mile conservative daytime drive (though it's the current king of regen, that trip was mostly highway). Hey, guess it's time to hit the road again and drive that same loop in the i!

So, back on the road, and the iMiEV made the same run in the same time with apparent consumption from the pack of 7 kwh. Sorry, the guessometer doesn't get any more accurate than the nearest kwh per bar on the graph. That would match the Ghia's performanceof 6.82 apparent kwh. (I minimized regen by shifting into neutral and coasting or braking as required to better match the Ghia driving style, and used no heat.)

So Mitsu, whassup with that? You produce the most efficient vehicle ever rated by EPA, and it's no better or maybe a bit worse than my homebuilt drag racer built out of surplus and rebuilt castoffs and a heavy truck tranny? Time for more tests and better instrumentation!