Info from Tesla - 277v feed to Wall Connector (HPWC) - Which Cars Support It

[eprosenx]

Why all the concern about using big transformers to drop all the way to 208? A small 2kVA 32v buck transformer is all that is needed here. 277v-32v is 245v. Good to know that the model 3 does support 277 natively though.

2kVA is not enough for a decent charge rate on a Tesla. I assume you are referring to the rating of the transformer when not used as an "autotransformer" (in which case as an autotransformer its rating will be many multiples of the 2KVA).

It is still expensive to need a transformer for each EVSE (or to put multiple on one transformer). Much easier to just hook to 277v if that is available!

I agree with @wws that SAE should extend the J1772 spec to support 277v. I don't see 277v going away and it just seems like incorporating this to the standard would eventually allow its use once new vehicles cycle out and everything supports it.

Unless the increased materials cost to allow 277v was prohibitive or otherwise unsafe?

 

[nwdiver]

2kVA is not enough for a decent charge rate on a Tesla. I assume you are referring to the rating of the transformer when not used as an "autotransformer" (in which case as an autotransformer its rating will be many multiples of the 2KVA).

It is still expensive to need a transformer for each EVSE (or to put multiple on one transformer). Much easier to just hook to 277v if that is available!

I agree with @wws that SAE should extend the J1772 spec to support 277v. I don't see 277v going away and it just seems like incorporating this to the standard would eventually allow its use once new vehicles cycle out and everything supports it.

Unless the increased materials cost to allow 277v was prohibitive or otherwise unsafe?

My understanding is that everything <600v is treated the same. Shouldn’t be any cost or safety difference vs 208 or 240.

 

[eprosenx]

My understanding is that everything <600v is treated the same. Shouldn’t be any cost or safety difference vs 208 or 240.

Most wire is rated 600v, but there are exceptions. SJOOW for instance is only rated 300v (the “J” means junior).

But I was mostly referring to the rating of the charging circuitry in the Tesla or the guts of the Wall Connector. They could only be rated to 240v for instance (but clearly it sounds like everything is safe at 277v, but some models of the onboard chargers may kick off at 280 something volts).

 

[Schenkzoola]

My point was that there was talk of adding transformers to drop to 208. This implies an isolation transformer, which would be large, expensive, and inefficient. A 2KVA 32v buck transformer (autotransformer connection) would drop the 277 to a voltage that satisfies all Tesla vehicles (as well as other makes) and allow for a charge rate of about 50A.

 

[Schenkzoola]

I do agree that no trasformer at all is better from an efficiency and cost standpoint.

 

[miimura]

My point was that there was talk of adding transformers to drop to 208. This implies an isolation transformer, which would be large, expensive, and inefficient. A 2KVA 32v buck transformer (autotransformer connection) would drop the 277 to a voltage that satisfies all Tesla vehicles (as well as other makes) and allow for a charge rate of about 50A.

The problem is that some people are not very creative. 277Y480V has its own style of panel. Doing 1 to 3 HPWCs with individual buck transformers wired L-N from 277V -> 240V makes sense. However, if you wanted to put a panel out in the parking lot to wire up a larger number of EVSE, they would only think to do the isolation transformer and a 120Y208V installation. In reality, it would probably be cheaper and better to run them with a 277Y 3-phase panel running a bucked 240Y415V.

Edit: one consideration is that an installation that mixes Tesla and J1772 EVSEs may be be able to use 240V L-N power. I just checked Clipper Creek and they do not support this. They only allow line voltages 120V above ground. 240V Detla is only supported with center tap grounded legs.

 

[EfficientWatts]

Edit: one consideration is that an installation that mixes Tesla and J1772 EVSEs may be be able to use 240V L-N power. I just checked Clipper Creek and they do not support this. They only allow line voltages 120V above ground. 240V Detla is only supported with center tap grounded legs.

They would probably have to use a J1772 that is an international model (clipper seems to have some of them), or use a station that can support L-N. I know Chagepoint can do L-N as there are some of their J1772 overseas. Interestingly the Tesla UMC doesn't care if it's L-N or L-L, it just works (see examples of people using the NA UMC in Europe). I would guess mobile connectors may be less picky about this.

L-N doesn't preclude J1772, though that means doing a little bit of extra leg work to find models that do work.

 

[eprosenx]

The problem is that some people are not very creative. 277Y480V has its own style of panel. Doing 1 to 3 HPWCs with individual buck transformers wired L-N from 277V -> 240V makes sense. However, if you wanted to put a panel out in the parking lot to wire up a larger number of EVSE, they would only think to do the isolation transformer and a 120Y208V installation. In reality, it would probably be cheaper and better to run them with a 277Y 3-phase panel running a bucked 240Y415V.

Edit: one consideration is that an installation that mixes Tesla and J1772 EVSEs may be be able to use 240V L-N power. I just checked Clipper Creek and they do not support this. They only allow line voltages 120V above ground. 240V Detla is only supported with center tap grounded legs.

I like your idea!

I had been thinking it would be cool if someone made a 277Y480V to 138Y240V transformer. Now this would not save on the cost of the transformer (since it would be pretty similar to a 120Y208V transformer), but on the plus side it would allow you to connect a bunch of EVSE's hot-to-hot all at 240v so you did not take the 15% hit in speed to 208v. This would also solve for the center tap vs. L-N problem. I think the issue would be you would have to buy a panelboard rated for something above 120/208v which could make it really expensive as you might have to buy a 277/480v panel?

Note that the Tesla Wall Connector is almost always hooked to center tapped 240v or 208v. The one exception is 277v where it is L-N. There is a dip switch in the Wall Connector they tell you to throw which I wonder if that puts it into a mode where it only tests for potential between Line and ground instead of testing for potential between both Lines and ground? While the Wall Connector does not state it would support 120v (which would be L-N) I do wonder if it would work if hooked up and the dip switch flipped.

I have wondered how the UMC does its safety checks. Since it supports both 120v and 240v, how does it know which it is hooked to? I guess it could try to figure out what the configuration is of the circuit it is plugged into by testing potential between the two hots (or one hot and neutral depending on how configured), plus between the two hots (or one of them Neutral) and ground.

The more I think of it, the lack of 277v support in J1772 is sad. For charging at commercial locations 277v is clearly superior in the US. It really should be the standard.

 

[jamcl3]

2kVA is not enough for a decent charge rate on a Tesla. I assume you are referring to the rating of the transformer when not used as an "autotransformer" (in which case as an autotransformer its rating will be many multiples of the 2KVA).

It is still expensive to need a transformer for each EVSE (or to put multiple on one transformer). Much easier to just hook to 277v if that is available!

I agree with @wws that SAE should extend the J1772 spec to support 277v. I don't see 277v going away and it just seems like incorporating this to the standard would eventually allow its use once new vehicles cycle out and everything supports it.

Unless the increased materials cost to allow 277v was prohibitive or otherwise unsafe?

2 kVA at 32 V is 62.5 amps, which is a decent charge rate. The 2 kVA number does not apply to the full output, just the buck voltage.

J1772 is not likely to entertain a proposal to extend the voltage range to 277, as far as I can tell. J3068 supports 277 (and above) and the required control protocol could be applied to single phase connectors like J1772 but 240 V would likely be required in EVSE in public locations for backward compatibility.

 

[Fronhofer]

So, I did it! I bought a s/x mobile charger 40amp on EBay. And at work where we have 480V 3p power, I wired up an outlet 270V 1p+neutral(grey wire on 480v)+GND. Plugged in my Model 3. 42m/hr
No problem with any it. Everything is purring along. Was getting 31m/hr at 208.

 

[eprosenx]

View attachment 365656
So, I did it! I bought a s/x mobile charger 40amp on EBay. And at work where we have 480V 3p power, I wired up an outlet 270V 1p+neutral(grey wire on 480v)+GND. Plugged in my Model 3. 42m/hr
No problem with any it. Everything is purring along. Was getting 31m/hr at 208.

I simultaneously think this is awesome and am also concerned from a safety standpoint. I don’t think the UMC is rated for 277v. Or at least the receptacle (did you use a 14-50?) is not rated for it. What did you do with the fourth pin if you used a 14-50?

That is a horribly dangerous outlet to have exist (what if someone plugged in an RV or a welder?)

That is really bad ass though charge speed wise.

480 is nothing to mess with. Arc flash is dangerous among other things...

 

[Fronhofer]

Thank you for your interest and concern. I am of course being as careful as any electrical worker would be. And based on the information the first poster acquired from Tesla, I decided to experiment.
Yes, don’t try this at home kids, I’m a self taught professional. As stated earlier the car will limit and reject unacceptable power.
The charger and 14-50 are stock. And I hard wired a pigtail to a existing welding outlet FOR THIS TEMPORARY TEST the neutral on the 14-50 is unused it appears because the car only wants the original 240v legs and the power just goes directly to the car after the “yes we are safely connected” handshake. I was just concerned the voltage regulator for the handshake electronics might not take the 277v.
Yes overall KW are increased by around 15% but amps are still 40 and that in my understanding is how we size wiring.
My initial thoughts on permanence are cut off the plug and source a 277v or 480v 50amp plug with neutral. None of the equipment we use here needs a neutral so the outlets only have 3P and gnd. But I wired the building and ran neutrals with every run, 480v & 208v.
Or convert one of the Tesla plug ends into a pig tail that plugs into the correct sourced outlet. That way the UMC is unmolested.
Thank you for your polite words. Sometimes a guy just wants to give it a try. Hope this is exciting for you too. ฿^)

 

[Fronhofer]

50 Amp, 277 Volt, NEMA 7-50P, 2P, 3W, Plug, Straight Blade, Industrial Grade, Grounding, Angle

This might be the way to go.

 

[TMeister]

Great experiment @Fronhofer! Don't forget that the gen 1 UMC uses resistors in the plug adapters to set the pilot signal and control max current. This link shows the values. How do adapters signal max amperage to UMC?

 

[Fronhofer]

Nice info thanks. Looks like I’m going to install the 7-50 outlet on the wall and build a 7-50 to 14-50 extension cord. With orange and black “NON STANDARD 277VAC” stickers.

 

[tga]

Nice info thanks. Looks like I’m going to install the 7-50 outlet on the wall and build a 7-50 to 14-50 extension cord. With orange and black “NON STANDARD 277VAC” stickers.

Skip the 7-50 extension cord/adapter. These guys can supply you the parts to make your own 7-50 adapter (or build it for you) - EVSEadapters.com electrical adapters for Tesla drivers, welders, RVs

 

[miimura]

Skip the 7-50 extension cord/adapter. These guys can supply you the parts to make your own 7-50 adapter (or build it for you) - EVSEadapters.com electrical adapters for Tesla drivers, welders, RVs

LOL. The guy already wired the whole building himself. He's not going to go third party on a cord.

 

[eprosenx]

As stated earlier the car will limit and reject unacceptable power.
The charger and 14-50 are stock. And I hard wired a pigtail to a existing welding outlet FOR THIS TEMPORARY TEST the neutral on the 14-50 is unused it appears because the car only wants the original 240v legs and the power just goes directly to the car after the “yes we are safely connected” handshake. I was just concerned the voltage regulator for the handshake electronics might not take the 277v.
Yes overall KW are increased by around 15% but amps are still 40 and that in my understanding is how we size wiring.
My initial thoughts on permanence are cut off the plug and source a 277v or 480v 50amp plug with neutral. None of the equipment we use here needs a neutral so the outlets only have 3P and gnd. But I wired the building and ran neutrals with every run, 480v & 208v.
Or convert one of the Tesla plug ends into a pig tail that plugs into the correct sourced outlet. That way the UMC is unmolested.
Thank you for your polite words. Sometimes a guy just wants to give it a try. Hope this is exciting for you too. ฿^)

So from your post above you must have bought a UMC Gen 1 right? So that does not have the 12" adapters that the UMC Gen 2 does. I think your 7-50 to 14-50 custom extension cord / adapter is not a horrible solution for this. Just label it well as you stated.

With that being said, I have a couple of concerns here. You definitely are offroading on a non-UL approved path. ;-) The electronics in the UMC I bet run off a standard DC power supply like what your cell phone or laptop might use. These are normally rated for 100-240v. So 277v is a bit high. The other concern I would have is the contactor in the UMC. Basically the UMC has a big relay in it that does not energize power until it successfully talks to the car. I would be worried about it not being rated for 277v. If it had to open under load it might be unable due to the higher voltage (though there is a halfway decent chance that the part Tesla sourced for this might under the hood be rated to 277v itself). I guess also on the PCB and such in the UMC and any other internal components, there may be things without sufficient isolation for 277 vs 240v (though again, likely you are ok but are just eating into the safety margin).

Definitely this would be DANGEROUS to pull out from the wall plug under load. This is why the Tesla's lock the cord into the car while pulling current.

I am pretty excited that you tested this. Very cool. Not sure I would have had the guts to test it myself... lol...

Skip the 7-50 extension cord/adapter. These guys can supply you the parts to make your own 7-50 adapter (or build it for you) - EVSEadapters.com electrical adapters for Tesla drivers, welders, RVs

I think the OP has a UMC Gen 1 so you can't modify one of the factory adapters I don't think.

 

[tga]

I think the OP has a UMC Gen 1 so you can't modify one of the factory adapters I don't think.

They have a Gen 1 to custom plug pigtail -
Custom Adapter for Tesla Model S and X Gen 1

 

[eprosenx]

They have a Gen 1 to custom plug pigtail -
Custom Adapter for Tesla Model S and X Gen 1

Thanks for pointing that out! I realized it after I posted that... Doh! I should have clicked the link before posting. That solution would be even safer as it would not require a dangerous extension cord/adapter to exist.

One other thing to add to this thread that I just realized: 277 is only nominally more voltage than 240, but there is a big difference between 240 (which is 120v if potential to ground) and 277 which is 277v to ground.

If you manage to touch a “hot” on 240 and you are grounded you only get a 120v shock. On 277 you get a 277v shock.

Please be careful!

P.S. I wonder if this will work on a UMC Gen 2? Do you perhaps have one you would be willing try?