Why are some stations 208V?

[mknox]

Right, I think they're likely saying that to maximize the car's draw, because it's based on amps, that installing a 208:250 transformer with a 60A primary rating could give a full 10 kW @ 250V/40A on the secondary, to the car.

Yep. I was basing my comment on connecting it to his existing 50 amp (40 amp continuous) 208 volt circuit. If you could upgrade that circuit to 60 amps, then we're on to something. The question in my mind is whether the expense and bother is worth the slight increase in charging performance. Maybe it would be cheaper and easier to just connect that upgraded 60 amp (or more, if the service can handle it) 208 volts to a HPWC and throw the UMC into the frunk for road trips.

 

[FlasherZ]

Yep. I was basing my comment on connecting it to his existing 50 amp (40 amp continuous) 208 volt circuit. If you could upgrade that circuit to 60 amps, then we're on to something. The question in my mind is whether the expense and bother is worth the slight increase in charging performance. Maybe it would be cheaper and easier to just connect that upgraded 60 amp (or more, if the service can handle it) 208 volts to a HPWC and throw the UMC into the frunk for road trips.

It really hinges on one question for me - and I'm not sure if it's been answered definitively yet. If the car has only a single charger, does it restrict charging to 40A? Since wire sizes and circuit board traces and such are dependent upon current, not power, it seems that it may very well do that. If so, you'd only get 8.3 kW from a single charger on 208V.

Having the answer to that question would also help answer a curious question I've had in the opposite direction -- a 277V input at 40A would result in 11 kW charging power and a 10% reduction in charging time. So is the charger really a max 40A charger, as opposed to a 10 kW charger?

 

[qwk]

^^^ From everything I have read, it sure seems like the limit is 40A and somewhere around 250V(even though the specs on the charger say 277V). The voltage limit I think is mainly a UMC thing, so J1772 could very well function @ more than 250V, which would be more than the advertised 10kw(before charging losses).

 

[FlasherZ]

^^^ From everything I have read, it sure seems like the limit is 40A and somewhere around 250V(even though the specs on the charger say 277V). The voltage limit I think is mainly a UMC thing, so J1772 could very well function @ more than 250V, which would be more than the advertised 10kw(before charging losses).

There are reports that the stickers on the charger in the car say 277V (the Tesla site had 265V last time I looked), and that would make sense for SuperChargers using N-L 277V off a 480Y/277 transformer bank. The UMC uses the same type of switching PS to drive the contactors in it.

Basically, what I want to know boils down to 2 questions:
1. Will a single-charger car charge at > 40A when voltage would limit the max power to < 10 kW?
2. Will a single-charger car charge at > 10 kW when voltage would cause 40A to exceed 10 kW?

 

[mknox]

^^^ From everything I have read, it sure seems like the limit is 40A and somewhere around 250V(even though the specs on the charger say 277V). The voltage limit I think is mainly a UMC thing, so J1772 could very well function @ more than 250V, which would be more than the advertised 10kw(before charging losses).

I would also guess that there is a hard limit on current at 40 amps, but there could be a range of voltages that the on-board charger can deal with. Probably in the range of 100 to 250 volts (but that's just a guess on my part).

EDIT: Just saw FlasherZ's post. Looks like max voltage may be as high as 277 volts.

 

[qwk]

Basically, what I want to know boils down to 2 questions:
1. Will a single-charger car charge at > 40A when voltage would limit the max power to < 10 kW?
2. Will a single-charger car charge at > 10 kW when voltage would cause 40A to exceed 10 kW?

This is going to be a very difficult thing to test, as you would have to plug a car outfitted with a single charger into a HPC or a J1772 plug that had more than 250V @40+A. Finding one that meets both criteria is going to be tough.

 

[vcor]

I'd be very concerned about running it at the maximum voltage. This spec is usually a "do not exceed" kind of rating under any circumstances. For 240V circuits, it's the buffer should there be a slightly higher voltage, up to +15%, that would not cause any damage. If using 277V, any over voltage might kill the charger! It's likely built to handle more voltage as a safety margin, but I wouldn't take the chance unless directly told by Tesla it is designed to handle 277V. If Tesla tells you it handles 277V, with a 15% buffer, it should be specified that it handles 318V (which is not the case).

 

[smorgasbord]

Obligatory video comment:

 

[RDoc]

This is going to be a very difficult thing to test, as you would have to plug a car outfitted with a single charger into a HPC or a J1772 plug that had more than 250V @40+A. Finding one that meets both criteria is going to be tough.

Actually, aren't a lot of the Sun Country Highway chargers 60 or 70 Amp? I wouldn't be surprised if a lot of them were also 208V, so if the charger is power limited rather than amperage, it would draw over 40A. The wiring in the car up to the charger must be able to handle more than 40A, so the issue is how the charger itself is built. It's not unbelievable that Tesla would have designed them for maximum power at 208V since that's so common, but thus far it all seems like speculation.

It is an interesting question though because if the chargers are power limited and many public chargers are 208V 60A, then the marginal utility of dual chargers is greatly lessened. At least for the Sun Country units, at 208V the dual chargers really only would make a difference for chargers over the CS-70's since its continuous output is limited to 58A which is barely over 10kW at 208V.

 

[FlasherZ]

Actually, aren't a lot of the Sun Country Highway chargers 60 or 70 Amp? I wouldn't be surprised if a lot of them were also 208V, so if the charger is power limited rather than amperage, it would draw over 40A. The wiring in the car up to the charger must be able to handle more than 40A, so the issue is how the charger itself is built. It's not unbelievable that Tesla would have designed them for maximum power at 208V since that's so common, but thus far it all seems like speculation.

It is an interesting question though because if the chargers are power limited and many public chargers are 208V 60A, then the marginal utility of dual chargers is greatly lessened. At least for the Sun Country units, at 208V the dual chargers really only would make a difference for chargers over the CS-70's since its continuous output is limited to 58A which is barely over 10kW at 208V.

I suspect the whole 10 kW number is a red herring, and that's nominal at 250V and confusing all of us. I suspect that the maximum charge current per charger, regardless of voltage, is 40A. This means at 208V, single charger gets you 8.3 kW, dual gets you up to 16.6 kW. At 120V (if the car didn't artificially limit it to 20A), single charger could in theory give you 4.8 kW, dual 9.6 kW. At 277V, single charger could give you 11 kW, dual could give you 22 kW... and so forth.

- - - Updated - - -

I'd be very concerned about running it at the maximum voltage. This spec is usually a "do not exceed" kind of rating under any circumstances. For 240V circuits, it's the buffer should there be a slightly higher voltage, up to +15%, that would not cause any damage. If using 277V, any over voltage might kill the charger! It's likely built to handle more voltage as a safety margin, but I wouldn't take the chance unless directly told by Tesla it is designed to handle 277V. If Tesla tells you it handles 277V, with a 15% buffer, it should be specified that it handles 318V (which is not the case).

My guess is that the tolerance is a bit lower at the high end of the spectrum (perhaps 5% instead of 15%), but that 277V is safe for it. It would be logical to support N-L voltage for 480Y/277 systems in the US, especially for SuperCharging. That's a difference of 150A for a single SC connection.

- - - Updated - - -

Obligatory video comment:

You don't know how many times that's quoted to me... all the time... if I had a nickel...

 

[Doug_G]

Actually, aren't a lot of the Sun Country Highway chargers 60 or 70 Amp? I wouldn't be surprised if a lot of them were also 208V, so if the charger is power limited rather than amperage, it would draw over 40A. The wiring in the car up to the charger must be able to handle more than 40A, so the issue is how the charger itself is built. It's not unbelievable that Tesla would have designed them for maximum power at 208V since that's so common, but thus far it all seems like speculation.

The vast majority of the Sun Country Chargers are 90 Amp (70 continuous), in part because the company sees it as a sales differentiator. Why install a lower-power charger now when you will probably have to upgrade in the future? Also it's what Tesla owners need now, and they're definitely people you want to attract to your business.

However some locations are simply unable to provide that much power, and occasionally the location owners simply aren't willing to pop for the more expensive option.

The very first location installed that I could use is only 30A, because that was all the location's panel could support. While this location made routine Ottawa-Toronto travel possible for the first time, I no longer use it as there is now a CS-90 one kilometer away.

Similarly, the first hotel in Kingston to install a charger opted for 30A - apparently that's all they wanted to pay for. Kudos for being first, but another hotel 2 km away recently installed a CS-90, so you can guess who gets my business.

The other dozen-odd stations within range of my house are all CS-90's. (Actually Shannonville Motorsports has both a CS-90 and a CS-40, because the site couldn't handle two at full power, but 90 is available so it doesn't count!)

It is an interesting question though because if the chargers are power limited and many public chargers are 208V 60A, then the marginal utility of dual chargers is greatly lessened. At least for the Sun Country units, at 208V the dual chargers really only would make a difference for chargers over the CS-70's since its continuous output is limited to 58A which is barely over 10kW at 208V.

A good percentage of the locations are 208V simply because three phase power is commonly used for commercial locations. The simple reality is that 240V is mainly residential service, and only very small (house-sized) commercial buildings have that.

The dual chargers may be rated by kW, but I would not be surprised to hear that their limits are actually based on current rather than power. It would be easy for someone with a single charger to figure it out - go plug in to a 208V 90A charging station and see if you can pull more than 40A. Personally, I doubt it.

 

[wycolo]

> A good percentage of the locations are 208V simply because three phase power is commonly used for commercial locations. The simple reality is that 240V is mainly residential service, and only very small (house-sized) commercial buildings have that. [Doug_G]

I'm still ruminating about this. What was the original motivation for 3 phase distribution? Sure motors are more 'efficient' on 3 phase (area under curve), but 208v is 15% less than 240, so what is the result?

Resistance heating: true your comment about resistance elements always, by definition, converting 100% of the electrical energy into heat. I was thinking from the pov of, for example, an existing workshop with a full florescent lighting setup now going to 3 phase service. What will be the result: more lumens(?) the same lumens but less meter cost(?).

What if the Power Co delivered 3 phase @ 240v? Would resistance heaters now burn up? Flourescents suffer shorter life?

I suspect the gains achieved by switching to 3 phase are mostly in the distribution and not for the end user. End user maybe stays the same, but huge overall gains in distribution. Hence the motivation.

[off to wiki this topic].
--

 

[TEG]

Three-phase electric power - Wikipedia, the free encyclopedia

...A three-phase system is usually more economical than an equivalent single-phase or two-phase system at the same voltage because it uses less conductor material to transmit electrical power...

...The phase currents tend to cancel out one another, summing to zero in the case of a linear balanced load. This makes it possible to reduce the size of the neutral conductor; all the phase conductors carry the same current and so can be the same size, for a balanced load...

...Three-phase systems can produce a magnetic field that rotates in a specified direction, which simplifies the design of electric motors...

It made more sense back a hundred years ago when a large part of industrial use was big motors to power mills, conveyors for factories, etc.
So some of the reason it is what it is comes from historical / legacy reasons.

 

[rolosrevenge]

Most of the way the grid is configured today is legacy reasons.

 

[Robert.Boston]

Power is generated at 3-phase; generators are rotating gear, so 3-phase is the most efficient way of taking power off. Delivering 3-phase power to large customers ensures that the load on each phase stays balanced.

 

[rolosrevenge]

Right, but a lot of the distribution grid practices in the US these days are largely legacy reasons, like split phase transformers and fuses etc.

 

[Robert.Boston]

Right, but a lot of the distribution grid practices in the US these days are largely legacy reasons, like split phase transformers and fuses etc.

Fair, but it's worth remembering that the bulk power (transmission) system is intrinsically 3-phase. And then there are those little wires.... ;-)

 

[rolosrevenge]

Fair, but it's worth remembering that the bulk power (transmission) system is intrinsically 3-phase. And then there are those little wires.... ;-)

But those little wires are form network an order of magnitude larger representing twice the total capital expenditure.

 

[hcsharp]

Power is generated at 3-phase; generators are rotating gear, so 3-phase is the most efficient way of taking power off. Delivering 3-phase power to large customers ensures that the load on each phase stays balanced.

Why does that ensure the load on each phase stays balanced?

 

[Robert.Boston]

Why does that ensure the load on each phase stays balanced?

It won't if the customer then splits the phases. I was thinking about the case where the industrial or commercial customer uses all three phases in its big loads: motors, electric arc furnaces, commercial lighting, etc. Although there'll be some single-phase load on site, too (e.g. office equipment), these are less of an issue in balancing the system than the big motors and resistive loads.