Charging efficiency/losses for Level 1 and Level 2?

[metroplex]

I've read a few articles that show Level 1 charging had the most losses at 20% or more. Many articles mention increasing the current and definitely increasing the voltage helps reduce these losses down to like 10%. However I am using a 6-15 outlet at home (12A / 240V charging). My local utility company has an app that allows you to track when and how much power you use. It never matches what the Tesla app reports because of rounding with the app. However, it doesn't match what the car says for my efficiency.

I average 180-190 Wh/mi in my commutes (22 Model 3 LR) but based on how much power I use (utility company app) and for the miles I drive, that is more like 250 Wh/mi.

That tells me my losses are more like 25%-26% with 6-15 Level 2 charging.

Has anyone else seen this for lower current Level 2 charging?

 

[E90alex]

You are mixing together several things here. There is going to be efficiency loss at every step of transmission and conversion.

Driving efficiency of the car is purely just battery power used divided by miles driven. That’s what the car is indicating.

Your power company app is showing the power usage recorded by your meter, which will include power used by everything else in your house. Unless you shut off every single other circuit breaker in your house when charging your car, that’s not going to be an accurate measure of energy used to charge the car. Even if you shut off every other breaker there’s going to be transmission losses through your panel, through the breaker, through the wiring, through the outlet, and through your EVSE.

The Tesla app shows energy input into the car at the charge port. This will give you the closest calculation for charge efficiency if you don’t have any other data (assuming you’re using the mobile connector with 6-15 adapter). The charge efficiency is how much power is input versus how much power is actually stored in the battery. You’ll have to calculate the starting and ending battery level and compare that to how much was put into the car from the Tesla app. This is not very precise as the Tesla app only shows rounded off numbers. If you had a wall connector or other smart EVSE it may provide more details as to how much power was dispensed by the EVSE.

 

[metroplex]

Your power company app is showing the power usage recorded by your meter, which will include power used by everything else in your house. Unless you shut off every single other circuit breaker in your house when charging your car, that’s not going to be an accurate measure of energy used to charge the car. Even if you shut off every other breaker there’s going to be transmission losses through your panel, through the breaker, through the wiring, through the outlet, and through your EVSE.

The Tesla app shows energy input into the car at the charge port. This will give you the closest calculation for charge efficiency if you don’t have any other data (assuming you’re using the mobile connector with 6-15 adapter). The charge efficiency is how much power is input versus how much power is actually stored in the battery. You’ll have to calculate the starting and ending battery level and compare that to how much was put into the car from the Tesla app. This is not very precise as the Tesla app only shows rounded off numbers. If you had a wall connector or other smart EVSE it may provide more details as to how much power was dispensed by the EVSE.

I'm using the Tesla Mobile Connector with 6-15 adapter.

I schedule my charge at 0300 and there's nothing else using big power at the time (can confirm this), and even if there was, its about 100W and I already accounted for it. I am an energy miser and basically don't run anything else in the house at that time.

Either way you slice it, that's about a 25% difference, nowhere close to the 10% or lower figures I've read/heard about for Level 2 charging.

Tesla app will say 5kWh, but my utility company reports roughly 5.3-5.4 kWh used. I can understand the rounding, not a big deal. But based on driving efficiency that should be more like 4.3 kWh. That's roughly 1 kWh delta, which is significant.

 

[E90alex]

Also keep in mind the trip meters only track energy usage while driving. It does not include any energy used while parked, including sentry mode, standby usage from being awake, climate preconditioning, cabin overheat protection, sitting in your car to eat lunch, etc.

 

[metroplex]

Also keep in mind the trip meters only track energy usage while driving. It does not include any energy used while parked, including sentry mode, standby usage from being awake, climate preconditioning, cabin overheat protection, sitting in your car to eat lunch, etc.

Good points, but I only drive the car from Point A to Point B. No sentry mode at all, no climate preconditioning or cabin overheat protection, I don't sit in the car to eat lunch. I don't use the A/C even in the summer heat and specifically not for the several days of specific data I used to compare with the app, in-car efficiency/energy, and my utility company app (that tracks it down to the hour, day, etc...) I do notice the energy usage display shows stuff that uses power when parked, and I don't see much usage if at all during these specific days I used for the analysis (if anything less than 0.3% for standby or whatever).

Even if I was listening to music for 5 minutes extra, it would not account for 1 kWh delta. This is fairly big energy comparatively speaking. Like I said before, this is like 25%-30% loss versus the 10% or less people cite for Level 2 charging at home. Maybe it has to do with 12A at 240V versus the normal 32A at 240V people cite as Level 2 charging?

 

[E90alex]

How are you determining the energy used by the car?

Yes 12A will be less efficient than higher amperage. The peak efficiency seems to be at about 34-42A. Beyond that you’re losing more to heat.

Most of the efficiency loss is due to the energy used to keep the electronics running while the car is charging.

I think you’re just running off bad data. At ~5kW, just +/-100W in any of your numbers will throw off calculations by several %.

But again, charging efficiency is the amount of electricity used vs amount of energy stored into the battery.

Vehicle efficiency is the amount of energy used vs distance driven.

It seems you’re trying to combine the two into one number.

 

[metroplex]

How are you determining the energy used by the car?

Yes 12A will be less efficient than higher amperage. The peak efficiency seems to be at about 34-42A. Beyond that you’re losing more to heat.

Most of the efficiency loss is due to the energy used to keep the electronics running while the car is charging.

I think you’re just running off bad data. At ~5kW, just +/-100W in any of your numbers will throw off calculations by several %.

But again, charging efficiency is the amount of electricity used vs amount of energy stored into the battery.

Vehicle efficiency is the amount of energy used vs distance driven.

It seems you’re trying to combine the two into one number.

App rounds down to 5 kWh. My utility company data shows about 5.3-5.4 kWh of usage and that I have taken into account whatever is running at the time in the house which is almost constant throughout the day. I suspect it is my fridge. So 5.3-5.4 kWh of usage during charging and charging only (nothing else in the house is on or part of this number).

My car's energy usage data and driving efficiency shows about 4.3 kWh consumed. Keep in mind I'm not doing anything in the car when it isn't driving. I don't have sentry on, etc... I don't see significant power usage in park mode (no preconditioning, no overheat cabin blah blah).

I don't really care too much about vehicle efficiency, other than how much power I am consuming to charge the vehicle for the number of miles driven. In other words, why is there a 25%-30% discrepancy in losses with Level 2 charging when everyone claims Level 2 is only 10% or less in losses? 25%-30% loss is almost like Level 1 charging. This is about 1 kWh worth of delta per day when it is charging. Not a 100W off.

The question really focuses on how much actual loss others experience with the lowest tier of Level 2 charging (6-15/ 12A at 240V). Don't talk about A/C or preconditioning because it isn't a factor. I even purposely set the charge time to start hours after I've driven the car, so it avoids having to cool off the battery and the mornings/evenings didn't drop below 70F.

 

[AlanSubie4Life]

My car's energy usage data and driving efficiency shows about 4.3 kWh consumed.

Use rated miles to determine the energy added rather than trip meter. Just look up the constant (Wh per rated mile) for your vehicle and remember to multiply displayed rated miles by 0.955 to convert from the constant to the actual energy content per displayed rated mile. (I can probably tell you what it is if there is doubt.)

This added energy accuracy will be limited by rounding error and BMS accuracy so large charging events (10-100% would be great) are preferred.

Then redo your calculations.

Note the energy added on the screen in % display mode will be incorrect (high by 4.7%) - this is not a measured value.

For wall energy, I’d just use voltage x current x time for input energy to eliminate wiring losses (which may be significant and relevant, but can be looked at separately - you can concurrently measure via your method). I think this will be more accurate than wall metering without a dedicated meter, though it is still limited by the accuracy of the current displayed in the car (but I think that is pretty close…but would be more comfortable with this method at 48A or whatever, since rounding errors would only be 1-2%).

Note while plugged in since you are using rated miles, I’d be sure to turn off anything that might add to overhead during the charging event (doors open/AC etc.). Should be minimal assuming a large overnight charging event that is precisely timed, but still something to be aware of.

 

[AlanSubie4Life]

everyone claims Level 2 is only 10% or less in losses?

I’ve measured this for 240V/40A charging and it’s around 10% losses. Best case it’s about 8-9% probably at 11.5kW input power. Most of the loss is conversion losses at that input power with 1-2% overhead. Of course the overhead is a much larger % at lower input powers!

The question really focuses on how much actual loss others experience with the lowest tier of Level 2 charging (6-15/ 12A at 240V).

So your efficiency here would be lower; you can estimate what it would be from the datapoint I provided above. For example, overhead would be around 5%.

Overall you’d probably be at 84-86% efficiency best case. Just roughly.

 

[metroplex]

So in other words no one else can

Use rated miles to determine the energy added rather than trip meter. Just look up the constant (Wh per rated mile) for your vehicle and remember to multiply displayed rated miles by 0.955 to convert from the constant to the actual energy content per displayed rated mile. (I can probably tell you what it is if there is doubt.)

This added energy accuracy will be limited by rounding error and BMS accuracy so large charging events (10-100% would be great) are preferred.

Then redo your calculations.

Note the energy added on the screen in % display mode will be incorrect (high by 4.7%) - this is not a measured value.

For wall energy, I’d just use voltage x current x time for input energy to eliminate wiring losses (which may be significant and relevant, but can be looked at separately - you can concurrently measure via your method). I think this will be more accurate than wall metering without a dedicated meter, though it is still limited by the accuracy of the current displayed in the car (but I think that is pretty close…but would be more comfortable with this method at 48A or whatever, since rounding errors would only be 1-2%).

Note while plugged in since you are using rated miles, I’d be sure to turn off anything that might add to overhead during the charging event (doors open/AC etc.). Should be minimal assuming a large overnight charging event that is precisely timed, but still something to be aware of.

Can you show me which screen/display you're looking at for this info?

Sounds like I'm on the right track with 12A/240V being less efficient than the higher current Level 2 charging. I'm guessing its not going to be far off from Level 1 charging losses?

 

[AlanSubie4Life]

Can you show me which screen/display you're looking at for this info?

Just the display in the car when the current has ramped up (get the voltage - the current will be what you set). And then you have to precisely time the charge of course. That has to be done manually or use your whole-house meter to get the start/end times.

For the rated miles constant you just need to know what car you have.

Sounds like I'm on the right track with 12A/240V being less efficient than the higher current Level 2 charging. I'm guessing its not going to be far off from Level 1 charging losses?

Yes it is worse than higher currents of course, due to overhead.

But way better than 1440W charging. That overhead is about 150W or perhaps more, so it really hurts.

It’ll have half the impact at 240V all else being equal. And halve the impact again if you double the current.

This all just gets your charging efficiency of course. The trip meter will only give you a lower result (can be substantially lower but depends on situation).