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Why can't the Model 3 software allow charging greater than 48A on TWC?

Why can't the Model 3 software allow charging greater than 48A on TWC?

The Model 3 Long Range EPA Document states "The Model 3 is capable of accepting DC current up to 525 Amps from an off-board charger (Supercharger)." The Tesla Wall Connector (TWC) is capable of 80 Amps on a 100 amp service, yet the software limits charging from the TWC to 48 amps.

fazman | 16. April 2019

Only Elon knows why

tommypham | 16. April 2019

Superchargers are DC to DC power to the battery, bypassing the onboard charger. Using the wall connector provides AC power to the on-board charger which generates DC power to the battery. The on-board charger is only capable of taking a max of 48A most likely due to cost.

asevstr | 16. April 2019

DC vs AC.

Rt002k | 16. April 2019

Anyone got a Bill Nye episode explaining the difference betwen AC and DC to share?

leo33 | 16. April 2019

@Rhaekar explained it best. {@Rt002k, AC is alternating current, like what the plugs in your house provide. DC is direct current, like what batteries provide.)

lbowroom | 16. April 2019

The OP wants to know why he can't get the full 80 amps from the TWC, not the supercharging current. Anyways, same answer, on board charger on Model 3 is only capable of 48A.

Rt002k | 16. April 2019

@Leo - I know, I'm an engineer, it's basic stuff, something that would have been explained by Bill Nye the Science Guy in 7th grade.

Carl Thompson | 16. April 2019

Cost.

lbowroom | 16. April 2019

Great explanation Carl. Really technical and complete

beaver | 16. April 2019

The on board charger converts AC to DC power using 6-8 expensive power transistors, they have a current limit so the charger was built for 48A max.

crmedved | 16. April 2019

The MR, SR, and SR+ only get 32A, so be happy :p

rpc_in_va | 16. April 2019

In the case of a TWC, I assumed it was doing the AC/DC conversion. The onboard converter is only capable of 32A. So (continuing my reasoning) 48A is the limit of the TWC converter. Could be wrong, of course, but that seems consistent with all the information I’ve seen.

ADinM3 | 16. April 2019

@Carl, +1 (cost & complexity both on car and house)

Very few homes are capable of readily supplying 100A and even fewer people need it in real world. Not to mention heavier/bulkier charging cables and also gets increasingly dangerous.

Lastly, if you have ever tried pulling 2-ga or 1/0-ga wire you will know it sucks. Between the cost to pull wire and likely addition of additional sub-panel in most cases, assuming you don't also need to upgrade service as well, install costs could easily be several times more expensive in many cases.

kaffine | 16. April 2019

rpc_in_va | April 16, 2019
In the case of a TWC, I assumed it was doing the AC/DC conversion. The onboard converter is only capable of 32A. So (continuing my reasoning) 48A is the limit of the TWC converter. Could be wrong, of course, but that seems consistent with all the information I’ve seen.

No the wall connector (TWC) is not doing the conversion to DC. The TWC just passes the AC to the on-board charger. The on-board charger for the LR is capable of 48A while the on-board charger for the SR is only 32A.

LoveMyM3 | 16. April 2019

While we are on the subject I visited a supercharger for the first time. By default, I noted it was charging at 25 AMPS and the setting was greyed out so I couldn't change anything. Is this correct? At home obviously, it does 48 Amps

crmedved | 16. April 2019

Eh. It's kind of saying "you don't need to know". It is... a lot higher than 25 amps :) Like probably 10x that, regardless of what it is showing there.

mrburke | 16. April 2019

What charges batteries is watts (power), not amps (current). No pun intended.

beaver | 16. April 2019

FYI supercharging at 120 kW, I saw 360 V at 333 A

mrburke | 16. April 2019

@beaver - "120 kW" - Thank You.

Pepperidge | 17. April 2019

The AC/DC converter is 16A per module. LR has 3 modules and MR/SR has 2 modules.

rpc_in_va | 17. April 2019

@kaffine

Thanks for the correction. Always happy to learn.

timary | 17. April 2019

Thank you to all of the very quick responses. I was not sure what voltage the Superchargers operate at and should have researched that first. Online guesses range from 400VDC@ 300A (120 KW) to 480VDC @ 400A (192KW). Beaver's input was 360VDC @ 333A (120KW). Using 1.414 to convert 120KW DC Power yields ~170KW AC Power. The TWC charges 48A @ 220 VAC yields ~10.6KW or less than 10% of the above calculation. None of this takes into account the Model 3 AC to DC conversion efficiency this could range between 75-90%.

I think that Pepperidge's response is the best real answer. The limitation is NOT the difference between AC to DC conversion nor the gauge wire inside the Model 3, but the AC/DC converters inside the Model 3. Too bad I spent the money for 100A service and the TWC. Ideally, the TWC would have the AC/DC converters to allow for the higher currents.

P.S. Snarky commenters only showed they did not know the answer.

kevin_rf | 17. April 2019

The LR having the 48a is nice at the end of the day when you need some quick electrons before going out again for the evening. The extra umph as you herd cats into the car can make or break you some nights.

M3BlueGeorgia | 17. April 2019

@timary
In North America, you aren't going to get 220V, you'll either get 240V or 208V, depending on the source.

Magic 8 Ball | 17. April 2019

You spent more money than you needed to? Ha Ha

Rt002k | 17. April 2019

Snarky commenter was simply pointing out that the capability of DC charging does not inform the capability of AC charging. The wording of the question implied you expected AC performance to be higher because DC performance is high.

TeslaTap.com | 17. April 2019

@timary - "Too bad I spent the money for 100A service and the TWC".

Actually you get several benefits:
1) By using thicker wires for 100 amp service, you reduce losses through the wires heating up. So over years you save some money (perhaps not a lot, but some).
2) Hard wired connections are more reliable than a NEMA 14-50.
3) Faster charging - 48 amps, vs 32 from the Mobile Cable.
4) You can leave the MC in your car, rather than moving it back and forth between your house and the car.

mrburke | 17. April 2019

@timary - "Too bad I spent the money for 100A service and the TWC".

The good news is if you get a second Tesla and a second TWC they can share the same 100A circuit. I believe that up to 4 TWC can share a single circuit.

tommypham | 17. April 2019

@timary: I think you're missing the point.

If the wall connector had an AC/DC converter, it would increase the cost substantially. Most people at home don't need crazy fast charging since you could/should be charging overnight when needed. Using the TWC on a 60A breaker gets you ~45mph which is plenty fast for home charging.

Even the UMC on a NEMA 14-50 is sufficient.

You probably overpaid a couple hundred dollars running wiring for 100A vs the 60A needed. The TWC vs UMC on a NEMA 14-50 has its benefits though.

timary | 17. April 2019

M3BlueGeorgia is correct, I should have used 240 VAC and not 220VAC.
TeslaTap.com made 4 excellent points, especially that with the Mobile Connector, I would be at 32A, not 48A .
Rhaeker was almost certainly correct that an AC/DC converter for 240VAC @ 80A would be $$$$$$$$$
mrburke made a good point about a second Tesla, maybe the new Roadster that could use 80A. I wish!!!!!

Thanks again to all the comments, they were very helpful, especially Pepperidge and TeslaTap.com.