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JohnSnowNW
Active Member
mikeash
Active Member
You have a 48A charger in the car, but you're limited by the capacity of what you plug into. Circuit ratings are for intermittent loads, and have to be derated by 20% for continuous loads. A 50A circuit is only good for 40A of continuous load such as charging a car.
If you plug into a Tesla Wall Connector or J1772 charger that can provide more than 40A, you should see up to 48A before your car becomes the limiting factor.
If you plug into a Tesla Wall Connector or J1772 charger that can provide more than 40A, you should see up to 48A before your car becomes the limiting factor.
To charge at 48A you need a Tesla Wall Connector or J1772 charger hooked to a 60A breaker. (With appropriate sized wires, etc.)
Zaphod
Galaxy President (former)
You need to use a HPWC to get more than 40A. Electrical code only allows power draw of 80% of rating, so 80% of 50A = 40A.
jeffro01
Active Member
This must be why Tesla took dual chargers off the order page when the car previously had a 40A charger or the option of dual chargers. No matter how clear the explanation on the Tesla website site charging page, the order page, and I'm sure from the Tesla rep if the buyer ordered it in a store, this just goes right past some people who don't understand it or don't think they need to pay attention to such details.
Charging from the UMC, which means charging by plugging into an outlet, is limited to a maximum of 40A. It doesn't matter what you have in the car.
Charging from the UMC, which means charging by plugging into an outlet, is limited to a maximum of 40A. It doesn't matter what you have in the car.
No. You're dealing with three discrete limits here, the lowest of which sets your maximum.
The first limit is the car's maximum capacity, which in this case is 48A (upgradeable to 72 Amps after delivery by giving Tesla more money.)
The second limit is the maximum capacity of the charging hardware itself. For the UMC, that's 40A. For the HPWC, that's 80A. J1772 systems can be anywhere from 6A to 80A.
The third limit is what the charging hardware is set to so as to protect the wires. This is carried by the J1772 protocol to the car - on the UMC, the different plug adapters for it have different limits coded into them and automatically change this signal when you switch plugs.
To go higher than 40A, you really need a dedicated hard wired EVSE like the HPWC (which can be set on installation for anything from 12A up to 80A if I remember right.)
kritlop
Member
Tesla changed to delivering a single charger that is capable of 48 or 72 amps, depending on the software option chosen. Using a UMC limits things to 40 amps.
I'm well aware of that. I was referring to the dual chargers because people had the same misunderstanding then as they do now with the 48 or 72A chargers regarding when they get the benefit of that and when they don't.
kritlop
Member
Since Tesla seems to like to include the hardware and just limit it by software, I'm hoping at some point they have a fire sale on "options" or maybe do a holiday discount thing or something like that. I would definitely consider adding a few options if they were on sale. Eyeing the 72A charger and the 60->75kw upgrade 
BrokerDon
Active Member
IHMO the difference between charging at 40A vs. 48A is a negligible and (from my experience)... and charging over 40A is likely unnecessary on Tesla home charging. We got a Tesla HPWC as part of our "inventory" vehicle purchase which will charge at 80A since our 2015 P85D came with Dual Chargers. However we only charge at 50A 99% of the time to keep the temperature on the HPWC, the HPWC cable, and our P85D charge port cool. Charging at 80A heats these items up quite a bit which will probably shorten their life. For us charging at 80A is unnecessary since our low SCE "Super Off Peak" electrical rates are from 10:00 PM to 8:00 AM (10 hours)... WAY more time than needed for 99% of our home charging even at 40A with a depleted 85Kwh battery. We routinely charge at 50A so both Dual Chargers share the load and everything stays nice and cool... and because we can with our HPWC. If the HPWC hadn't come with our inventory P85D purchase we wouldn't have bought one for $750, especially after driving / charging 12,000 miles.
YMMV
Amateur Driver / Closed Garage
(pun on Professional Driver / Closed Course for people with insensitive Funny Bones)
YMMV
Amateur Driver / Closed Garage
(pun on Professional Driver / Closed Course for people with insensitive Funny Bones)
As some have pointed out, charging at home at more than 40 or 48A is usually no big deal, but having the dual chargers or 72A charger may be a big deal on the road if you need to charge at an AC charger and it happens to be more than 40A. It gives you a chance to get back on the road faster.
And it frees up the destination charger HPWC for another person to use.
@BrokerDon, I agree that in your home charging example 50A charging works fine for you (though I am not aware of any evidence that charging at 50A vs. 80A will lengthen the useful life of your HPWC, cable, and onboard chargers). However, as the number of Tesla Destination Chargers grows rapidly, those that are capable of delivering 80A when used by those Teslas that can AC charge at amperages over 48 will be able to service more cars more efficiently.
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