240 vs. 208 Volt level II charging

Many people view 208 V and 240 V as the same thing, but they are not. The 208 V is a result of three phase power, and 240 V is the result of two phase (a.k.a. one phase) power. But I've taken my level II charger off the wall and on road trips before so I can drive long distance through places that don't have level II chargers, but do have 30A and 50A plugs for 208/240V. The higher voltage charges faster.

Have others noticed this too? This could also be observed from many commercial chargers being a little slower where they are likely to have 208 3-phase, vs. the 240V 2-phase at residential and some commercial locations. I carry around a multimeter now to measure the voltage where I plug in, but it is not always possible if there is not a normal 240/208 plug around.

The second question is whether anyone has heard of using a 3phase to 2 phase converter to speed up the charging at these 208V locations. 2-phase to 3 phase converters are available, so one could also go the other way. If I knew more about exactly what type of load the (leaf) charger presents to the EVSE plug, then maybe I could make one from just passive circuit elements like capacitors, inductors, and resistors.

Another way to do this phase conversion could be with a solid state converter which could either produce two phases directly out of sync or to just boost the voltage (by drawing more current) to 240V (or even better 250V). I say 250V because I also have noticed that the leaf charges faster at 250V than at 240V. My house has a line voltage of 245-255V, and I usually charge 35% in one hour.

The challenge is that there are number of combination of receptacle for 208V and 240V as well as 30 A and 50A rating. You have to prepare the right plug adapter to the receptacle for your charger plug. You can made the adapter yourself for different variation as long as the X, Y,Z to X,Y,W are lined up. You also need to deal with locking type receptacle as many commercial facility use locking type. It will be quite difficult to equip yourself with multiple adapter type.
As far as phase converter, I don't know if there is any static phase converter helped increase the line voltage from 208V to 240V. My understanding it will require transformer to change the voltage.

Yes, this is a well-known effect typically observed at commercial installations with three-phase power. I would not be aware of any practical means to step up the voltage from 208 to 240V.

I always wondered if the Leaf would charge at 277V. Not enough to try it though.

Staque said:

I always wondered if the Leaf would charge at 277V. Not enough to try it though.

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Don't do it man! At least not on using EVSE Upgrade L1.

Ingineer and I had discussion about it, when I inadvertently came up with 277V on my Voltmeter while trying to find two 120v outlets in my office (to combine for my homebrew Quick 220). He told me that if I'd just plugged the EVSE upgrade unit in, without checking first...well, it would have been bad!

I have a 2011 Leaf, it is supposed to be limited to 16 amps, however when charging at 208V, and IF the pilot is above 16amps, it will draw a slightly higher number.
Bottom line, if your pilot signal is higher than what your car can actually use, the speed of 208 or 240 will be the same, otherwise, 240 will be faster.

BOOM!

Staque said:

I always wondered if the Leaf would charge at 277V. Not enough to try it though.

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I suppose if you added up the time it took to acquire and assemble something that would work (a 208 to 240 volt transformer), plus factor in the time you had to work to earn the money to buy such a device, you would be better off time wise just to wait a bit longer for your car to charge on those rare occasions you have 208 v instead of 240.

I guess you could also use a 240/24 step down transformer like an auto transformer if you wanted to..just upsize it a bit because the primary is running on 208 instead of 240... then you could add 24 volts to the 208 get you a bit closer to your 240.

208->240 just needs a 15:13 turn ratio. For the truly adventurous you could probably rejigger an old arc welder to do the job over a weekend!

=Smidge=

When designing remote television production trailers, which nominally require split 240, we use buck/boost transformers to cover the range of 190 to 290. They are cheap and reasonably small... I really don't see the ROI in doing something like this for charging a Leaf, though...

Smidge204 said:

208->240 just needs a 15:13 turn ratio. For the truly adventurous you could probably rejigger an old arc welder to do the job over a weekend!

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Its called a "buck-boost transformer", and it will take your 208 single phase up to 240 single phase if you really feel you need a slightly faster charge rate.

EDIT: Oops. TomT already stated that.

TomT said:

When designing remote television production trailers, which nominally require split 240, we use buck/boost transformers to cover the range of 190 to 290. They are cheap and reasonably small... I really don't see the ROI in doing something like this for charging a Leaf, though...

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TomT - Correct about the buck/boost transformer. I have done the same and for the same reason. All they are is a transformer that takes the 240/208 as the primary and is wired to put the 32V secondary inline with one of the hot leads going to the load. If you wire one way it adds to the voltage delivered (boost), the other way it subtracts (buck).

Would be safe in a hard-wired install where you take time and verify voltages, but in portable use? Risk for accidental use of boost on a line that is already 240V and sending 272V to the unit would be something I would not want to risk (will it smoke?).

As you say, the gain does not seem worth it.

jlatl said:

Would be safe in a hard-wired install where you take time and verify voltages, but in portable use? Risk for accidental use of boost on a line that is already 240V and sending 272V to the unit would be something I would not want to risk (will it smoke?).

As you say, the gain does not seem worth it.

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I carried a 40 volt boost transformer with me during BC2BC-2013. The difference in time charging is 240/208, or about 15% faster. Over thousands of miles of charging during the two weeks I was on the road (first, from San Diego to Canada, then return to Mexico), that adds up to hours wasted on 208 volt.

Start at page 152 of this document:

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Of course, because I can also pull more than 30 amps that most public charge stations offer, I usually went to RV parks, where I got both 240 volt (but it could vary a LOT !!!) and 40 amps.

As to the 277 volt question, Tesla products (like what my Rav4 EV uses) can safely use 277 volts at the charger, but the amperage is automatically limited to not exceed 10kW per charger (40 amps * 250 volt or 36 amps at 277 volt).

I think the portable 40 amp Tesla UMC is officially limited to 265 volts (again, I'm guessing), and it works well in any J1772 equipped car with our JELSAtm conversion. It would be awesome to have a 277 volt capable unit !!!

208 v is always slower than 240 vac. This is normal I find many of the Blink public charging units all are set to the same low amps of 24. So on a 208 circuit it's very slow and we pay by the half minute in Arizona. Other states allow paying by kWh so you get the better value. . It doesn't seem fair.

I use a EVSE spy and can read the volts amps and kWh used at any charge location. I then post it on Plugsdhare so EV drivers know if it's a good deal or not.