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Setting Amp level on control panel

haroldo

Member
Apr 20, 2021
394
205
NJ
Dumb questions from a newbie...
What setting should you use for amps in control panel/charging?
I've read that you're supposed to set the amp level to 80% of the charger's rated level, is that right? If my local generic charger is 32A, I assume I'm supposed manually adjust the car to 26A. If I forget to change it, and go to a Tesla Supercharger, presumably a lot higher amp, will the car know to adjust up the level (because it's a Tesla facility), of will it be limited by what is set on the control panel?
Thanks!
 

RTPEV

Active Member
Mar 21, 2016
1,115
1,307
Durham, NC
Several issues with your statements.

The 80% restriction applies to the car's (and EVSE's) continuous current draw compared to the breaker rating in your panel. For example, if you had a 40A breaker, 80% of that is your 32A continuous power draw limit. This limit should be set in the EVSE itself, and then the EVSE communicates that limit to the car. You don't have to do anything special in the car as long as your EVSE is set up correctly. Sometimes EVSEs can be "programmed" (via DIP switches or similar), other times they just specify that you need to use a 40A breaker for example, and they are hard-wired to 32A limit (or whatever the numbers happen to be for that specific EVSE).

The current limit that you set in the car (at least in North America, I can't speak to other geographies) only applies to L1 (120V) charging, and would be useful to people that are plugging their portable connector into a domestic outlet that has other things plugged into the same circuit (e.g. a fridge). You might want to cut down the charge current from the default of 12A (which is already 80% of the typical 15A breaker, see how that's already taken care of for you?) to something lower like 8A so you don't trip the breaker when the fridge kicks on. Don't worry about that limit affecting your charging at regular L2 charging stations, destination chargers, or Superchargers. That limit doesn't apply to those charging stations. It's only there for 120V charging.
 

haroldo

Member
Apr 20, 2021
394
205
NJ
Okay, thanks. I only charge at work (free 32A charging stations) and Supercharger if/when I go on a long trip. I am not set up to charge at home.
Assuming I already played around with the amp limit on the charging control panel page, where should I set it (again, work is 32A). If I never do home charging, I assume I should never bother with this setting, right?
 

srs5694

Active Member
Jan 15, 2019
1,276
1,587
Woonsocket, RI
For the most part, you shouldn't need to set it. The 80% rule applies to the circuit in the house, and the EVSE should already handle that. That is, a 32A EVSE is probably installed on a 40A circuit, so it's already running at 80% of the 40A circuit. Your car then negotiates its charge rate with the EVSE and automatically draws 32A or less. (Your Model 3 LR is capable of pulling 48A, but it will only pull 32A on your 32A EVSE.)

The ability to adjust the amperage in the car is handy if you know the circuit is dodgy, if you're using adapters that hide the circuit's true limits, if you know the circuit has other devices on it (which would mainly apply to 120V L1 charging), or if you want to slow down charging for some reason. Most of these are situations that you'd want to avoid, especially for your primary charging source; but you might run into them in the real world from time to time when traveling, hence the ability to adjust the L1/L2 charge amperage.

Don't worry about Supercharging amperage. AFAIK, you can't manually adjust the amperage at a Supercharger, so even if you do override your L1 or L2 charge rates, that won't affect Supercharging. The amperage is set by negotiation between the car and the Supercharger, much like with an L1/L2 EVSE; but with Supercharging, the amperage varies over the course of the charge to obtain what Tesla engineers believe is the best compromise between charge speed and battery health. In particular, the amperage will be higher at a low battery state of charge (SoC) and drop over time, to avoid overheating and damaging the battery.
 
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srs5694

Active Member
Jan 15, 2019
1,276
1,587
Woonsocket, RI
Okay, thanks. I only charge at work (free 32A charging stations) and Supercharger if/when I go on a long trip. I am not set up to charge at home.
Assuming I already played around with the amp limit on the charging control panel page, where should I set it (again, work is 32A). If I never do home charging, I assume I should never bother with this setting, right?
If you've already dropped it down, just increase it back to the maximum in the same screen.
 
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mociaf9

Active Member
Oct 18, 2018
2,933
6,087
CA
Okay, so what you're talking about is the duty rating for electrical circuits. And the issue is that continuous loads are derated to 80% of the max allowed load on a circuit. For example, let's say you installed a NEMA 14-50 receptacle in your garage. It's on a 50A circuit breaker and has been properly wired to deliver 50A. Then for any normal, non-continuous load you can plug in and get 50A. But charging an EV is considered a continuous load, so the max you should charge at when plugged into that outlet is 40A (80% of 50).

Almost always this derating has been taken care of for you. In your example, where you're getting 32A from a charger, almost certainly that's because the charger is wired on a 40A circuit and 32A is the 80% allowable continuous load. If you're using the correct adapter plug for the outlet (and assuming a nominally powered outlet) with a Tesla Mobile Connector, then this derating is taken care of for you automatically by the hardware. Same is true when using a Tesla Wall Connector, when setting up the hardware the derating is taken care of. Same is true whenever you plug into a public charger, it's already been set up to take the 80% continuous load limit into account.

Needing to adjust the current limit in the car is really rare. I can only think of 2 times it's usually necessary. 1) If you're using a homemade plug adapter that will effectively trick the Mobile Connector into setting the wrong limit, e.g. using a NEMA 14-30 to 14-50 adapter because you don't have the 14-30 plug for your Mobile Connector and you do have the 14-50 one. 2) If you're plugged into a normal wall outlet somewhere that has other things already plugged in on the same circuit, so you need to lower the power draw so you don't overload the circuit; or where the the breaker trips after you've been charging for a few hours, in which case setting a lower current may help you avoid the breaker trips.
 
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LoudMusic

Member
Jul 21, 2020
713
778
Arkansas
Several issues with your statements.

The 80% restriction applies to the car's (and EVSE's) continuous current draw compared to the breaker rating in your panel. For example, if you had a 40A breaker, 80% of that is your 32A continuous power draw limit. This limit should be set in the EVSE itself, and then the EVSE communicates that limit to the car. You don't have to do anything special in the car as long as your EVSE is set up correctly. Sometimes EVSEs can be "programmed" (via DIP switches or similar), other times they just specify that you need to use a 40A breaker for example, and they are hard-wired to 32A limit (or whatever the numbers happen to be for that specific EVSE).

The current limit that you set in the car (at least in North America, I can't speak to other geographies) only applies to L1 (120V) charging, and would be useful to people that are plugging their portable connector into a domestic outlet that has other things plugged into the same circuit (e.g. a fridge). You might want to cut down the charge current from the default of 12A (which is already 80% of the typical 15A breaker, see how that's already taken care of for you?) to something lower like 8A so you don't trip the breaker when the fridge kicks on. Don't worry about that limit affecting your charging at regular L2 charging stations, destination chargers, or Superchargers. That limit doesn't apply to those charging stations. It's only there for 120V charging.

I believe this is incorrect - you can set the Amps for any non-DC charging. I know for certain I can set it on a 240v50a circuit.

If you're using a Tesla NEMA adapter it somehow informs the car of what type of adapter is being used and sets the maximum amps automatically based on the 80% rule, and can be adjusted DOWN from there. This also works with appropriately built 3rd party adapters that fit the gen 2 mobile charger. It works for my 30A marine locking style adapter I have for use at marinas.


Unfortunately you can't manually adjust amps when DC fast charging. The point is to fast charge so theoretically you're wanting to get out of there as quickly as possible. But with congested charging locations they probably also don't want people just setting the speed lower so they don't have to pay idle fees.
 
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RTPEV

Active Member
Mar 21, 2016
1,115
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Durham, NC
I believe this is incorrect - you can set the Amps for any non-DC charging. I know for certain I can set it on a 240v50a circuit.
I think you are right...I have my limit set to 8A for charging when I plug into my in-laws' outlet, and I know for sure that I charge faster than that at home from my EVSE! I guess it maintains two different limits, one for 120V and one for 240V. It must only bring up the 120V limit when you're actually plugged in to 120V.

If you're using a Tesla NEMA adapter it somehow informs the car of what type of adapter is being used and sets the maximum amps automatically based on the 80% rule, and can be adjusted DOWN from there. This also works with appropriately built 3rd party adapters that fit the gen 2 mobile charger. It works for my 30A marine locking style adapter I have for use at marinas.
The Tesla mobile connector negotiates the maximum charge rate with the car, and in turn, the Tesla mobile connector sets its limit based on which adapter you are using (as you say). I imagine it's some kind of jumper in the adapter that sets this. Pretty smart solution.

Unfortunately you can't manually adjust amps when DC fast charging. The point is to fast charge so theoretically you're wanting to get out of there as quickly as possible. But with congested charging locations they probably also don't want people just setting the speed lower so they don't have to pay idle fees.
Once you get past the constant-current stage of fast charging (which is when the taper down happens) it's the physics of the battery itself that controls the amps anyway. So even if you could set a charge speed limit, it would only work until you reached 20-50% SOC anyway, although I suppose if you set it low enough, it could take awhile to reach that SOC. That said, it's usually about wanting to go as quickly as possible at a Supercharger.
 
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srs5694

Active Member
Jan 15, 2019
1,276
1,587
Woonsocket, RI
the Tesla mobile connector sets its limit based on which adapter you are using (as you say). I imagine it's some kind of jumper in the adapter that sets this. Pretty smart solution.
Here's an article that goes into all the technical details of how this is done:

 
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Rocky_H

Well-Known Member
Feb 19, 2015
7,075
8,686
Boise, ID
I think you are right...I have my limit set to 8A for charging when I plug into my in-laws' outlet, and I know for sure that I charge faster than that at home from my EVSE! I guess it maintains two different limits, one for 120V and one for 240V. It must only bring up the 120V limit when you're actually plugged in to 120V.
It's not two different limits by voltage. You are plugging in at your in-laws' house, which is a different location. When you charge at a place and turn the amps down from the maximum, it sets a memorized amp level tagged to that GPS location, so when you charge there again, it will use that same amp level again.
 
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srs5694

Active Member
Jan 15, 2019
1,276
1,587
Woonsocket, RI
It's not two different limits by voltage. You are plugging in at your in-laws' house, which is a different location. When you charge at a place and turn the amps down from the maximum, it sets a memorized amp level tagged to that GPS location, so when you charge there again, it will use that same amp level again.
This is my understanding, too; however, I'd caution against relying on the car to remember such a setting, if it's important. My Tesla occasionally records my GPS coordinates as being slightly off (like at my next-door neighbor's house rather than my own house), and it's always possible that a setting like this would be lost or corrupted in the computer's storage. Thus, if you know that running at too high an amperage would cause problems, it's best to double-check the setting when you begin charging (or before; I don't recall offhand when the car shows the changed amperage -- before or after you plug in).
 

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