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48A vs. 40A for home charging??

What amperage do you recommend for home charging an R1S?


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Zoidz

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Not sure if this was a typo - but you can't charge at 40amps with a 40amp breaker. The max you can charge is at 80% of the Breaker rating.
You can charge at 40 amps on a 40 amp breaker, but it violates the National Electric Code due to the 80% requirement. Most breakers will not trip at exactly the rated current. A 40 amp breaker might not trip until 42-45 amps, depending on ambient temperature.
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jimmyb2

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Not sure if this was a typo - but you can't charge at 40amps with a 40amp breaker. The max you can charge is at 80% of the Breaker rating.
Respectfully speaking, the 80% that everyone talks about is a code requirement. Nothing against you as no one person can be knowledgeable in everything. I am certain you could find my knowledge lacking in your field of expertise.

Circuit breakers don’t trip at 80% of their rating. I charge my R1S from a 240V. circuit that supplies my clothes dryer. The breaker on that circuit is properly sized, and it has a 30 A. rating. However, when I charge my R1S it normally draws between 33 A. and 35 A. The breaker has never tripped, and it is functioning properly. It is not “broken”.

So, with that in mind, it would be “possible” to charge at 40 A. on a 40 A. breaker. Now, I don’t know if @centexR1S actually measured the current flow or was just stating “40 A.”becuz he has a 40 A. breaker installed; so I can’t speak to what level of current he actually charged at. On the other hand, I can speak to the current flow when I charge as I have actually measured it.
 

jimmyb2

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You can charge at 40 amps on a 40 amp breaker, but it violates the National Electric Code due to the 80% requirement. Most breakers will not trip at exactly the rated current. A 40 amp breaker might not trip until 42-45 amps, depending on ambient temperature.
Agree 100% except for “until 42-45 amps”. There are a number of variables to consider when predicting when a circuit breaker will trip, and that is after discounting mfg. tolerance.

I have tested 15 A. breakers that required 76 A. for “instantaneous” trip, and they were functioning properly.
 

Zoidz

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Agree 100% except for “until 42-45 amps”. There are a number of variables to consider when predicting when a circuit breaker will trip, and that is after discounting mfg. tolerance.

I have tested 15 A. breakers that required 76 A. for “instantaneous” trip, and they were functioning properly.
I'm specifically referring to thermal trip in the context of this discussion (drawing 40 amps on a 40 amp breaker), that's why I mentioned ambient temperature. I agree there are other variables, I'm quite familiar with breaker TC curves. Instantaneous trip doesn't come into consideration under the OP's use case.
 

HarryBrowne

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I do the missing 3rd option - 30-40 amp charging on a 60 amp circuit. My EVSE can charge at 48A if I need to, but rarely do I need to. Since I plan on keeping the R1S past the warranty, I charge at a lower rate to *theoretically* prolong the battery life. Based on my use patterns, I don't need to top off the battery in 4 hours, I'm fine with 6 or 7. No time of day cost reduction programs, my utility is still in the 1960s mentality.
This is exactly what we chose to do, also in the hope that it would prolong battery life. Haven't yet needed faster charging, but could fairly easily change the dip switches if I needed to.
 

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Feetdry

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I'm new to this but everything is controlled by the Rivian charger application on my WIFI network. I know I wanted more charge than the 80 per cent that I had originally dialed in and just moved the slide bar to 100 per cent. I'm new at this range thing and wanted her to go as far as she was capable of, just in case. I know I can adjust the charging rate but I haven't moved it off 48 amps so far.
 

jimmyb2

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I'm specifically referring to thermal trip in the context of this discussion (drawing 40 amps on a 40 amp breaker), that's why I mentioned ambient temperature. I agree there are other variables, I'm quite familiar with breaker TC curves. Instantaneous trip doesn't come into consideration under the OP's use case.
You are correct that instantaneous trip would not generally be a consideration in OP’s case. I should not have brought that up.

However, I still disagree with your “42-45 amps”. Yes, it might trip at those currents, but it also might go on forever without tripping at those levels. Actually, a 40 amp. breaker is more likely to hold forever than to trip at 42-45 A.

You might want to look at those TC curves.

My use of “forever” is probably wrong, but it could truthfully be replaced with “months” or “years”.
 

jplblue

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For those charging below their 48 amp capacity:
1) Is it possible charging LONGER and slower could be worse for the battery than charging faster but for a shorter period of time? (Level 2 only, obviously)
2) Any concerns about overhead? If I recall correctly, 800-1000w are wasted on overhead. Is that a concern for extending charging at lower rate?
 

Zoidz

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However, I still disagree with your “42-45 amps”. Yes, it might trip at those currents, but it also might go on forever without tripping at those levels. Actually, a 40 amp. breaker is more likely to hold forever than to trip at 42-45 A.
You're misunderstanding my post. That's exactly what I am saying - there's nothing to disagree with.

My post - "A 40 amp breaker might not trip until 42-45 amps, depending on ambient temperature."

I was not saying or implying that it WILL trip at 42 - 45 amps (hence the words MIGHT NOT), only that it will allow more than 40 amps without tripping, using 42-45 as an EXAMPLE.

Time to stop beating a dead horse. Cheers!

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tjordhei

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When we built our home 5 years ago, I had a 50amp breaker with NEMA 14-50 receptacle installed in our garage thinking we’d likely have an EV or plug-in hybrid in the future. When I got my R1S I decided to start by using the Rivian Portable Charger and leave it plugged in to the NEMA 14-50 receptacle. The Portable Charger is limited to 32amps but so far - only 7 weeks - I’ve been able to get all the charge I need overnight, even up to 100% for a couple road trip days. I will keep monitoring and may invest in the hardwired 60amp circuit /48amp charging approach at some point.
 

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Oldsmobile_Mike

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Respectfully speaking, the 80% that everyone talks about is a code requirement.
.02 cents, I don't know why anyone would spend $80k+ on a vehicle and then "cheap out" by not installing electrical equipment that is safe and "to code". Some of these comments just seem eye-rollingly dumb to me.

Good luck charging at 48A on a 30A breaker, or whatever it is some of y'all are trying to do, LOL. 🤷🔥🔥🔥🔥🔥🔥
 

Jay565

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.02 cents, I don't know why anyone would spend $80k+ on a vehicle and then "cheap out" by not installing electrical equipment that is safe and "to code". Some of these comments just seem eye-rollingly dumb to me.

Good luck charging at 48A on a 30A breaker, or whatever it is some of y'all are trying to do, LOL. 🤷🔥🔥🔥🔥🔥🔥
Totally agree. I had my 240 volt nema outlet melt with just using the rivian portable charger. Thankfully nothing burned down. Those trying to charge up to the breaker size are running a big risk of wires inside the walls melting and fires starting. I now have the tesla wall connector it can go to 48 amps, but I run it now at 24 amps, not for battery health, but to keep temps low. When I ran it at 48amps in the summer the tesla wall connector reported temps of 160 degrees. Still within specs and technically safety, but too hot for my comfort.
 

87Ducks

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I have a 50amp breaker (which was recommended back in 2019 when we were building our house) but keep it at 40A with the Rivian charger. I normally keep the vehicle between 40-70% but no problem getting a full charge to 100% overnight if going on longer trip in the morning. I could pay to upgrade to 60A but I don't think it is worth it for my situation.
 

centexR1S

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Not sure if this was a typo - but you can't charge at 40amps with a 40amp breaker. The max you can charge is at 80% of the Breaker rating.
Good catch. I should have said I charge at a “nominal 40A”. My charger (or the firmware) automatically drops it down to 32A using the 80% rule. This is a good spot to point out the need to manually lower the charge amperage to 80% of the breaker rating when using a dog bone adaptor or charging at a friends house. Check the breaker. Thanks for pointing out my post was vague and for everyone’s safety point out anything else wrong on this thread.
 

jimmyb2

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.02 cents, I don't know why anyone would spend $80k+ on a vehicle and then "cheap out" by not installing electrical equipment that is safe and "to code". Some of these comments just seem eye-rollingly dumb to me.

Good luck charging at 48A on a 30A breaker, or whatever it is some of y'all are trying to do, LOL. 🤷🔥🔥🔥🔥🔥🔥

Totally agree. I had my 240 volt nema outlet melt with just using the rivian portable charger. Thankfully nothing burned down. Those trying to charge up to the breaker size are running a big risk of wires inside the walls melting and fires starting. I now have the tesla wall connector it can go to 48 amps, but I run it now at 24 amps, not for battery health, but to keep temps low. When I ran it at 48amps in the summer the tesla wall connector reported temps of 160 degrees. Still within specs and technically safety, but too hot for my comfort.

Good catch. I should have said I charge at a “nominal 40A”. My charger (or the firmware) automatically drops it down to 32A using the 80% rule. This is a good spot to point out the need to manually lower the charge amperage to 80% of the breaker rating when using a dog bone adaptor or charging at a friends house. Check the breaker. Thanks for pointing out my post was vague and for everyone’s safety point out anything else wrong on this thread.

Obviously, you did not really understand what @Zoidz and I were talking about in our back and forth discussion. I don't look down on any of you for not understanding as I am certain each of you can probably discuss things that would be "over my head" as well. @Zoidz and I may have gotten a little carried away in our back and forth, but ...

In no way were @Zoidz and I instructing or even suggesting that anyone should charge at rates above 80% of the in house electrical equipment rating. Our intent was to inform others of the fact that the circuit breaker or other electrical equipment in your house is NOT going to control the charging rate by tripping at 80% or even at 100% of it's rating.

The take-away from our discussion should have been that if you want to limit the charging rate to 80% of your in-house electrical equipment ratings it will not automatically happen ... YOU must control that. How?

By choosing the correct settings in your vehicle. On the "Energy" screen near the bottom right corner is where you would select the "Charging amperage". This is where you ensure that you choose a value that is no more than 80% of the ratings of your in-house electrical equipment. This applies not only to the circuit breaker rating, but to the ratings of ALL in-house electrical equipment between your breaker panel and your vehicle. The vehicle settings, not the EVSE settings, are where the real control of current flow occurs. Some EVSEs have settings for current flow, and some do not. Again, the vehicle is where you exert this control.
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