Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

Charging rate from 40 amp J1772 question

This site may earn commission on affiliate links.

invisik

Member
Supporting Member
Mar 13, 2014
660
14
Minneapolis
Hi!

I have a Leviton J1772 charger at my office (208v). It says on the front of it that it is 40 amp. When I plug my car in, it charges at 30 amps. VisibleTesla shows the pilot current is 40 amps (attached screenshot of when charging).

Shouldn't the car charge at the full 40 amps in this situation? I understand when charging off a 14-50 or similar plug it uses 80% of the line capacity but I didn't think that applied to fixed-mounted EVSE's like this (or for that matter a Chargepoint or Blink unit out there in the world). I am using the J1772 to Tesla adapter. If not, shouldn't it charge at 32 amps (80% of 40) ?

Is there something wrong with the installation of this unit or is this normal?

Thanks.

-m

Untitled.jpg
 
If the pilot current is truly 40 amps, then, yes, you should be able to charge at 40 amps. Can you take a picture of your car's screen when charging? It doesn't have anything to do with the voltage. Perhaps the current got limited by the car due to a perceived charging fault, or you dialed down the charging current in the car for that location and forgot to dial it back up? What model Leviton is it?
 
This is a common source of confusion. EVSE makers identify their equipment by the amperage of the circuit that's needed, not the output of the unit. For example, one of the high amp level 2 chargers is the Clipper Creek CS-60, which requires a 60A circuit and has 48A output. Perhaps it's a safety measure, so an installer doesn't see "30A" on the label and assume it uses a 30A circuit?

EDIT- My mistake. Leviton apparently doesn't follow this convention. Here they advertise a "40A charging station, requires 50A circuit":
Evr-Green 400 Charging Station, Surface Mount, 25-Foot Cord, 40-Amp, Requires 50Amp Circuit, EVB40-PST : Electric Vehicle Charging Station

So it's probably a resistance in the circuit somewhere that's causing the car to drop the amps by 25% to 30A for safety.
 
Last edited:
Hi, I ran down there and started it up charging again. No errors. Saw the amp number on the touchscreen said 30..... So I tapped the up arrow for the hell of it and it increased.... my bad, I was able to increase it all the way to 40 and it ramped up all the way to 40. I have no idea why/when I set it to 30. My fault, sorry.

But this brings up a point, we should see full amp from a Chargepoint or similar, not 10% less, right? The car is smart enough to know when it should limit by 10% and when it shouldn't? Or is that the pilot number that is the amount it can pull?

Thanks...

-m
 
The pilot signal indicates the max amount of current the car can pull.

It is up to the installer of the EVSE to use wiring and a breaker that is 25% greater than the pilot signal to provide an NEC compliant installation.

In your case, the 40A Leviton EVSE requires a 50A circuit to be compliant (20% derating for EV charging loads).

(Before anyone corrects "25%" in line 2, 40A + 25% (10A) = 50A, 50A - 20% (10A) = 40A)
 
Well, of course. In Canada, those are imperial unit amps, not the regular American ones :)

Looks like a bug to me. I too have a CS-60, but only a single charger, so it just reports 40/48 Amps for me. Maybe tell/email Tesla ownership and see what they say.