OK here
is some free consulting. LOL you get what you pay for.
In selecting a vehicle and charging system, one formula is very basic and very important. But don't turn your brain off even if you don't want to do calcs, you don't have to, just follow along.
W=V*A
Voltage
will always be 240V on a 2 Phase (which uses a 2 pole breaker), in your area
that might be 230V no big difference in the calcs.
The
Average peak charging rate shown in the spreadsheet is 6.6 kW, plug that in and
solve for Amps
6600 W=240
*A
AMP=
27.5
The
other main max charging rates are 10kW, and for the Tesla an option for 20kW
10,000
=240 * A solves A for 41.67A
20,000 = 240 * A solves A for
83.33A
Now a
very important observation from over a decade of solar PV work, and the NEC
(National Electric Code) has been slowly adopting more conservative codes to
reflect that fact that solar circuit
often operate near peak load, and for a long time. This means the wires heat up over time, and
over time the insulation takes a beating, as well as the connections whether
they are wire nutted or bolted.
The main
effect of Amperage is in selecting wire size, at least in conventional systems. But PV electric systems, and car charging
system are similar in one important way, and so the knowledge gleaned from PV
systems is directly applicable to EV Charging systems, and that similarity is
that they both run near peak amperage for long periods of time, many
hours. This creates heat, and also losses, and the higher the heat, the higher the losses, so it is like a cat chasing it's tail.
One
other aspect of PV, because of the heat issue, is that the most recent codes
require that any wire that is in a run of conduit, that is situated where it
can be directly lit by the sun must be further “derated” and this simply means
you must jump up one wire size from the other calculations which also have some
conservatism built into them.
I will
introduce quickly one other concept that is affected by wire and breaker sizing
– the amount of electricity lost while running through the wire (it’s lost as
heat). The smaller the wire the bigger
the loss. In most modern electrical
systems, it is almost always a nobrainer to upsize the wire as the additional
cost will be more than paid for by lower losses.
The
minimal “derate” on solar PV is done by multiplying the expected Amps time 125%,
and sometimes this is also multiplied by another 125%. 125% *125% = 156%
If you
take the 27.5A Charging amp above and use the 156% multiplier you get 42.9A,
which would use a 50A 2 Pole breaker.
So yes,
a 50A 240V (2 Pole) circuit would be pretty comfortable for all the currently
available electric cars.
How
about the Volkswagen at 7.2kW charging rate?
7200 W =
240 *A = 30 A
30A
*156% = 46.8A
You work
out the numbers for the BMW at 7.4kW  try it, there is no rocket science
here. You will leave your EV or PV “Salesman”
in the dust though, with just this amount of knowledge.
The
Tesla at 20kW
20,000 =
240 * A solves for 83.33 A times 156%
would be 130A in this conservative calc, and even using a 125% multiplier would
be 104A.
It
should be clear if you are following that a 50A 2 Pole service (or breaker if
you will) would be definitely pushing the limit to charge the Tesla at the 10kW
rate, and may even violate local codes.
The manufacturers of the car and charger may also have their own
requirements, which you can never go under, but you can definitely, and
probably should, go over in picking breaker and wire size.
Electricians
will probably want to “bid” the smallest breaker and wire size, not for your
long term benefit, but because they want a better chance of winning bid, and if
they upsize your wire and breaker to get you the safer system and the one with
less power losses over time, they will lose the bid. So be aware, they will convincingly try to
assure you the smaller wire and breaker is “fine” and meets code.
And back
to the concept of electrical losses, the bigger wire and breaker will provide
less electricity losses, especially on system that run often and for many
hours. So I wouldn’t necessarily rip out a 40A
charging circuit, and replace it with a 50A because that project cost would
probably not be justified. But if
designing fresh, I would almost always choose the 50A as the upgraded cost is
minimal.
One
final thought. You might be designing
a charging system for a Chevy Volt at 3.3kW.
That only gives you 11 Miles for each hour of charging. That might be really inconvenient at times,
you may want a quicker charge rate. You
might “put up with that” on your first EV, but I strongly feel that as time
goes on, people are going to insist on faster charging rates, and future
vehicles and chargers will require a fast, strong shot of electricity  big
Amps. So doing it right, once, and on
the first system, makes a lot of sense.
Doing it over can cost A LOT more, and with less electricity losses,
doing the larger system gives you benefits right out of the gate, even if your
second EV is many years down the road.
Stock out
Model

Max
Charge

~Miles
Added Per Hour

100%
Electric or PHEV

Audi
A3 etron

3.3
kW

11

PHEV

BMW
i3

7.4
kW

25

100%
Electric / REx

Cadillac
ELR

3.3
kW

11

PHEV

Chevy
Spark EV

3.3
kW

11

100%
Electric

Chevy
Volt

3.3
kW

11

PHEV

Fiat
500e

6.6
kW

22

100%
Electric

Ford
CMax Energi

3.3
kW

11

PHEV

Ford
Fusion Energi

3.3
kW

11

PHEV

Ford
Focus Electric

6.6
kW

22

100%
Electric

Honda
Accord PlugIn Hybrid

6.6
kW

22

PHEV

Hyundai
Sonata Plugin Hybrid

3.3
kW

11

PHEV

Kia
Soul EV

6.6
kW

22

100%
Electric

Mercedes
BClass Electric

10
kW

29

100%
Electric

Mercedes
S550 Plugin Hybrid

3.3
kW

11

PHEV

Mercedes
C350 Plugin Hybrid

3.3
kW

11

PHEV

Mitsubishi
iMiEV

3.3
kW

11

100%
Electric

Nissan
LEAF

3.3
kW / 6.6 kW

11
/ 22

100%
Electric

Porsche
Cayenne S EHybrid

3.6
kW / 7.2 kW

12
/ 24

PHEV

Porsche
Panamera S EHybrid

3
kW

10

PHEV

Smart
Electric Drive

3.3
kW

11

100%
Electric

Tesla
Model S

10
kW / 20 kW

29
/ 58

100%
Electric

Tesla
Model X

10
kW / 20 kW

29
/ 58

100%
Electric

Toyota
Prius PlugIn

3.3
kW

11

PHEV

Volkswagen
eGolf

3.6
kW / 7.2 kW

12
/ 24

100%
Electric
