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

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LMF5000

Active member
Joined
Oct 20, 2017
Messages
41
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.
 
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.
 
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.
 
smkettner said:
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/solutions/articles/6000052145-how-do-i-set-the-maximum-current-available-to-the-vehicle-) might help the OP and will let him max current via the pilot signal low enough?
 
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%
 
OP is in a 220v country, 8a @ 220v = 1760w or almost double what his 1kW 220v generator could handle.
 
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).
 
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).
 
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.
 
GerryAZ said:
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.
 
jjeff said:
GerryAZ said:
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.

I bought the transformer when I had the 2011 which would draw a maximum of 12 amperes at 120 volts regardless of EVSE pilot signal so it did double the charging rate on generator for that car. The transformer is heavy (probably about 50 pounds), but it has a 3-wire 120/240-volt output so I can use it for a lot more than just charging the car. I would have purchased a 120/240-volt generator if an inverter model with lots of sound insulation had been available back when I bought my Honda EU3000is.
 
Hi All,

Thank you for the replies so far. I'm already learning a lot!

I looked at the EVSE upgrade cable and I find it a bit disappointing that on a €300 product I would have to short two pins with a paperclip and repeatedly press the handle to set the charging current. There are DC-DC converters for sale on eBay with buttons and displays for less than €5 including shipping, how much would it have cost to add a decent user interface to the EVSE?

Regarding converting from one voltage to another, the instant you mentioned it I immediately thought of weight. You need lots of iron to do power conversion at a low frequency of 50Hz (which is why aircraft electrical systems for example operate at 400Hz AC and inverters, power supplies and other electronically-controlled power conversion devices operate their transformers at some 25kHz).

Sure enough, a 1kVA 240 to 120V transformer weighs 15kg and costs €268 (I'm looking at the Mouser 530-DU-1). For reference, my 1kVA inverter generator cost €220 and weighs around 15kg too. At those prices and specs it actually makes more sense for me to sell my generator and buy a 2kW generator. Or look at different electric car options :lol:
 
LMF5000 said:
I looked at the EVSE upgrade cable and I find it a bit disappointing that on a €300 product I would have to short two pins with a paperclip and repeatedly press the handle to set the charging current. There are DC-DC converters for sale on eBay with buttons and displays for less than €5 including shipping, how much would it have cost to add a decent user interface to the EVSE?
I agree it seems, and maybe is a bit hokey but I believe the designer wanted to change the case as little as possible, possibly thinking of people turning their EVSE in at the end of a lease. It was probably also done for weather tightness, an upgraded EVSE is just as weatherproof as an OEM EVSE. That said I'd probably agree that there are now other ways of adjusting current that don't require buttons. My older Zencar EVSE uses a shaking method, each hard shake of the EVSE increments to the next highest setting. This works OK for my Zencar EVSE that only has 3 amp settings but would be kind of a pain for the EVSE upgrade that has 15 possible amperage settings. The new Zencar EVSEs use a proximity card to increment the amp settings, one to increment amps and one to lower amps(I believe it works this way) that would be the best way to adjust without buttons IMO. Another cool option is what my old Juicebox uses, a small RF remote with + and - buttons to adjust output, of course, the new Juiceboxes use your smartphone to adjust but the downside is I believe you need WiFi and the internet to do it.
The paperclip method is quite ingenious though and quite easy to adjust.
 
LMF5000 said:
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
Yea I think for everything involved either figure out the charging or have it shipped.
Only other option might be to rent a larger generator that can power the included OEM cord.
 
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