Range Loss Over Time, What Can Be Expected, Efficiency, How to Maintain Battery Health

[jpbelair66]

2021 M3 standard plus. Have a 240v nema 14-50 charger in garage.
So, what is the cheapest/most efficient way to charge the car? we have a 3.84kwh solar set up at home.
Best to charge at like 20a when the sun is shining until 4pm( when it’s peak electricity rates)? And or let it trickle charge in the middle of the night at like 5-10a until the sun comes out.

If we do have to charge at night, what amps are the best of time is not a factor, but we want to keep cost down?

Does it matter if we charge at night at 15a vs 20a for 8 hrs? Besides the range of course

What’s the best for the battery? Long slow charging?

Thx!

 

[dhrivnak]

If you have the same power rates it does not matter, Does not matter at all. But if rates are cheaper at night I would use it. It will not matter to the car. 15 to 20 amps really does not matter. If rates are the same you can do like I do and typically charge during the day when the sun is shining. It makes me feel good but the reality it does nothing, not to the car or the grid. For the record I do believe that slower charging, with at least 240 is likely SLIGHTLY better. Faster typically wears all things out quickly.

 

[jjrandorin]

2021 M3 standard plus. Have a 240v nema 14-50 charger in garage.
So, what is the cheapest/most efficient way to charge the car? we have a 3.84kwh solar set up at home.
Best to charge at like 20a when the sun is shining until 4pm( when it’s peak electricity rates)? And or let it trickle charge in the middle of the night at like 5-10a until the sun comes out.

If we do have to charge at night, what amps are the best of time is not a factor, but we want to keep cost down?

Does it matter if we charge at night at 15a vs 20a for 8 hrs? Besides the range of course

What’s the best for the battery? Long slow charging?

Thx!

All home charging is slow charging. all of those are fine, none if it will make any difference to charging your car. Whats best for you will depend on your electricity plan, rates, home usage, how much you are sending to the grid, when, etc.

Just dont charge the car between 4-9 at peak electricity rates. The rest of it you will have to figure out from your own home usage. Its not going to matter to the car in any way, shape or form.

 

[AlanSubie4Life]

Thanks. Puts my mind at ease. I may be over analyzing Tesla data

Yep it is no big deal. You have (presumably) a 2018 or 2019 with about 14% capacity loss, about 67kWh including the buffer, give or take ~1kWh. Very normal.

 

[rfgarza8]

Yep it is no big deal. You have (presumably) a 2018 or 2019 with about 14% capacity loss, about 67kWh including the buffer, give or take ~1kWh. Very normal.

Thanks. She's slowly climbing up a bit. Going to try to not charge daily and let the BMS take readings at different levels to see if I can improve it a bit.

 

[fishacura]

I didn't realize the M3 gives you the ability to set the power draw. I just had a NEMA 14-50 installed. I think the max for the M3 is 32 Amps. But here's my question:

Given my daily commute I think I could charge at far less than 32A and be fully charged overnight. Is there a proven benefit to lowering the amps to the lowest number that will still give me an overnight full charge or is there zero long term benefit to that and I should just set it to max?

Thx!!!

 

[jjrandorin]

Is there a proven benefit to lowering the amps to the lowest number that will still give me an overnight full charge or is there zero long term benefit to that and I should just set it to max?

Zero long term benefit as far as battery health. All home charging is "slow charging" to the car.

 

[Rocky_H]

Given my daily commute I think I could charge at far less than 32A and be fully charged overnight. Is there a proven benefit to lowering the amps to the lowest number that will still give me an overnight full charge or is there zero long term benefit to that and I should just set it to max?

Zero long term benefit as far as battery health. All home charging is "slow charging" to the car.

@fishacura For the car, it doesn't care in the least. You're questioning the difference between 7 kW or something less than that for something that can accept over 200 kW charging power. That's not going to make any difference at all. Where there might be some benefit (and something I am doing) is possibly not wearing out your charging cord as fast if you are using the charging cable that came with it. It is built and rated to run at 32A maximum and can get kind of warm running at maximum level every day. Those cycles of hot/cold/hot/cold every day can cause some stress on electrical connections and electronics, so turning it down a little bit from 32A if you don't need that every day will probably extend the life of your cable by keeping it cooler.

 

[rfgarza8]

New Tesla owner here. I have access to Teslafi and learning the metrics. What story is this telling me?

Good? Bad? Any info will help. Thanks!

 

[jjrandorin]

New Tesla owner here. I have access to Teslafi and learning the metrics. What story is this telling me?

View attachment 741243

Good? Bad? Any info will help. Thanks!

It doesnt tell you anything, really. a 5 mile drive wont tell you a thing. Actually, what it tells you is.....

Thanks. Puts my mind at ease. I may be over analyzing Tesla data

 

[rfgarza8]

It doesnt tell you anything, really. a 5 mile drive wont tell you a thing. Actually, what it tells you is.....

Touché! Lol.

 

[AlanSubie4Life]

New Tesla owner here. I have access to Teslafi and learning the metrics. What story is this telling me?

View attachment 741243

Good? Bad? Any info will help. Thanks!

It tells you TeslaFi uses 245Wh/rmi (217*1.13) for the rated efficiency for your car. (Rmi is a rated mile, a measure of energy, not a measure of distance.)

Note however that while that is the correct constant for a 2018/2019, the discharge constant is 95.5% of that, due to the 4.5% buffer, so get about 234Wh/mi if you want mile-for-rated mile rolloff. In reality it is ~1% lower than this, or about 230Wh/mi for “parity,” due to unmetered “heat” losses.

The charging constant is just a nominal hard coded value and you can’t use it in calculations to determine how much energy your car has used. It’s only applicable when calculating your full capacity (because that value includes the buffer so it’s appropriate to use the full 100% value of the constant in that case).

 

[jpbelair66]

@fishacura For the car, it doesn't care in the least. You're questioning the difference between 7 kW or something less than that for something that can accept over 200 kW charging power. That's not going to make any difference at all. Where there might be some benefit (and something I am doing) is possibly not wearing out your charging cord as fast if you are using the charging cable that came with it. It is built and rated to run at 32A maximum and can get kind of warm running at maximum level every day. Those cycles of hot/cold/hot/cold every day can cause some stress on electrical connections and electronics, so turning it down a little bit from 32A if you don't need that every day will probably extend the life of your cable by keeping it cooler.

But what about cost from the grid? 10 ,20,32amps. Higher amps must cost more yes?
I need to figure what the max is for our solar panels ( 3.84kwh max)

 

[Candleflame]

But what about cost from the grid? 10 ,20,32amps. Higher amps must cost more yes?
I need to figure what the max is for our solar panels ( 3.84kwh max)

no because private households do not pay extra for demand charges.
you do loose charge efficieincy when charging faster (Sweetspot i think was 5kw or something like that), however, charging for longer also causes some vampire drain as the car systems need to be supplied with electricity so charging at 11kw is just the best.

 

[Tazzman]

But what about cost from the grid? 10 ,20,32amps. Higher amps must cost more yes?
I need to figure what the max is for our solar panels ( 3.84kwh max)

On the weekends when I am home I use the extra power from my solar panels to charge my car. Other then that you have to watch the time of day you charge depending on your electric rates.

 

[ElectricIAC]

Yep it is no big deal. You have (presumably) a 2018 or 2019 with about 14% capacity loss, about 67kWh including the buffer, give or take ~1kWh. Very normal.

That seems excessive, no?

 

[Rocky_H]

But what about cost from the grid? 10 ,20,32amps. Higher amps must cost more yes?

No, not at all. Residential electricity is by the quantity of energy used, not by how fast you use it. It doesn't have the peak power demand charges like some industrial plans use, which @Candleflame mentioned.

 

[AlanSubie4Life]

That seems excessive, no?

No; it’s normal for these packs, though less is certainly possible.

 

[ElectricIAC]

No; it’s normal for these packs, though less is certainly possible.

That’s worrisome, even our somewhat abused BTX5 Model X (high DCFC use) has only seen 7% degradation over 53K miles meanwhile our P3D with 46K is showing closer to 10% degradation with mostly AC charging.

 

[bedoig]

That’s worrisome, even our somewhat abused BTX5 Model X (high DCFC use) has only seen 7% degradation over 53K miles meanwhile our P3D with 46K is showing closer to 10% degradation with mostly AC charging.

Welcome to the club!

On the plus side, you can see the tapering off of losses.