Electrical charging - measured results, 120v vs. 240v

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leafme

Well-known member
Joined
Apr 22, 2010
Messages
108
Location
San Diego, CA
Measured my LEAF tonight while charging to get a feel for the power input for 120v and 240v EVSE conditions.

Equipment used:

P3 International P4400 Kill A Watt, 15a, 120v electricity usage monitor (primarily for power factor, PF)
Fluke 289 True RMS recording multimeter
Fluke i410 AC/DC current clamp
Fluke T5-600 Volt/Amp/ohm meter

Used all equipment to verify consistency which was within approximately 1%. Assumed the Kill A Watt power factor was accurate and used its value for calculating power when using Fluke measured values at 240v.

The power factor indicated 0.98. A power factor close to 1 is expected since we are just charging a battery here and no reactive load is expected.

The Kill A Watt indicated 120.4v, 11.94a and 1,406w with PF of 0.98. It fluctuated over the few minutes I measured it but stuck very close to 1400-1420w. This is a good thing since the plug on the portable EVSE is rated 120v, 15a. The NEC limits continuous loads to 80% of equipment rating (unless equipment is rated for 100% loading which almost nothing is) which equates to the 12a continuous load I measured (11.94a). While the manual does indicate a 20a branch circuit is needed, errata supplied with the owners package corrects this indicating only a 120v, 15a branch circuit is necessary. Good thing since the plug on the portable EVSE is a 15a plug NOT a 20a plug. At 120v, 12a, 0.98 PF, you can squeeze 1,411w out of the wall as input to the LEAF. As the charge begins, the LEAF smoothly ramps the current up from 0a to 12a in 5 seconds. A nice smooth ramp up. Nice job on that design Nissan. Fairly easy to do with power converter technology but at least they chose to do it.

To measure the 240v EVSE supply on my garage wall I used the Fluke 289 and the i410 current probe and verified the measured values with the T5-600 and assumed the power factor to be the same, 0.98. This indicated 15.55a and 245v which yields 3,809va or 3,733w. This too ramped up in 5 seconds from zero. After about 3-5 minutes the current settled out at 15.67a, 243v or 3,731w. Nissan also kept this rate at under the 16a max current allowed on a 20a branch circuit by code even though my EVSE and installed 40a branch circuit is capable of 32a at 240v. As an fyi, the Blink is rated at a maximum of 240v at 30a. This "larger" branch circuit provides the capability to charge at almost twice the 3,733 rate in the future if I choose to upgrade the power converter in the LEAF when Nissan releases the upgrade in a couple of years. Mark Perry told me its coming but I knew better than to ask him the price at this time.

So what we see here is 1,410w for the 120v EVSE and 3,771w for the 240v EVSE or a ratio of 0.37, or (1/x) at 2.67. This is to say the 120v EVSE will charge at 37% of the 240v EVSE rate or the 240v EVSE will charge at 267% of the 120v EVSE rate. In any case, the indicator in the car usually states a 3 or 4 to one difference (and only estimates to the half hour).

As you can see here, my measurements indicate a 2.67 to one ratio. Extending these measurements to miles (range) gained per charge time, and noting that Randy and I got 18 miles for 1.5 hr of charge on our "111 mi trip" (12 mi/hr), I would expect the 120v EVSE to boost the battery by 12/2.67 or 4.5 mi/hr. If I come across a single phase power meter I'll verify the power factor at 240v (but I bet it's very close to the same at 0.98).

For general travel planning purposes, I plan my trips for non-eco driving, add 5-6 miles for good measure (I call it anti-walking measure) and then drive almost 100% of the time in eco mode with the climate control in auto. I've only owned my LEAF since Tuesday so I'll need a few more travel data points to draw conclusions on my forecasting ability but for now, I haven't had to walk yet.

Owning and driving an electric car does take a different mindset. But so far, man, this is a blast.

Malcolm :geek:
 
Thanks for that report. And good to know the LEAF will not cut off at 3.3kW. It actually got you 14% more than expected :p

So ... rather than limiting to 3300/243 = 13.58A, and seeing a 30A max pilot signal, the LEAF's charger allowed almost the full 16A. I wonder what will happen at a public charging location with 208V nominal (not 240). Will the LEAF charge at 16A (almost) also (3328W), or increase the current a little to reach a similar 3731W ?
 
leafme said:
Measured my LEAF tonight while charging to get a feel for the power input for 120v and 240v EVSE conditions.

This is great information! Thanks for taking such careful measurements and writing it up for everyone's benefit.
 
LEAFer said:
Thanks for that report. And good to know the LEAF will not cut off at 3.3kW. It actually got you 14% more than expected :p

So ... rather than limiting to 3300/243 = 13.58A, and seeing a 30A max pilot signal, the LEAF's charger allowed almost the full 16A. I wonder what will happen at a public charging location with 208V nominal (not 240). Will the LEAF charge at 16A (almost) also (3328W), or increase the current a little to reach a similar 3731W ?

My measurements were input power to the LEAF power converter. Assuming the battery charge cycle and the power converter have a combined efficiency of about 85%, there is likely around 3.3kw actually increasing battery state of charge. Not sure these are exact values but you get the idea. Of course we don't know exactly how Nissan characterized their 3.3kw value but this could explain their 3.3kw language (but of course I'm just guessing here).

As to how Nissan designed the battery charge power converter I don't know. I could guess at 16a max but as soon as I did I could easily be wrong.

Malcolm :geek:
 
walterbays said:
leafme said:
Measured my LEAF tonight while charging to get a feel for the power input for 120v and 240v EVSE conditions.

This is great information! Thanks for taking such careful measurements and writing it up for everyone's benefit.

My pleasure walterbays. My adoption of the geek icon was not random. Just trying to move the knowledge forward with what I can contribute as all of us on this forum are trying to do (which is why this is such a cool forum).

Malcolm :geek:
 
leafme said:
LEAFer said:
Thanks for that report. And good to know the LEAF will not cut off at 3.3kW. It actually got you 14% more than expected :p

So ... rather than limiting to 3300/243 = 13.58A, and seeing a 30A max pilot signal, the LEAF's charger allowed almost the full 16A. I wonder what will happen at a public charging location with 208V nominal (not 240). Will the LEAF charge at 16A (almost) also (3328W), or increase the current a little to reach a similar 3731W ?

My measurements were input power to the LEAF power converter. Assuming the battery charge cycle and the power converter have a combined efficiency of about 85%, there is likely around 3.3kw actually increasing battery state of charge. Not sure these are exact values but you get the idea. Of course we don't know exactly how Nissan characterized their 3.3kw value but this could explain their 3.3kw language (but of course I'm just guessing here).

As to how Nissan designed the battery charge power converter I don't know. I could guess at 16a max but as soon as I did I could easily be wrong.

Malcolm :geek:
Sure thing ... I wasn't implying that there is no loss, just good to see that from a wall AC perspective we are apparently blessed with 3.7 not 3.3kW (subject to additional corroboration). Wall-to-battery (miles per hour charged) is still open (actual measurement).
 
LEAFer said:
Wall-to-battery (miles per hour charged) is still open (actual measurement).


Here's a data point:

Yesterday we drove 22.1 miles (with 4 adults in the car, in Eco, being rather gentle but including a bit of freeway and some climbing/descending - basically a typical San Diego area trip). Carwings reports net consumption of 4.2 kWh (5.6 kWh to the motor - 1.7 kWh regen + .3 kWh accessories).

Last night's recharge to 80% (10 bars, reported as 83%), which is also where we started yesterday morning before the drive in question (i.e. after an identically configured charge the night before) took exactly 1:48 (1.8 hours.) Malcolm reports that the Clipper Creek unit (which I also have) sucks up 3771w continuous, implying I pulled 6.8 kWh from the wall.

22.1/6.8 = 3.25 Miles per (wall) kWh.

So the car thinks it used 4.2, but I fed it 6.8. That's a little bothersome because it implies the overall charging efficiency is only 62%. A far cry from 85%, and it may result in real world electric bill vs. car mileage measurements that don't jibe with the cost per mile claims being made in the marketing literature.

On the other hand, the bottom line figure of 3.25 miles/purchased (or solar generated) kWh isn't completely horrifying.

Disclaimer...this is ONE trip and ONE matching recharge and I know there are unaccounted for variables...but I believe those variables may be somewhat minor and I won't be surprised if this is about where things end up when we get more data.

EDIT: whoops - I think I misinterpreted Malcolm's data. The 3771W was from the EVSE into the car - I was assuming that was downstream of the meter, before the EVSE. So if it's even more going into the EVSE, with some losses within that device and the cabling, the 3.25 is going to drop further....
 
Though of course if there is some taper off even before you get to 80% that would make the numbers look better. I think I'd like to hear what someone's TED says rather than depend on back calculation from a wall clock.
 
The wall clock is only helpful if the current usage is constant.

However, from graphs of the current, the LEAF takes a substantial "siesta" before the last "burst" of charging.

Thus, the constant-current assumption that you were using is substantially wrong, especially for short-duration charges like your 1.8 hour charge. Perhaps 0.4 hours were "siesta" (zero current), and another 0.4 hours with the current tapering off (perhaps averaging 75% of full current).

During the "siesta", the cells MIGHT be doing some voltage-equalizing.
 
leafme said:
Measured my LEAF tonight while charging to get a feel for the power input for 120v and 240v EVSE conditions.
Malcolm :geek:

Malcolm, thanks a lot for this great data. Your 240 V measurement seems to corroborate my TED's reading of 3.74 kW while charging Omkar's LEAF on my AV EVSE on Jan 1.
 
great info!! the advantage of 240 over 110 is much more than i had anticipated. i was looking for a closer to a slightly under 50%.

now, i will be using Killawatt for all my home charging so will have a good line on charging efficiency using 110 volts.

now, as i understand it, the faster the charge, the lower the efficiency due to greater heat generation?
 
garygid said:
The wall clock is only helpful if the current usage is constant.

However, from graphs of the current, the LEAF takes a substantial "siesta" before the last "burst" of charging.

Thus, the constant-current assumption that you were using is substantially wrong, especially for short-duration charges like your 1.8 hour charge. Perhaps 0.4 hours were "siesta" (zero current), and another 0.4 hours with the current tapering off (perhaps averaging 75% of full current).

During the "siesta", the cells MIGHT be doing some voltage-equalizing.

That's an encouraging concept - but do you believe it holds true to that extent even for an 80% charge? If it is the case, and the described L2 charge took less than the estimate based on constant current, that would indicate L1 charging is vastly less efficient, because the 14.85 kWh L1 charge to 80% (and accompanying low m/kWh) was measured, not estimated. That L1 charge measured total was also pretty well in line with the max constant L1 current multiplied by the elapsed time (14.85 kWh/11.5 hours = 1290 watts), which points to minimal "siesta" time if any when going to 80%, at least at L1.
 
DaveinOlyWA said:
now, as i understand it, the faster the charge, the lower the efficiency due to greater heat generation?

In general yes, but the car's cells have very low internal resistance, and both L1 and L2 are very low rates of charge relative to the pack's capabilities, that I don't expect we'll see any pack heating with either. We should see a thermal difference between L1 and DC quick/L3 though.
 
When we see the actual charging graph for an 80% charge, we will know more.

It is quite possible that an 80% charge does not include the "equilization" period, and the top-up. But then, when would equilization ever get done?

I seem to remember some mention that some equilization gets done (at least started) each time you turn the car ON.
 
garygid said:
When we see the actual charging graph for an 80% charge, we will know more.

It is quite possible that an 80% charge does not include the "equilization" period, and the top-up. But then, when would equilization ever get done?

I seem to remember some mention that some equilization gets done (at least started) each time you turn the car ON.
There shouldn't be any reason to balance cells at any time during a charge from 0-80%. The little bit of info in the service manual suggests higher cell voltages and those won't happen until we get into the 90-100% range unless we have some really out of whack cells. Maybe later as the cells age, but shouldn't be happening this early in the pack's life.
 
It will be interesting to see if the designers foresaw this possibility and programmed in a "forced 100%" charge every now and then (every few thousand miles?) to ensure cell balancing. Without some per-cell electronics (which I admit, may exist for all I know), I don't believe you'd be able to ever equalize the pack otherwise..
 
Balancing is something that should be working all the time even at 80%. If not then overcharging of high cells would be nearly unavoidable if charging to 100% which is one reason why 100% charging can be problematic.
Something I thought about was setting charge to 80% then letting it sit a bit then charging to 100% but not sure if the times would work with 110 volt charging being so slow
 
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