Optimal Charging Amperage

[jjrandorin]

There is no proof that any of this that you are talking about from a home user charging point of view (worrying about keeping the car awake longer for a few HOURS by slow charging, vs a few days, weeks etc) will matter even enough to measure over a 4-5 year period.

Right, none of this should be worried about, but you seem to want to worry about it. There is no proof that either leaving it at 10% for a few hours, or slow charging for a few hours is harmful to the battery.

What is NOT UP FOR DEBATE however, is that slower charging will keep the car awake longer, thus costing the person more money, and put more "miles" of usage on the battery. Whether the additional usage matters or not is up for debate, but what ISNT, is that the longer you keep the car awake, the more its going to cost to charge, and the more you will add usage (miles) to the battery.

You do you, though.

 

[!igs]

Right, none of this should be worried about, but you seem to want to worry about it. There is no proof that either leaving it at 10% for a few hours, or slow charging for a few hours is harmful to the battery.

What is NOT UP FOR DEBATE however, is that slower charging will keep the car awake longer, thus costing the person more money, and put more "miles" of usage on the battery. Whether the additional usage matters or not is up for debate, but what ISNT, is that the longer you keep the car awake, the more its going to cost to charge, and the more you will add usage (miles) to the battery.

You do you, though.

I'm not trying to debate what you claim is not debatable, but for some reason you keep going back to it.

Again, I am debating SOC and secondarily ROC, which is what this thread is about. I am not debating COC or EOC.

Different people have different priorities, maybe COC is imprtant to you but it's not to me and it's not what this thread is about.

 

[sleepydoc]

What is NOT UP FOR DEBATE however, is that slower charging will keep the car awake longer, thus costing the person more money, and put more "miles" of usage on the battery.

If it’s plugged in the power won’t come from the battery and there will be no extra ‘miles.’ The other thing you are neglecting is the increased power lost from higher current which may in fact negate the power used keeping the system on.

 

[jjrandorin]

If it’s plugged in the power won’t come from the battery and there will be no extra ‘miles.’ The other thing you are neglecting is the increased power lost from higher current which may in fact negate the power used keeping the system on.

From pretty much everything I have read here, that isnt actually the case. The power always comes from the battery, even if on shore power. The shore power just tops up the battery when it drops 2-3%. There also is no increased power lost from higher current, in fact, everything I have read both here and elsewhere states the opposite is the case. The car uses 250w of power just staying awake so the longer its awake, that drain is happening no matter what else is going on.

 

[sleepydoc]

There also is no increased power lost from higher current

And that is absolutely false. To dispute it shows complete ignorance of the facts of physics. Further discussion at this point is pointless.

 

[jjrandorin]

And that is absolutely false. To dispute it shows complete ignorance of the facts of physics. Further discussion at this point is pointless.

If you have something that shows that, for a Tesla model 3 or Y, higher L2 charging speed will result in more power lost than the 250w the car uses keeping the car awake, I would be interested to see it.

 

[Mrbrock]

If you have something that shows that, for a Tesla model 3 or Y, higher L2 charging speed will result in more power lost than the 250w the car uses keeping the car awake, I would be interested to see it.

He is not comparing it to your 250W figure. He is strictly going on say 240V X 20A vs 230V X 48A (example only not actual).

However, beyond that you are talking different parts of the equation. To Docs point, there is power loss, however, it is on the house side of the charger and isn’t power loss in the car relating to battery charging. To JJs point, the 250W draw is always there whether charging at low are high amperage. Look at 120V charging. The mIles per amp is lower because 250W is 17% of the power provided at 12A.

Relating To the power loss at higher amperage, you would need to measure the draw at the meter vs draw at the charger to see what losses are incurred on the house side of the equation. To assume all these costs are on the homeowner assumes a constant voltage supply at the meter. If that is the case, then I must have 260V at my meter because I see 250V at the car at 40A.

 

[davewill]

Jeez. All of this stuff is WAY down in the noise. If we're talking about 24-48a charging speeds, none of these efficiency or battery longevity claims are big enough to spend any time thinking about. If we're talking about 120v charging, then the car's fixed overhead becomes a significant concern, and upgrading to a faster method will result in real savings, otherwise do what's most convenient.

 

[MY-Y]

Jeez. All of this stuff is WAY down in the noise. If we're talking about 24-48a charging speeds, none of these efficiency or battery longevity claims are big enough to spend any time thinking about. If we're talking about 120v charging, then the car's fixed overhead becomes a significant concern, and upgrading to a faster method will result in real savings, otherwise do what's most convenient.

You are cluttering up an emotional thread with science, logic, and reason.

 

[TacoslayerSLR]

Anyone know what the battery drain is in sleep mode vs the supposed 250w while awake? Is that awake mode mostly computer stuff or is that factoring in the water pump/cooling system running or both? For those of you with the Tesla scan hardware (I forget the name) does that device give you the details?

 

[Big Earl]

Anyone know what the battery drain is in sleep mode vs the supposed 250w while awake? Is that awake mode mostly computer stuff or is that factoring in the water pump/cooling system running or both? For those of you with the Tesla scan hardware (I forget the name) does that device give you the details?

One of my cars has been parked for 5.5 weeks and has lost 7%. It has woken up three times to check and download new software.

 

[TacoslayerSLR]

One of my cars has been parked for 5.5 weeks and has lost 7%. It has woken up three times to check and download new software.

Thanks for the info Earl! What year/model/config? I'm driving a 2020 SLR

 

[Big Earl]

Thanks for the info Earl! What year/model/config? I'm driving a 2020 SLR

2018 dual motor Model 3 with 166,000 miles.

 

[dhanson865]

If you have something that shows that, for a Tesla model 3 or Y, higher L2 charging speed will result in more power lost than the 250w the car uses keeping the car awake, I would be interested to see it.

you are right that higher amps is likely to be lower power wasted. It isn't guaranteed that it's always the highest amps though.

on a 2012 Leaf Max efficiency for the 3.6KW charger was around 89% (maybe 89.5 or so). But around 12a not 16a.

on later leafs the Max efficiency for the 6.6KW charger was around 90% (maybe 90.5 or so). More amps is better on this one (the max amps it could take was also the max efficiency)

on the old Tesla Model S with dual chargers there were three peaks at 25A, 40A, and 80A but very low amps are swamped by that background power draw you were talking about. Absolute Best efficiency in those tests were at 40A.

Model S Gen2 Charger Efficiency Testing

(Been a while since I started a thread here! :P) I recently finished some efficiency testing on the Model S Gen2 chargers (pre-refresh, but VIN > ~20k). Tests were done at 240V single phase. 5 amps, 82.77% 10 amps, 89.53% 15 amps, 89.06% 20 amps, 90.04% 25 amps, 91.03% 30 amps, 90.37% 35...

teslamotorsclub.com

Someone would need to do testing like that on a Model Y to see if the most efficient point is max Amps (it probably is, but it might not be, it might be half of max or some multiple of 2 amps other than half max and full max).

and yep none of this matters for battery longevity / degradation. Charge as fast or slow as you want, the car won't care at these charging speeds. But your electrical bill might be higher or lower depending on the amps you select.

 

[dhanson865]

This is an example of a charger efficiency curve. Higher amps during charging is generally better. Higher Volts in the electrical supply is always better (for L1 and L2 AC charging) (240v is better than 208v is better than 120v).

note: it's only an example, not from a Tesla. But is likely a similar shape to a Tesla charger curve.

 

[mbdionio]

so for home charging, its better to be near the 30A range as we dont gain much in efficiency at 40ishA?

 

[dhanson865]

so for home charging, its better to be near the 30A range as we don't gain much in efficiency at 40ishA?

If you have Time of Use billing do whatever it takes to optimize for that.

If you have Peak Demand charges you should do whatever it take to minimize those.

If you pay a flat rate for energy you should find out what the optimal rate of charge is and if you aren't sure use the max.

30A vs 32A vs 40A the difference is minimal but if you don't like throwing money away charging at the higher rate at home is likely cheaper (assuming it doesn't trigger a Peak Demand charge).

If you are asking about 30A vs 40A for babying the car battery don't bother. It doesn't matter enough to even measure.

If you are asking about 30A vs 40A because you have poor wiring in your house get an electrician to run a fresh wire pull and then you don't need to worry. Or lower the amps and know you are paying more per charging session but less for skipping the wiring upgrade. As long as your house doesn't catch on fire the difference in cost per charge won't be noticeable.

 

[MB11]

Just trying to charge my new MY LR for the first time tonight, before plugging anything in I went to the charging screen and tried to schedule it for my off-peak time (1:30 - 8:30). The screen shows a maximum charge rate of 16a, although my home charger is 32a? There doesn’t appear to be any way to move it past 16a to 32, the + burton is grey out When you get to 16a. Any advise welcome?

 

[dhanson865]

Just trying to charge my new MY LR for the first time tonight, before plugging anything in I went to the charging screen and tried to schedule it for my off-peak time (1:30 - 8:30). The screen shows a maximum charge rate of 16a, although my home charger is 32a? There doesn’t appear to be any way to move it past 16a to 32, the + button is greyed out When you get to 16a. Any advise welcome?

Power Conversion System (PCS) failure is one possibility (warranty will pay for the repair)

Charging Goes from 32A to 16A is another (Overheating at the plug, the adapter not fully inserted in the UMC, or a bad connection somewhere between the breaker and the outlet.)

best to follow up in one of those threads (whichever seems to apply)

 

[sleepydoc]

This is an example of a charger efficiency curve. Higher amps during charging is generally better. Higher Volts in the electrical supply is always better (for L1 and L2 AC charging) (240v is better than 208v is better than 120v).

note: it's only an example, not from a Tesla. But is likely a similar shape to a Tesla charger curve.

View attachment 854319

higher amps always means higher power loss. For a given power, higher voltage means lower amperage and thus lower power loss/higher efficiency.

In general, there are 3 sources of losses in charging:

1. The power used by the car to stay awake
2. losses due to the resistance of the circuit
3. and energy used to cool the battery from number 2.

Number 1 increases linearly with time to charge. Number 3 is dependent on number 2 as well as the ambient temperature. Number 2 increases with the square of the current (doubling the current means 4x the resistive power loss.) This also includes resistive losses in the equipment that connects to the car. If you don’t believe number 2 is an issue, then ask yourself why Tesla built cooling lines into the battery? I also saw a post a while back from someone complaining that the cabin got to 90º F while they were supercharging. They didn’t understand that the A/C was being used to cool the battery temp and had limited capacity to cool the cabin on top of that.

At some point number 1 will be balance by numbers 2 and 3. Exactly where that point is is difficult for anyone here to say without more data.