Charging to 100% at home on the wall charger, is there a taper?

[A-Wimoweh]

So I'm going on a road trip tomorrow afternoon, and I want to start with the car at 100%. I usually only charge to 80%, and just let it go overnight, without any worry as to when it finishes. But I want the 100% to finish about 30 minutes to an hour before I leave.
When charging from say like 60% to 80% I'll see 11 to 12 kwh at 48 amps, 238V or so. Will this rate continue all the way up to 100%? If I am at 80%, how long will it take to charge the rest of the way to 100%? Brand new S75D, with about 1200 miles on it.

 

[cpa]

Yes, there is a taper on a wall charger. However, it does not kick in until around 95% depending upon current, at least that is what I recall from memory. The final 5% or so will take 30+ minutes if I recall correctly.

 

[gaswalla]

no taper (it's actually related to balancing of the battery vs a taper like at a supercharger) but the car charges from 98/99% to 100% VERY slowly (1-5 amps) especially if you haven't charged up to a 100% for a while. I would not worry about letting the car sit at 100% for even a couple of hours.
If you want to time it, set the range to 100% and then start charging immediately and look at the time remaining (eg: 6 hours).. then, add an extra hour to that time.. your car will require that amount of time to reach 100%

 

[A-Wimoweh]

So I guess the way to approach this is when I put the car on the charger tonight, set the charge to 100%, and see how long the car it thinks it will take to complete the charge. Then adjust the charging rate so that the charge time will finish about 2 hours before I want to leave tomorrow?

 

[Tslrsx]

So I guess the way to approach this is when I put the car on the charger tonight, set the charge to 100%, and see how long the car it thinks it will take to complete the charge. Then adjust the charging rate so that the charge time will finish about 2 hours before I want to leave tomorrow?

Good idea

 

[ewoodrick]

From simply a using the car perspective. Set it for 100% and let it charge. It doesn't matter if it sits at 100% for a few hours, that's not going to damage the battery.

If you would rather it take the entire period, just reduce the charge rate until it stops when you want. I don't know how precise this will be though.

Yes, there is a taper.

Just enjoy the car, don't fret over the charging.

 

[Tech_Guy]

I usually set my car to 90% the night before and then about 1- 1.25 hours before I want to leave I set it to 100% and it will be 99 or 100% in that time. Keep in mind I have a High Amp charger / 90 Amp Circuit that charges my car at 72 Amps vs the 48 Amp Standard charger so you might want 2 hours before if you have the slower charger... The car does taper the charging rate but only when its 95% or more as it can't overcharge the battery it will get slower as the battery gets fuller.

 

[mknox]

Yes, there is a taper on a wall charger. However, it does not kick in until around 95% depending upon current, at least that is what I recall from memory. The final 5% or so will take 30+ minutes if I recall correctly.

This is how I recall the taper working as well. However, my final 5% could take several hours depending how out of balance the pack was. I noticed my March 2018 Model X 100D starting to taper at about 85%. I send my home energy monitor logs to Tesla and they checked them along with the logs they pulled from my car. They say this is (now?) normal.

 

[ucmndd]

This is how I recall the taper working as well. However, my final 5% could take several hours depending how out of balance the pack was. I noticed my March 2018 Model X 100D starting to taper at about 85%. I send my home energy monitor logs to Tesla and they checked them along with the logs they pulled from my car. They say this is (now?) normal.

Sometimes mine will do the same, with charge trickling in at 1-2kw for an extended period even after the battery is at “100%”.

 

[Tech_Guy]

So I wanted to provide some extra info to the thread... heres my most recent charge graphs for a 90% charge and a 100% charge.

As you can see no charge tapering occurred in the 90% charge at all it maintained 72 amps throughout the charge.

On the 100% charge you can see the taper occurred at 97% when it was almost to 98% charge

 

[Russell]

So I guess the way to approach this is when I put the car on the charger tonight, set the charge to 100%, and see how long the car it thinks it will take to complete the charge. Then adjust the charging rate so that the charge time will finish about 2 hours before I want to leave tomorrow?

Yes that works. That's what I do.

 

[gnuarm]

So I guess the way to approach this is when I put the car on the charger tonight, set the charge to 100%, and see how long the car it thinks it will take to complete the charge. Then adjust the charging rate so that the charge time will finish about 2 hours before I want to leave tomorrow?

Sounds like an option to add to the charging screen, start charging in time to reach the goal by some time point.

But this assumes it is important to not leave the car at 100% for very long in terms of hours. I believe there is a graph of data on a variety of charging situations which shows even full time 100% charging results in minimal degradation of the battery.

 

[scaesare]

I usually set my car to 90% the night before and then about 1- 1.25 hours before I want to leave I set it to 100% and it will be 99 or 100% in that time. Keep in mind I have a High Amp charger / 90 Amp Circuit that charges my car at 72 Amps vs the 48 Amp Standard charger so you might want 2 hours before if you have the slower charger... The car does taper the charging rate but only when its 95% or more as it can't overcharge the battery it will get slower as the battery gets fuller.

Generally my approach as well, although it can take 90-120 minutes to actually reach 100%... however it's always the last 2% that can stretch out the last half hour, so at that point I unplug and go...

 

[mknox]

So I wanted to provide some extra info to the thread... heres my most recent charge graphs for a 90% charge and a 100% charge.

Here is a curve from my home energy meter with the car charging from 67 to 90% SOC. I was charging at 240 volts, 30 amps. I don't have the SOC mapped, but it starts to taper somewhere around 80%. I sent the data to Tesla to investigate, and they told me it was perfectly "normal".

 

[sorka]

When my P85D was new, it my 80 amp HPWC would stay at 19KW until about 98% before tapering down.

Now at 76K miles, it starts tapering at 93%. By 95% it's down to 40 amps. I don't know if it's due to battery age or software changes to be intended to stress the battery less when charging to full.

Given my voltage drop at 1600 amps is barely more than it was new, I suspect the latter since I haven't had any obvious increase in IR.

 

[animorph]

Here's my X (72A max) charging to 100% on an HPWC. TeslaFi data at 1 minute intervals so it's a little choppy:

X-axis is SoC in percent, Y-axis is charge power in Watts (about 17 kW at full power)

The actual starting SoC was 20%, but charge power was constant up to 97%.
Tapering is starting at 97%-98% and falls like a rock. Though it's a slow rock.
The taper lasted 37 minutes from 98% to "charge complete". It registered 100% for 26 minutes of that.
The entire 80% to complete 100% charge took 107 minutes.

I assume a 32A charge would taper at higher SoC like 99% to 100%, wherever the charge power matches the taper power here.