Why is home charging only 32 amps on SR when supercharging is so much faster?

[STS-134]

Finally: As pointed out above, the charge rate at DC Superchargers isn't affected. You can still get 250 kW at a SC into a Tesla SR (at least, for a short while, while the battery's mostly discharged) just like the LR and P guys do, so it should take a little shorter time for an SR to get in and out than a P or LR.

You sure about that? I thought the SR doesn't take a full 250 kW, even when plugged into a V3 supercharger at 0% SoC.

 

[jjrandorin]

You sure about that? I though the SR doesn't take a full 250 kW, even when plugged into a V3 supercharger at 0% SoC.

I think (but am not positive) that a Standard Range / SR+ Tesla model 3 maxes out at 170kW. I dont follow that closely (and dont have that vehicle) but seem to remember people saying that somewhere.

I realize thats a lot of "I think I read somewhere" so I am not trying to say thats definitive.

 

[AlanSubie4Life]

You sure about that? I though the SR doesn't take a full 250 kW, even when plugged into a V3 supercharger at 0% SoC.

That’s right, it should be about 31/46*250kW, so ~168kW. In reality of course it could be slightly higher.

 

[Tronguy]

That’s right, it should be about 31/46*250kW, so ~168kW. In reality of course it could be slightly higher.

Jeez, that'll learn my to spout my mouth. I stand corrected.

 

[AlanSubie4Life]

Now, take a SR. It has a smaller battery. Checking on-line.. 60 kW-hr.

SR+ - 52.5kWh
SR - 52.5kWh (but locked out 220/240 of the capacity)
SR+ 2170L - ~53.5kWh (but 55.4kWh FPWN)
SR+ LFP - 55.1kWh
RWD - 60.5kWh

 

[stopcrazypp]

I think (but am not positive) that a Standard Range / SR+ Tesla model 3 maxes out at 170kW. I dont follow that closely (and dont have that vehicle) but seem to remember people saying that somewhere.

I realize thats a lot of "I think I read somewhere" so I am not trying to say thats definitive.

I have a 2021 SR+ (still with the Panasonic battery not the LFP) and it maxes at 170kW. I haven't seen any cases where SR goes to 250kW.

 

[stopcrazypp]

I don’t think that this is the case. The DC fast charger negotiates with the car to provide the correct voltage/current directly to the battery.

There is a DC-DC in the vehicle, but that converts from HV to the “12V” bus which powers the computers and such (and charges the 12V battery). Not sure the specs exactly but something like several kW output.

Corrections appreciated if I am wrong, but having a DC-DC converter at 250kW input in the car seems problematic even with “low” loss. Plus there is not a need since the fast charger can make appropriate adjustments just one time, as it converts AC to DC.

You are correct, for fast charging there is no DC-DC involved, it is a direct connection to the battery pack and vehicle communicates with the offboard charger for what DC voltage and current it wants.

There is an exception to this for cars with 800V architectures (like Porsche's Taycan), where when they plug into a charger that is only max 400V-500V capable, there is a built in DC-DC converter for backwards compatibility. However, this doesn't apply for Teslas given they all operate around 400V.

 

[davewill]

The charger inside the vehicle is a smaller version of the charger in the DCFC, it takes AC and converts it to DC at a variable voltage. The ability to vary the voltage serves two purposes. One is to adapt to the current voltage of the battery, a full battery is at a higher voltage than an empty one, and different cars have batteries that are built for different voltages.

The second purpose is to control the current being used to charge the battery. To charge a battery at all, you feed it a higher voltage than it is currently at. To charge it faster (higher current) you feed it a higher voltage. The BMS in the battery communicates to the charger (whether the internal one or an external DCFC) and tells it what voltage and current it can handle in it's present state, and the charger delivers that, subject to it's own limitations, like an EVSE that can only deliver 240v/20a or a Supercharger than only has 75kW available.