Low-power EVSE: how low can you go?

[LeavesThatAreGreen]

I'd like to be able to charge my 2018 Leaf from a low-power source (preferably a single-phase 120VAC source); potentially in some kind of long-running emergency

I see an EVCARS / ZENCAR EVSE on Amazon (B08FM3L8QK) that claims to be able to configure the charging current down to 6A. So, that's a good start. If that unit actually works, then it ought to be a good match with my 1000/2000W cargenerator.com inverter (paired with an ICE or hybrid vehicle).

But even at 6A it wouldn't be a great match with, say, a "1000W" solar panel, and a "300W" panel would be right out.

(Now, obviously a "300W" solar panel is going to go nowhere slowly in terms of charging my 40kWh battery, even if I actually got a full 300W out of the panel. But the point isn't to figure out how to quickly charge the Leaf during an emergency, potentially I could get a generator as large as I want or a complete home solar kit for that matter and then use the L2 charger I already have.)

The point, rather, is that if I'm in a long-running emergency and what I actually have is a 1000W solar panel, or a 600W panel, or even a 300W panel, then I'd want to be able to hook the Leaf up to it and get whatever benefit I could.


So, what are the lowest-power options out there on the EVSE front?

Are there any technical limitations with the Leaf such that even if a 120VAC EVSE were able to go down to, say, 1A, that this simply wouldn't work with the Leaf?

Thank you!

 

[cornbinder89]

From what I can find in the Leaf service manual, the onboard charger is fixed at 10 amps when it is supplied 120 volts, and no "customizing" of current draw is possible on 120 volts. This is direct contrast to 240 volts, where the EVSE can communicate the current allowed, but there is still a lower limit.
The SAE J1772 protocol come into to play here, and it sets the limits all onboard chargers must meet to use the protocol.
This is all kind of moot anyway, as charging below 10-12 amps at 120 volts is going to be practically useless anyway
https://en.wikipedia.org/wiki/SAE_J1772Read the SAE protocol, as far as I can see 6 amps at 240 volts is the minimum level 2

 

[knightmb]

6A is the lowest that you can go. I built an EVSE years back that is adjustable, so at that setting, I can remember measuring that it draws about 700 watts from the outlet. You can't go much lower because nearly +400 watts of that is used to run the water pumps, on board charger, 12V charging, etc. That leaves very little to actually put into the battery. I'll attach a screen-shot to how little power this puts in since I need to do my monthly testing of my backup EVSE in the Leaf anyway.
If my memory serves, the settings standard was something like 6A, 8A, 10A, 12A, 14A, 16A, etc.

 

[knightmb]

The point, rather, is that if I'm in a long-running emergency and what I actually have is a 1000W solar panel, or a 600W panel, or even a 300W panel, then I'd want to be able to hook the Leaf up to it and get whatever benefit I could.

The 1000W panel would be the only one that could run the lowest setting of 6A, provided you have ideal sun on a continuous basis during the emergency.

In theory, you could even do 8A, but that would mean reaching the near max of the panel in perfect conditions.

 

[LeavesThatAreGreen]

From what I can find in the Leaf service manual, the onboard charger is fixed at 10 amps when it is supplied 120 volts, and no "customizing" of current draw is possible on 120 volts.

Thanks for following up! A 10amp minimum @ 120VAC would squelch my idea, certainly. Does that service manual cover 2018 Leafs?

The SAE J1772 protocol come into to play here, and it sets the limits all onboard chargers must meet to use the protocol.

Going outside the bounds of a standard wouldn't my first choice. I have this discussion with other firmware developers on a regular basis...the "but I tested it and it worked!" argument is much more likely to convince me if they _also_ checked it against the data sheet.

That said, if I had an EVSE that supported current-limiting signaling even in 120VAC mode, and had good reason to believe that the Leaf was honoring those signals (even in 120VAC mode), then certainly in an emergency situation (and maybe otherwise) I'd consider it.

It would be a poor tradeoff to find out afterwords that I'd damaged the Leaf, of course! I'd like to think that tripping a breaker on the EVSE or something upstream would be safe enough, as far as potential damage to the Leaf. Perhaps brownout wouldn't be good for a Leaf?

This is all kind of moot anyway, as charging below 10-12 amps at 120 volts is going to be practically useless anyway

Hmm. Practically useless for the purpose of charging my car for my daily commute, sure.

I'll admit that I hadn't appreciated how much overheard there'd be to charging the Leaf. But it sounds like even 6A @120VAC (if it works safely) charging would still provide enough charging headroom above that overhead that it could re-supply a useful amount of charge into a Leaf after it spent a night keeping my boiler's pumps running and the refrigerator cooling. And 8A @120VAC would likely facilitate recharging after a short trip into the nearby town...if not every day.

 

[LeavesThatAreGreen]

6A is the lowest that you can go. I built an EVSE years back that is adjustable, so at that setting, I can remember measuring that it draws about 700 watts from the outlet.

Thanks for following up! This is very encouraging. Did you see cornbinder89's comment about the Leaf service manual? Any thoughts?

I see you have a 2018 Leaf; have you tried your EVSE on it in 6A & 8A mode using 120VAC?

You can't go much lower because nearly +400 watts of that is used to run the water pumps, on board charger, 12V charging, etc. That leaves very little to actually put into the battery.

Oh. Well, that makes sense. Not a lot of point of thinking about ways to make use of a 300W solar panel, or really even a 500W panel, then! Well, I guess I could charge a battery with a low-wattage panel, and then once the battery is charged I could use it to charge the Leaf...(with yet another efficiency hit on top of everything else, of course).

Since I don't have any solar panels at all yet, I'll have to decide if this inspires me to get a larger quantity of panels, or if it pushes me to drop the whole idea!

I'll attach a screen-shot to how little power this puts in since I need to do my monthly testing of my backup EVSE in the Leaf anyway.

Nice! I like to see a good SOP. I'm curious, though, why monthly instead of, oh, either weekly on the one hand, or, say, twice a year on the other hand?

 

[cornbinder89]

You can try and see. these things are fairly fail-safe in that regard, if it doesn't fall inside the norm, and being outside would be dangerous, it would lock out.
The Service Manual is available for free on the NICO site for MY 2015 and down, I suspect much of the info would still be valid. I would suggest all owners who plan on doing any work themselves to download a copy. The copies are free, just don't try and sell them, and you'll be ok.
All my info is what is in the protocol, that doesn't mean going outside it will cause a problem, it just may not work.

 

[knightmb]

I see you have a 2018 Leaf; have you tried your EVSE on it in 6A & 8A mode using 120VAC?

Yes, works without any issues.

 

[knightmb]

Nice! I like to see a good SOP. I'm curious, though, why monthly instead of, oh, either weekly on the one hand, or, say, twice a year on the other hand?

I do a lot of driving to places that often don't have any fast charging or even L2 charging to be found. So I might go months without thinking about it, but I want to make sure it works in an emergency so I try to do a schedule and it gives me an excuse to clean out the dust that builds up in the back after a while.