EVSE source current

[LEAFer]

So, as you guys now agree, the EVSE tells the charger what it can pull but it is the charger itself that actually controls how much it does pull. So far as I know, the SAE standard doesn't force the charger to pull the maximum the EVSE allows. Is it trivial for the charger to provide both 12A and 16A charging? If not, what are the chances that passing the 16A signal from the EVSE will make any difference at all in how fast you charge from 120v?

I think passing a 16A signal from the EVSE to the charger in the car while using 120V *should* work, but then again, we don't know if Nissan has (or will by firmware change) include an additional safeguard of downgrading to 12A for Level 1. I hope they don't. I hope they simply accept the EVSE's signal as "gospel" and draw (subject to the initial 3.3kW limit) that much current. If you use Nissan's included L1 EVSE it will ( I agree ) be hard-coded to signal 12A. If you build your own EVSE and signal 16A the car's charger should be drawing 16A.

But what happens if you provide 240V at 16A ? That's 3.84kW, exceeding the 3.3kW. In that case the charger will limit the current (I doubt it can limit the voltage) to 13.75A (3300/240), or more likely 12A (the next more logical lower increment).

[LEAFer]

The AV Level 2 (240v) EVSE, wired to a 40-amp dedicated breaker, should "tell" the car "32 amps MAX". The "rollout" LEAF will probably use a maximum of 15 amps (maybe 16).

The "upgraded" charger might use up to 30 or 32 amps, for substantially faster charging.

The "included" Level 1 (120v) EVSE will probably "tell" the car "12 amps MAX".

Don't forget, the UL listing is for only 30A, and AV will likely stick to that (i.e. the charge dock will be hard-coded to that level).

And as I posted above, with the 3.3kW limit, at 240V the "rollout" LEAF -- even though it is being signaled 30A max. -- will probably draw only 13.75 or 12A, not 15 or 16. (Unless their 3.3kW limit is "flexible", which it might be. Notice that 6.6kW is 220*30, i.e. the mis-informed double-pole voltage level times the UL 30A limit. Not exactly "real-world" ! My house is overvolted. So if it supplies 249V will the 3.3kW charger in the car "hard-limit" to exactly 13.25amps in real-time ? Then again, Nissan firmware might assume anything L2 = 220V ... divided into 3,300watt = 15amps (What Gary said !) )

[AndyH]

So, as you guys now agree, the EVSE tells the charger what it can pull but it is the charger itself that actually controls how much it does pull. So far as I know, the SAE standard doesn't force the charger to pull the maximum the EVSE allows. Is it trivial for the charger to provide both 12A and 16A charging? If not, what are the chances that passing the 16A signal from the EVSE will make any difference at all in how fast you charge from 120v?

I think passing a 16A signal from the EVSE to the charger in the car while using 120V *should* work, but then again, we don't know if Nissan has (or will by firmware change) include an additional safeguard of downgrading to 12A for Level 1. I hope they don't. I hope they simply accept the EVSE's signal as "gospel" and draw (subject to the initial 3.3kW limit) that much current. If you use Nissan's included L1 EVSE it will ( I agree ) be hard-coded to signal 12A. If you build your own EVSE and signal 16A the car's charger should be drawing 16A.

But what happens if you provide 240V at 16A ? That's 3.84kW, exceeding the 3.3kW. In that case the charger will limit the current (I doubt it can limit the voltage) to 13.75A (3300/240), or more likely 12A (the next more logical lower increment).

If Nissan uses the standard rather than going their own way, the it should properly respond to a signal from a Level 1 120V EVSE that signals 16A available. The car 'end' of the process shouldn't care what EVSE is connected (it has no way of knowing) - it should sense the incoming voltage and read the pilot signal from the EVSE to make sure it draws no more than what's available.

Since Watts = Volts x Amps, if the car's on-board charger is capable of up to 3.3kW, and one feeds the charger with 250V, then the charger should draw no more than 13.2A even if the EVSE reports via the pilot signal that 20A is available.

[garygid]

I suspect that the AV L2 EVSE can be set to 15 (or 16) amps when it is necessary to use it with a 20-amp breaker.

I asked the AV rep if the 40-amp breaker setting was 30 or 32 amps, and he either did not know or did not really understand the question. In any case he side-stepped the question by answering that the LEAF would only use 3.3 kW ... which is more likely to be only a "nominal" value, as mentioned above.

Also, "upgrading" to a Grid-Controlled EVSE is likely to be voluntary, not required.

[garygid]

Using a "16-amp" setting on a L1 EVSE connected to a 15-amp breaker will most likely blow the breaker (after some, maybe many minutes, perhaps not immediately).

If the L1 EVSE is on a 40-amp 120v breaker with no other loads, a 32-amp EVSE setting might be appropriate, and should not harm the car. The car still decides how much, or little current to draw.

[AndyH]

Using a "16-amp" setting on a L1 EVSE connected to a 15-amp breaker will most likely blow the breaker (after some, maybe many minutes, perhaps not immediately).

If the L1 EVSE is on a 40-amp 120v breaker with no other loads, a 32-amp EVSE setting might be appropriate, and should not harm the car. The car still decides how much, or little current to draw.

Sigh.

I'm running a charger that draws 20A and it hasn't blown the 15A breaker in the four months the charger's been in use.

That being said, it's not the best option.

I don't know where your 40A L1 comment is coming from - the EVSE options so far are 12A (15A source) and 16A (20A source).

None of these settings or options will 'harm the car' as the EVSE is only reporting what is AVAILABLE - the car's equipment will stay within it's comfort zone - there's nothing in the J1772 current messaging that FORCES a charger to draw a certain amount of current, or to exceed it's limits -- the EVSE only tells the charger what is available from 'upstream'.

[planet4ever]

I guess I didn't state my question well, since no one seems to be addressing my point. We all believe the portable EVSE Nissan will supply will be for 12A, 120v. I hear you guys talking about jimmying together a level 1 EVSE that can tell the Leaf you've got a 20A 120v circuit, so it can pull 16A. My suspicion is that won't do any good, because the onboard charger will just ignore that higher capacity and still pull only 12A.

[garygid]

PLanet...
Good suspicion, but possibly, maybe, perhaps wrong.
We are guessing the LEAF will "eat" 15 (or 16) amps, even at 120 volts.
But, maybe not.

[AndyH]

I guess I didn't state my question well, since no one seems to be addressing my point. We all believe the portable EVSE Nissan will supply will be for 12A, 120v. I hear you guys talking about jimmying together a level 1 EVSE that can tell the Leaf you've got a 20A 120v circuit, so it can pull 16A. My suspicion is that won't do any good, because the onboard charger will just ignore that higher capacity and still pull only 12A.

Here's an important part of the current J1772 spec:



The J1772 spec shows that the EVSE uses a pilot signal to communicate the maximum power available to the car's on-board charger. The EVSE doesn't communicate voltage - only the max current available. If the wiring feeding the EVSE only supplies 12A, then the EVSE will signal the charger by sending a pilot signal with a 20% duty cycle - 1 part 'on' and 4 parts 'off'. The charger will know, then, that regardless of the incoming voltage that it detects, it must not try to pull more than 12A.

The 3.3kW charger installed in the Leaf is likely an auto-range device that can use 120 and 240V automatically. The charger I use daily auto-adjusts and can charge from any voltage I connect it to from 85VAC to 250VAC. I expect the Leaf unit will do the same. (This is my guess - modern chargers can do this.)

If connected to 240V, the charger could draw as much as 13.75A. If connected to 120V, it could draw as much as 27.5A. It's important that the charger ALWAYS 'read' the pilot signal before beginning to charge as it must know the max current capability of the power source.

So - any EVSE - level 1 or 2 - must be set to report the correct current limit to the charger. And there's no reason why the charger should self-censor to a lower level, unless and until the battery management unit tells it to slow down.

I hope that helps,
Andy

[pgrovetom]

I guess I didn't state my question well, since no one seems to be addressing my point. We all believe the portable EVSE Nissan will supply will be for 12A, 120v. I hear you guys talking about jimmying together a level 1 EVSE that can tell the Leaf you've got a 20A 120v circuit, so it can pull 16A. My suspicion is that won't do any good, because the onboard charger will just ignore that higher capacity and still pull only 12A.

I agree that since the Leaf charger is able to operate at Level 2 in the 32A range, there is no reason for its software to censor the defined PWM signal charge level to 12A if 16A is ok as defined by the PWM signal duty cycle at level 1. This assumes the battery needs that level of charge rate. If the battery is near full capacity, the software will gradually drop below the PWM defined level. If the battery is empty, it will accept up the lesser of the PWM defined maximum or it's own maximum. The charger will also probably limit at it's own maximum spec even if the PWM said it could take 60A but not below 30A. Why would they do that since the SAE 1772 spec was cleverly designed to allow the source maximum and 12A versus 16A is one of the key reasons. That charger spec will be defined by it's weakest internal link from the SA1772 connector pins to the batteries themselves but won' be below 32A. There is no design reason to censor it while there are some VERY good reasons to charge as fast as possible. As I've said before, 12A versus 16A might be the boundary between making it overnight or not for the average 9-5 person. If you only get 50 miles one way, you probably get home around 6PM. If you plug in at 6PM, you can get 14 hours if you leave at 8AM. 16A will probably get close to a full charge in 14 hours while 12A won't get close. If I was the designer, stuck with those kind of times, I'd do my best to use the 16A level if the EVSE said I could. Otherwise the battery slowly goes dry - not good. That is what makes Nissan nervous about Level 1. Its very close if you use most of the battery charge for your commute.