Will energy usage to charge vary with voltage, charger used?

A question for those of you guys who are more electrically astute than I.

Will I use the same amount of kWh of my home electrical power to charge my Leaf if I charge it using the 115V trickle charge cable, the 240V 3.3 kW charger, or the possibly future 6.6 kW charger?

In other words, are there efficiency gains to be made by using the highest capacity Level 2 charger and amperage available, or is the AC power usage equivalent regardless if which charging supply I use, as long as I don't mind waiting 20 hours for a full charge?

I realized that time-of-use rates will give me the most efficient cost per kWh if I charge during a brief period in the middle of the night, but I am talking about kWh usage, not monetary charges. I was told by a contractor that it is much more costly in kWh to heat a spa using a 115V supply than using a 240V supply. Does this apply to charging an EV as well?

Boomer...


Unless there is more waste (heat) involved with each level of charger, I would think the amount of energy you use would be very close to the same with each level of charger. The battery size and the amount of watts that they absorb doesn't change, so delivering that amount over 16 hours, 8 hours or 30 minutes doesn't change the volume of wattage delivered.

If you're on Time Of Use electrical billing, then the cost may vary a bit depending on when you take the power from the electric company, but that's all.

BTW, the total kwh that the battery can hold depends on the rate of charging. Slower the charging, more energy the battery can hold.

One more thing, 3.3KW charging that will take 8 hours is just above trickle charge. IIRC, trickle charge is C/10 or less i.e. 10 or more hours to charge.

evnow said:

BTW, the total kwh that the battery can hold depends on the rate of charging. Slower the charging, more energy the battery can hold.

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This should not make a HUGE difference, IMHO. 5% maybe ... max! Except, of course, when using the QuickCharge, which may not be capable of trickle charging (or will "refuse" to trickle, lest it defeat the purpose of "quick"). If the BMS in the LEAF is as good as I look forward to, then whatever L1/L2 rate of charge you select will automatically throttle to a slower rate to complete the charge. ( I am assuming that most of the charging process, let's say from 0% to 75% or higher, is linear. After 80%+ SOC it might (or should automatically) slow down.)

evnow said:

One more thing, 3.3KW charging that will take 8 hours is just above trickle charge.

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Actually, at 120V, 3,300/120=27.5amps ! Or at 240V=13.75amps. Neither one of which is really a "trickle".

LEAFer said:

Actually, at 120V, 3,300/120=27.5amps ! Or at 240V=13.75amps. Neither one of which is really a "trickle".

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the 120V L1 charger provided with the Leaf will not draw anywhere near 27.5 AMPS, it is designed to plug into a standard 120V/20A circuit, It will draw 16A or less, I suspect is will only be drawing 12A to be compatible with 120V/15A circuits. Try 1440 watts max when using the 120V charging cord...

mitch672 said:

LEAFer said:

Actually, at 120V, 3,300/120=27.5amps ! Or at 240V=13.75amps. Neither one of which is really a "trickle".

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the 120V L1 charger provided with the Leaf will not draw anywhere near 27.5 AMPS, it is designed to plug into a standard 120V/20A circuit, It will draw 16A or less, I suspect is will only be drawing 12A to be compatible with 120V/15A circuits. Try 1440 watts max when using the 120V charging cord...

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Of course. My point was ... 3.3kWh is not a "trickle". Then again, I still want to see the 3.3 throttle raised to 6.6 at no cost to the initial owners, and ASAP (or earlier ... like at delivery of the first LEAF).

Boomer23 said:

Will I use the same amount of kWh of my home electrical power to charge my Leaf if I charge it using the 115V trickle charge cable, the 240V 3.3 kW charger, or the possibly future 6.6 kW charger?

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One other point to make here. Whether you are charging at 110-120v or at 208-240v, whether at 12A, 14A, or 27A, the charger is inside the LEAF, and you only have one charger in the LEAF. (Quick charge is another matter, but you won't have a $17,000 quick charger in your garage.)

So the issue is not the efficiency of what is mounted in your garage or stored in the trunk of your car, but rather the efficiency of what is under the LEAF's hood and under its seats.

LEAFer said:

Of course. My point was ... 3.3kWh is not a "trickle". Then again, I still want to see the 3.3 throttle raised to 6.6 at no cost to the initial owners, and ASAP (or earlier ... like at delivery of the first LEAF).

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Then don't buy the first model year Leaf, on all of the powerpoint slides I have seen, the "6.6KW High" charger in only shown on the "MY2012" Leaf. We don't know if they will retrofit, but I tend to doubt it...

Back to the OP, I'm certain that lower charging rates will use fewer kWh to refill the car. Resistive power losses scale with the charging current squared. Some other losses could be proportional to charging current, but the sum should be greater than just proportional.

DeaneG said:

Back to the OP, I'm certain that lower charging rates will use fewer kWh to refill the car. Resistive power losses scale with the charging current squared. Some other losses could be proportional to charging current, but the sum should be greater than just proportional.

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Let us say, R = loss resistence of battery.

Power=V.I = I.R.I = R.I**2

To fill a nominal 24 KWH, it takes T=24/(V.I) hours.

Total resistive heat loss = R.I.I.24/(V.I) = 24.R.I/V

So, to the extent I&V are proportional, the total heat loss will be same.

But, with a cap of 3.3KW, the current at 110V and 220V will both be 15 Amps, but will take half the time to charge @ 220V. Thus, level 2 @ 3.3KW will dessipate half the heat than Level 1 @ 15 Amps. Level 2 @ 6.6KW will dessipate the same amount of heat as level 1 @ 110V.

Someone pls check the math, I've done this since my engineering days :lol:

L1 (120v) is likely to be limited to 12 amps.
L2 at "3.3kw" might be 15 or 16 amps (on a 20-amp breaker).
L2 at "6.6kW" might be 30 or 32 amps (on a 40-amp breaker).

However true "resistive" losses should be small compared to heating in the battery cells and efficiency "losses" in the on-board charger.

DeaneG said:

Back to the OP, I'm certain that lower charging rates will use fewer kWh to refill the car. Resistive power losses scale with the charging current squared. Some other losses could be proportional to charging current, but the sum should be greater than just proportional.

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That doesn't make sense. If that were so ... why would utility companies transfer power at 50,000 volts, then step it down. Similarly, large machinery is always 240 ... not 110. How could you reconcile lower charging rates using fewer Kwh? What's even MORE intriguing to me is Nissan is now saying the the traction battery pack will actually last LONGER on the large format/quick charger. That really has me scratching my head.

hill said:

That doesn't make sense. If that were so ... why would utility companies transfer power at 50,000 volts, then step it down. Similarly, large machinery is always 240 ... not 110. How could you reconcile lower charging rates using fewer Kwh? What's even MORE intriguing to me is Nissan is now saying the the traction battery pack will actually last LONGER on the large format/quick charger. That really has me scratching my head.

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Energy transmission is not the same as stuffing energy into a chemical storage battery. The faster you charge a battery the less efficient it is. The internal resistance goes up and you get more waste heat. If you get too aggressive you damage the battery, too.

The power being delivered to the battery is all DC. The losses in the interconnects goes up with higher charge currents, resulting in more waste heat. A/C is a lot more efficient.

DC fast charging has terrible efficiency. And no, Nissan is saying that fast DC charging does negatively affect the capacity of the battery, especially over the long term. They also limit fast charging to 80% of the total battery capacity.

hill said:

What's even MORE intriguing to me is Nissan is now saying the the traction battery pack will actually last LONGER on the large format/quick charger. That really has me scratching my head.

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I don't think so ... I think they said the opposite (back to making sense).

Will the DC fast chargers degrade the battery faster?

If fast charging is the primary way that a Leaf owner recharges, then the gradual capacity loss is about 10 percent more than 220-volt charging. In other words, it will bring the capacity loss closer to 70 percent after 10 years.

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(from HERE.)

hill said:

...If that were so ... why would utility companies transfer power at 50,000 volts, then step it down. Similarly, large machinery is always 240 ... not 110. How could you reconcile lower charging rates using fewer Kwh? What's even MORE intriguing to me is Nissan is now saying the the traction battery pack will actually last LONGER on the large format/quick charger. That really has me scratching my head.

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Power companies use high voltages for transmission specifically to minimize current (and hence power loss) for the same amount of power transferred. But here I am not talking about the voltage you plug the car into, only what happens in the car's charging circuitry and its battery.

I am saying that when charging an electric vehicle, some of the losses will behave as resistive losses in the high voltage portion inside the car. This circuitry would be operating at the relatively fixed battery voltage. If you charge the battery faster, that means the current through the charging electronics and into the battery is higher. Anything that can be modeled as a resistance in the charging circuit or in the battery is going to dissipate more power when more current is run through it, corresponding to the square of the current going into the battery.

Let's say the battery is 400 volts for example. Charging at 120V and 12A (the "emergency cable" capacity which comes with the Leaf) will try to force 120V*12A = 1.44kW into the battery. This is 1440W/400V or 3.6 amps into the battery.

Now let's charge the battery using 240V at 13.7A. This is the rated charging speed of the circuitry on the first Leafs. It corresponds to 3.3kW. And 3300W/400V = 8.25 amps into the battery.

So the instantaneous power loss difference for 240V charging compared to 120V charging, for resistive losses at least, would be the square of (8.25/3.6) or about 5x larger power loss during 240v charging.

However, 240V charging is also 8.25/3.6 times faster, so the total energy loss, for resistive losses at least, for 240V charging is only 8.25/3.6 = 2.3 x greater.

Other losses which could be modeled as voltage drops will increase only directly with the charging current at the battery. These energy losses will be independent of the charging rate.

Right, higher current, higher resistive power losses, nothing to do with voltage.

High power line voltages (20,000 locally and up to 1,000,000 on big tower lines) are used to minimize current, thus minimize resistive losses.

However, the higher voltages have other losses associated with their use.

Bicster said:

DC fast charging has terrible efficiency. And no, Nissan is saying that fast DC charging does negatively affect the capacity of the battery, especially over the long term. They also limit fast charging to 80% of the total battery capacity.

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I think most of us can agree that fast charging puts less energy into the battery per kWh input to the charger, but "terrible" is a pejorative term. Can some battery expert among us quantify that? My uneducated guess would have been something like the difference between 90% efficient transfer and 80%. "Terrible" sounds to me like it drops well below 50%.

I'd also like to question the capacity limit when using fast charging. Yes, we've heard many times that you can charge 80% in under half an hour (or even, sometimes, "in 24 minutes"). But I've always interpreted that as meaning one of two things, and wasn't sure which:
a) The last 20% wouldn't be quite as fast, so the point is you can get most of the capacity in a reasonable time.
b) Assuming 24kWh usable with a light that comes on at 4kWh left, and a quick charge done when the light comes on, the 80% adds 19.2kWh to the battery, leaving you pretty darn close to 100% (23.2/24).

to the OP; yes it makes a difference what voltage is used when charging. if using the same cable, the higher amperage will cause higher heat loss which is energy and will increase total amount of charge sent to battery.

now, 3 phase power is more efficient than single phase power. so that would be a bonus of possible higher voltage applications.

as far as electrical line transmissions. losses are due to current, not voltage. so to reduce line losses over distance, that is why the voltage is higher when P=IE

power=wattage
I= current
V= voltage. so for given power, the i varies inversely with voltage. iow, as voltage goes up, current goes down. so 50,000 volts and 250 milliamps loses 3% of the power as dissipated heat but same power at 5,000 volts and 2.5 amps will lose 5% and so on. the amount of power lost depends on gauge of wire and distance traveled.

I just recently read two test drive reports for the Volt that stated that they measured over 13 kWh used to charge the 9 or 10 kWh of usable pack. I'm assuming that these journalists used L1 charging from a home or office 110 V outlet.

Do you think that this is expectable charging losses at L1, or that the Volt is taking on more kWh than these writers knew about, or something else is going on?

http://www.insideline.com/chevrolet/volt/2011/2011-chevrolet-volt-full-test-and-video.html

http://www.caranddriver.com/reviews/car/10q4/2011_chevrolet_volt_full_test-road_test

LEAFer said:

Then again, I still want to see the 3.3 throttle raised to 6.6 at no cost to the initial owners, and ASAP (or earlier ... like at delivery of the first LEAF).

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If they're going to increase it, I'd like to see them go all the way to 7.2kW so we can use all of the 30A that a typical L2 EVSE will supply. While this would be overkill for most overnight home charging (I'm planning to use a 16A Leviton here at home), it would be great for destination charging at public charge points. For instance, if I drive 60 miles to a destination (say a store) with a charger (at freeway speed), I may want to replenish my LEAF's battery in an hour or less so that I can make the trip home without range anxiety. 6.6 kW would take half the time of 3.3 kW, and 7.2 kW would be even better! If I could pick up 7.2 kWh in an hour, that might translate to 25-30 extra miles of range.