Tesla charging less amps than whats displayed, any solution?

[MA308]

Tesla model S - 2017

Both the car and app show 30amp charging (level 2 charger), but the charging app I used for the level 2 charger only shows 29amps being used.

When I charged a newer model S, the charging app displayed the appropriate 30amps (just like in the car and in the Tesla app). It even charges the new car faster than mine.

So I believe the problem is with my car alone. Any suggestions?

 

[ewoodrick]

1 amp really isn't that big of deal. What's the voltage? Did it stary high and come down?

1A @240V is only about 1 mile per hour difference in charging speed.

What size circuit it is on? What's the wire gauge?

 

[MA308]

1 amp really isn't that big of deal. What's the voltage? Did it stary high and come down?

1A @240V is only about 1 mile per hour difference in charging speed.

What size circuit it is on? What's the wire gauge?

1) voltage is 209. And no, it remains steady at 29 amps. I can use the Tesla app and lower it to 25 or 20, but when I bring it up to 30, the charging app only displays 29amps being used.

2) fair enough not a huge difference. Mine was charging at 30-31km/h, the other Tesla was 37-38km/h

3) unsure of the specs. But both cars used the same cable and same adapter.

Thank you for your reply!
Overall I’m not concerned, just wondering if it’s a glitch or a solvable problem.

 

[ucmndd]

2) fair enough not a huge difference. Mine was charging at 30-31km/h, the other Tesla was 37-38km/h

You cannot use km/hr as a charging speed comparison between two different cars because it's a derived metric based on efficiency. The new Model S is more efficient than your 2017, thus it gets more km/hr out of the exact same power input.

I often see off-by-one issues like this using third party EVSEs. I have a 32 amp clipper creek EVSE we use to charge our other car, it very often only shows "31" amps when I use it to charge the Tesla. From what I can tell there's really no problem or issue to solve.

 

[GtiMart]

Yeah, that looks like a rounding error in display more than anything else...

 

[MA308]

Awesome, thank you for your replies!

 

[ewoodrick]

1) voltage is 209. And no, it remains steady at 29 amps. I can use the Tesla app and lower it to 25 or 20, but when I bring it up to 30, the charging app only displays 29amps being used.

2) fair enough not a huge difference. Mine was charging at 30-31km/h, the other Tesla was 37-38km/h

3) unsure of the specs. But both cars used the same cable and same adapter.

Thank you for your reply!
Overall I’m not concerned, just wondering if it’s a glitch or a solvable problem.

209 sounds low and it probably the reason why a car is dropping the charge rate. It should be closer to 240 and can be the result of an inferior socket, wiring, or breaker.

(Assuming that it is a residential installation)

Low voltage means that something has higher than expected resistance. Voltage drop across a resistance creates heat.

Too much heat can burn a car down.


It is VERY common when charging at these high currents that a socket can weaken.

 

[ucmndd]

209 sounds low and it probably the reason why a car is dropping the charge rate. It should be closer to 240 and can be the result of an inferior socket, wiring, or breaker.

(Assuming that it is a residential installation)

Low voltage means that something has higher than expected resistance. Voltage drop across a resistance creates heat.

Too much heat can burn a car down.


It is VERY common when charging at these high currents that a socket can weaken.

A wall connector showing 209 volts is almost certainly on a 3-phase 120/208v supply and is perfectly normal/nominal.

If the voltage actually did drop from ~240-209 the wall connector would back off the current by at least 50%, not just a single amp, and there would be error messages in the car explaining as much.

 

[Zuikkis]

The car and app show 30amp charging (level 2 charger), but the charging app I used for the level 2 charger only shows 29amps being used.

So 29A is the measured "real" current? does it have decimals or just integer measurement?

If you set charging amps to 30A, it sets the upper limit what car can draw from the socket. It will never be >30A, but typically something like 29.5A or 29.7A. Something safe that it won't trip a 30A breaker.

If your measured current only has integer precision, even a very small change can make it change between 29 and 30A.. like 29.49A probably shows as 29A but 29.50A might be 30A.

 

[ewoodrick]

A wall connector showing 209 volts is almost certainly on a 3-phase 120/208v supply and is perfectly normal/nominal.

If the voltage actually did drop from ~240-209 the wall connector would back off the current by at least 50%, not just a single amp, and there would be error messages in the car explaining as much.

That would make sense if it was installed at a business.
But exceptionally rare if installed at a residence.

Residential service in the US is center tapped 240V. (120/120V)

 

[ucmndd]

But exceptionally rare if installed at a residence.

Residential service in the US is center tapped 240V. (120/120V)

3-phase power is far from “exceptionally rare” at residences.

Single family homes? Maybe. But more than 30% of North Americans live in multi-unit dwellings where 3-phase is the norm and individual units are served by 2 of the 3 hot legs for 120/208.

And the rest of my post stands - what OP describes is absolutely not what would happen if a 240v circuit dropped to 209v under load, so your advice is misleading and not applicable.

 

[ks1972]

I think it’s a software issue. My 2020 model S was doing the exact same thing for months while my 3 showed correct amps in the app. It now displays correctly after 2023.7.10 update

 

[Rocky_H]

That would make sense if it was installed at a business.
But exceptionally rare if installed at a residence.

Rethink what the word "business" actually means there. Most condominiums and apartment buildings are "commercial" or "business" buildings. Lots of people live in those, and they usually will have 208V supplies. A suburb lot with a standalone stick-built house--sure, that usually does have the "residential" 240V supply. And with it showing 209V, that's definitely not from a 240V connection.