Max AMP Available

[evma582]

Hello!

Took ownership of my S75 last week and a bit confused on the max amperage available when charging. I have an EVSE that I've been using for the last two and half years while I leased an i3. The panel says that the outlet allows 30A, so I had limited what the EVSE could pull (BMW didn't allow granularity on the charge speed). I thought it was at 30A, but the S said it maxed at 20A. Curious about what the outlet could do, I plugged the Tesla charger into the outlet and the S started pulling at 40A. I double checked the breaker and it's labeled at 30A. I've upped the limit on the EVSE to 30A and matched it in settings, but I'm curious as to why the charger allows more than the circuit shows available?

 

[TexasEV]

I'm confused. Are you plugging the car into the EVSE with the J1772 adapter, or are you plugging the car into an outlet with the UMC? If so, what kind of outlet is it? It sounds like you may have a 50A outlet installed on a 30A circuit. If so that's a major danger.

 

[evma582]

I'm confused. Are you plugging the car into the EVSE with the J1772 adapter, or are you plugging the car into an outlet with the UMC? If so, what kind of outlet is it? It sounds like you may have a 50A outlet installed on a 30A circuit. If so that's a major danger.

It's a NEMA outlet. First I did EVSE with the J1772 adapter. Then, I unplugged the EVSE and tried the UMC with the NEMA adapter.

 

[TexasEV]

Do you mean a NEMA 14-50 outlet? (Calling it a NEMA outlet is like saying it weighs pounds without specifying how many). If so, it's a code violation and very dangerous. You need to get an electrician out to install a proper 50A circuit as shown here:
https://www.tesla.com/sites/default/files/downloads/US/universalmobileconnector_nema_14-50.pdf

In the meantime you need to manually turn down the amps on the charging screen to 24A. The car thinks it's a 50A circuit when the UMC is plugged into a 14-50 and will try to draw 40A.

It it's something other than a NEMA14-50 outlet, please specify, or maybe show a picture.

 

[evma582]

Do you mean a NEMA 14-50 outlet? (Calling it a NEMA outlet is like saying it weighs pounds without specifying how many). If so, it's a code violation and very dangerous. You need to get an electrician out to install a proper 50A circuit as shown here:
https://www.tesla.com/sites/default/files/downloads/US/universalmobileconnector_nema_14-50.pdf

In the meantime you need to manually turn down the amps on the charging screen to 24A. The car thinks it's a 50A circuit when the UMC is plugged into a 14-50 and will try to draw 40A.

It it's something other than a NEMA14-50 outlet, please specify, or maybe show a picture.

It's a NEMA 14-50. Thanks for the advice. I'll limit the amps further and get it chcecked out.

 

[Snowstorm]

It is the amps that matters, period.
I have a 30A circuit for a dryer adapted to a 14-50 plug so I can use the adapter and UMC. No issues as I dial it down to 24A from 32A default and it remembers the location. Just check it after firmware updates to make sure it doesn't reset.

 

[TexasEV]

It is the amps that matters, period.
I have a 30A circuit for a dryer adapted to a 14-50 plug so I can use the adapter and UMC. No issues as I dial it down to 24A from 32A default and it remembers the location. Just check it after firmware updates to make sure it doesn't reset.

That's just not safe no matter how you try to justify it. Did you know that Tesla has a 14-30 UMC adapter for dryer outlets?

 

[mblakele]

That's just not safe no matter how you try to justify it. Did you know that Tesla has a 14-30 UMC adapter for dryer outlets?

Nothing is 100% safe — but if the OP checks the setting like he says, why is this so dangerous? Why did Tesla give us control over the amps at all?

Personally I've found that the charging system itself is pretty good at detecting problems, as a second line of defense. It's saved the day a couple of times when I've plugged into mis-wired or mislabeled circuits.

 

[xbox4me62]

It's a NEMA 14-50. Thanks for the advice. I'll limit the amps further and get it chcecked out.

Do you really have a 14-50 outlet on a 30a breaker??? Where did you find the electrician to install the outlet for you?

 

[Rocky_H]

Nothing is 100% safe — but if the OP checks the setting like he says, why is this so dangerous?

Because there have been multiple cases of the car forgetting the amp setting for a few reasons. It is tied to GPS location, and sometimes the car gets a little off in its recognition of the address it's at, so it will go back to the default of 40A. Or I've seen a few people report that from a new firmware update, it reset some of the car's settings, including the amp limit, so it went back up to 40A. Hopefully the breaker will trip in time as it's heating up, but that's a pretty scary thing to rely on, especially when Tesla does actually have a real dryer plug that you can get while will keep the amps limited all the time without having to worry about a glitch in GPS or firmware update messing something up.

Why did Tesla give us control over the amps at all?

There are few cases that make this handy. Sometimes public J1772 stations are done with pretty crummy wiring runs with too much voltage drop or crummy equipment and don't keep running at their advertised rate. To keep them going, sometimes turning the current down some lets them get by.
Also, running the UMC at its 40A maximum rating can make it pretty hot. Heat and especially heat cycling of hot/cold/hot/cold every single day is one of the main factors for degrading the lifetime of electronics, so many people (myself included) keep their setting down to the low 30's for daily use to keep the UMC cool.
Sometimes the outlets at RV parks and campgrounds have either old/degraded wiring or old/degraded connections on the outlets. I've seen several people report that they had to turn down the current from 40A to be able to keep it consistently running without tripping the breaker.

(Calling it a NEMA outlet is like saying it weighs pounds without specifying how many).

Thanks for covering that; this is one of my pet peeves. Every outlet in everyone's house is a type of NEMA outlet. I use the analogy of the word "metric", since NEMA is the even more general overall naming system.

 

[davewill]

It might help to post what kind of EVSE you have. Since it seems to be switchable, set it to 24a (or the highest setting it has below that, which may have been why it was set to 20a) and then feel free to use it with your car. No worries about setting the car lower or having it forget. After that, look into either changing the outlet to a 14-30, hard-wiring the EVSE, or upgrading the circuit to 50a.

 

[Rocky_H]

Hello!

Took ownership of my S75 last week and a bit confused on the max amperage available when charging. I have an EVSE that I've been using for the last two and half years while I leased an i3. The panel says that the outlet allows 30A, so I had limited what the EVSE could pull (BMW didn't allow granularity on the charge speed). I thought it was at 30A, but the S said it maxed at 20A. Curious about what the outlet could do, I plugged the Tesla charger into the outlet and the S started pulling at 40A. I double checked the breaker and it's labeled at 30A. I've upped the limit on the EVSE to 30A and matched it in settings, but I'm curious as to why the charger allows more than the circuit shows available?

I remembered a couple of other things I should mention about your original EVSE setup. As @davewill mentioned, it would really help if you could tell the model number of the EVSE that you have. It is kind of frustrating and confusing that the names of some of them from different brands seem to sometimes refer to the circuit rating they are on, or the current provided to the vehicle, and those are never the same, so it's hard to tell what it is from just one number. Electric code dictates that you can supply no more than 80% of the circuit rating for constant loads, so 20A from a 30A circuit is very common. But if it's a 30A circuit, that should NEVER be a 14-50 outlet. That is a bad code violation.

But, there are some EVSEs that are a little weird like this:
20A Level 2 EVSE LCS-25P with NEMA 14-50 | ClipperCreek
It has a cord and plug for a 14-50 outlet, but it is lower power and only provides 20A to the car. That's still fine to just pull less power from an outlet than it's capable of, but it doesn't relate to how the outlet was installed.