Quantifying Regeneration and Consumption

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Staff member
Dec 15, 2011
Hills above Silicon Valley, California
The question on the table is: what is the maximum regeneration in the iMiEV relative to the maximum power draw?


This gauge seems to be nothing more than a damped analog ammeter with a pretty background, showing colors instead of numbers.

Maximum power draw has the needle all the way to the right (white zone "Power"); maximum regeneration has the needle pegged all the way to the left (blue zone "Charge"). Mitsubishi calls it the Energy Usage Indicator, and I had previously suggested that we call it a Power Gauge, ... maybe Eco Gauge is a cutsier title.

Anyway, if the display is linear, then it would appear that maximum regeneration shown is only 1/3 of the maximum that can be drawn. I don't think this is correct, as my impression is that there is more retardation (e.g., when lightly touching the brakes and thus adding even more regen) even when the needle is pegged all the way to the left in the blue zone.

Does anyone have any data on this?

Probably the only way to find out is to clamp a CT (current transformer) onto one of the battery wires...

The reason for bringing this up is my attempt to quantify energy usage as part of the hypermiling discussions...

Edit 7/15/12: added "and Consumption" to thread title.
Joe, I sure wish you were in the hood, we could do one heckuva garage and track day for the i. I've got the equipment to log these values, but haven't had the time yet. Since you've brought it up, makes me want to deploy them dataloggers! In related news, there's a dandy new option to wirelessly monitor and log your DMM through an Android device. Here's hoping it makes the jump to iPhone/iPad soon.
Y'know, it's tempting to get an extra service plug from the parts counter and modify it to accept a shunt! Old school metering simplicity, and would also enable one to track the total amp-hrs in and out of the battery, if using an old reliable device like the E-Meter or Link10. Not many new options at 300+ volts, unless you can afford the awesome offerings from http://www.metricmind.com/category/ev-instrumentation/.
OK, I have a Hall-effect clamp-on 200A ammeter with a a six-foot cord which enables me to read amps while driving. Put the clamp on one of the wires going from the battery pack to the controller, and took our iMiEV for a drive.

Here are the ammeter readings correlating to the Power Gauge markings:
(usual disclaimer as I'm using an uncalibrated instrument - but it's close)

Power ON, needle midway between blue and green: 0.0A
(this is an update as I had previously said 0.3A - that was simple instrument offset error)
First Tick Mark 45A
Second Tick Mark 95A
Max Tick Mark 154A (when briefly floored at about 60mph); otherwise I was getting 152.6A at lower speeds.

Regeneration (blue zone):

Seems to be linear, with max tick mark reading ~50A
Regen continues on up despite the needle being pegged, with a maximum reading seen of 104A when letting off the go pedal in "B" at around 65mph. I didn't try also applying the brakes to see if it would further increase.

This is really good news, as it means that our iMiEV indeed has quite powerful regeneration. :cool:

Dang, liking this car even more as time goes on...

Update 4/18/12: corrected "zero" reading

It sounds like you are saying that we can regen back in at a rate of 2/3 of the power we can send out? That sounds pretty great to me, at least much better than I expected.

jjlink: that's a cute graphic! :)

jenn: you're right - the iMiEV regen appears to be 2/3 of max power, which I consider really good! No wonder both the Fuel Gauge and RR came up on the long downhills to/from Santa Cruz!

Now that we have a rough idea of the calibration of that power gauge, what's needed is a windless perfectly level road to compare power consumption at various speeds. I've been unsuccessful in all my attempts, as there are no perfectly level traffic-free roads around my house. Four data points should be enough: halfway to the first tick mark (22.5A), first tick mark (45A), halfway to the second tick mark (70A), and second tick mark (95A). Post your results here of the speed you measured at these points, and we'll see what we can make of the numbers. Maybe this will allow us to quantify the iMiEV's range-robbing aerodynamic drag effects (or maybe not...) :roll:
The actual unit I'm using is comprised of a Hall Effect clamp-on current sensor and a separate ammeter readout.
I have about 6' of wire between them and simply used the iMiEV's 12V to power it. I ran the wires up from the controller and between the seats, with the ammeter readout sitting on the passenger's seat. To check for zero, I used a small 12v battery to drive the ammeter with the iMiEV's power off.

how do you get the wire from outside the cabin (from the controller) into the cabin? Or is there something I am not understanding and it is all inside the cabin?


WeeJohn, thank you for these datapoints. Would like many more. I'll be carrying a voice recorder with me so if conditions are good I can capture the info. Especially interested in the low end to see how the iMiEV's efficiency increases as speeds drop.

Jenn, sorry for not being clear: I had opened up the aft compartment for access to the wiring, and simply brought the wires up into the cabin and then gently screwed down the lid onto the wires to seal off the compartment again.
I (but not i) stopped to check out some of the Washington Electric Highway installations en route to B.C. last weekend, and it's an interesting balance that has been struck. Level II chargers are located at highway rest stops (where you generally don't want to spend much time) and the CHAdeMO stations are at shopping centers every 30-40 miles along I-5. Seems the opposite priority would've been better, to encourage longer stays at the shopping centers and short stops at the rest areas. Most rest stations probably don't have 50 kw of spare service, though...
Anyway, we've got plenty of infrastructure now on the Upper Left Coast.
Relating to the topic at hand, the AeroVironment CHAdeMO stations that have been installed spec out at 50 kW or 120A max.
For our 330V packs, that's a charge rate of 39.6 kW (could be a bit more, as the pack voltage may be lower to start off)
BUT, the regen rate of at least 50 A and up to 104 Amps beats CHAdeMO hands down. If it weren't for the labor requirements, quick charge via forced regen would be much cheaper option (strap 'er to the powered rollers or hitch up to a tow vehicle for 20 minutes)... ;)
If I can figure out a tow bar for the i, a 'hybrid convoy' will be in it's future... (flat tow past a few exits, drive past a few exits, etc.) It would need to be a stout tow vehicle though, as 50 to 104 amps of regen would suck up 67 to 139 hp (at the wheels) from the tow vehicle!
Imagining a 'third world' quick charge service- either strap your car onto the rollers powered by an old truck chassis (fueled with clean natural gas at regular pipeline pressure), or accept a short tow by the old truck's younger brother! :lol:
As you may have noticed, I changed the title of this thread to include measuring consumption in addition to regeneration.

Got ambitious a few days ago and had a few hours available to play with the iMiEV. First I lengthened the display cable on my clamp-on Hall Effect ammeter so I could mount the display on the steering column. Here's the instrument information:

Display: http://www.semarine.com/store/product.php?productid=281&cat=192&page=1
Sensor: http://www.semarine.com/store/product.php?productid=321&cat=192&page=1

Did a quick benchtop calibration check which showed a dc offset of +0.3A, then installed the sensor onto one of the two cables coming from the battery orienting the sensor's polarity s.t. a negative reading means power going from the battery into the controller.


Then Velcro'd the display on top of the steering column, as you can see in the photo below. I don't know how stable the red needle was at the moment I snapped this photo, but it shows 34.4A (-34.1-0.3) for a needle position that's roughly at the 3/4 point.


Then I went off on a brief drive. First, I confirmed the red-needle-position vs. amps readings I had previously taken, and I was happy to see the numbers very close to those I had previously recorded. Then I was hoping to get photographs of speed vs. needle position vs. current. Inasmuch as I didn't have much time for this test and was driving in town in heavy traffic, I immediately ran into difficulty getting all this data properly recorded. There are two problems:

1) The red-needle display (really an analog ammeter) is heavily damped whereas the digital display is almost instantaneous, and thus the go-pedal needs to be held very steady for a few seconds in order for the red needle to catch up and stabilize. Hard to do in city traffic.

2) As noted in another thread, it is very very difficult to find a perfectly flat windless zero-traffic location whereby one can stabilize the vehicle speed in order to get a good ammeter reading for it. Unless all those conditions are met, any such speed vs. amps reading is simply not valid.

Watching the display and holding the camera while trying to snap a photograph at just the right moment proved hopeless in traffic, so I simply set the camera to movie mode and let her rip for a few minutes with my hand-held camera until I ran out of camera memory.

Inasmuch as I was fascinated by the fact that I had previously managed to pinpoint a flat-windless-zero-traffic speed of 22mph for a red needle positioned exactly straddling the bottom edge of the green zone, I focused on duplicating this condition and at least getting this recorded. I did have a brief moment during this drive that I think came close to meeting all the requirements, and what you see below is a screenshot of that moment:


Interpreting what you're looking at: at 22mph the iMiEV is drawing 2.0Amps out of its (nominal) 330V pack, thus consuming 0.66kW at 22mph.

What this means, if we get really greedy and say that we have a fully-usable 16kWhr pack, then we could go (16/0.66)*22 = 533 miles at 22mph on one charge. Let me repeat that: a range of 533 miles at 22 mph on a single charge. :!: :!:

Update - note the fallacy here: the current being measured at the controller relates to only motive power and does not take into account all the other vehicle energy consumers. See BlueLightning's post below: http://myimiev.com/forum/viewtopic.php?p=7080#p7080

I love it! Even if, say, we're off by a factor of two or three or even four and derate the usable battery capacity, this confirms what I've subjectively felt all along: that with our very low rolling resistance at low speeds where aerodynamic effects are still minimal, our little iMiEV is truly an energizer bunny!

There are many many caveats associated with this, including instrument error, reading error, unstable speed, less than the desirable zero-wind zero-traffic perfectly flat terrain, and the fact that I'm running 60psi in my tires; nevertheless, from a practical standpoint what this means to us is that if you think you may have a problem getting to your destination then get off the main highway and simply slow way down if at all possible and keep that red needle at the bottom of the green zone ... you WILL get there!

This was a very brief experiment aimed at determining the practicality of this test setup. The proper way to do this is to have a hard-mounted video camera recording this information; moreover, as I've said before, unless you have perfectly windless, perfectly flat, zero-traffic (i.e., no one in front disturbing airflow) steady-state conditions, then any speed vs. amps readings will simply not be valid.
I think your tests are ultimately going to prove something I've suspected all along Joe - That speed is the biggest killer of range . . . . much worse than using the climate control. The faster you go, the shorter the range. Peukerts Law and aerodynamic drag combine to really take a toll on the battery bank as you speed up

I've noticed that we're getting what I consider to be really great range even running the A/C very heavily all the time, probably because most of our driving is between 30 and about 45

We had a full day running around yesterday and the car showed 15 miles remaing before we left to go out for dinner. Ordinarily I would have plugged the car in at that point for a couple hours but my daughter had come over and her car was blocking our acces to the garage, plus the restaurant we were headed to was only 5 or 6 miles away. Long story short, the RR gauge was flickering between 3 and 4 when we got back and we had gone 69 miles total, all of it liberally using the A/C - It was the 'usual' 90 degrees here yesterday

I suspect 50+ speeds are a much bigger killer of range than using the A/C

Yup, high speed is a range killer. My Prius has an average sipped display and in my neighborhood (city/suburban) it usually averages 17 mph. So I do great with my miev.
Consumption of each vehicle circuit

An interesting post from triphase » Jeu 31 01 , 2013 1:20,
"Consommation de chaque circuit du véhicule" triphase, http://www.vehiculeselectriques.fr/membre11029.html

A small analysis using pf78 http://www.vehiculeselectriques.fr/membre11603.html canyon of ...

Key second step (without the "contact"), all off: 240W

engine running (so to speak): 430W (includes daytime running lights)

At the base value of 430W should be added if they are enabled consumers to:

headlights: 220W (included taillights)
beam: 175W (plus beam)
AB lights AV + AR: 125W
Stop lights: 30W
warning lights: 140W (modulated at 50%)
radio: 0 to 20W about
rear window defroster: 170W
ventilation: 180W or 270W 0 to mode "push max"
vacuum pump: 70W
AC: about 800W (works sometimes, not always, when following or strange logic outside temperature)
0 to 6kW heating about
wiper, windshield washer, power steering operation untested because rare (not so rare front windshield of course)

Note that the 12V circuit is powered directly from the battery charger accessory (well this is how it feels), which serves no purpose except perhaps have in case of failure of the main battery.

I failed to thank BlueLightning for his posting quantifying so many of our iMiEV's energy consumers. Note that the heater and aircon energy consumption can easily exceed the energy required to propel the car! For this reason, all discussions about the iMiEV's range must exclude heating and aircon use as those are uncontrolled variables. I realize this requires a paradigm shift on the part of vehicle reviewers, but separating propulsion from creature comfort perceived 'needs' will provide a more accurate assessment of EV 'range'.