HPWC: 50A or 60A circuit?

[Rocinante777]

Apologies if this is a FAQ--I found a number of related discussions but not this specific answer:

What is the real-world impact on charging time with an HPWC set at 48A vs 40A for a 2023MS? I need to have a new circuit installed either way, and am looking at the additional cost of a 60A circuit. I can do the math for putting watts into a 100KWh battery, but I suspect there are inefficiencies involved to complicate things.

 

[ucmndd]

I can do the math for putting watts into a 100KWh battery, but I suspect there are inefficiencies involved to complicate things.

Not enough to matter really. 9.6kw vs 11.5kw. 48 A is about 17% faster.

 

[Cosmacelf]

Apologies if this is a FAQ--I found a number of related discussions but not this specific answer:

What is the real-world impact on charging time with an HPWC set at 48A vs 40A for a 2023MS? I need to have a new circuit installed either way, and am looking at the additional cost of a 60A circuit. I can do the math for putting watts into a 100KWh battery, but I suspect there are inefficiencies involved to complicate things.

If you drive an average amount of miles, you aren't going to notice any difference 98% of the time. If you do a long trip and drive back in the morning fairly empty, and want to charge during the day so you can drive at night, you might have wanted slightly more charge, but probably only if you were doing another long trip, in which case you've got Superchargers as back up.

Occasionally when coming back from a long trip, you might not be able to get back to 90% full in a midnight to 6am off-peak time, so you'd spill over into semi off peak.

 

[beatle]

I don't think 60A is worth it. If you ever plan on daisy-chaining a second HPWC off the first, the extra juice may be a bit more useful, or if you end up with an especially short TOU window and dramatic pricing differences between peak and off peak. Otherwise being able to charge at slightly higher rates is a convenience you'll likely never even notice if you always charge overnight.

 

[ucmndd]

I don't think 60A is worth it.

Can you state that without quantifying what “worth it” actually is?

For most installs the difference between 50 and 60 amps is a rounding error in the overall cost (yes there are exceptions). If the cost is damn close to free, even if the benefits are occasional, why wouldn’t you? There have been infrequent (but non-zero) occasions where it would have been nice to be able to add juice to my car at home at as high of a rate as possible.

 

[SageBrush]

Not enough to matter really. 9.6kw vs 11.5kw. 48 A is about 17% faster.

Yep.
For a 48 Amp circuit,

The OBC is operating for ~ 40/48 of the time, but
There are (48/40)^2 more heat losses

IIRC the OBC uses about 200 watts,
While the pack is around 150 mOhm

The 48 Amp circuit saves about 30 watts at the OBC and wastes about 100 watts more in heat. All told, 70 watts of the 1920 watts extra is wasted. 40 Amps is a sweet spot, but 48 Amps is also a nice choice if a good reason to use it exists. E.g., a truck

 

[beatle]

Can you state that without quantifying what “worth it” actually is?

For most installs the difference between 50 and 60 amps is a rounding error in the overall cost (yes there are exceptions). If the cost is damn close to free, even if the benefits are occasional, why wouldn’t you? There have been infrequent (but non-zero) occasions where it would have been nice to be able to add juice to my car at home at as high of a rate as possible.

Whatever the difference in 6awg vs 4awg is. We'll have to find out from the OP.

 

[SageBrush]

Whatever the difference in 6awg vs 4awg is. We'll have to find out from the OP.

Maybe, or the difference might be NM-B ("Romex") Vs conduit. The latter is going to be a lot more expensive for a non-short run due to the cost of conduit and the labor involved.

 

[ucmndd]

Whatever the difference in 6awg vs 4awg is. We'll have to find out from the OP.

4awg is definitely not required for a 60 amp circuit. 6awg in conduit or 6/2 MC cable is also perfectly acceptable. A bit of googling suggests that MC cable is about a 15% premium over NM-B and installs in an essentially identical way (i.e. no additional labor). The difference for a 50 foot run would be about $30.

 

[bandido]

I would suggest the 60 amp circuit for future proofing. The biggest cost in your install is the labor. I have one Tesla HPWC and two Chargepoint chargers all on 60 amp circuits. I only occasionally charge at the full 48, but always easier to turn down the charge rate than wish you could turn it up...

 

[dafish]

The exact answer to what is the difference:

Tesla advises plugging in every night. I've a 30 amp 240v plug I'm going to remove and hardwire the wall connector to @ 30 amp breaker/24 amp charge. 22 miless of range per hour. In 10 hours, a common "at home" evening for us, I'll have been able to add 220 miles of range. More than enough for the average next day, and rare will be the time it gets home with more than 100 miles of range used. IRL I expect this to be most adequate.

Should experience teach me otherwise I'm have two drops of 6-6-6-6 SER installed and be done w/it.

 

[airborne spoon]

damn these new chargers suck ass you can only top out at 48A like some kind of peasant? i mean damn, the mobile charge cable does 40A for crying out loud. I put in a 100A breaker for the 80A charge when i installed mine.

But if they new ones do suck this much I'd say go with the 60A as the cost difference should be very minimal and it will allow for upgrades in the future

 

[ucmndd]

damn these new chargers suck ass you can only top out at 48A like some kind of peasant?

Tesla hasn't sold a car with a >48 amp onboard charger in at least 4 years.

 

[airborne spoon]

Tesla hasn't sold a car with a >48 amp onboard charger in at least 4 years.

damn that sucks for the new car owners. that makes reason #13214 why I'm never selling my car.

 

[beatle]

4awg is definitely not required for a 60 amp circuit. 6awg in conduit or 6/2 MC cable is also perfectly acceptable. A bit of googling suggests that MC cable is about a 15% premium over NM-B and installs in an essentially identical way (i.e. no additional labor). The difference for a 50 foot run would be about $30.

If it's only a $50 difference, why is there even a thread on this?

 

[STS-134]

I don't think 60A is worth it. If you ever plan on daisy-chaining a second HPWC off the first, the extra juice may be a bit more useful, or if you end up with an especially short TOU window and dramatic pricing differences between peak and off peak. Otherwise being able to charge at slightly higher rates is a convenience you'll likely never even notice if you always charge overnight.

It's definitely worth it. Not worth it if you have an existing circuit already in place but definitely worth it if running new wiring, which the OP is.

Yep.
For a 48 Amp circuit,

The OBC is operating for ~ 40/48 of the time, but
There are (48/40)^2 more heat losses

IIRC the OBC uses about 200 watts,
While the pack is around 150 mOhm

The 48 Amp circuit saves about 30 watts at the OBC and wastes about 100 watts more in heat. All told, 70 watts of the 1920 watts extra is wasted. 40 Amps is a sweet spot, but 48 Amps is also a nice choice if a good reason to use it exists. E.g., a truck

You're forgetting that the car wastes 150-300W whenever it's charging because the computer is awake. By charging faster, the car sleeps sooner and this waste is reduced.

 

[father_of_6]

If it's only a $50 difference, why is there even a thread on this?

Because duh... we have to spend hundreds of dollars in labor to justify the extra $50 in materials. We're dudes, that's what we do.

 

[SageBrush]

Yep.
For a 48 Amp circuit,

Spreadsheet -- less arithmetic errors