J1772 EV Charging Insights and Detection

The J1772 protocol uses PWM to increase charging current rates in 1 AMP increments.
So a smart EVSE is constantly monitoring how much solar is putting back into the grid and adjusting max allowed charge current dynamically. Such an EVSE is still nothing more than a glorified (modulated) extension cord.
It is still the built in the car charger that does the actual work, and sense should be able to detect the startup pattern to recognize the EV.
A friend of mine (with sense installed) has a ford Focus EV and his wife a hybrid Honda Clarity and neither of them are yet detected by sense.

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Thanks for the explanation. But I could see the start-up pattern being highly variable with current modulation, highly dependent on solar output when charging starts. There would probably also be an additional detection problem if charging started at too low a current level (say less than 5A) - I’m sure the Sense EV detectors are built around charging patterns at the nominal power setting for each vehicle.

The J1772 protocol specifies minimum of 6 amp charging at a 10% duty cycle:


[image from openevse documentation]

That signal is the max the onboard charger can pull, but an EV can always decide to pull less.
eg: when you plug a chevy bolt/volt into a 120 volt outlet, it could theoretically pull 80% of 16 amp breaker is 12 amps @ 120 volt = 1440 watt.
But the bolt/volt standard assumes it isn’t the only device on that breaker and will limit the onboard charger to 5 amps, unless you touch some buttons on the onboard display charging settings, then it will go to max 12 amps. My toyota rav4ev with tesla technology would charge up to 30 amps at 120 volt :wink:

Imo the ramping up of the charge power is how sense currently recognizes EV’s.
I assume sense currently also has some logic that says “it should at least charge with xx amps”
I think in my setup 22 amps is the minimum where it recognizes the bolt , when I set it to lower amps it just goes to other.

EV charging probably deserves its own thread. J1772 is tricky because it is 4 standards in one - 2 AC modes (level 1 and 2) and 2 DC modes (level 1 and 2). I’m assuming that the ramp-up and ramp-down signatures at the mains are different for all 4, even for the same EV. And that’s before you consider how the signature for each of the 4 might vary based on current settings.

I would imagine that a 240V 6A AC ramp up would look very different from a 240V 80A ramp-up to Sense.

Maybe it should. Can you do that as Volunteer Moderator?

SAE J1772 (IEC 62196 Type 1), also known as a J plug, is a North American standard for electrical connectors for electric vehicles maintained by the SAE International and has the formal title “SAE Surface Vehicle Recommended Practice J1772, SAE Electric Vehicle Conductive Charge Coupler”
It covers the general physical, electrical, communication protocol, and performance requirements for the electric vehicle conductive charge system and coupler. The intent is to define a common electric vehicle conductive charging system architecture including operational requirements and the functional and dimensional requirements for the vehicle inlet and mating connector.
Source: SAE J1772 - Wikipedia

J1772 evolved in different versions, currently there are 7 versions (1996-2017)
In the later versions DC fast charging was introduced.

The onboard charger in the car basically consists of a rectifier (AC → DC) and then DC-DC converters to make from lower voltage the charging voltage for the batteries.
A block diagram is posted in this document:

With DC charging, you are connected directly to the battery. No electronics in between.
Just a lot of data like amps, volt, temp are exchanged many times per second.
The external charger is the thing converting the AC from the grid to the DC of the battery.
Basically constant current power supply with increasing voltage as the battery gets charged up.

So when you charge your EV with AC from the grid (either 120/208/240/277(tesla is capable of that) ) the onboard charger generates/determines the ramp up of the AC power consumption.
You can imagine if you rectify 120 volt x square root of 2 (± 1.41) you get a maximum DC voltage of about 170 volt. To charge a battery in an EV of eg 500 volt you would have to step up that voltage quite a bit. When you do that from 240 Volt AC → 340 Volt DC it is easier. Hence why charging an EV from 240 volt is more efficient then charging with 120 Volt AC.

With DC fast charging, there is no AC you can measure since that is all done in the external unit.
Most of those unit are fed from either 277V or 480V AC 3 phase.

Why are you under that impression?
Why does Sense detect my EV if I charge with anything within 22 amps to 32 amps?

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22 vs 32A probably doesn’t make that big of a difference. But 6A (min) vs. 80A (max) charging ramps could look very different in my mind. I could probably experiment with my Model 3 HPWC and car settings on DCM, just to look at the difference power ramp. Just have to clear time to do that.

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after a poweroutage and the 300 second rule of NEC, do you think sense would be able to recognize ramp up of solar inverter and distinguish eg enphase micro inverters from a SMA SB string inverter ? :wink:

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Sure, because Sense uses Direct Circuit Measurement (DCM) for the solar back-feed :wink: