[rkjnsn]

Several places I've been, including the trailhead of a nearby hike, have power boxes with 30 A 120 V service (24 A continuous) via a TT-30 connector. Since we know the EVSE that comes with the gen 2 is capable of operating at 240V and delivering 12 A, I was curious if I could connect the EVSE to a TT-30 through a 120 V to 240 V step-up transformer to obtain the full 2.88 kW of continuous power the TT-30 is capable of providing.

Has anyone tried this? Would the transformer losses be enough to draw too much current on the 120 V side? (I seem to recall that transformers are pretty efficient when under load, but I could be mistaken.) What other concerns should I consider?

Based on the suggested 50% safety overhead for continuous load, it sounds like I would want a 5000 W transformer. It looks like there are several available with a "universal" receptacle on the 240 V output, which would allow me to plug in the EVSE directly without an extra adapter. Does anyone have any suggestions or things to look out for? Is this a terrible idea?

 

[saghost]

I haven't read of anyone trying it. In theory, something along this line can work.

A couple of challenges - some versions of the OEM EVSE apparently can handle 240V, some of them can't. (None are rated for it.)

Also, You'll want to make sure the pilot signal matches the actual current available, so the car doesn't pull too much power. It actually sounds like this might happen to work out for you - the OEM EVSE pilot limits at 12A, which is where it seems like you'd want it.

 

[hellsop]

The real trick will be finding the transformer that's worth it. I've scoped out a bunch over the years (mostly for easily adapting a Euro-spec sailboat to US wiring) and it basically comes down to: 1) $200 Chinese units portable that may work, for a while at least, but not necessarily as you'd hope. (I've seen "5000 watt" units that turn out to have 24 amp breakers in them on both the 120 and 240 volt sides. Which means it's a 5000 watt step-down as long as you only use 2600 watts, or a 2600 watt step up that you can actually use all of. But it won't feed a 3kw Volt charger properly.) 2) $1000 wire-in transformers that actually made in such a way that they'll actually handle all 4000 watts they're rated for, but it's up to you to supply the connection wiring and a housing that supplies proper airflow and 4 inches of clearance on all sides and above. (If the Catalac 12m happens someday, that'll be the option I choose. Because pretty it's STILL cheaper than rewiring a 240 v boat to 120, and most of the stuff I'd want to use on there either has 240v options easily available or is dual voltage to begin with. You'd be AMAZED how much of your electronic runs just fine on 240V, and the wiring is so much cheaper. You can run space heaters on 14g wire.

 

[jsmay311]

When people say that the OEM EVSE can handle 240V, they mean 2-phase power. So 120V on 2 different pins out-of-phase with each other.

Simply taking 120V one-phase power and stepping it up to 240V is a totally different deal.

Other countries use 230V 50Hz one-phase power, but I doubt that that (or 240V 60Hz one-phase) would work with a Volt.

 

[saghost]

When people say that the OEM EVSE can handle 240V, they mean 2-phase power. So 120V on 2 different pins out-of-phase with each other.

Simply taking 120V one-phase power and stepping it up to 240V is a totally different deal.

Other countries use 230V 50Hz one-phase power, but I doubt that that (or 240V 60Hz one-phase) would work with a Volt.

I don't see how it is different for the device. The split phase 240V is accomplished by putting opposite phases onto the two wires, producing 240V rms of potential difference between the two wires. The transformer is also producing 240V rms between the two wires.

The transformer is more dangerous to handle because it moves further from ground, but it seems like it's exactly the same to the device.

 

[edk-austin]

Ground reference is an issue.

With an isolated 120V to 240V SPLIT phase transformer to power the EVSE you'll be ok. The center tap of the 240VAC xfmr secondary becomes the ground going into the EVSE, and connected to ground of the TT30. Transformer primary is N and H of the TT30.

There are also non isolated split phase step up transformers, but I'd worry about the ground to neutral voltage difference with 25+A on the TT30 neutral side.

Be careful of the thermal issues.

 

[Lumos]

L2 charging, in the US, is single phase 208V / 240V

When people say that the OEM EVSE can handle 240V, they mean 2-phase power. So 120V on 2 different pins out-of-phase with each other.

Simply taking 120V one-phase power and stepping it up to 240V is a totally different deal.

This is incorrect. if you step up from 120Vrms to 240Vrms all would be good. Essentially, they are both single phase as seen by the load ( the charger).

An analogous way to think about single phase concept is if one had 3 phase power, and connected a load between two of the phases, they'd have single phase power to their load. This is actually how we wind up with 208V L2 chargers. This site does an good job of illustrating this:http://www.oempanels.com/208v-single-phase-and-208v-3-phase

What the earlier poster is thinking about is that the panels in our homes in the US have two 120V phases that are 180 degrees apart ( simply the opposite of each other) - when one leg is at the peak positive voltage , the other leg is the minimum negative voltage. Connecting between the two of them see twice the voltage or 240Vrms.

The issue is more the size / cost of a 5KVA transformer - if it's a traditional 60Hz transformer it'll be around 75lbs, and cost a lot. Grainger shows them for > $1000, but that is high, I see them on Ebay fora couple of hundred.

-Lumos
2014 gen 1

 

[rkjnsn]

Some versions of the OEM EVSE apparently can handle 240V, some of them can't.

Based on the relevant thread, mine should be able to handle it.

Also, You'll want to make sure the pilot signal matches the actual current available, so the car doesn't pull too much power. It actually sounds like this might happen to work out for you - the OEM EVSE pilot limits at 12A, which is where it seems like you'd want it.

That's what I'm hoping.

I don't see how it is different for the device. The split phase 240V is accomplished by putting opposite phases onto the two wires, producing 240V rms of potential difference between the two wires. The transformer is also producing 240V rms between the two wires.

That's what I would suspect as well, though it would be nice to hear it from Chris TX or someone else who has actually analyzed the components. The only thing I can think of that might care would be the GFCI circuitry.

According to a review of the 3000W version of a.co/9CI30bZ, it looks like this one might actually create split-phase power. Relevant quote:

My measurements indicate that for the step-up mode in which I am operating, the neutral of the 120 V input appears to be at middle potential of the two power conductors of the 240 V output.

 

[Chris TX]

Using something like this could give you 3kW @ 240V. All you'd need is a TT-30 to 5-15 adapter. Since we would run it at a solid 3kW for 4-5 hours, I might modify the cooling system a bit.

http://www.ebay.com/itm/3000w-3000-...40V-to-110-120-Up-Down-110-220-/371663361912?

I've not used this model, but have used similar Trisonic ones when dealing with imported stuff.

 

[Neromanceres]

Ground reference is an issue.

With an isolated 120V to 240V SPLIT phase transformer to power the EVSE you'll be ok. The center tap of the 240VAC xfmr secondary becomes the ground going into the EVSE, and connected to ground of the TT30. Transformer primary is N and H of the TT30.

There are also non isolated split phase step up transformers, but I'd worry about the ground to neutral voltage difference with 25+A on the TT30 neutral side.

Be careful of the thermal issues.

I think this could work. If he does step up to a 5000VA transformer he should have plenty of overhead and it should mitigate any thermal issues. He could also connect the ground from the EVSE direct to ground from the TT-30 plug.

 

[edk-austin]

Using something like this could give you 3kW @ 240V. All you'd need is a TT-30 to 5-15 adapter. Since we would run it at a solid 3kW for 4-5 hours, I might modify the cooling system a bit.

http://www.ebay.com/itm/3000w-3000-...40V-to-110-120-Up-Down-110-220-/371663361912?

I'm not seeing that this is a split phase output. With out a center tap, you can't fix the ground reference on the secondary side to the middle. You'd have only a single phase of 240VAC that will have a 340V peak DC voltage on the L1 side. US 240V split phase never exceeds about 170V peak DC from ground. Which would be fine for Europe and places that really use single phase 240VAC, but I wouldn't want to test that on my car.

 

[AtomicPowered]

In North America if 120v is available, 240v is not far away. It's just the way electrical service is made available to the customer. My experience with camping is even 120v can have problems. Get a voltmeter and a 5-15 cube type circuit tester. They are both about $10 and small. Learn how to use them before you plug in anything valuable. If you do find a 30 amp 120v outlet in the wild it is probably not capable of 30 amps without a large voltage drop or it is close to a service transformer in which case 240v would be available.

 

[rkjnsn]

In North America if 120v is available, 240v is not far away. It's just the way electrical service is made available to the customer. My experience with camping is even 120v can have problems. Get a voltmeter and a 5-15 cube type circuit tester. They are both about $10 and small. Learn how to use them before you plug in anything valuable. If you do find a 30 amp 120v outlet in the wild it is probably not capable of 30 amps without a large voltage drop or it is close to a service transformer in which case 240v would be available.

In my experience, there are still a number of RV hookups at campgrounds and such with a TT-30 receptacle without a corresponding 14-50 receptacle, and a number of Tesla owners report charging at 24 amps from such receptacles without issue.

 

[edk-austin]

Volt will never draw more than 12A at 120V. The OBCM limits itself. Tesla OBCMs have greater operating range and heavier gauge wire to handle increased current.

 

[rkjnsn]

Volt will never draw more than 12A at 120V. The OBCM limits itself. Tesla OBCMs have greater operating range and heavier gauge wire to handle increased current.

Yes. That is why this thread is asking about the possibility of using a voltage transformer to step up the voltage to 240 to take advantage of the 2.9 kW available from the outlet. 240 V @ 12 A on the car side, drawing 120V @~25A (assuming a 95% efficient toroidal transformer) on the TT-30 side.

 

[Rampage_Rick]

It's certainly doable if you used a transformer with a center tap on the 240V side:

Note that the neutral/ground on the right side is connected to the ground on the input (left side)

As others have alluded to, the lack of a center tap on the 240V side would result in a voltage of 240V to ground instead of +120V / -120V to ground. A european market EVSE would tolerate 240V to ground but a North American market EVSE will likely either not function or self destruct. (I'd worry about self-immolation with the Gen2 EVSE because running it at 240V is already a kludge)

Personally I'd try to find two different TT-30 receptacles that give 240V hot-hot and build a big Y cable to reach. Same concept as the "Quick 220" http://gm-volt.com/forum/showthread...E-with-Quick240V-Device-from-two-120V-sources

 

[edk-austin]

Yes. That is why this thread is asking about the possibility of using a voltage transformer.

And I said yes, back in Post #6.