|The dealer had sent me off with a 100% charge in the battery, and I assumed that they had probably kept the car topped up close to that level over the months it was sitting on their lot. That's actually not so good for the lithium chemistry, which is most stable around mid-charge over long-term storage. While battery management systems have gotten quite good over time, their notion of net capacity can still drift, so it pays to let one re-calibrate its limits and coulomb count once in a while. My plan was to run that charge down as far as I possibly could before recharging for real. Everything I'd done with the car had been on that charge so far, and finally I was down to about 9% left one morning and figured this was the day to run 'er all the way down.|
|So I loaded up the "self-rescue kit" with both Yetis charged up, and all the scary widgets thrown in since it was all going to be part of a demo setup at some upcoming events, and headed out to drive around very locally for a while.|
|9 percent of 64 kWh is theoretically still over 20 miles worth, so it took a while to bring it down to the point when anything really changed. But finally I felt a significant sag in driving output and the expected "turtle" and other warnings finally started popping up. I was about halfway across town and actually wasn't too worried about being able to get back home, but was prepared to sit in a parking lot while the Yetis did their thing if necessary. I gingerly but handily made it the 2 or 3 miles back and things weren't critical yet, so as I got near home I started running the climate system as hard as I could guess how to burn off more of the energy.|
|After pulling safely into the driveway I kept running the climate system, now that I could freely drain everything down to the bitter end and not be stranded. At this state I was down to *two* blinking turtle icons; the car was really trying to tell me I was an idiot. Even in this state, the car would still move, so obviously it allows for a tiny bit of driveable "reserve" which could help someone limp to a charging spot.|
The energy-allocation display allowed me to keep tabs on realtime energy
use, and it was interesting that I could still waste 5 kilowatts worth
in the climate system -- in warm weather with the doors open.
But interestingly, after the miles-to-go guess became irrelevant, it seemed
that the only way I could force the system to actually keep using that
much was in defrost mode, where it makes sense to run both A/C and heat
at the same time.
Regular heating or A/C and cranking the setpoint temp either way didn't
really do it; perhaps the assumption is that windshield defrosting is a
more safety-critical operation, so expending energy into that is still
allowed when other usage is not.
Finally the car dropped to "ON" mode as opposed to "RUN", and refused to fully power up anymore. Dead! At that point all the control stuff was running on the 12V battery without any help from the downconverter, so I couldn't keep that up forever.
|Next, it was time to charge, fully bottom to top! I started with the Yeti packs, to test just how much they could push into the car in the "rescue" situation. This would take a while, but I had all day to test things in a controlled way and collect data.|
|With the granny-EVSE set to its max of 12 amps, the Yeti was pushing around 1350 watts -- close to its rated 1500 max, but still within its capability. That charge rate would nonetheless take a *long* time to fully charge the car -- more than two days, and even longer if the EVSE was set to a lower current.|
|The Yeti had its fans screaming and was generating a little extra overhead heat, out the obvious pair of outlets in this infrared shot. But most of its energy really was going into the car. Considering how that translates to over 120 amps from its internal pack full of 18650 cells, that's not bad.|
I emptied both Yeti bricks into the car, each of them down to nothing
left and in thermal-warning state.
The first one brought it from "---" state to a 1% charge, and a range
estimate of 1 mile.
The second one brought it from there up to 2% and 4 miles.
Given that each Yeti pack supplied one kWh minus a bit of loss from being
abused like this, those results told me the car's BMS seems to allow
somewhere around 750 Wh of "grace" beyond the zero-miles point.
That might still go as much as three extra miles before total failure,
so dumping in both Yetis' worth and very gentle driving could have this
rescue situation good for six or seven miles on the flat.
It's not a 5-gallon jerry can, but it's something. There *are* already companies making larger mobile fast-charging booster packs for exactly the same purpose -- the ability to bring maybe 20 kWh to a stranded EV and get it mobile enough, quickly enough, without a tow.
|Then I started charging for real, seeing the same 40A capability expressed in the pilot line. This would also be the first test of my whole EVSE power feed over the long haul, as it would be delivering a lot of power for the next 9 hours.|
The charging operation automatically brings on the low-voltage converter
at a modest level, to keep all the support electronics alive without
discharging the 12V battery.
The on-board charger [red arrow] does get a bit warm in operation, and after a long time the rest of the motor/electronics block and radiators do as well. At least one coolant pump runs during charging to keep the OBC happier, and all those components are tied together in one big loop. The hoses going to the pack, however, stayed cold in this case -- the level 2 charging rate wasn't enough to heat it significantly, so the 3-way valves that could include the pack into the loop kept it cut off.
|While the car was charging for the rest of the day, I happily busied myself with disassembling unrelated parts of it, as described in the "rip-n-tear" section -- at least going after parts that didn't require powering things down, since the basic "life support" systems had to stay up. It was kind of nice to get back into some of that again, since the early Prius days a decade-plus before, and frankly the physical aspects of how cars are generally put together and wired hadn't changed that much.|
|Towards evening, a healthy quantity of energy had passed through the GoPlug, still going strong, and the car was approaching full. The time estimate was way off, though; I suspected all the interrupted level-1 screwing around with the Yetis had confused things a little.|
|Things had been running at full power [well, the 30 amps that the car wanted] long enough for the thermal situation to stabilize, and I took a scan quite a while after the sun had passed over the house and all this was in shade. The dirt right next to the house was indeed slightly warmer from the cable maybe three inches down, and it was amusing to be able to see the trace of where the wire loops out around the corner. The EVSE and wire to the car got slightly warm but nowhere did I see any worrisome "hot spots". You have to take the infrared scale endpoints into account here; all of it is a very small delta. The feed wire going through the basement was barely warmish to the touch, as was the breaker in the panel.|
Finally the 100% mark was attained, and charging shut itself down.
The final figure on the GoPlug was in keeping with the known 92% or so
efficiency of the on-board charger, which had basically radiated on the
order of 700 watts into the air all day.
It seemed prudent to leave the hood open just to help let that out, as
well as to monitor things in general.
What was astounding and unexpected was the final figure on the "guess-O-meter" [that's apparently the technical term for it]. The car was already learning my driving style, and was estimating full range based on the recent consumption figures well north of 5 miles per kilowatt-hour. For perspective, the typical expectation is that most drivers will get 4 and a bit miles per kWh in most vehicles. A light foot driving a newer, efficient design can push far beyond that, so I was confident I'd usually be in the "300 club" most of the time and doing *better* for range than my Model-3 owning cohorts.
Observations like this are what help clinch my personal notion of "tipping
point" where electric vehicles are concerned.
I'd been saying for a while that once we could stuff about 300 miles worth
of *propulsive* energy into something about the size of a typical car's gas
tank, that would be a significant milestone for wide public acceptance.
The recent wave of longer-range cars like the Kona and its contemporaries
from other manufacturers get us just about to that point, with certain
The Kona pack does take up more volume than a gas tank but tucks out of the
way quite unobtrusively, and careful driving would still be needed to
achieve that range top to bottom but it *is* doable.
Llewellyn's youtube review,
"this is a game changer".
Of course we'd probably have the 700 or thousand-mile packs in another couple of years, but this still represents an impressive technical ramp-up.