[Oeva-list] charging efficiency

Alan Batie alan at batie.org
Tue May 17 14:29:46 PDT 2011

I think I need to adopt a tag line of "Having Range Anxiety so you don't
have to" ;-)

As I'm looking over the data from the trip this weekend (and there's a
lot more to think about than I imagined! so full report coming later),
I'm wondering about how to think about some of it:

My car reported that it used 19kwh to go to Portland Saturday, 23kwh -
4kwh in regeneration.  I charged for 3 hrs total at the 3.3kwh stations
along the way, and put in 15kwh at the fast charger, which adds up to
about 25kwh, which seems consistent, since I know there is "overhead" in

When I got home, I pushed it by going directly from Salem to home ---
I'd charged enough to make it to LBCC, but when I got to Albany, I
realized that at the rate I was going, I could just make it, and did
(albeit by driving 5mph below the speed limit from Albany to a couple
miles from home): it said "10 miles" left, with the 2 red bars
and the Blink reported that that charge used 20.5kwh.  That is
consistent with the 24kwh spec on the battery pack --- the 12 bars make
it 2kwh/bar, so the 10 white bars add up to 20kwh.  But 20kwh of battery
should mean 27kwh consumed at 75%...

The Salem Nissan is almost exactly at the halfway point, and I left
there about 2/3rds full showing "47 miles"
 The "10 miles" left is consistent with what I've found to be a useful
ball park of 5 freeway miles/bar (it's better than that a little, but it
makes a good rule of thumb).

Going the other direction, if I assume that the charging efficiency is
about 75% (19/25), that makes it 16kwh, which means it's more like 32kwh
to get to Portland, and *that's* more consistent with what I'm seeing
for the range on the car.

One problem is that the bars are too coarse --- the 6 white bars I had
when I left Salem could be "just barely past 5" so it could have been
essentially 60% charge, which is consistent with what the car's
reporting that indicates I could almost make it to Portland without

I'm thinking about testing that this weekend: after stopping to check
the PGE station and a 1hr charge there, and doing the whole trip at
60mph, see if I can make it all the way.  If I can, I might even be able
to bring it up to an OEVA meeting ;-)

Which is bringing up another consideration I didn't think I'd remotely
have with an EV: the mileage on a lease.  At 15,000/yr, that's way more
than I thought it capable of, but I have 900 miles on it now, after a
month ;-)  That's 11K/year --- safe, but a lot closer than I expected!

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