50 amp vs 40 amp vs 30 amp

[Lou Borella]

Hello Everyone ...
New to the forum and hoping you all can answer my question.
My R1T is scheduled for delivery in November 2023.
I received my wall charger already and I am looking at the install options.
I want to know if there is a charging speed benefit when using a 50 amp config vs 40 amp 30 amp configs?
I know that most of the charging will be done at the end of the day and overnight so any speed benefit will really be pointless. So any benefit will really only be helpful in a mid-day-emergency-charge situation.

So is there a charge speed difference with the 3 options and is difference is big enough to bother putting a 50 amp line in my garage?

(does this question make sense?)

Thanks in advance!!

Lou

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[EVTrukHog]

The short answer is Yes... there is a speed difference. The subjective part is whether the difference is meaningful during an overnight charge. Do you really care if it takes 180 minutes in lieu of 90 minutes to reach your target SOC if it is charging overnight?

Watts = Volts x Amps
This will tell you the various speeds of the configurations you're considering.

 

[Zoidz]

You've pretty much identified the value - faster charging speed. The other possible value of a larger circuit is potentially installing a second charger on the same circuit if/when you need to charge 2 EVs in the future.

 

[Lou Borella]

The short answer is Yes... there is a speed difference. The subjective part is whether the difference is meaningful during an overnight charge. Do you really care if it takes 180 minutes in lieu of 90 minutes to reach your target SOC if it is charging overnight?

Watts = Volts x Amps
This will tell you the various speeds of the configurations you're considering.

I know the speed difference is pointless while charging overnight.
Im wondering if the speed difference is large enough to be beneficial when I might need to charge in the middle of the day.
How much more range will I get in a pinch over a 50 amp line vs a 30 amp line?

 

[Lou Borella]

You've pretty much identified the value - faster charging speed. The other possible value of a larger circuit is potentially installing a second charger on the same circuit if/when you need to charge 2 EVs in the future.

Thanks Zoids
Will a 50 amp config be enough to power 2 chargers on the same circuit and simultaneously charge 2 EVs overnight?

 

[Monkey]

It's a pretty big battery, so depending on how much daily driving you do on average, you will find more or less value in higher charge rates.

The amps you select are the circuit breaker size, not the charging rate. So, if you select 50A, then you will be installed on a 50A breaker and charging will operate up to a sustained rate of 40A. The Rivian wall charger allows for installation on up to a 60A circuit for up to 48A sustained charging -- or 11.5kW output.

Will a 50 amp config be enough to power 2 chargers on the same circuit and simultaneously charge 2 EVs overnight?

You can't install two chargers on the same circuit, the Rivian wall chargers are not set up for that, nor does it comply with electric code. Some chargers on the market are capable of load sharing, like the Tesla wall chargers. The only ones I'm aware of that could ever be installed on the same branch circuit are the 2nd generation Tesla chargers, that used a wired interconnect for the units to communicate their load balancing needs. They're 3rd generation chargers, and others on the market that I'm aware of, communicate wirelessly and require each charger to be on their own branch circuit. The wireless comms allow them to balance the load so they don't overdraw your electrical service.

Depending on how much you drive, 50A is probably not enough to charge two EVs overnight. But this is a highly generalized statement. We currently have a Model Y LR and a Ford Lightning ER that share a single 50A charger -- 40A sustained charge rate. It's plenty for the Model Y. However, it can take 13+ hours to charge the Lightning to 90% if I'm plugging in at less than 20%. We've been in this sharing arrangement for almost a year now and there has only been twice where we both needed to charge on the same night. So I just took the Lightning to the EA charger a couple miles away. I'd love to have a second charger, but I'd have to upgrade my service and massive panel upgrade and all that. Not worth it at this time. Load balancing two chargers isn't going to solve my dilemma as it works better to simply alternate charging nights... Or at least not with the 50A total I can allow for it. I can probably load balance with 70~80 Amps, which would be perfect, during the winter months when I'm not running AC. But not good enough if not a year-round solution.

Tesla sells their new universal wall charger that has an integrated J1772 adapter for charging non-Teslas. It's a nice charger and load-balances if you can install multiple.

We can all offer suggestions and such here. But the more specifics you can give us, the better. It also might help if you can hire an electrician to help you out and install chargers, preferably one who understands EVs. Shockingly, many of them do not understand.

 

[EVTrukHog]

220V x 30A = 6.6kW @ 2 mi/kWh = 13.2 miles per hour charging rate

220V x 48A = 10.6kW @ 2 mi/kWh = 21.2 miles per hour charging rate

insert your configuration into the equation and it will tell you the speed differences

 

[jjswan33]

To be clear here, it may matter for overnight depending on your situation. For example I charge between 10pm and 6am when my rates are the lowest. With my R1T if I get home with a low SOC at a later hour (lets say midnight) and plug in I only have 6 hours to charge at lower rates. I have a 50A circuit (40A charging) so if I come home below 10% no chance I am getting to 70% before 6am.

So think about charging time:

>=60A circuit assume 48A charging (11.5kW) means it will take ~11 hours to fully charge a Rivian (Up to 7 hours to 70%)
50A circuit assume 40A charging (9.6kW) means ~13 hours to fully charge a Rivian (or ~9 hours to 70%)
40A circuit assume 32A charging (7.7kW) means ~17 hours to fully charge a Rivian (or ~12 hours to 70%)
30A circuit assume 24A charging (5.8kW) means ~22 hours to fully charge a Rivian (or ~15 hours to 70%)

You can start to see how overnight charging speed can matter with a vehicle that has as large of a battery as a Rivian. I don't think needing to top-off mid-day is that much of a factor, most likely you will need to find DCFC if you really need some juice in a hurry.

 

[Ingo B]

If you are only overnight charging, speed won't matter as much, but for those times you need it NOW, speed matters. I am firmly entrenched in Camp Prepare For The Worst. As my dad likes to say, "always better to have it and not need it, than need it and not have it."

All things being equal, get the 60A circuit.

 

[Lou Borella]

To be clear here, it may matter for overnight depending on your situation. For example I charge between 10pm and 6am when my rates are the lowest. With my R1T if I get home with a low SOC at a later hour (lets say midnight) and plug in I only have 6 hours to charge at lower rates. I have a 50A circuit (40A charging) so if I come home below 10% no chance I am getting to 70% before 6am.

So think about charging time:

>=60A circuit assume 48A charging (11.5kW) means it will take ~11 hours to fully charge a Rivian (Up to 7 hours to 70%)
50A circuit assume 40A charging (9.6kW) means ~13 hours to fully charge a Rivian (or ~9 hours to 70%)
40A circuit assume 32A charging (7.7kW) means ~17 hours to fully charge a Rivian (or ~12 hours to 70%)
30A circuit assume 24A charging (5.8kW) means ~22 hours to fully charge a Rivian (or ~15 hours to 70%)

You can start to see how overnight charging speed can matter with a vehicle that has as large of a battery as a Rivian. I don't think needing to top-off mid-day is that much of a factor, most likely you will need to find DCFC if you really need some juice in a hurry.

Thank You JJ!!
This is the answer I was looking for.
This seems like a fairly common scenario.
So really the "top-off middle of the day" issue is really the pointless scenario since even the highest amperage isn't really going to give you much.
But the amount of charge can really change in the overnight scenario with higher amperage and longer charge times.

Thanks!!

 

[Matthuw]

Put in the biggest line your main panel, garage, and charger will support, AND that you can afford. If you aren't concerned with the overnight speed of the charging, you can always reduce the amperage and charge slower.

 

[Zoidz]

Thanks Zoids
Will a 50 amp config be enough to power 2 chargers on the same circuit and simultaneously charge 2 EVs overnight?

NEC 625.42(B) allows more than one EVSE on a branch circuit if the EVSE is configurable for the maximum current it can draw. So you could put two EVSEs on a 50 Amp circuit, setting each for 20 Amps max to comply with the 80% rule of 40A on a 50A circuit.

Is that enough to charge two vehicles? Depends on your use case and the two vehicles. Two Rivian R1 that need full charge? No. An R1 and an R2 that need topping off overnight? Sure.

With all this said, I prefer spending more one time and done. I installed a 100A subpanel in my garage to take care of any future needs.

 

[Zoidz]

You can't install two chargers on the same circuit, the Rivian wall chargers are not set up for that, nor does it comply with electric code.

2023 NEC 625.42(B) does allow for if the EVSE has "restricted access to an ampere adjusting means". I do not have a Rivian charger (I have OpenEVSE which is software configurable), but I believe the dip switches qualify as restricted access.

 

[Oldsmobile_Mike]

For my money I would always recommend 60A circuit. Obv. if your panel can't support that (or your budget, etc.) go with the best you can. Never know, it might even improve the value of your home further down the road. ?

 

[foxerson]

For my money I would always recommend 60A circuit. Obv. if your panel can't support that (or your budget, etc.) go with the best you can. Never know, it might even improve the value of your home further down the road. ?

^^this^^

+ my $.02
The Rivian mobile charger and many public level-2 chargers are designed for 40A circuits and therefore top out at 32A (7.7kW). I have found this to be frustratingly slow compared to the Rivian wall charger on a 60A circuit supplying 48A (11.5kW) of power.

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