Questions regarding charging

[DRS247]

Hi all,

In the car we can change the maximum current (can set it up to 16A in M3.. don’t know if it’s different in S/X). My question is, how does reducing the current affect the charging speeds on both AC n DC (supercharger) charging ? Will it impact the maximum charging speed ? For eg in case of AC, I can charge it at up to 11kW, but how will this be affected if I reduce the maximum current from 16A to 10A for eg. ?
Just trying to understand why this option to change charging current exists and how does it affect charging.

Thanks a lot for your answers.

 

[jjrandorin]

Welcome to TMC.'

The short answer is, all home charging is slow charging to the car, and slowing the charging down simply keeps the car awake longer (resulting in more energy used).

 

[RayK]

And Supercharging is DC and that does not allow you to reduce the charge current manually.

As to WHY you can reduce the current when Level 1 and 2 (120VAC and 240VAC) charging, I can guess there may be these reasons:

• If you figure the math correctly, reducing the charge current will stretch out the charging session so that your car will be fully charged (to whatever level you have specified) just before you leave
• If there is a problem with your power connection (dirty socket, bad connection), reducing the current will also reduce the amount of heat generated
• While it's not recommended to be on a shared circuit, if your 120V/240V outlet is also shared with some other equipment, lowering the current may prevent the breaker from tripping

 

[Don.Church]

And, you cannot change any amp setting while DC charging.
The amp setting is only for AC charging, which may be helpful if you have electrical infrastructure limitations. Normally the car will pick the proper amperage.

 

[DRS247]

And Supercharging is DC and that does not allow you to reduce the charge current manually.

As to WHY you can reduce the current when Level 1 and 2 (120VAC and 240VAC) charging, I can guess there may be these reasons:

• If you figure the math correctly, reducing the charge current will stretch out the charging session so that your car will be fully charged (to whatever level you have specified) just before you leave
• If there is a problem with your power connection (dirty socket, bad connection), reducing the current will also reduce the amount of heat generated
• While it's not recommended to be on a shared circuit, if your 120V/240V outlet is also shared with some other equipment, lowering the current may prevent the breaker from tripping

Thanks for the reply.
I figured that changing Amperes would only impact AC charging. I’m looking to confirm my understanding of how exactly (numerically) would changing the Amperes impact charging speeds.
My current understanding is
A = 16Amperes
V = 240Volts
Power = 16x240x3 (for three phase AC) = 11,5 Kw

If I reduce A to 11A in the car the charging speed will reduce to
11x240x3 = 7,9 Kw.

Is this correct ? I charge my car on public charging infrastructure for my daily use and only use supercharger for trips. on Public AC chargers, the price of KwH changes drastically if I charge at speeds beyond 8Kw. Thats why I am trying to figure if I can change A within the car’s settings to charge it at less than 8Kw.

Thanks again!

 

[Big Earl]

Thanks for the reply.
I figured that changing Amperes would only impact AC charging. I’m looking to confirm my understanding of how exactly (numerically) would changing the Amperes impact charging speeds.
My current understanding is
A = 16Amperes
V = 240Volts
Power = 16x240x3 (for three phase AC) = 11,5 Kw

If I reduce A to 11A in the car the charging speed will reduce to
11x240x3 = 7,9 Kw.

Is this correct ? I charge my car on public charging infrastructure for my daily use and only use supercharger for trips. on Public AC chargers, the price of KwH changes drastically if I charge at speeds beyond 8Kw. Thats why I am trying to figure if I can change A within the car’s settings to charge it at less than 8Kw.

Thanks again!

Correct!

 

[Resist]

Wish we could change the Amp setting with DC charging, so we'd have more time to get something to eat. Since Tesla increased the charging speeds, never is enough time to do anything yet too long to stay in the car.

 

[DRS247]

Wish we could change the Amp setting with DC charging, so we'd have more time to get something to eat. Since Tesla increased the charging speeds, never is enough time to do anything yet too long to stay in the car.

Yes I totally hear you.
To counter that, for city use I only ever use supercharging when I really don’t have much battery left (around 15%). Charging from that level to 100% (I have LFP) takes sometime so I can do whatever N not just sit in the car.
On trips I just follow the itinerary the car tells me to with the stops for charging. And I don’t really need/want charging to take long in this case so it’s perfect. Also, I don’t wait to get to 100% while supercharing on trips as post 80-85% charging slows down.

 

[GtiMart]

Wish we could change the Amp setting with DC charging, so we'd have more time to get something to eat.

No! We all want you out of there pronto!

 

[Resist]

Yes I totally hear you.
To counter that, for city use I only ever use supercharging when I really don’t have much battery left (around 15%). Charging from that level to 100% (I have LFP) takes sometime so I can do whatever N not just sit in the car.

The problem with charging to 100% is that while it will give you time to go get something to eat, if other cars fill up the station then your charge limit will be reduced and then you can get an idle fee. So Keep an eye on the app run like crazy to get back if it notifies you.

 

[Big Earl]

The problem with charging to 100% is that while it will give you time to go get something to eat, if other cars fill up the station then your charge limit will be reduced and then you can get an idle fee. So Keep an eye on the app run like crazy to get back if it notifies you.

I’ve never seen the charge limit get reduced during a charging session.

 

[Rocky_H]

Sure, keep an eye on the app, but you wouldn't have to "run like crazy" to go back to the car. If it does turn down your charge limit to 80% and you see it in the app, you can raise it back up there in the app.

 

[Resist]

I just charged today and I had it set to 100% but it stopped at 80% because of the station being busy, it did say it would do that and it did. I didn't even think to try and raise the limit back up to 100% via the app. So I can't confirm that works.

 

[RayK]

In my experience, it does work. However, I only went to 90% after being told the station was busy and the limit would be (and was) changed to 80%.

 

[Rocky_H]

@Resist If you're in the car and it first shows that message that it's lowering your limit, it even says right there that you can raise it back up higher if you really need more. So yes, it does work.

 

[Resist]

@Resist If you're in the car and it first shows that message that it's lowering your limit, it even says right there that you can raise it back up higher if you really need more. So yes, it does work.

I didn't pay that close of attention to the message, so thanks, I will next time.

 

[theothertom]

I’ve never seen the charge limit get reduced during a charging session.

I've had my charge limit limited to 80% if the charger location is busy. I don't remember if I got an alert when I plugged in, or the alert came when the charge neared 80%. In some cases, I needed more than 80%, so I had to go back to the car, unplug and plug back in again to restart the charge to get to my preset limit (which was >80%).

 

[derotam]

I've had my charge limit limited to 80% if the charger location is busy. I don't remember if I got an alert when I plugged in, or the alert came when the charge neared 80%. In some cases, I needed more than 80%, so I had to go back to the car, unplug and plug back in again to restart the charge to get to my preset limit (which was >80%).

The way it has worked in the past, and I don't believe this would have changed...is that when you arrive at a SC and it is congested, when you plug in it will set the limit to 80% and give a notification on the screen. You can change it back up to 100% at that time, or you can do it in the app. Obviously some people will just plug their car in and then walk away right away so they won't know unless they looked at their app.

 

[theothertom]

is that when you arrive at a SC and it is congested, when you plug in it will set the limit to 80% and give a notification on the screen.

Thanks. Yeah, I typically walk away and the alert comes later.

 

[Randy-12]

Thanks for the reply.
I figured that changing Amperes would only impact AC charging. I’m looking to confirm my understanding of how exactly (numerically) would changing the Amperes impact charging speeds.
My current understanding is
A = 16Amperes
V = 240Volts
Power = 16x240x3 (for three phase AC) = 11,5 Kw

If I reduce A to 11A in the car the charging speed will reduce to
11x240x3 = 7,9 Kw.

Is this correct ? I charge my car on public charging infrastructure for my daily use and only use supercharger for trips. on Public AC chargers, the price of KwH changes drastically if I charge at speeds beyond 8Kw. Thats why I am trying to figure if I can change A within the car’s settings to charge it at less than 8Kw.

Thanks again!

This might help you out.
From the wall connector page, shows the amp and mile/hr charge

Wall Connector

The Tesla Wall Connector is the most efficient way to charge a Tesla at home — just plug in your vehicle overnight and wake up to a charged vehicle.

www.tesla.com

Please refer to the table below for charging speeds for each power level option.

Wall Connector Technical details	Charge Speed Max miles of range per hour of charge*
Circuit breaker (amps)	Maximum output (amps)	Power at 240 volts (kilowatt)	Model S (mph)	Model 3† (mph)	Model X (mph)	Model Y (mph)
60	48	11.5 kW	41	44	35	44
50	40	9.6 kW	34	37	29	37
40	32	7.7 kW	27	30	23	30
30	24	5.7 kW	21	22	17	22
20	16	3.8 kW	14	15	12	15
15	12	2.8 kW	10	11	9	11

*All charge speeds are approximate.
†Maximum charge rate for Model 3 Rear-Wheel Drive is 32A (7.7kW) - up to 30 miles of range per hour.