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Explanation of 72 amp vs. 48 amp on board charger

Explanation of 72 amp vs. 48 amp on board charger

Hi - sorry to be a Tesla dummy - could someone explain (in simple terms) what this means? We just had an electrician put in a wall charger yesterday and I think it's set to 40 amps or maybe 50 amps (220v).

Does the 72 amp car charger means the car will charge faster or is it irrelevant since our wall charger is only set to 40 or 50?

thank you!

dortor | 19. November 2015

yes - it does not matter - the car and the charger negotiate the highest common amperage

car says I can do 72 amps
charger says I can do 40 amps
car say ok let's do 40 amps!

car says I can do 40 amps
wall charger says I can do 80 amps
car says ok let's do 40 amps

or something like that

the car can't pull more than it can pull
the charger can't provide more than it can provide
they meet in the middle.

rossRallen | 19. November 2015

Actually, they meet at the lowest rate. Either the supply or the on-board charger sets the low limit.

Supercharger bypass the on-board charger, so 48A or 72A doesn't matter.

In general, unless you need a quick turnaround overnight or at a destination, you're better off using the lowest rate that will get you to the charge level you need when you need it. That preserves battery life.

gordonbremer | 19. November 2015

You should ask any electrician to determine the maximum breaker amperage that can be installed on your electrical panel. There are formulas to determine this based on your service and the other existing breakers. Have him install that amperage breaker. Then, set the HPWC to align with that amperage per the HPWCmanual.

You want the breaker and HPWC setting to be set as high as possible. 40 or 50 amps seems low, but perhaps that is the maximum your home service can handle.

MYYModelX | 19. November 2015

thank you!