No 800v for Model 3/Y, but maybe for Cybertruck?

[Crissa]

Five Years Ahead is back with some math looking at possible pack configurations for the new Model Y and some examination of what was said on the earnings call.

As we know, there are some basic trade-offs for going to a higher voltage, but this video goes into some. Higher voltage needs new chargers, new electronics, new insulation, new certifications, and lost cells means more battery capacity lost as the pack ages.

But looking at the cell chains shown at the Cyber Rodeo gives us some ideas on what the configuration is. There's also some evidence that they might be unlocking a slightly higher per-cell maximum charge voltage with a manganese rich cathode.

Remember, cells in series raises voltage and parallel raises the amperage in a battery.

-Crissa

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[rr6013]

Not an EE. Question after watching the video, why stop at 800v? Tesla J1772 compatible spec plug is certified 900v. IF Tesla plug is going up—voltage, why not rev just one-time. Go max!

 

[Jhodgesatmb]

At the last quarterly report (I think) someone asked about 800v and they said they had run the numbers and that it wasn’t worth it. FWIW.

 

[Deleted member 12457]

Have a question for an EE. When charging is voltage or amperage the most important thing? High voltage, same or lower amperage. Will that charge faster than higher amperage, lower voltage? I assume a 400-900V charger isn't going to be available at most utility-connected houses in the USA. This would require either a transformer or higher voltage utility lines. If you're using solar connected to batteries, I presume you could find (maybe?) an inverter that could handle a 400-900V DC input with a high output but you'd also need a very large solar array to charge it.

 

[Crissa]

Not an EE. That stuff was hard. But I do have a vocational amount.

Not an EE. Question after watching the video, why stop at 800v? Tesla J1772 compatible spec plug is certified 900v. IF Tesla plug is going up—voltage, why not rev just one-time. Go max!

That's why Porsche did use 900v. It's about getting the right balance of cells, equipment costs, and math.

Also, the math around the actual energy starts getting really weird at high voltage. What's a conductor and what's an insulator and where the current chooses to flow shifts around.

Have a question for an EE. When charging is voltage or amperage the most important thing?

Neither. Though at conventional levels, more current means more heat, so higher voltage can be more efficient.

Wattage is what's import to get work done. And that V*A.

High voltage, same or lower amperage. Will that charge faster than higher amperage, lower voltage? I assume a 400-900V charger isn't going to be available at most utility-connected houses in the USA. This would require either a transformer or higher voltage utility lines. If you're using solar connected to batteries, I presume you could find (maybe?) an inverter that could handle a 400-900V DC input with a high output but you'd also need a very large solar array to charge it.

CCS stations and the AC chargers in cars do exactly that.

It's just more specialized equipment, not unknown things.

-Crissa

 

[ajdelange]

Have a question for an EE. When charging is voltage or amperage the most important thing?

That's akin to asking whether the cost per potato or the number of potatoes one buys is more important in determining the size of one's bill.


The battery charges by moving ions and electrons from cathode to anode across a potential (the cell voltage ~ cost per potato) through, resepectively, the electrolyte and an external circuit. The higher the voltage the more energy is required to move a particle so the energy stored per particle depends on the voltage and, obviously, the total energy stored depends on the number of particles (number of potatoes) which is the number of particles per second multiplied by the number of seconds. Thus voltage and current are equally important. The energy stored in a cell is the product of the cell voltage times the current times the charge time.

The thing that gets people confused is the way packs are put together. A typical lithium cell operates at 3.65V. If you force one ampere through it for one second you will add (3.65)*1*1 = 3.65 ampere-volt-second = 3.65 watt-second = 3.65/3600 watt-hour. To force any current through it at all you must apply a voltage greater than the cell voltage i.e. more than 3.65V so if the cell is charged to 3.65 volt and you put 3.7 volt across it an amp will flow charging the battery which causes its voltage to rise. The power supply is delivering 1 * 3.7 = 3.7 Watts. The current will decline as the cell voltage increases stopping entirely when it reaches 3.7V. To charge further the applied voltage will have to be increased.

If you connect 2 cells in parallel (+ to + and - to -) the situation is the same. You must apply 3.7 volt across a cell to get it to accept 1 ampere. But that is 1 ampere per cell and so the power supply must now supply 3.7V at 2 A = 7.4 Watt.

Now put the two cells in series (+ to - and - to +). The voltage across each is 3.65 (assuming the "pack" is equalized) but the voltage across the pair is 7.3. To make current flow our power supply must now deliver 7.4 V at 1 amp equal to 7.4 Watts just as before.

High voltage, same or lower amperage. Will that charge faster than higher amperage, lower voltage?

As the example of the preceding paragraphs shows 7.4 watts delivered at 7.4V to 2 cells delivered to cells in series puts 1 amp through each with 3.7 V across each and thus charges the cells at exactly the same rate as 7.4 Watts delivered at 3.7 V to two cells in parallel.

I assume a 400-900V charger isn't going to be available at most utility-connected houses in the USA.

I have one in my car. It converts 120 or 240V AC into 400V DC to charge my cars batteries. Lucid owners have a 900 V charger in their cars.

This would require either a transformer or higher voltage utility lines.

There is a transformer in my charger to step up the voltage (and isolate the battery from the utility). In fact it was observed a few years ago that the early SC supercharger cabinets appeared to be loaded with multiples of the charger used in the model S.

If you're using solar connected to batteries, I presume you could find (maybe?) an inverter that could handle a 400-900V DC input with a high output but you'd also need a very large solar array to charge it.

I charge from solar but it is no different from charging from the utility. Micro inverters turn the low DC voltage from the PV cells into 240VAC which goes to the vehicle on-board charger (perhaps after being first converted to 50 VDC for storage in the Powerwalls and then back to 240 VAC) which converts the AC to 400V DC. It would be possible to skip steps and go from PV cell voltage to battery pack voltage with fewer conversions (and attendant losses) but doing so would complicate the interface and preclude use of the PV array for other uses.

 

[Deleted member 12457]

Thank all of you for the technical information. I have a simple question.

The typical EV charger installed in your house uses 220/240V 40-60A service, correct? Would this be the same requirements for a 400V, 800V or 900V charging system? I understand home chargers don't need to be fast chargers but I'm sure some Tesla owners would want this fast charging capability.

My landlord is considering adding EV chargers to a group of rental houses along my street. Every house was upgraded to 200A service (he bought a utility pole to make things easier) with a 200A meter (future proofing). Is this all he'd need for just about any level of charging system?

 

[ajdelange]

The typical EV charger installed in your house uses 220/240V 40-60A service, correct?

Yes

Would this be the same requirements for a 400V, 800V or 900V charging system?

The thing installed in your house is not a charger. It is an Electric Vehicle Supply Equipment (EVSE). All it does is communicate with the car and the house wiring and connect them if everything is appropriate. The charger is in the car and it is a 400, 800, or 900V charger using 240 V a 24 - 48 A depending on the feeder circuit to which the EVSE connects it. Note that the maximum it can take is 48 * 240 = 11520 Watts (11.52 kW).

I understand home chargers don't need to be fast chargers but I'm sure some Tesla owners would want this fast charging capability.

The maximum any Tesla auto will draw at the present is 48 A for 11.52 kW but my first Model X took 72 A (for 17.28 kW) and some of the early Model S could take 80 A (19.2 kW). These options have been discontinued so any Tesla owners who want them (I'd have no need) are out of luck.

My landlord is considering adding EV chargers to a group of rental houses along my street. Every house was upgraded to 200A service (he bought a utility pole to make things easier) with a 200A meter (future proofing). Is this all he'd need for just about any level of charging system?

200A should be adequate for modest sized houses which do not have large electric loads given the currently available in car chargers. Even so a 48A charger requires a 60A circuit which is 30% of the capacity of a 200A panel.

One can (and people do - Ford- is that a DCFC?) build DC fast chargers which could be installed in a home. A 25 KW DCFC powered by a single phase 240V supply would require a 130A circuit (65% of the panel rating) and a 50 kW charger a 260A circuit which exceeds the house service. So no, 200 A service is good for not much more than what is currently available.

 

[ajdelange]

...If you're using solar connected to batteries, I presume you could find (maybe?) an inverter that could handle a 400-900V DC input with a high output but you'd also need a very large solar array to charge it.

I forgot to respond to this last bit. Power is the rate at which energy is transferred. It takes 482 Watt hours (energy) to move my car 1 mile. Thus if I drive (and must replace) 100 miles per day (the average American's round trip commute is 37.6 miles per day) I'll need to replace 48200 Watt hours (Wh) each day. My array is 45 panels capable of producing 13 kW in full sun. Thus, to get my 48.2 kWh I need 48.2/13 = 3.7 hours of full sun equivalent. Where I live I get, on average, in December, 3.48 hours per day. So in December I wouldn't quite make it for 100 mi/da on the 45 panels 13 kW system I have. But for this time of year when I average 5.5 hours full sun equivalent per day I'd be fine.

To summarize: The micro inverters turn the panels' 30VDC into 240V AC which feeds the car's charger which converts it to 400V DC which charges the battery. Most of the year a 45 panel system collects (in my climate) plenty of energy to replace 100 miles per day. A 45 panel system is certainly not "very large" (but it might be considered largish).

 

[ajdelange]

As the ancient philosopher said "The more I know the more I know I don't know".

 

[Crissa]

Remember, it's okay to ask questions. ^-^

The typical EV charger installed in your house uses 220/240V 40-60A service, correct?

Yes. That would be 7.6kW to 11kW Level 2 AC 'Destination' charging. It's really just a fancy outlet and extension cable that tells the car's AC charger how much power to pull without popping the breaker.

This gets you about 20-36 miles back per hour charging.

Would this be the same requirements for a 400V, 800V or 900V charging system?

Yes, because the car has it's own charger inside. On my motorcycle, it's an addon that adds about $2500 cost and twenty more pounds of weight and takes up the storage compartment I put my first aid kit in. But cars don't have that problem ^-^

A CCS Fast charging station (DC charging or colloquially Level 3 charging) has voltages from 250-920. It's basically a giant version of what's in the car, capable of 10x to 40x the wattage. The car has to communicate with it constantly to get the right voltage and charging ramp.

My landlord is considering adding EV chargers to a group of rental houses along my street. Every house was upgraded to 200A service (he bought a utility pole to make things easier) with a 200A meter (future proofing). Is this all he'd need for just about any level of charging system?

Probably more than! Well, you need to get the power from the panel, into the Electric Vehicle Service Equipment (EVSE or colloquially 'wall charger') which is usually the expensive part. But getting the power drop from the neighborhood lines is often the hard part.

Smart EVSEs like the Tesla Destination Wall chargers can be programmed to share power consumption at the breaker, so multiple vehicles can plug in at once and get their fair share of the electricity.

-Crissa

 

[ajdelange]

Not an EE. Question after watching the video, why stop at 800v? Tesla J1772 compatible spec plug is certified 900v. IF Tesla plug is going up—voltage, why not rev just one-time. Go max!

I think the video makes the answer pretty clear. There isn't enough advantage in going to 800 V to make it worth while and the marginal advantages in going to 900 do not add enough to make 900 worth while either.

 

[Deleted member 12457]

Probably more than! Well, you need to get the power from the panel, into the Electric Vehicle Service Equipment (EVSE or colloquially 'wall charger') which is usually the expensive part. But getting the power drop from the neighborhood lines is often the hard part.

Smart EVSEs like the Tesla Destination Wall chargers can be programmed to share power consumption at the breaker, so multiple vehicles can plug in at once and get their fair share of the electricity.

-Crissa

All the houses, duplexes and apartment have plenty of power to the house. I already discussed it with the owner who said it would be easy to run a conduit from my panel (North side of house) through the attic (accessible) to the south side where the charger could be placed. That's where I park. It would be a little tricky for most of the other houses since they use street parking.

As for sharing a common breaker, we pay for our own electricity but the owner pays for some utilities (flat fee to us) so it wouldn't be out of the question if he was able to position charging stations in common areas. He sees it as a feature that would benefit his renters. Is this something other landlords even think of????

 

[ajdelange]

It's really just a fancy outlet and extension cable that tells the car's AC charger how much power to pull without popping the breaker.

Hardly. It's job is, first, to detect that a car is connected to it. This is so that it will not energize if the plug is not safely buried and locked into a vehicel charging port and disconnect if, during a charge, the vehicle somehow gets disconnected. Second, it detects whether the cars batteries emit gas when charging and if they do, insures that the ventilation system is on (not important with Li batteries), Third it checks that the vehicle is properly grounded, Fourth it informs the car as to the most the car can draw without violating the 80% derating rule (a car drawing 45A on a 50 A circuit would NOT trip the breaker but would violate the rule), Fifth, it measures current drawn, Sixth (Tesla only) it sends a signal to the car to open the charge port door to start the car or to terminate charging and unlock the wand (or just unlock it if charging is complete), Seventh it measures internal temperatures to make sure connections are good (reduce fire hazzard), Eighth it may have WiFi and or Bluetooth capabilities for control of sharing or for use with a smartphoe app, and Eigth it has a contactor which it will close sending electricity to the car only when it determines things are OK.

Some extension cord!

This gets you about 20-36 miles back per hour charging.

If you install on a 60A circuit the most you will get with a CT will be about 21 miles/hour (the charger in the truck will be about 90% efficient and the consumption will be about 500 Wh/mi).

A CCS Fast charging station (DC charging or colloquially Level 3 charging) has voltages from 250-920. It's basically a giant version of what's in the car, capable of 10x to 40x the wattage. The car has to communicate with it constantly to get the right voltage and charging ramp.

A Tesla SC is what it is but it is not a CCS/CHArIN station. The latter HPC350 stations can support currents up to 500 @ at voltages between 50 (?) and 500 as long as the power is 350 kW or less. That 350/11.52 = 30 times what the in car charger can supply.

Probably more than!

Definitelu not! The calculations are in a previous post. You would probably be OK with one EVSE on a 60A circuit (and I think because of the high consumption of a CT you will want that but adding a second or third unit might cause raised eyebrows depending on what else is in the panel. 200A just isn't that much in these days of electric everything (including cars).

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