Month: May 2019

Some real-world numbers

Posted on by Bill

We’ve had the car for a bit more than a week.  It got to Boise on the 6th.  I got down there on the 8th to drive it and pay for it.  Without any real-world numbers on miles/kWh or charging rates, I planned a route for brining it home, a trip of about 500 miles.  It would have been a fun adventure.  Other family issues made us re-think our need and capacity for adventure at that time.  So we shipped the car home.

It arrived on the 16th.  We have about three hundred miles on the odometer and have charged twice at home and once on a public DC charger.

The car says it is getting 3.1 km per kWh.  That’s 1.9 miles per kWh and the car can, in theory, spit out 76 kWh before calling it good.  That suggests the range on 80 percent of a full battery is 146 miles.  That’s way off the advertised 204 miles and the 212 miles the car says it has on a full battery.  We need more time to sort out the real range of this thing.

We have a two 240V, 40A circuits in the garage with NEMA 14-50 receptacles.  The car’s charging unit fits that receptacle.  Technically, the ‘gizmo’ they give you is called an EVSE, electric car supply equipment.  The charger is in the car.  The ESVE has a NEMA plug on one side and a J1772 connector on the other.  It has control electronics that keep everyone safe while charging and not charging.

The circuit we have should charge the car at 9.6 kWh.  But we only get 4.4 kWh.  That means a full charge should take around 25 hours, much longer than the 9 hours Audi advertises.  I did notice the ESVE says “50%”, which is close to 4.4 kWh.  I just can’t find any switch to make it work at 100%!

Today I charged at a 50 kWh DC EVgo station at the local shopping center.  I was able to charge from 57% to 95% in 42 minutes.  My math says that’s 36.1 kWh, but the charger says it delivered 35.3 kWh.  Close enough.  That’s 0.84 kWh per minute or 50 kWh per hour.  At that rate, a full (20% to 100%) charge should take 90 minutes.  A 150 kWh charger should be almost three times faster.

The cost of the 50 kWh charger, for 35 kWh was $13.40.  That’s roughly 20 cents per mile.  At $4/gal, my Q7 costs about the same to operate.  The lesson here is — charge at home!

Bottom line

On the highway, two hours of driving will take you about 150 miles and run your battery down to twenty percent.  It will take about thirty minutes to recharge that if you can find 150 kWh charger, 90 minutes otherwise.

Around town, the same 150 miles will take you two to three days in the suburbs and will require 17 hours to refill.  It’s probably best to charge every night.

Overall impressions of the car

We love it!  It’s super comfortable, luxurious actually.  It drives well, is fast enough and handles nicely.  The audio is good.  Features are outstanding, it’s fully loaded.  (We have the Edition One.)  You do feel like you are driving the future of automobiles.

Negatives include CarPlay (which is flaky as heck), no user manuals and slow charging at home.

We need to find a 150 kWh charger and get more real-world mileage before we take a road trip.  Spokane is a common destination for us.  We see ElectrifyAmerica will have a 150 kWh charger on that route soon.  But there is nothing high-speed near family in Spokane.  So we can get there, but will need a long time to charge enough to get back to the high-speed charger.  For now, this is an around-town car.  But a really, really nice one!

Can’t plug that!

Posted on by Bill

Apologies to MC Hammer….

So you need to charge your rolling battery.  We discussed in the previous post that a bigger charger can add more miles, in the form of kilowatt-hours (kWh), than a smaller charger.  Chargers sort-a, kind-a come in three sizes called L1, L2 and L3.  L means ‘level’.

Each level can charger faster than the one below.

L1 is your regular ol’ household outlet.  That’s 110 volts at 15 amps.  That’s 1.65kW, or, not much.  I know my arithmetic is correct; 110 times 15 IS 1,650.  But many web pages I see describe L1 having more like 3.7kW.  They may be assuming 30 amps. Audi says an L1 charger can add 80 percent, 76kW, in 90 hours.  I think that means they are assuming 0.84kW.  Whatever… there’s clearly not a lot of ‘go’ in that plug.

A lot of chargers listed on PlugShare are L1.  It’s helpful to set your filters to ignore these chargers.  (See below.)

L2 uses more voltage and more amps.  So way more kW.  We have a 30 amp, 240 volt outlet in our garage.  That’s 7.2kW.  We need 76kW to go from empty (20%) to full.  It should take 10 hours.  And indeed, Audi says 9 hours on an L2 charger will fill the tank.

Both L1 and L2 are alternating current (AC).  You know, the normal household stuff, but with a little more kick in the L2 case.

L3 is direct current, or DC.  We generally don’t have this stuff in our homes.  At least not in any wall plugs.  ElectrifyAmerica and others are building nationwide networks of L3 chargers.  EA has 50kW and 150kW chargers in metro areas and 150kW and 350kW chargers along major interstate highways.

Three-hundred and fifty kilowatts is, well, a lot.  Fifteen minutes on a 350kW charger will deliver 87.5kW or more than we need to go from 20% to full in the Audi e-tron.  We can cut our refueling time in half.  Sort-of…

The other eighty percent

We already know that most EVs think 20 percent state-of-charge (SOC) is empty.  L3 chargers slow down when the SOC reaches 80 percent.  I’m not sure why.   Apparently, L3 charges approach L2 speeds when the battery gets to 80% SOC.  If the cost per minute of an L3 charger is higher than that of an L2 charger, it might be cost-effective to switch at 80% SOC.

A 350kW L3 charger can push the e-tron battery from 20% to 80% in just under 10 minutes.  And that’s about 115 miles.  If you had enough chargers along a route, you could drive 115 miles, charge for ten minutes, drive 115 miles, charge for ten minutes, etc.  I’m not sure that’s better, but you are supposed to take frequent breaks!

You can plug that

There are a bunch of charger plugs out there.  The one, or two, you want are dictated by your car.  Tesla has their own adaptor.  Ignoring that, you’ll find three plugs on public charging stations.

They look like this:

Plug-Icon-J1772 Plug-Icon-CHAdeMO Plug-Icon-J1772-Combo
J1772 CHAdeMO SAE Combo CCS

The J1772 plug is very common either by itself or in the CCS combo plug.  Teslas have their own super-chargers and plugs, but they can use the J1772 with an adaptor.  The e-tron uses the CCS adaptor.  Which means it can also use the J1772.

The J1772 is an L2 plug.  L3 chargers, other for non-Teslas, use the CCS plug.  That bottom part of the CCS is the DC connector.  The good stuff…

Nissan Leafs use the CHAdeMO plug.  It does not fit the e-tron.

Bottom line

L3 is best, L2 is second best, L1 won’t cut it while traveling.  The difference between L3 and L2 is substantial.  Use L3 when possible.

Continue reading →

Huh, a killa-what?

Posted on by Bill

Oh, a kilowatt.  Or kW.  I see.  So in electricity, a watt is a unit of power.  It takes more power to light a room with a 100W bulb than it does with a 60W bulb.  More power through the lightbulb, more light. A kilowatt is 1,000 watts.  So ten 100W lightbulbs.  Sort of.

A kilowatt-hour is the amount of energy we use when we push a kilowatt around for an hour.  Light those ten bulbs for an hour, that’s 1kWh.  Do it all night, that’s, um, more kWh.  Depends on how long your night is. According to Wikipedia, so you know it’s true, the average US customer pays 12 cents per kWh.  So ten 100W bulbs for an hours costs a bit more than a dime.

If I have a battery that holds, say, 95 kWh we can light those 10 100W bulbs for 95 hours. Or five of them for 190 hours.  Or one for 950 hours.

This thing here:

IMG_1762

Is a rolling 95kWh battery.  It’s an Audi e-tron.  It’s sitting in Boise, ID.  We live near Seattle.  It’s 500 miles.  And we have a battery measured not in miles, but in kWh.  Can we make it?

No.

Well, not in one fell-swoop, as they say.  The key thing we need to know is, how many miles can you get per kWh.  With a full charge, the car said it could go 250 miles.  That’s 2.63 miles per kWH.  Starting the car and running the A/C brought that quickly down to 212.  Reviews on the web estimate 200 to 208.  EVs (electric vehicles, if that wasn’t obvious) don’t let their batteries get below some threshold.  Apparently a Tesla will use up to 90 percent or so of its juice.  Rumor says Audi dialed that to around 20 percent. And they brag, a lot, about how little time it takes to charge the battery 80 percent.  So let’s guess that they only use… 80 percent, or 76 kWh.

They also say owners get 1000 kWh free at ElectrifyAmerican charging stations and that amount of energy is roughly equivalent to 2,000 miles.

So… 2 miles per kWh.  That’s 76 kWh (using the 20 percent floor) times 2m/kWh is right about 150 miles per ‘tank’.  At 0.12 per kWh the cost is just over $9.  That’s six cents a mile!

But what about getting from point A to point B?

First you have to find a charger every 150 miles.  Ok, we have an app for that.  The app lets you enter your start and destination addresses and details about your car (distance it can cover, how many miles you have remaining, when you start) and they find you chargers every, say 150s miles, along the route.  Can any particular charger on the route get you the next, say 150 miles, down the road?  Time for more math!  You knew there would be math, right?

Keeping our 2m/kWh estimate, we need to get 75kWh into the car.  If a charger produces 75kWh, it will take one hour to ‘fill the tank’.  I’m making a boatload (technical term) of assumptions here about charge rates and the car’s ability to suck up the juice.  But they match up pretty well with info Audi is advertising and publishing on the web.

Anyway, a 150kW charge needs a half-hour to add 75kW to the car.  This exactly matches an Audi claim.  That is, on a high-speed DC charger, you can add 80 percent distance in thirty minutes.  Electrify America is Volkswagen (owns Audi) Corporation’s partial atonement for ‘diesel-gate’.  They are investing $2B to build a (USA) nation-wide network of chargers.  Their chargers will be 50kW, 150kW and 350kW units.

So, if we can find 150kWh chargers every 150 miles apart, we’re good to go.  Let’s see… Maybe we can average 75mph on the highway.  That’s two hours per leg of the trip.  So we:

  • Drive two hours
  • Charge for one-half hour
  • Drive two hours
  • Charge for one-half hour
  • Drive two hours
  • Charge for one-half hour
  • Drive for two-thirds of an hour

And we’re home!  EA charges $0.30 to $0.35 per minute.  That’s nine dollars per charge. This trip costs $27 for fuel not counting the top-off at the end of the trip.  Plus one and a half-hour in time.  My Q7 gets 20 mpg on the highway at almost $4 per gallon.  That’s about a hundred bucks but less time.

None of this reduces my enthusiasm for an electric car.  And the e-tron is a great car. Good size, between the Q5 and Q7, all-wheel drive, lots of luxury features, etc.

So, are we going to drive it or ship it?  Driving would be a fun adventure.  But other things going on at the moment argue against an adventure at this moment.  If we do drive it, we’ll describe the trip here.

In the meantime. I’ve done some research on charging ports, which matter, that I might post here.  Plus specifics about charger levels, home chargers, getting accounts with charger companies. etc.  More to follow…