Lowering Charge Current - Public J1772

[Snow Drift]

Today, I went to my first Chargepoint J1772 station for a charge while shopping. The car automatically set the Current to 30/30A on the Charging screen.

I believe it is advised to reduce it by 20%, so I lowered it to 24/30A.

Was I correct, or am I being paranoid and should have left it at 30/30A?

And for your enjoyment:

 

[smatthew]

The 20% derating is on the wiring. Go for as much as the EVSE allows

 

[Crispix]

No need to reduce on a public charger like that. The 20% thing is usually just applicable to your home wiring, e.g. if you have a 40-amp circuit, continuous load should only be 32 amps. Or for a 50-amp circuit (like a NEMA 14-50), you can use 40 amps continuous. But some NEMA 14-50s are installed on 40-amp circuits, thus the recommendation to set the car to only use 32 amps.

 

[eprosenx]

Today, I went to my first Chargepoint J1772 station for a charge while shopping. The car automatically set the Current to 30/30A on the Charging screen.

I believe it is advised to reduce it by 20%, so I lowered it to 24/30A.

Was I correct, or am I being paranoid and should have left it at 30/30A?

And for your enjoyment:

View attachment 335307 View attachment 335308

Yeah, the 30a offered by the charger is already derated. I can basically guarantee you that he charger in question is connected to a 40a circuit.

I have no idea why 30a is so popular in the J1772 charging space. 32a would be more logical (80% of 40a), but for whatever reason a lot of J1772 units top out at 30a.

You do not need to worry about this at public charging stations (unless they were installed vastly wrong).

The times you need to worry about this are in improperly wired setups, or when we are doing “hackish” things to get temporary power at a destination like using a 14-50r to 10-30p adapter, cutting a neutral pin off a 14-50r, etc...

 

[TexasEV]

The EVSE delivers what it is supposed to deliver. Just like when your 5-15 UMC adapter automatically sets the proper current of 12A when you plug into a 15A outlet. The car is almost idiot proof as long as you don’t use any kludge homemade adapters.

A 30A EVSE can deliver 30A because it’s wired on a 40A circuit. But you don’t need to know that. Just accept what the car draws on a J1772.

Edit- posted the same time as @eprosenx. And to answer his question, J1772s are 30A because that was the minimum requirement for funding in the 2008 stimulus. They’re stil only 30A (or some 32A) rather than 40 or 48A or higher because non-Teslas don’t have larger chargers and ChargePoint, etc.’s target market are short range EVs.

ChargePoint’s motto— “We’re overpriced, but we’re underpowered”.

 

[TT97]

30A (and typically 208V) is slow enough, why would you want to slow it down more?

 

[Snow Drift]

Thanks everyone!

 

[ratsbew]

My home setup is a NEMA 6-20 which does 16A at 248V (high voltage at my house!) which gives right about 4KW of charging. Public stations at 30A and 208V only give 6.2KW which is still painfully slow for anything other than destination charging. You can't really get any meaningful charge on a 1hr stop unless you're already practically in your own neighborhood.