LMF5000
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Can you limit charge current to 1kW for emergency charging with a generator?

Fri Oct 20, 2017 9:29 am

I'm not an EV owner, but currently doing my research to see whether I can switch over the coming years.

One question I have is, does the leaf allow the possibility of limiting the charge current to around 1kW?

Reason being, most small portable generators deliver around that much power and it would make a great emergency supply for one-off long road trips to carry one in the boot in case things really, really go belly-up in the search for charging points.

My generator weighs around 15kg, delivers 1kW continuously (4.16A @ 240V) and runs 5 hours on 5 liters of petrol, so that's theoretically enough to take the 20kWh battery from 0% to maybe 20-25% - i.e. enough to get a stranded leaf to a charger!

Also, many portable solar panel/battery/inverter combos can generate 1kW continuous, so this question might be relevant to such a setup too.

smkettner
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Re: Can you limit charge current to 1kW for emergency charging with a generator?

Fri Oct 20, 2017 10:25 am

You will need an adjustable EVSE or charging cord. The cord or EVSE device actually limits the current not the car. I believe the J1772 standard has a minimum of 6 amps so you really need a 7 amp 240 volt generator or get down to 120 volts. Honda 2000 should work with the standard cord at 120v.
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jjeff
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Re: Can you limit charge current to 1kW for emergency charging with a generator?

Fri Oct 20, 2017 2:20 pm

Yes I don't think you'll be able to get down to 4a, I believe 6a is the minimum you can set. That said, 6a @ 120v=720w which just about any generator should be able to handle. Of course, if you only have access to 220v generators you'd need a 1320w minimum generator. Not sure about generators in your country but in N. America many portable generators are ~2000w with the smaller ones being ~1600w, still enough to power the 1300w draw, of course all our small ones are only 120v.
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cwerdna
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Re: Can you limit charge current to 1kW for emergency charging with a generator?

Sat Oct 21, 2017 2:04 am

smkettner wrote:You will need an adjustable EVSE or charging cord. The cord or EVSE device actually limits the current not the car.

Some vehicles let you turn down the charging rate via some UI on the car (e.g. BMW i3 and Tesla Model S), but not the Leaf.

Maybe OpenEVSE (https://openev.freshdesk.com/support/so ... e-vehicle-) might help the OP and will let him max current via the pilot signal low enough?

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DaveinOlyWA
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Re: Can you limit charge current to 1kW for emergency charging with a generator?

Sat Oct 21, 2017 7:02 am

IIRC EVSE upgrade allows you to lower the current to 8 amps or so which would be just at 1KW. realize that you are in the "barely treading" water stage since overhead and BMS support systems will borrow from that resulting in a greater loss of effective power exceeding 30%
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jjeff
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Re: Can you limit charge current to 1kW for emergency charging with a generator?

Sat Oct 21, 2017 11:31 am

OP is in a 220v country, 8a @ 220v = 1760w or almost double what his 1kW 220v generator could handle.
2012 SL purchased used 2/'16
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LMF5000
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Re: Can you limit charge current to 1kW for emergency charging with a generator?

Sat Oct 21, 2017 5:53 pm

As jjeff said, I'm in Malta, which uses the UK system. 50Hz 240V AC, standard plugs are fitted with 13A fuse giving a max theoretical power of around 3.2kW. So anything 110V or American-spec wouldn't apply this side of the pond.

I saw the model S allowing charge rate to be varied from the touchscreen on a YouTube video - someone was charging it with a portable 2kW (actually 1.6kW) honda eu2000i generator. That's pretty neat. It's nice to know the i3 does that as well. I'm surprised the leaf doesn't. Problem with the i3, and in fact most EVs is cost. A Renault Zoe in Malta costs €35k new (if you buy the battery outright). For that price I can buy three Ford Ka's!

I thought of buying a cheap used leaf in the UK and driving it down to Malta, but my calculations show it will need recharging a minimum of 17 times over the distance of the trip. That's why I need some sort of backup in case I find charging stations broken or occupied. Course I could have it shipped to Malta directly for €950 like I did with my last car, but where's the fun in that? :D

Oh, before I forget, some background since this is my first thread on the forum. I'm a warranted mechanical engineer, though I spent the first few years of my career programming robots and doing R&D in a semiconductor factory (that among other things makes the gyros, accelerometers, microphones and other sensors in many well-known smartphone brands). I'm well-versed with electrical theory (up to and including 3-phase AC theory). I'm also an RC car and helicopter hobbyist, which is where I learnt to put theory into practice. Electric cars are after all a scaled-up version of the systems in a hobby-grade RC car (though the RC ones use DC brushless motors driven by a rudimentary ESC whereas most full size EVs seem to prefer induction motors driven by a full-fledged VFD).

When I charge a battery, I normally do it using a dedicated charger directly connected to the battery terminals, setting appropriate voltage and current limits. Seems EVs add an extra level of obfuscation to the process to make it fool-proof to the majority of drivers, who simply want to plug in a wire that magically tells the car how much power it can draw, without having to set it themselves.

Unfortunately this means that in unique situations like mine with the 1kw generator, it becomes a bit tricky to get the desired behaviour from the car because I'd have to know how the charging standards work - i.e. what signals or voltages to send to which pins to tell it to limit itself to 4A at 240V. Well, either that, or spend €300 on the appropriate cable, which essentially consists of a few plugs, some copper wire, and some circuitry that could probably be mimicked by an Arduino board costing a few dollars.

It's made worse by the fact that there isn't a single universal standard that applies to all electric cars, each car only supports a subset of them, and sometimes it even varies by model year for the same car (look at the Renault Zoe for instance, the early model years were hopelessly inefficient at charging from wall sockets, the later years sacrificed super high power charging for more efficient low-power house socket charging).

GerryAZ
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Re: Can you limit charge current to 1kW for emergency charging with a generator?

Sat Oct 21, 2017 7:13 pm

The J1772 standard goes down to 6 amperes at anywhere between 120 and 240 volts (probably down to 100 volts, but I don't have the standard in front of me). The later versions of EVSE Upgrade units are adjustable down to 6 amperes at any voltage. You could use a 1.5 kVA transformer to drop the voltage from 220 to 110 and use an EVSE Upgrade unit set at 6 amperes to charge with your generator. I actually do the opposite. I have a 3 kVA transformer that I use with my 3 kW Honda generator which operates at 120 volts to charge the car at 12 amperes and 240 volts with my EVSE Upgrade unit in emergencies (or to run the generator periodically under load).
Gerry
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GlennD
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Re: Can you limit charge current to 1kW for emergency charging with a generator?

Sat Oct 21, 2017 8:13 pm

The EVSE generates a 1Khz square wave. The current is determined by the duty cycle. At 30A it is symmetrical. The car analyzes the wave and sets the the current accordingly. If your EVSE signals that only 6A is available then the car charger will set itself to 6A. If more current is available then the car will set itself to its maximum and it will ignore the rest. An enhanced Leaf will draw 27A from A 30A or 40A EVSE. It will simply take what it needs and it will ignore the rest.
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jjeff
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Re: Can you limit charge current to 1kW for emergency charging with a generator?

Sun Oct 22, 2017 5:06 am

GerryAZ wrote:The J1772 standard goes down to 6 amperes at anywhere between 120 and 240 volts (probably down to 100 volts, but I don't have the standard in front of me). The later versions of EVSE Upgrade units are adjustable down to 6 amperes at any voltage. You could use a 1.5 kVA transformer to drop the voltage from 220 to 110 and use an EVSE Upgrade unit set at 6 amperes to charge with your generator. I actually do the opposite. I have a 3 kVA transformer that I use with my 3 kW Honda generator which operates at 120 volts to charge the car at 12 amperes and 240 volts with my EVSE Upgrade unit in emergencies (or to run the generator periodically under load).

Not that you'd probably want to spend more money, but you could also just get an EVSE that would output full amps(27.5) @ 120v :)
I have several EVSEs that will do that, allowing me to fully utilize up to a 120v 3300w continuous generator. In your case with a 3000w generator you should be able to charge at ~24a @ 120v with your generator, avoiding the losses of your transformer(and also having to lug around what I'd have to believe might be a heavy?? transformer.
One scenario where I could see your transformer being handy would be with one of the old(pre '13) Leafs that maxed out at 12a @ 120v and I'm thinking the post '12 S Leafs without the charger package may also have the 12a 120v limitation, but I'm not sure of that. With those you should be able to almost double your charge rate with your transformer.
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
Zencar 13, 20, 30a L1/L2 portable EVSE
GE Durastation 30a

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