110V Penalty?

[omarsultan]

So, this might be a dumb question, but looking a the Tesla charging calculator there is a penalty for charging at 110V vs 240V. To add 5 miles of range, @110V uses 2.2 kWh of energy, but using any of the 240V options, it only uses 1.7 kWh of energy or ~30% less which seems like a lot.

I am curious why? Is this an efficiency thing of 110V vs 240V or something else?

 

[phigment]

So, this might be a dumb question, but looking a the Tesla charging calculator there is a penalty for charging at 110V vs 240V. To add 5 miles of range, @110V uses 2.2 kWh of energy, but using any of the 240V options, it only uses 1.7 kWh of energy or ~30% less which seems like a lot.

I am curious why? Is this an efficiency thing of 110V vs 240V or something else?

I believe the majority of efficiency loss is due to running the pack maintenance modules (cooling/heating). With 110V it is a higher percentage of available charging power that is used for a longer duration.

If I'm wrong, please correct me or add any details!

 

[wk057]

So, this might be a dumb question, but looking a the Tesla charging calculator there is a penalty for charging at 110V vs 240V. To add 5 miles of range, @110V uses 2.2 kWh of energy, but using any of the 240V options, it only uses 1.7 kWh of energy or ~30% less which seems like a lot.

I am curious why? Is this an efficiency thing of 110V vs 240V or something else?

120V low power charging is not as efficient as 240V charging at higher power. The chargers seem to be most efficient at full power (240V/40A).

The percentage of the incoming power that ends up being used to run the cooling pumps and other misc items that must stay on while the car is charging is much greater at 120V/16A as it is at 240V/40A also.

 

[Rocky_H]

I explained it here in this thread:

http://www.teslamotorsclub.com/show...or-or-240V-Outlet/page2?p=1377085#post1377085

Pasted here:

Well, you’re partially right, but are still confusing things. You are correct that it’s not about the voltage exactly, but when people refer to those, they are comparing a NEMA 5-15 outlet, which is providing 1.4 kW to the car, versus something like a NEMA 14-50, which is providing about 9.6 kW. The power level definitely does contribute to an efficiency difference, because there is a decent level of overhead power being consumed by running the charging system. I think it’s around 400 W or so, so it’s about 1/3 of the power of the 120V wall outlet is being lost just going to running the charging circuit. That is why going to a 5-20 adapter makes such a difference if you have to use a wall outlet. It’s increasing the current from 12A to 16A, so a 33% increase in power, but the amount of energy getting into the car’s battery is a lot faster than 33% increase, because the overhead is already covered, so all the extra is going into the battery, rather than being partially lost.

So what you are referring to is at the high power levels, where loss from resistance in the wiring is the main thing that could be hurting efficiency, but it seems you were not considering about at really low power levels, where resistive losses are negligible, but the dominant factor is wasting a lot of energy from keeping the charging circuit running much longer than it needs to.

 

[omarsultan]

OK - cool - thanks to everyone - its fun hanging out with smart people

 

[TSLA Pilot]

There is a bit more to consider. I'd posit that a major portion of the 220-volt benefit can be attributed to this factor.

The equation for electrical energy loss is:

P loss = I[SUP]2[/SUP]R

Where I is the amperage and R is the resistance of conductor. (Refresher: Watts = Volts X Amps) At any given load, if one can increase the voltage and decrease the amps, less energy is wasted. Notice how the "I" is squared. (And that's why you see very high voltage power lines for long-distance energy transmission.)

But I am not an electrical engineer so feel free to chime in if you are . . . .

 

[DoubleDownOn9]

It will be more expensive too. We use 120v to charge our RAV4 EV when we don't want to play musical charger. Since we are on the PGE EV rate plan it makes charging more expensive during evening or day. Many times the I get home at 6pm and my RAV wants to start charging immediately (in order to be charged by the time we leave for work the next day). If you don't pay attention to it then you end up using peak power (expensive) to charge your EV because it can need up to 40 hours to charge at 120v. We are looking into to getting a 2nd 240v line to our garage.

 

[mikeash]

I[SUP]2[/SUP]R means it's more efficient to, for example, charge at 240V and 6A than 120V and 12A. But for 120V/12A versus 240V/40A, the I[SUP]2[/SUP]R loss is greater in the 240V case, since the current is much higher. Yet charging at 240V/40A is more efficient, so that loss is smaller than gains elsewhere.

 

[brucet999]

I[SUP]2[/SUP]R means it's more efficient to, for example, charge at 240V and 6A than 120V and 12A. But for 120V/12A versus 240V/40A, the I[SUP]2[/SUP]R loss is greater in the 240V case, since the current is much higher. Yet charging at 240V/40A is more efficient, so that loss is smaller than gains elsewhere.

I think the onboard charger may be more efficient at higher current flow rates.