Charging when home only has 30A circuit

[atrieger]

My main breaker box has a 240v 30A line that goes to a female port in the garage.
It can serve, when the house is off the grid (MAINS OFF) as a place to connect an emergency 5kw generator I have.
I have a short adapter to go from the 4 wires in this sort of twisting locking receptacle (don't know the official name) to Nema 14-50 and then when I had my Tesla X, the portable charger plugs into that and into the car. It worked because the Tesla when you set the charge limit down to 28A it would remember the setting and always only draw that much. Code violation but safe.


I turned in my tesla and got an R1S and the same setup would work except Rivian doesn't remember the amperage setting, each time it resets to 32A which is *just* enough over to sometimes blow the circuit and sometimes not which is potentially dangerous when I forget to set it, not great.

So I submitted a feature request for them to have the UI remember amperage settings per location, hope that gets done some day that'll be great, in the mean time for safety I bought a $200 portable charger off amazon that similarly goes from nema 14-50 to J1772 and it can be configured to only allow 24A. So now I don't have to worry that the truck will try and draw more than my 30A circuit can provide, so that's good.

I just wanted to share what actually happens, because I have a current monitor on this circuit, is the truck and the adaptor keep negotiating.. the truck will never get more than 24A, but it gets that then asks for 26A, doesnt get it, drops down and renegotiates and the power delivery instead of being very smooth is a sort of choppy spikey graph going between 23A and 24A... if I manually get in the rivian and tell it to reduce amp draw to 24, it stops trying to negotiate and sits nice and clean, flat graph.

This isn't supported by rivian, but I think it's better to be safe than to keep having to remember to amperage down in the truck, or upgrade the line to 50A which is what the rivian portable charger wants of course.

Just sharing in case others are contemplating this.
The 3rd party charger I got is this one: QPQ Level 2 EV Charger 40A adjustable:
https://www.amazon.com/dp/B0C1N386GG?ref=ppx_yo2ov_dt_b_product_details&th=1

Sponsored

 

[zefram47]

Buy an EVSE with a settable current limit. DO NOT rely on the vehicle to respect a current limit in software...the EVSE tells it what the max charge current is. I've been charging on a 30A outlet for years now and set the EVSE to 24A with no issues.

 

[HaveBlue]

You might want to open your panel and check to see what size wire is supplying your outlet in case it is bigger than #10.

 

[Tanuki68]

Tesla wall connector (NACS and J1772) have pins where you set the max amperage the unit can deliver. You’d be buying a system that’s more future proof than most too. https://shop.tesla.com/product/universal-wall-connector

 

[Proxy]

So much fail!

1. Using a vehicle to set the maximum amps (glad you don’t do this anymore)

2. Adding a load to your panel without doing a load calculation since you are using a backup power circuit

3. Using an outlet rated for 50 amps on a 30 amp circuit (although this seems to be a very common thing on posts in forums)

4. Possibly sending electricity through a circuit breaker the wrong direction (although many breakers are bi directional)

5. Setting 28 amp on a 30 amp circuit for a continuous load (at least you don’t do this anymore)

 

[defcon888]

My main breaker box has a 240v 30A line that goes to a female port in the garage.
It can serve, when the house is off the grid (MAINS OFF) as a place to connect an emergency 5kw generator I have.
I have a short adapter to go from the 4 wires in this sort of twisting locking receptacle (don't know the official name) to Nema 14-50 and then when I had my Tesla X, the portable charger plugs into that and into the car. It worked because the Tesla when you set the charge limit down to 28A it would remember the setting and always only draw that much. Code violation but safe.

Get an electrician to install a 50a breaker. That is what we have and it never has popped. We have a Lectron 32a charger.

 

[Whale Blubber]

I charge nightly on a Rivian wall charger running off a 30A breaker, and the car charges automatically at 24A on that circuit. I have no idea how it knows to do this, but I suppose the wall charger passes along the relevant information to the car.

 

[edman007]

I charge nightly on a Rivian wall charger running off a 30A breaker, and the car charges automatically at 24A on that circuit. I have no idea how it knows to do this, but I suppose the wall charger passes along the relevant information to the car.

Because the EVSE has a setting to control this, setting it correctly is code, and failure to do is is very much a fire hazard.

 

[Whale Blubber]

Good to know the installer knew what he was doing. lol

 

[350Industrial]

I charge nightly on a Rivian wall charger running off a 30A breaker, and the car charges automatically at 24A on that circuit. I have no idea how it knows to do this, but I suppose the wall charger passes along the relevant information to the car.

The Rivian wall charger knows the max amperage because when it was installed the installer has to set dip switches inside of the unit that limit max charging current. That max current is determined by the breaker/wire size feeding the Rivian wall charger- so in your case, 80% of a 30amp feed is 24amps max charging current.

 

[DADDYSLILGRANDPA]

What gauge is the wire? If it’s at least 8 you could pop in a 40amp breaker. You’ll need at least 6 gauge wiring for 50+ amps.

I ran a 8 gauge 40amp for my Tesla and charge my new R1S on it. Fast charging at home is overrated IMO.

 

[atrieger]

So much fail!

1. Using a vehicle to set the maximum amps (glad you don’t do this anymore)

2. Adding a load to your panel without doing a load calculation since you are using a backup power circuit

3. Using an outlet rated for 50 amps on a 30 amp circuit (although this seems to be a very common thing on posts in forums)

4. Possibly sending electricity through a circuit breaker the wrong direction (although many breakers are bi directional)

5. Setting 28 amp on a 30 amp circuit for a continuous load (at least you don’t do this anymore)

Good info.
Not doing 1, right.
2/4 electrician verified these so I guess they're not fails? (what might he have missed you think?)
3. Definitely bad idea BUT in my (weak) defense it's obvious, the port on the wall is a 30A with a 30A connector, so that's code. I just have a 1 foot 4 prong 30A to nema 14-50 adaptor plugged into it and then rivian charger into that so anyone else would ideally see that that's just making wires match not magically creating more power, and if it's violated and someone tries to draw more, breaker is there but still, I probably should spend the $1000 to just upgrade the breaker, wires, and outlet to 50A.

5. This I dont understand, you think that's a fail because it's too close to the max? Should circuits generally not be used so close to their breaker's max?

 

[emoore]

Good info.
Not doing 1, right.
2/4 electrician verified these so I guess they're not fails? (what might he have missed you think?)
3. Definitely bad idea BUT in my (weak) defense it's obvious, the port on the wall is a 30A with a 30A connector, so that's code. I just have a 1 foot 4 prong 30A to nema 14-50 adaptor plugged into it and then rivian charger into that so anyone else would ideally see that that's just making wires match not magically creating more power, and if it's violated and someone tries to draw more, breaker is there but still, I probably should spend the $1000 to just upgrade the breaker, wires, and outlet to 50A.

5. This I dont understand, you think that's a fail because it's too close to the max? Should circuits generally not be used so close to their breaker's max?

For a continuous load (ie charging an EV) you should set it to 80% of the max. Hence all the posts saying 24A.

 

[Proxy]

Good info.
Not doing 1, right.
2/4 electrician verified these so I guess they're not fails? (what might he have missed you think?)
3. Definitely bad idea BUT in my (weak) defense it's obvious, the port on the wall is a 30A with a 30A connector, so that's code. I just have a 1 foot 4 prong 30A to nema 14-50 adaptor plugged into it and then rivian charger into that so anyone else would ideally see that that's just making wires match not magically creating more power, and if it's violated and someone tries to draw more, breaker is there but still, I probably should spend the $1000 to just upgrade the breaker, wires, and outlet to 50A.

5. This I dont understand, you think that's a fail because it's too close to the max? Should circuits generally not be used so close to their breaker's max?

2/4 If an electrician installed it as a normal outlet then you are using it as designed when charging your vehicles and can ignore that part. I might have misunderstood your first post. I read that the receptacle you are using was installed by an electrician only to allow you to turn off your main breaker to power your home with a backup generator. Your home’s electrical panel has a limit too and I was concerned you might exceed that limit if the sole purpose of the install was for emergencies.

3/5 Portable EVSE’s plugs help set the proper current. Circuits are designed basically for a non continuous load up to the maximum and continuous loads at 80%. An EVSE with a 50 amp plug will allow no more than 40. One with a 30 amp plug allows 24 and so on. Charging a car is considered a continuous load so 28 amps was too much.

 

[Ghens]

My main breaker box has a 240v 30A line that goes to a female port in the garage.
It can serve, when the house is off the grid (MAINS OFF) as a place to connect an emergency 5kw generator I have.
I have a short adapter to go from the 4 wires in this sort of twisting locking receptacle (don't know the official name) to Nema 14-50 and then when I had my Tesla X, the portable charger plugs into that and into the car. It worked because the Tesla when you set the charge limit down to 28A it would remember the setting and always only draw that much. Code violation but safe.


I turned in my tesla and got an R1S and the same setup would work except Rivian doesn't remember the amperage setting, each time it resets to 32A which is *just* enough over to sometimes blow the circuit and sometimes not which is potentially dangerous when I forget to set it, not great.

So I submitted a feature request for them to have the UI remember amperage settings per location, hope that gets done some day that'll be great, in the mean time for safety I bought a $200 portable charger off amazon that similarly goes from nema 14-50 to J1772 and it can be configured to only allow 24A. So now I don't have to worry that the truck will try and draw more than my 30A circuit can provide, so that's good.

I just wanted to share what actually happens, because I have a current monitor on this circuit, is the truck and the adaptor keep negotiating.. the truck will never get more than 24A, but it gets that then asks for 26A, doesnt get it, drops down and renegotiates and the power delivery instead of being very smooth is a sort of choppy spikey graph going between 23A and 24A... if I manually get in the rivian and tell it to reduce amp draw to 24, it stops trying to negotiate and sits nice and clean, flat graph.

This isn't supported by rivian, but I think it's better to be safe than to keep having to remember to amperage down in the truck, or upgrade the line to 50A which is what the rivian portable charger wants of course.

Just sharing in case others are contemplating this.
The 3rd party charger I got is this one: QPQ Level 2 EV Charger 40A adjustable:
https://www.amazon.com/dp/B0C1N386GG?ref=ppx_yo2ov_dt_b_product_details&th=1

You can set up a 24 hour schedule where the amperage setting is located. Anytime you plug it in at home, it will default to the amperage you set in the schedule.

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