Anyone Measure Actual KWH's Used with a Meter?

My Nissan Leaf Forum

Help Support My Nissan Leaf Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

tony17112acst

Member
Joined
Mar 21, 2022
Messages
24
Hi there,

My electric bill is way, WAY higher than what it should be after subtracting my Leaf's KWhs used for a month!

So I'm wondering if the meter in the dashboard for my 2022 Leaf is accurate - the one reporting Miles/KWh.

To find out how many KWh's my Leaf uses each month, I simple divide how many miles I drove (for the moth) by the miles/KWh reported on the dash. This is my 1st year with my Leaf, so I have many years to look how many KWh's I use in my home normally for each month. I am the only one here and I am a stickler with energy use and I even keep track of the avg. daily temperature for each month, so I am not missing info with my home electricity use.

Has anyone ever hooked up an electric meter to measure ACTUAL KWh's drawn from the "wall" and then compared it to the reported info on the dash to see if they are similar? I have a whole house meter connected to my water heater to track usage, so I'm thinking of doing the electrical work to switch it to the car's outlet/line, but I don't want to do all the work if someone else already did.

Thank you!
-Tony
 
A couple of things right off the bat: there are inefficiencies in the charging system and battery, so you buy more electricity than you store and use in the car. Your meter would certainly show you these numbers but losses are possibly in the 15-20% range? Then there is the car's estimated m/kWh- LeafSpy the phone app will give you a better picture of ACTUAL use but in my case the dashboard is not too far off, maybe in the 5% range.
 
Are you "trickle charging" and if so, do you just need the wattage during charging? Trickle charging is all I need here, and have used a Brultech GEM for several years now to monitor all my AC circuits.
 
tony17112acst said:
Has anyone ever hooked up an electric meter to measure ACTUAL KWh's drawn from the "wall" and then compared it to the reported info on the dash to see if they are similar?

Yes, user GerryAZ has done this. Search his posts or wait for his reply.
 
Thanks for the replies so far. I'm doing level 2 charging in my garage. I stop at around 80%.

dmacarthur: Yes I assumed there were inefficiencies, but I always assumed the miles per KWh used the KWhs from "the wall." Why else would we care about miles/KWh other than to know how much we're paying for everything?

This would be an outrage if the miles/KWh isn't measuring how much electricity we're actually paying for ...everything else is useless! Sure maybe 3% of all nerds might want to know how many miles they get per KWh AFTER inefficiencies, but isn't the reason it's even on the dash is to know how much electricity we're using?

Well, I wired up a proper electric meter - one that a whole house uses - to my line going to the car's charging outlet. I will be measuring the actual KWhs used ...which is what we really want to know. I'll report back on this thread what I find. If it's different, it should be a sticky note and flashed on every forum topic: MILES/KWH ARE WRONG. Nissan could easily measure the KWhs coming into the charging cable.
 
tony17112acst said:
Hi there,

My electric bill is way, WAY higher than what it should be after subtracting my Leaf's KWhs used for a month!
-Tony
What kind of L2 charger are you using at home. Seems like your asking if you can measure at your electrical panel you power consumption overall. Are you comparing actual Kwh or just comparing $$ on your current electric bill vs an older bill? I know I am paying nearly 1.5 times more as my kwh rate went up.
 
R1200RT,

(1) I am using the level 2 charger Nissan includes in the sale. However it is not germane to my question. It makes no difference which charger I am using if the KWhs coming out of the wall are different than the amount reported by the dashboard (in miles/KWhs).

(2) I am NOT asking if I can measure power consumption from the electric panel. I am asking if anyone measured the panel consumption, and is it accurate compared to the Nissan miles/KWh reported on the dashboard.

(3) I am comparing KWhs in my message, not dollars (please see my original post).
 
L2 charging has about 12% losses. The Miles/kWh display in the car does not include charging losses. No outrage here, since it is meant to reflect driving range given a starting kWh capacity and an average miles/kWh consumption rate. There are subtleties here that vary between manufacturers that crop up when car pack energy is used but the car is not moving or not in 'drive'. Some count that power and others do not.

Measuring power delivery with a CT is easy, cheap, and believable to within a small error
 
tony17112acst said:
(2) I am NOT asking if I can measure power consumption from the electric panel. I am asking if anyone measured the panel consumption, and is it accurate compared to the Nissan miles/KWh reported on the dashboard.

The two don't work that way. The Leaf measures the power going into the battery and the power coming out of the battery. It doesn't keep a separate measurement for how much power the cooling system or OBC is using during the charging. The 6.6 kW OBC, when given the full 28 amps @ 240V is only going to put 6 kW into the battery. The rest of it is lost to the cooling system, heat generated during charging, running all the electronics, etc. That's why if you measure how much power comes from the wall, then measure how much power comes from the battery, the two numbers will always have the power gap of the wall being higher than the battery.

At the same time, that's why charging at 120V instead of 240V uses more power in the long run. Those charging loses are longer. If it takes 10 hours to charge my Leaf from 0% battery on the L2, that's also 10 hours of extra power for the charging system. If I plug my Leaf into a 120V outlet and it takes 44 hours to charge my Leaf on the L1, that's 4 times more extra power for the charging system because that charging penalty is there no matter how fast or slow you charge the battery.
 
knightmb said:
tony17112acst said:
(2) I am NOT asking if I can measure power consumption from the electric panel. I am asking if anyone measured the panel consumption, and is it accurate compared to the Nissan miles/KWh reported on the dashboard.

The two don't work that way. The Leaf measures the power going into the battery and the power coming out of the battery. It doesn't keep a separate measurement for how much power the cooling system or OBC is using during the charging. The 6.6 kW OBC, when given the full 28 amps @ 240V is only going to put 6 kW into the battery. The rest of it is lost to the cooling system, heat generated during charging, running all the electronics, etc. That's why if you measure how much power comes from the wall, then measure how much power comes from the battery, the two numbers will always have the power gap of the wall being higher than the battery.

At the same time, that's why charging at 120V instead of 240V uses more power in the long run. Those charging loses are longer. If it takes 10 hours to charge my Leaf from 0% battery on the L2, that's also 10 hours of extra power for the charging system. If I plug my Leaf into a 120V outlet and it takes 44 hours to charge my Leaf on the L1, that's 4 times more extra power for the charging system because that charging penalty is there no matter how fast or slow you charge the battery.

And there's also a power loss the result of the effective internal resistance of the battery while charging, small for L2 compared to L3.
 
It is so variable based on how you drive, where you drive, weather, etc....

I find all the GUESS O METERS: Miles Per KW, Range, Percentage Charge, to be accurate BALL PARK, with limitations.

I have had my 2015 LEAF SV since late 2017, 5 years now. I know what the data is telling me and how approximate they are or when they are lying. RANGE is based on recorded Miles/Kw or PAST usage. However if you start driving way more aggressive or Hyper-Mile eco mode it will respond. RANGE does not include reserve (with out turtle limp mode) or with turtle limp mode. I got to limp mode once 4 miles from my house. Normally I can plan and get home with mileage to spare. On that trip I went about 17 miles more than what range told me I could go when I started this trip home.
'
I can get 3.8 M/Kwh to 5.3 Mi/Kw.... the 5.3 was a record and rare, partly because all my trips are short. If I drive like I don't care I get sub 4. On average I see 4.1 to 4.5 Mi/Kw.... That is actually pretty good.
 
Thanks for the responses.

I DO know that there are losses via resistance, heat loss, electronics, etc. But my question is: Has anyone measured actual KWh's used with a meter? I want to compare that actual KWhs from the wall to the dash reported mi/KWh.

gmcpilot: I do already know all that, but my question is: Has anyone measured actual KWhs used with a meter? Your examples of mi/KWh are from readings from the dash, not actual KWhs coming from the wall outlet (metered). All your info on mi/KWh being affected by temp, driving style, heat, A/C, etc. isn't relevant to the question on how the actual electricity used/paid for from the wall compares to the dash ...because both will account for all that equally.

Again, I am looking for info about actual mi/KWh's from the wall. I have since found that the EPA uses KWhs from the wall to calculate their estimates ...which is the right thing to do, when we calculate whether it's financially advantageous to purchase an electric car.

Since I mentioned (above) that I wired a whole house electric meter to the charging outlet only, I have been able to get two calculations so far after two chargings, the 2nd is cumulative.

(1) Actual from the wall: 110 miles/39 KWhs = 2.82 mi/KWh, but dash reported 3.3 mi/KWh. 2.82 actual is 85.5% of dash (from battery).
(2) Actual from the wall: 225 miles/79 KWhs = 2.85 mi/KWh, but dash reported 3.3 mi/KWh. 2.85 actual is 86.4% of dash (from battery).

So the average mi/KWh actually used from the wall (what we paid) is about 86% of what the dashboard reports.

I am measuring the entire month of December, so I will post my data at the end to get even more accurate info since it will be cumulative.
 
It is interesting data.
Do you have a way to compare the amount of time that was spent charging versus the amount of power going in? It would help provide data to the "charging faster uses less power" theory that we all like to repeat here a lot. :D
 
PICKLE RICK!!

I'm pretty sure my two charges of 39 KWhs and 40 KWhs were 6 hour charges since I have my timer set to 6 hours.

Then I had a 46 KWh charge at 7 hours (the 2nd timer I have set).

Both charges were starting at about 15% battery.

The timer is the one in the car and the charge cable is the one provided by Nissan at purchase. I have a 2022 SV+. I'll check to see if it's in my signature.
 
I have been recording data since 2011. I did not have a meter to record charging energy from the wall when the 2011 was new, but eventually installed a revenue accuracy meter at the input to the Level 2 EVSE. The dash display in the 2011 was the most optimistic, typically showing about 4 miles/kWh while calculations from the meter and odometer readings were typically about 3 miles/kWh. The 2015 dash display was closer, but still quite optimistic. The 2019 dash display is still optimistic, but more accurate than the 2015. Here are actual numbers from charging last night:

153.6 miles on trip meter
odometer error of about 3.5% yields 159.0 actual miles driven (tires are one size larger than standard)
3.4 miles/kWh on dash display
52.95 kWh charging energy from the wall (247.3 volts and 27.0 amperes when charging was started with dash display showing 2% SOC)
159.0 miles / 52.95 kWh = 3.00 miles/kWh actual wall-to-wheels efficiency
 
GerryAZ said:
from charging last night:

153.6 miles on trip meter
odometer error of about 3.5% yields 159.0 actual miles driven (tires are one size larger than standard)
3.4 miles/kWh on dash display
52.95 kWh charging energy from the wall (247.3 volts and 27.0 amperes when charging was started with dash display showing 2% SOC)
159.0 miles / 52.95 kWh = 3.00 miles/kWh actual wall-to-wheels efficiency

12% losses during charging on L2 is a decent guess, so the 3.4 miles/kWh shown on the dash would be 3.4*0.88 = 2.99 miles kWh actual efficiency. I'm surprised that dash meter is that good.
 
GerryAZ said:
I have been recording data since 2011. I did not have a meter to record charging energy from the wall when the 2011 was new, but eventually installed a revenue accuracy meter at the input to the Level 2 EVSE. The dash display in the 2011 was the most optimistic, typically showing about 4 miles/kWh while calculations from the meter and odometer readings were typically about 3 miles/kWh. The 2015 dash display was closer, but still quite optimistic. The 2019 dash display is still optimistic, but more accurate than the 2015. Here are actual numbers from charging last night:

153.6 miles on trip meter
odometer error of about 3.5% yields 159.0 actual miles driven (tires are one size larger than standard)
3.4 miles/kWh on dash display
52.95 kWh charging energy from the wall (247.3 volts and 27.0 amperes when charging was started with dash display showing 2% SOC)
159.0 miles / 52.95 kWh = 3.00 miles/kWh actual wall-to-wheels efficiency

And then when charging at L3, the charging efficiency decreases, i.e. by the increased R*I^2 battery losses - battery heat.
 
Back
Top