48 amps and battery health

[Laguna M3]

Just installed my Wall Connector and am wondering if it's better to charge overnight as 48 amps, or to reduce it down to 32 amps for long-term battery health. I can easily get the charge I need overnight at 32 amps, so 48 is unnecessary. Having 48 will be nice when I need faster daytime charging.

Also, is it safer to charge at 32 given some of the issues the Gen 3 Wall Connector has had with some users.

 

[drtimhill]

Just installed my Wall Connector and am wondering if it's better to charge overnight as 48 amps, or to reduce it down to 32 amps for long-term battery health. I can easily get the charge I need overnight at 32 amps, so 48 is unnecessary. Having 48 will be nice when I need faster daytime charging.

Also, is it safer to charge at 32 given some of the issues the Gen 3 Wall Connector has had with some users.

No real difference for the car, it’s in the noise floor compared to (say) supercharging. But bear in mind there is a certain fixed overhead power draw that goes to non-charging tasks, so charging at 48A is more efficient overall (and thus cheaper).

 

[Laguna M3]

No real difference for the car, it’s in the noise floor compared to (say) supercharging. But bear in mind there is a certain fixed overhead power draw that goes to non-charging tasks, so charging at 48A is more efficient overall (and thus cheaper).

Thank you for the reply. What do you mean by noise floor?

 

[jcanoe]

You may be able to sign up for a time of use (TOU) 5 rate plan with your local power utility. This provides a much lower off-peak charging rate from 1200 to 0600 AM. If you have the Wall Connector set up for 48 amps I would use it that way but you can set the maximum charging amperage lower if you want. The battery pack is so much larger in capacity (78kWh total capacity) than the 240V/48A (11.5kW) maximum charging rate that the higher setting will not have a measurable impact on the life of the battery pack.

 

[frankvb]

Thank you for the reply. What do you mean by noise floor?

While the car is 'on' (could be driving/charging/sentry mode) it will draw a few 100 W just to keep its systems running. So it's slightly more efficient to charge at a higher rate as the car needs to stay 'on' for a shorter time.

 

[SSedan]

When thinking of fast vs slow charging think about the time to charge from empty to full.
Is 5-6-7hours to fully charge from empty fast charging? No it's not, not even close.

 

[Laguna M3]

You may be able to sign up for a time of use (TOU) 5 rate plan with your local power utility. This provides a much lower off-peak charging rate from 1200 to 0600 AM. If you have the Wall Connector set up for 48 amps I would use it that way but you can set the maximum charging amperage lower if you want. The battery pack is so much larger in capacity (78kWh total capacity) than the 240V/48A (11.5kW) maximum charging rate that the higher setting will not have a measurable impact on the life of the battery pack.

Thank you. I have solar and am on a TOU plan that has very low rates from midnight to 6am.

 

[jcanoe]

Thank you. I have solar and am on a TOU plan that has very low rates from midnight to 6am.

Depending on your daily charging needs the 48A charging setting could be an advantage. The higher charging level (11.5kW) would help to ensure that your charging session would be able to complete within the off-peak rate charging window i.e. 1200 to 0600 AM.

 

[Laguna M3]

Depending on your daily charging needs the 48A charging setting could be an advantage. The higher charging level (11.5kW) would help to ensure that your charging session would be able to complete within the off-peak rate charging window i.e. 1200 to 0600 AM.

I suppose if my battery is really low that it would help. It's good to know that from a battery health perspective that it doesn't matter either way.

 

[drtimhill]

Thank you for the reply. What do you mean by noise floor?

The car is capable of being charged from a humble 120V outlet all the way up to a 250kW V3 supercharger. Although a matter of some debate, in general you can assume the lower power charging modes are more “gentle” on the battery (but don’t take that to mean you should never supercharge!). However, the difference between (say) a 32A and 40A 240V charge rate is so small as to be negligible when it comes to battery health.

 

[TMills]

I have had a model Y for a short time now. We have supercharged once but charge at home daily to 80%.
Although I do know little about the Tesla charge system I know quite a lot about electrical systems. In my opinion I charge on my 240 nominal L2 charger at home at a lower amperage between 10-20a. My thoughts are that at these lower amps there is less voltage drop in the circuit.
I like to see the AC voltage running at 241-245. I feel at the lower amperage/higher voltage it results in less voltage drop and less heat lost within the conductors serving the EVSE.
If I crank it up to 40a the voltage sags to 236. I’m ignorant of the Tesla charging system but from a wiring efficiency viewpoint 16a/242VAC is more efficient than 40a/236VAC.
Now this is purely talking electrical efficiency. Of course if I need to charge up in a couple hours I would not be doing this. Regularly having over 8 hrs to charge it does not bother me to set it at a lower rate.
If I am wrong about any of this I would like to learn why.

 

[drtimhill]

If I crank it up to 40a the voltage sags to 236. I’m ignorant of the Tesla charging system but from a wiring efficiency viewpoint 16a/242VAC is more efficient than 40a/236VAC.
Now this is purely talking electrical efficiency. Of course if I need to charge up in a couple hours I would not be doing this. Regularly having over 8 hrs to charge it does not bother me to set it at a lower rate.
If I am wrong about any of this I would like to learn why.

You've left out one important variable. The car takes a fixed load to run the various charging systems and computers. So, for any charge power input to the car, you need to subtract that fixed power load to get the actual power that is being delivered to charge the battery. So, of course, the longer you charge, the more excess energy is used by the various systems. At 110V (in the US), the fixed load is a VERY significant percentage of the wall power. For 240V its less so, but this still means that the faster you charge the car the less energy is used by the charging systems, so that tends to mean higher current means more efficient charging.

I'm surprised you see this much voltage sag at higher currents, is your wiring up to code?

 

[TMills]

You've left out one important variable. The car takes a fixed load to run the various charging systems and computers. So, for any charge power input to the car, you need to subtract that fixed power load to get the actual power that is being delivered to charge the battery. So, of course, the longer you charge, the more excess energy is used by the various systems. At 110V (in the US), the fixed load is a VERY significant percentage of the wall power. For 240V its less so, but this still means that the faster you charge the car the less energy is used by the charging systems, so that tends to mean higher current means more efficient charging.

I'm surprised you see this much voltage sag at higher currents, is your wiring up to code?

Yes it’s hardwired directly to the main distribution panel. It’s a clipper creak HCS-50. Very short run. I was able to use the conductors that came with the EVSE. I was able shorten them by a 6” too. The service is supplied by 4/0 al.

 

[mrwug]

I have had a model Y for a short time now. We have supercharged once but charge at home daily to 80%.
Although I do know little about the Tesla charge system I know quite a lot about electrical systems. In my opinion I charge on my 240 nominal L2 charger at home at a lower amperage between 10-20a. My thoughts are that at these lower amps there is less voltage drop in the circuit.
I like to see the AC voltage running at 241-245. I feel at the lower amperage/higher voltage it results in less voltage drop and less heat lost within the conductors serving the EVSE.
If I crank it up to 40a the voltage sags to 236. I’m ignorant of the Tesla charging system but from a wiring efficiency viewpoint 16a/242VAC is more efficient than 40a/236VAC.
Now this is purely talking electrical efficiency. Of course if I need to charge up in a couple hours I would not be doing this. Regularly having over 8 hrs to charge it does not bother me to set it at a lower rate.
If I am wrong about any of this I would like to learn why.

Resistive losses in your wiring aren't the only source of inefficiency. Someone here collected data on their car and it appeared that the greatest L2 efficiency (measured by increased battery KWh relative to KWh flowing through the EVSE) was around 40A. I'm too lazy to find it for you but the thread is out there if you're interested in details. Usual caveats about limited sample size apply.

 

[TMills]

Resistive losses in your wiring aren't the only source of inefficiency. Someone here collected data on their car and it appeared that the greatest L2 efficiency (measured by increased battery KWh relative to KWh flowing through the EVSE) was around 40A. I'm too lazy to find it for you but the thread is out there if you're interested in details. Usual caveats about limited sample size apply.

I’ll search it out. I am getting a home energy monitor one of these days. The Wiser unit. Maybe if it can tease out the EVSE I’ll be able to do some testing. Measure kWh drawn and compare it to KWh delivered into the Tesla at a couple different charge rates.