Home charging 110 vs 240 - Efficiency?
- Thread starter JeffKeryk
- Start date
Smart meters display the voltage accurately. Mine is about 240, but varies about 6 volts, I look at it all the time. Also can accurately see the real time kilowatts being used and the total kWh. Very useful device.
The Volt owners manual stated 240 is more efficient, which is the efficiency of the onboard charging system, not the supply. It varies between ev’s they all have their own kinds of chargers and not are all the same.
The Volt owners manual stated 240 is more efficient, which is the efficiency of the onboard charging system, not the supply. It varies between ev’s they all have their own kinds of chargers and not are all the same.
JHZR2
Staff member
120V/240V Charging Efficiency - Answers!
TL;DR: Conclusion: Charging a Model 3 at 240V is very efficient, and noticeably more efficient than charging at 120V.forums.tesla.com
Setup:
Temperature: 75-85F (24-29C) in my garage
Equipment used:
- IoTaWatt in the Circuit breaker box, with dedicated monitors per circuit
- Stats running on my phone, querying the car's API
- Gen 2 Mobile Connector charging at 32A @ 240V, or 12A @ 120V.
Technique:
- Charging started in the evening, stopped in the morning. IoTaWatt and Stats were queried to find how much power was drawn from the house panel, and how much was stored in the battery.
- The 240V outlet and 120V outlet are very short runs from the Circuit Breaker box, minimizing power loss in the wiring. The 240V circuit is about 15' of AWG 6, and the 120V circuit is about about 5' of AWG 12.
Results:
At 240V (Measured average about 252V), Stats showed 40.62 kwh added to the battery. IoTaWatt showed 42.5 kwh pulled from the wall. Efficiency = 40.62/42.5=95.6%.
At 120V (Measured average about 126V), Stats showed 10.15 kwh added to the battery. IoTaWatt showed 11.9 kwh pulled from the wall. Efficiency = 10.15/11.9=85.2%
Conclusion
Charging at 240V is very efficient, and noticeably more efficient than charging at 120V. You will pay about 12% more to charge at 120V compared with charging at 240V.
Example: Driving 10,000 miles per year, at 250 Wh/mile, will take about 2500 kwh from the battery. At 240V, you'll pull (2500/0.956) = 2600 kwh from the wall over the year to recharge the battery. At 120V, you'll pull (2500/.852)=2900 kwh from the wall over the year, which is 12% more power and likely 12% more money.
I’m not sure I buy this, especially without a better explanation of the charger topology and it’s effect on the rectified dc and the losses. Is it the same charger for 110 and 220? Are the IGBTs employed differently? Different levels of ripple? Do we have actual waveforms?
Conductor resistance is a thing. Losses increase with the square of current, doesn’t matter if it’s 110 or 220 or something else. You go higher voltage to reduce current.
The report you gave didn’t cite battery %SOC or temperatures. The impedances of batteries do change, and that may be a factor.
The question really is what conditions result in higher losses?
They can be:
1) IGBT switching losses and noise (which will be worse at low current levels)
2) conductor losses - mains power
3) cell (ESR) losses
4) cooling system losses
5) BMS on-state losses
6) BMS balancing energy burned
7) conductor losses (internal to battery and charger)
8) vehicle control system losses
Each of these can be discussed in more detail. Perhaps some time I will.
For now I’ll just address briefly one by one:
1) favors faster charging, as the losses are higher as a percentage the lower you go (though the net may be higher). The topology of the charging converter may also play in here at higher vs lower mains input. I do suspect that all other things being equal, this will drive it, but given that it’s likely to be the same design and topology employed either line-line (220) or line-neutral (120), how much difference and how much it is compared to other factors is hard to say for certain. It’s not like we’re talking one vs three phase, potentially with phase shifting transformers and other goodies to make a much nicer/better dc like you can if we’re talking split phase 220 versus say, three phase 480.
2) favors lower current charging, regardless of voltage. Losses are I^2 *R, and R is not affected by voltage at the same frequency.
3) favors lower current as in cell losses and heating are also I^2 *R. There are activation losses that drive the need for over potential, and aso it may be U-shaped.
Example of an impedance curve for NCA cells:
So there can be a greater than 10% difference in ohmic losses based just on what the starting and ending SOC is.
4) This depends upon the approach used for cooling system operations while on. If it’s always on, and there’s a minimum flow rate, it’s going to be a higher percentage at lower charge rate.
5) irrelevant to charging voltage. Sunk cost.
6) Assume tesla has set resistive balancing. Thus the losses are proportional to cel group voltage regardless of charging input power. A faster charge will drive a higher overpotential and marginally higher energy burn per ohms law.
7) favors lower current levels
8) constant value irrelevant to mains power in.
In the end I have no doubt that #1 could drive single percentage point efficiency drops favoring higher voltage input and higher current.
No way I’m buying the 10% difference in favor of 240 without more/better explanation and tracing as to why... unless the onboard charger is just that bad.
Technical commentary and rebuttal welcome.
Last edited:
JHZR2
Staff member
110/220 is nominal, 120/240 is closer to actual, and can be higher. Residential power is called “split phase”, so the two 120v legs coming into your house make the 240V. It’s potential, so for any location, the 2xx V one sees is the mathematical sum of the two 1xx V that they measure.
Much of the rest of it is highly dependent upon the actual topology of the Tesla onboard charger, and some of the other things I mention above.
The confounding factor there is that the 240 V circuit uses #6 AWG conductors, whereas the 120 V one uses #12.120V/240V Charging Efficiency - Answers!
TL;DR: Conclusion: Charging a Model 3 at 240V is very efficient, and noticeably more efficient than charging at 120V.
Setup:
Temperature: 75-85F (24-29C) in my garage
Equipment used:
- IoTaWatt in the Circuit breaker box, with dedicated monitors per circuit
- Stats running on my phone, querying the car's API
- Gen 2 Mobile Connector charging at 32A @ 240V, or 12A @ 120V.
Technique:
- Charging started in the evening, stopped in the morning. IoTaWatt and Stats were queried to find how much power was drawn from the house panel, and how much was stored in the battery.
- The 240V outlet and 120V outlet are very short runs from the Circuit Breaker box, minimizing power loss in the wiring. The 240V circuit is about 15' of AWG 6, and the 120V circuit is about about 5' of AWG 12.
Results:
At 240V (Measured average about 252V), Stats showed 40.62 kwh added to the battery. IoTaWatt showed 42.5 kwh pulled from the wall. Efficiency = 40.62/42.5=95.6%.
At 120V (Measured average about 126V), Stats showed 10.15 kwh added to the battery. IoTaWatt showed 11.9 kwh pulled from the wall. Efficiency = 10.15/11.9=85.2%
Conclusion
Charging at 240V is very efficient, and noticeably more efficient than charging at 120V. You will pay about 12% more to charge at 120V compared with charging at 240V.
Example: Driving 10,000 miles per year, at 250 Wh/mile, will take about 2500 kwh from the battery. At 240V, you'll pull (2500/0.956) = 2600 kwh from the wall over the year to recharge the battery. At 120V, you'll pull (2500/.852)=2900 kwh from the wall over the year, which is 12% more power and likely 12% more money.
The #6 is a much "larger pipe", and will pass current with much lower losses (and therefore much higher efficiency).
I'd like to see a true apples-to-apples comparison.
Efficiency matters over time.
For sure 240 can really move the meter, but Im not certain its an absolute truth you cant get usable range from 120
That depends on what you need the next day, and how many hours "a night" is.
It depends on the provider and rate plan you've got.
It varies from pretty cheap to absolutely brutal sometime within the same day on a time of use plan.
I’m not sure I buy this, especially without a better explanation of the charger topology and it’s effect on the rectified dc and the losses. Is it the same charger for 110 and 220? Are the IGBTs employed differently? Different levels of ripple? Do we have actual waveforms?
Conductor resistance is a thing. Losses increase with the square of current, doesn’t matter if it’s 110 or 220 or something else. You go higher voltage to reduce current.
The report you gave didn’t cite battery %SOC or temperatures. The impedances of batteries do change, and that may be a factor.
The question really is what conditions result in higher losses?
They can be:
1) IGBT switching losses and noise (which will be worse at low current levels)
2) conductor losses - mains power
3) cell (ESR) losses
4) cooling system losses
5) BMS on-state losses
6) BMS balancing energy burned
7) conductor losses (internal to battery and charger)
8) vehicle control system losses
Each of these can be discussed in more detail. Perhaps some time I will.
For now I’ll just address briefly one by one:
1) favors faster charging, as the losses are higher as a percentage the lower you go (though the net may be higher). The topology of the charging converter may also play in here at higher vs lower mains input. I do suspect that all other things being equal, this will drive it, but given that it’s likely to be the same design and topology employed either line-line (220) or line-neutral (120), how much difference and how much it is compared to other factors is hard to say for certain. It’s not like we’re talking one vs three phase, potentially with phase shifting transformers and other goodies to make a much nicer/better dc like you can if we’re talking split phase 220 versus say, three phase 480.
2) favors lower current charging, regardless of voltage. Losses are I^2 *R, and R is not affected by voltage at the same frequency.
3) favors lower current as in cell losses and heating are also I^2 *R. There are activation losses that drive the need for over potential, and aso it may be U-shaped.
Example of an impedance curve for NCA cells:
So there can be a greater than 10% difference in ohmic losses based just on what the starting and ending SOC is.
4) This depends upon the approach used for cooling system operations while on. If it’s always on, and there’s a minimum flow rate, it’s going to be a higher percentage at lower charge rate.
5) irrelevant to charging voltage. Sunk cost.
6) Assume tesla has set resistive balancing. Thus the losses are proportional to cel group voltage regardless of charging input power. A faster charge will drive a higher overpotential and marginally higher energy burn per ohms law.
7) favors lower current levels
8) constant value irrelevant to mains power in.
In the end I have no doubt that #1 could drive single percentage point efficiency drops favoring higher voltage input and higher current.
No way I’m buying the 10% difference in favor of 240 without more/better explanation and tracing as to why... unless the onboard charger is just that bad.
Technical commentary and rebuttal welcome.
That was a pretty simple test= measure from the wall, vs what ends up in the car- its results mirror pretty closely others I've seen.
We dont get waveforms or any great detail. You are one of the few that gets us charging profiles or waveforms. (thanks for all that time for that BTW)
With the data we have I can really only guess as to what makes any given delta - and my guesses would be
That 240 lower conductor resistance and line loss is one part
That charger design/topology yields more ripple at 120 than 240 when charging a 400 Volt battery and that using standard strategies to reduce it like a reservoir capacitor result in a bit more heat and loss of efficiency whereas the higher voltage will result in less ripple impact to manage.
Ill be looking to see what more I can learn and absorb as many tests as I can find.
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JHZR2
Staff member
I’ll be interested to see what else you find. I think understanding the ins and outs of this is good info for us all.
Spot on. The reason for my post.
Why do we in this country use 110/120 volt 60 cycle (hertz) and all Europe uses 220/240 volt 50 cycle (hertz) power?
I don’t know. Just asking.
I don’t know. Just asking.
Zee09
$200 Site Donor 2023
A fleet of EV commercial vehicles designed to be used with 480 volt
3 phase electric system would bring what to the table????
3 phase electric system would bring what to the table????
It's the way it's always been. If you think that's bad Japan has different standards on the same island. There may also have been an old school perception that 120 was tolerably non-lethal if you took it directly.
Edison's light bulb was the killer app for his 120V DC dynamo "Edison Plant". DC only covers short distances (~2 miles) so Edison wanted a licensed Edison power plant in every town.
Westinghouse waltzed in with his distance-capable AC power and electrified Buffalo via Niagra Falls, 20 miles away. He made his average voltage ~115 so it would work with Edison's light bulbs and basically "stole" them. The two hated each others guts!
These electrical standards bled over into television-- NTSC ran (nearly) 30 frames per second while the Euro standard was 25, as that was doable with the analog circuitry that ran off the mains frequencies.
JHZR2
Staff member
There are a variety of benefits associated with three (or polyphase) power. Some are related to motor and magnetic design, but the main benefit for charging systems is the ability to carry more power on fewer/less conductor, and provide cleaner dc with less ripple.
Here’s an example of split phase (single phase) vs three phase. Recall that AC power is sinusoidal in voltage and current.
Rectifying dc is the process of taking the alternating (AC) sinusoid, and making it into direct current which for the sake of this, is only positive offset. Rectification of single and three phase looks like this:
Note how bad the ripple is for the single rectified phase. Three phase overlays all the ripples and has significantly less. It’s “cleaner”. There can be polyphase rectifiers that are fed via phase shifting transformers to be even cleaner. Ripple is not good for batteries. I wouldn’t doubt that some larger charging stations might consider more phases.
Some examples:
In the end, the more phases/pulses, the cleaner the dc waveform, the easier to filter and smooth, the better it is for batteries and other equipment. Ultimately it’s a balance of cost, power quality, harmonics, size, efficiency, etc.
But feeding power with three phase, for loss that can take it, will be efficient conductor-wise and from a magnetic standpoint for motors and whatnot.
Funny you mention being at end of long street. We were at beginning of long street and were blowing out bulbs and a tv or two. I measured 130-135vac. Power company was turning up voltage at beginning of circuit/street so ppl at end would have enough. Very arrogant power company told me "things run better on higher voltage" and just buy 130 v bulbs! They finally came out, measured voltage, and installed another transformer. Just shows you gotta check everything these days.
Zee09
$200 Site Donor 2023
Very informative- thanks!There are a variety of benefits associated with three (or polyphase) power. Some are related to motor and magnetic design, but the main benefit for charging systems is the ability to carry more power on fewer/less conductor, and provide cleaner dc with less ripple.
Here’s an example of split phase (single phase) vs three phase. Recall that AC power is sinusoidal in voltage and current.
Rectifying dc is the process of taking the alternating (AC) sinusoid, and making it into direct current which for the sake of this, is only positive offset. Rectification of single and three phase looks like this:
Note how bad the ripple is for the single rectified phase. Three phase overlays all the ripples and has significantly less. It’s “cleaner”. There can be polyphase rectifiers that are fed via phase shifting transformers to be even cleaner. Ripple is not good for batteries. I wouldn’t doubt that some larger charging stations might consider more phases.
Some examples:
In the end, the more phases/pulses, the cleaner the dc waveform, the easier to filter and smooth, the better it is for batteries and other equipment. Ultimately it’s a balance of cost, power quality, harmonics, size, efficiency, etc.
But feeding power with three phase, for loss that can take it, will be efficient conductor-wise and from a magnetic standpoint for motors and whatnot.
On machine tools they seem to last about forever plus the instant reversing option and the super low amps
JHZR2
Staff member
The voltage part of it is related to conductor size (cost), perceptions of safety, etc.
The frequency thing is harder. I’ve heard it was due to the use of the metric system, due to the fact that base 60 is easy to calculate, refresh rates that the eye can perceive, magnetics, etc.
Generally, magnetic components like transformers are smaller at higher frequency for the same power, but the transmission is less efficient, and the amount of a conductor cross section that can be used is less. Honestly I don’t know the truth on 50 vs 60Hz, as the things I speak of won’t have a huge difference.
Over the course of time, electric company standards have gotten more stringent about allowable voltage drop. It was once acceptable for a customer at the end of a long street to have voltage drop down to 220, but as soon as that distribution system is re-engineered, that customer will be getting 240V.
As an example of this, the local power company has been upgrading the distribution in a neighborhood near me. Where they used to have one transformer to feed as many as 10 houses with secondary distribution between poles, they now have one transformer for every pole and that transformer only feeds 4 houses. There is no secondary distribution between poles anymore. They also replaced all the poles with new taller ones. That's the difference between the way things were done in 1960 and how they're done in 2021.
PECO in Pennsylvania is very expensive, too. Customers are paying off loses sustained by PECO's failed nuclear power plant, not the shareholders/owners. Nice to have your loses paid for by somebody else.
So an ev on board charger takes 120 or 240 ac and converts it to around 400 vdc for the battery, then the 400 vdc is converted to 3 phase ac for the motors?
As I mentioned, with a smart meter it is easy to see the exact voltage your home is getting and measure load to the watt, plus a total used. I have seen 237 to 243 variations, most of the time it is at 240 very close.
On that video the guy shows a charging cord stamped #10 wire, so no matter what kind of wiring goes to the wall charging switch, it is limited to about 30 amps by the charging cable on each 120v leg. I see Chargepoint chargers, which show the KW being fed in real time. At 6.6-6.9 kw the charging cable gets quite warm.
As I mentioned, with a smart meter it is easy to see the exact voltage your home is getting and measure load to the watt, plus a total used. I have seen 237 to 243 variations, most of the time it is at 240 very close.
On that video the guy shows a charging cord stamped #10 wire, so no matter what kind of wiring goes to the wall charging switch, it is limited to about 30 amps by the charging cable on each 120v leg. I see Chargepoint chargers, which show the KW being fed in real time. At 6.6-6.9 kw the charging cable gets quite warm.
Another thing to consider is that if you are charging at 120V, the outlet you are using is probably daisy-chained through half a dozen other ones with backstab connections. Probably not the best situation for voltage drop.
I would bet....
The 'efficiency' difference at the outlet would be negligible.
But, from the input to the car...
240 would need to be 'stepped up', chopped up less to make ultimate charge voltage, and better efficiency internal to car.
(Easier to make 400 volts from 240 than 120. less switching (if), less idle cycle, etc.)
The 'efficiency' difference at the outlet would be negligible.
But, from the input to the car...
240 would need to be 'stepped up', chopped up less to make ultimate charge voltage, and better efficiency internal to car.
(Easier to make 400 volts from 240 than 120. less switching (if), less idle cycle, etc.)
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