Charger current drop past 80% SOC

Hi everyone,

I’m a new Leaf owner, just bought a 2019 SV a few weeks ago. I’ve installed the stock Nissan L2 charger in my garage that came with the car and have been looking for an easy way to stop charging at 80%. I came across some anecdotal comments that the charger should start drawing less current around the 80% mark and therefore that could be detected and acted on accordingly. I’m very familiar with Arduinos, coding and some light electronics work so it seemed like something I could handle. So I tested my charger today with my clamp on ammeter and from 50% to 91% SOC it was always pulling ~27.5 amps the entire time. I was expecting to see a several amp drop but alas there was none. I stopped charging at 91% as this seemed to be a non-starter.

So my question... is anyone familiar with the “tapering off” these chargers are supposed to do, if any? The only drop I saw was a couple hundred milliamperes while in the low 80’s but that went up again after several minutes.

If this doesn’t work I may go back to my idea of integrating with the carwings API, but I was hoping to avoid that as it seems unreliable at best.

Thanks!

As I understand it, the 80% tapering only occurs with DCFC stations, not L-1 and L-2 stations, and the station determines when it should happen, not the onboard charger, which isn't used in DC fast charging. There is some tapering on L-1/L-2 charging, but as you found, it happens in the nineties state of charge range.

Someone correct me if I'm mistaken.

My 2016 ramps down at ~80%. I have a 32 amp ChargePoint and the charger’s graph shows a pretty steep decline that looks to start at around 80%. If you were using a 16 amp charger you wouldn’t see it until later.

Todd1561 said:

So I tested my charger today with my clamp on ammeter and from 50% to 91% SOC it was always pulling ~27.5 amps the entire time. I was expecting to see a several amp drop but alas there was none.

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Sounds right.

Kev994 said:

My 2016 ramps down at ~80%. I have a 32 amp ChargePoint and the charger’s graph shows a pretty steep decline that looks to start at around 80%. If you were using a 16 amp charger you wouldn’t see it until later.

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You sure it's happening at 80% on the dash display? On my current and former '13 (obviously only 24 kWh), the L2 ramp down never happens until the car's in the 90ish% on the dash display... more like 94+%.

I've plugged in plenty of other Leafs at work, including '18+ Leafs (we have some of every model year) and I've observed similar behavior of not much energy making it into the battery in the last hour or so due to ramp down and bounces. See https://www.mynissanleaf.com/viewtopic.php?p=521788#p521788 for an example.

Here was one of my graphs of this. Took me awhile to find it: https://www.mynissanleaf.com/viewtopic.php?p=490435#p490435.

At work, we have 30 amp EVSEs and our supply voltage is around 208 volts. Next time you can see the ramp down, power up your car and look at the dash display's % SoC. I can almost guarantee you that it'll be above 90%.

If I turn on my 80% limiter via midnight to midnight 80% timer (yes, it's gone on US '14+ Leafs), let it charge to 80%, it's full power the whole time until the abrupt drop at 80%. If I then via NissanConenct/Carwings app tell it to charge now, it'll charge at full power for at least 30 maybe 30 to 45 minutes before beginning ramping down followed by the 2 or 3 bounces.

Well, I guess that clears THAT up! :roll: Maybe they changed the charging algorithm with the 30kwh pack...

LeftieBiker said:

Well, I guess that clears THAT up! :roll: Maybe they changed the charging algorithm with the 30kwh pack...

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I don't think so. I'm pretty sure I've plugged in some 30 kWh Leafs (we have a bunch) at work judging by how much juice they drew. Drivers are supposed to put in the model year of their car in the registry but it's not like I go around checking before plugging them in. I have no reason. If I'm out at our stations, there are finished cars and waiting ones, I plug them in and start a session for them.

I don't think Kev994 is correct about his ramp down starting at ~80%. It's got to be higher.

cwerdna said:

You sure it's happening at 80% on the dash display? On my current and former '13 (obviously only 24 kWh), the L2 ramp down never happens until the car's in the 90ish% on the dash display... more like 94+%.

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Not very sure at all, I’m eyeballing off a graph with a poor scale, and now that I think of it, the x-axis shows time, where I was thinking of it as SOC

^^^
Would be curious to know... also, don't use NissanConnect/Carwings to check. I can't speak to '16 and '17 but on '13s (but NOT on '18+), the stupid % reported by the app will NOT match the dash display % SoC. Instead, it's only as granular as 1/12ths. So, if there are 9 battery bars visible --> 75% in the app. 10/12 bars visible --> 83% and so on... It will not show any values between 76 and 82% nor 84 to 91%.

Thanks for all the thorough explanations! It sounds like I would have seen a ramp down if I let it run a bit longer. But ultimately, for my purposes, it doesn’t really matter since I’ll apparently be well into the 90s by the time I can detect it, which is much more charge than I’m aiming for. I guess I’m back to using the carwings API. Oh and I heard about the low resolution of the carwings SOC, but seems to have been fixed in the latest iteration. It’s now down to at least 1% increments.

There’s no such thing as an aftermarket home charge station than can monitor actual charge level and auto shut off, correct? All my research has shown no one can do this.

LeftieBiker said:

As I understand it, the 80% tapering only occurs with DCFC stations, not L-1 and L-2 stations, and the station determines when it should happen, not the onboard charger, which isn't used in DC fast charging. There is some tapering on L-1/L-2 charging, but as you found, it happens in the nineties state of charge range.

Someone correct me if I'm mistaken.

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The car controls the DCFC session, not the station.

WetEV said:

LeftieBiker said:

As I understand it, the 80% tapering only occurs with DCFC stations, not L-1 and L-2 stations, and the station determines when it should happen, not the onboard charger, which isn't used in DC fast charging. There is some tapering on L-1/L-2 charging, but as you found, it happens in the nineties state of charge range.

Someone correct me if I'm mistaken.

Click to expand...

The car controls the DCFC session, not the station.

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So it's the car, and not the station, that initiates ramp-down at 80% with a DCFC?

Todd1561 said:

There’s no such thing as an aftermarket home charge station than can monitor actual charge level and auto shut off, correct? All my research has shown no one can do this.

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There's nothing in the J1772 protocol/standard (https://openev.freshdesk.com/support/solutions/articles/6000052074-basics-of-sae-j1772) for the connected vehicle to tell the EVSE its % state of charge. (DC FCing uses totally different protocols.)

That said, I hear JuiceBox can make guesstimates based upon user input and how much energy the EVSE has delivered.

LeftieBiker said:

So it's the car, and not the station, that initiates ramp-down at 80% with a DCFC?

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Yes.

Different cars have different ramp downs, which might be different with temperature and battery age. The DCQC can't be expected to be up to date on all of the different cars. So the communication between the car and the DCQC has commands the car gives to set the voltage and current limits for the DCQC. I know this is the case for CCS and Chademo. I suspect but don't know that Tesla DCQC is the same.

If anybody cares then tapering happens according to BMS command.
If one cell reaches maximum voltage (for example 4.12V) then current is reduced so voltage never exceeds that.
Sometimes at DC charger it happens slightly earlier, like 4.09.

Either way, if battery is very cold it will happen much earlier.
If battery is warm and new, it will accept 7kW charging rate for long, at least 90%.

Still having an Arduino that stops charging as soon as tapering starts is a good idea.
It is also possible to take different data inputs.
For example the third blue LED blinking on the dash.
When that starts...start timer for... lets say.. 1 hour and then stop charging session.