Quite a difference between 120 and 240 volt charging.

[timk225]

While looking at the charging chart here:

Model 3 NEMA Adapters

I see there's quite a difference in charging rate when going from the 5-15 and 5-20 120 volt plugs to any 240 volt plug. You'd think the miles per hour of charge would just double when going from 120 to 240 volts at the same amperage, but I think there is some sort of "electrical overhead" use, where part of the charging power is used to run the BMS and other things, and by the time that is taken care of, a 5-15 or 5-20 doesn't have much power left to actually charge the battery.

5-15 3 mph to 6-15 11 mph, 5-20 4 mph to 6-20 15 mph.

So while it CAN charge at 120 volts, it will take a long time. And in the winter, with some power being used to keep the battery warm, I'd be surprised if a 5-20 did 1-2 mph, if even that much.

 

[KJD]

What you are saying about electrical overhead is correct and that is why the 240 volts is so much more efficient.

On my model S the mobile connector is supposed to be able to do 40 amps, but I found the cord and handle would get pretty warm at that speed. I turned down the charging on the car to 30 amps when at home and have not had any problem since.

If the charging speed is a concern you can always buy the High Power Wall Charger (HPWC) and charge at 48 amps or 44 mph. See the details here.
Home charging installation

 

[ölbrenner]

So while it CAN charge at 120 volts, it will take a long time.

But if you have two 120V/15A outlets on opposite legs, you have 11mph charging available. Still not fast, but covers most commuting needs.

 

[obie_fl]

Physics 101. Has nothing to do with overhead. Current (Amperage) times Potential (Voltage) = Power(Watts) Stated another way power at the same amperage is doubled when you double the voltage.

 

[ölbrenner]

Physics 101. Has nothing to do with overhead. Current (Amperage) times Potential (Voltage) = Power(Watts) Stated another way power at the same amperage is doubled when you double the voltage.

In real world:
120V@12A = 1440VA = 3mph charge rate
240V@12A = 2880VA = 11mph charge rate

 

[obie_fl]

Sorry for the physics lesson I misread the OP. I went to public schools

 

[scaesare]

From a practical standpoint it's true that 240V charging does yield rates that more than double 120V rates at the same current, but much of this has to do with there being very few available high current 120V circuits.

However the above-mentioned physics lesson is correct... if you were able to plug in to a 30A/120V outlet, you'd get just about the same rate as the 15A/240V connection.

In all cases there appears to be a ~400W fixed overhead, which manifests as a larger percentage of the power usage as your supply power is lower, hence the more than double range gain when you from the lowest power circuit to the next step up...

 

[Stoneymonster]

There’s also more loss for a given power at lower voltage. That’s where some of the outsized nenefit of 240 comes from.

 

[ölbrenner]

There’s also more loss for a given power at lower voltage. That’s where some of the outsized nenefit of 240 comes from.

^ THIS

 

[ölbrenner]

However the above-mentioned physics lesson is correct... if you were able to plug in to a 30A/120V outlet, you'd get just about the same rate as the 15A/240V connection..

Have to again disagree:
120V@24A = ~6mph charge rate (linear extrapolation from real world verified 120V 20A socket charge rates, my guess actuality it would actually around ~5.5mph charge rate due to the higher current losses)
240V@12A = 11mph charge rate

 

[mongo]

Have to again disagree:
120V@24A = ~6mph charge rate (linear extrapolation from real world verified 120V 20A socket charge rates, my guess actuality it would actually around ~5.5mph charge rate due to the higher current losses)
240V@12A = 11mph charge rate

You can't linearly extrapolate with one point unless you use the base load of the vehicle as the second point (as opposed to the origin). At some non-zero wattage in, charge power hits 0.
(For example 400W no charge, 800W 400W charge, straight watt for watt after base load, but using 800/400, an origin extrapolation yeilds 50% charge efficiency)

But yeah, a 30A 120V over the same house wiring would have 4x the resistive losses getting to the car. But that circuit would be made with a larger gauge wire to maintain the same overall loss/ temp rise.

 

[scaesare]

Have to again disagree:
120V@24A = ~6mph charge rate (linear extrapolation from real world verified 120V 20A socket charge rates, my guess actuality it would actually around ~5.5mph charge rate due to the higher current losses)

I'll call your disagreeing guess, and raise you a real world experience:

...the TT-30 ... provides about 9 mph of charging

 

[scaesare]

You can't linearly extrapolate with one point unless you use the base load of the vehicle as the second point (as opposed to the origin). At some non-zero wattage in, charge power hits 0.
(For example 400W no charge, 800W 400W charge, straight watt for watt after base load, but using 800/400, an origin extrapolation yeilds 50% charge efficiency)

But yeah, a 30A 120V over the same house wiring would have 4x the resistive losses getting to the car. But that circuit would be made with a larger gauge wire to maintain the same overall loss/ temp rise.

Agreed... the fixed overheard from the car's constant consumption (~400W), has to be accounted for as a percentage of overall power delivered.

A 120V/12A delivers 1440W to the car, so the overhead eats 28% of that, leaving 72% of the power delivered for battery charging.

A 240 /12A circuit delivers 2880W to the car, which means the overhead is only 14%, leaving 86% power for the battery. A 240V/40A (9.4KW) circuit loses only about 4% to overhead, leaving 96% for the battery.

(All of the above ignore small variation due to system efficiency and current losses, which is why I said "about" in my earlier post)

 

[mongo]

Agreed... the fixed overheard from the car's constant consumption (~400W), has to be accounted for as a percentage of overall power delivered.

A 120V/12A delivers 1440W to the car, so the overhead eats 28% of that, leaving 72% of the power delivered for battery charging.

A 240 /12A circuit delivers 2880W to the car, which means the overhead is only 14%, leaving 86% power for the battery. A 240V/40A (9.4KW) circuit loses only about 4% to overhead, leaving 96% for the battery.

(All of the above ignore small variation due to system efficiency and current losses, which is why I said "about" in my earlier post)

The analogy I like is: Installing a second 100 MW power plant doesn't double your excess power, it increases it by 100 MW.

Percentage can be tricky due exactly to your example. Same sort of thing with accounting and fixed vs variable costs. More production less fixed cost per vehicle.

 

[n2mb_racing]

From a practical standpoint it's true that 240V charging does yield rates that more than double 120V rates at the same current, but much of this has to do with there being very few available high current 120V circuits.

However the above-mentioned physics lesson is correct... if you were able to plug in to a 30A/120V outlet, you'd get just about the same rate as the 15A/240V connection.

In all cases there appears to be a ~400W fixed overhead, which manifests as a larger percentage of the power usage as your supply power is lower, hence the more than double range gain when you from the lowest power circuit to the next step up...

Not really. I've charged 120v 30a at a campground and it is not as fast as 240v 15a.

More losses stepping the voltage from 120v to 400v...

 

[scaesare]

Not really. I've charged 120v 30a at a campground and it is not as fast as 240v 15a.

More losses stepping the voltage from 120v to 400v...

As I mentioned earlier, there's some losses, including from the higher current draw, but a 120V/30A connection is much closer to the rate of a 240V/15A circuit than it is the 5.5 MPH guess guessed at earlier.

Which is why I earlier said "about" the same.

 

[n2mb_racing]

As I mentioned earlier, there's some losses, including from the higher current draw, but a 120V/30A connection is much closer to the rate of a 240V/15A circuit than it is the 5.5 MPH guess guessed at earlier.

Which is why I earlier said "about" the same.

I think I got 8 mph on 120 30a vs 11 mph on 240 16a

 

[scaesare]

The earlier thread I linked had it as 9 for them.

You numbers don't quite line up though, are you talking charge rate in one case and circuit rating in the other?

 

[jsmay311]

I suspect those 120V mph numbers for the Model 3 are understated.

A Gen 1 Volt charges at nearly 4mph on 120V 12A and the Model 3 is ~24% more efficient that the Gen 1 Volt. So unless there's something weird with Tesla's charging systems, a Model 3 charging at 120V 12A should be closer to 5mph than 3mph.

 

[wine magnet]

With my 3/31/16 ordered M3 likely to arrive before May, i am ready to start preparing for charging at home, where I should have no problem with adding a 240V 50A circuit. At my commercial building, where I have a 68KW solar array which provides considerably more power than is currently consumed, I am wondering if I can benefit by using the DC power from the solar array before it goes to the inverters. Any thoughts?