Charging speed not slowing down at 90% SOC when using a 50kwh DC charger.

[iten]

Is it normal? I have been getting 48kwh regularly in different DC charger after hitting 85%.

When I super charge my Teslas, it always drop to below 20kwh after 80%.

I don't want to damage my battery....

I have been monitoring my battery temperature, and it's around 31-2 degree Celsius after DC charging.

Sponsored

 

[NC_Taycan]

You can't rely on battery temperature alone - it's state of charge and the time the battery is at a high state of charge. Assume anything < 85% on the Taycan battery is inconsequential. As you charge from 85% to 100% you are increasing stress on the cell anodes / cathodes, and the longer the cells are under stress, the greater the accumulated damage. A high rate of charge will also cause stress, but the battery controller will be forced to slow the charge rate at high SoC since the chemical reactions during charging must slow as there is less physical opportunity for the actual reaction to occur (e.g. less places on the nearly full anode to accept lithium ions from the cathode).

 

[chrisk]

Is it normal? I have been getting 48kwh regularly in different DC charger after hitting 85%.

When I super charge my Teslas, it always drop to below 20kwh after 80%.

I don't want to damage my battery....

I have been monitoring my battery temperature, and it's around 31-2 degree Celsius after DC charging.

Mine slows down once it hits 85%.
The attached graph is from a ChargePoint 50kwh charger. You can see the rate was steady close to 50kwh and then it starts gradually dropping until it was fully charged. It is not shown in the graph but the drop started when SoC was 85%.

 

[Reg]

As you charge from 85% to 100% you are increasing stress on the cell anodes / cathodes, and the longer the cells are under stress, the greater the accumulated damage. A high rate of charge will also cause stress, but the battery controller will be forced to slow the charge rate at high SoC since the chemical reactions during charging must slow as there is less physical opportunity for

could you explain that a bit more? I get what you are saying and I have heard it before, but I don’t understand the engineering/physics of it.

for example, why is it worse to charge from 85 to 95 at 100kw than it is to charge from 50 to 60 at 100kw.

naively, to me it seems that it is the same about of energy going in at the same rate

 

[daveo4EV]

it's a forcing function - as you get closer to "full" you have to taper the charge rate to not over tax each LiON cell - a battery engineer can explain it in detail - but the summary is as follows:

as LiON cells get closer to "full" you taper the charge rate so as not to damage the cell - charging the cells at a "fixed/linear" maximum rate will cause long term damage.

I know this to be true, but lacking a back ground in the electro-chemistry I can't tell you why…but it is true.

one of my co-workers who does batteries for a living says the following:

you can do most anything you want to a LiON cell, charge it, discharger, overcharge it, over discharge it - but if you do that it won't last very long.

The real trick is to do all those things and also have the battery last. To have a LiON battery "last" a long time (a high number of charge & discharge cycles) you do the following:

1. never charge or discharge it outside it's ideal range
2. don't let the battery sit near empty for very long
3. don't let the battery sit at full (100%) for very long
4. don't charge at it's near full rate continuously
5. don't run the battery from full to empty a lot
6. don't fast charge it all the time - the slower the charge rate the longer it will last…

 

[daveo4EV]

some good answers here…

https://www.quora.com/Why-do-lithiu...-rate-of-charge-gets-slower-as-it-gets-fuller

 

[Tay Tay]

The rough analogy I heard was it's like filling up a glass of water. Once you get near the top you have to slow down so you don't overflow the cup.

 

[HerrCooles]

could you explain that a bit more? I get what you are saying and I have heard it before, but I don’t understand the engineering/physics of it.

for example, why is it worse to charge from 85 to 95 at 100kw than it is to charge from 50 to 60 at 100kw.

naively, to me it seems that it is the same about of energy going in at the same rate

you have to imagine it like a parking garage where the cars drive in at high speed. As long as the parking garage is still relatively empty, the cars can quickly find a parking space. But when it is 80% full, everyone has to search a long time. This leads to a backlog at the entrance. Those waiting are angry and stressful. That is why the entrance is regulated so that there is no stress.

 

[iten]

Sorry, but seems like we are getting a bit off topic. Just want to know:

1) if anyone else are experiencing this issue?
2) It seems that the Car can actually communicate with a DC charger through the CCS plug...Is the charge rate determined by how much the charger is feeding the car or how much the car is drawing from the charger?
3) Is it possible to set the limit for DC charging to 85% since the manual says both profile and timer are not applicable to DC charging.

Thanks!

 

[NC_Taycan]

2) It seems that the Car can actually communicate with a DC charger through the CCS plug...Is the charge rate determined by how much the charger is feeding the car or how much the car is drawing from the charger?

Yes the CCS connector provides two-way communication. The car sets the charge rate and the EVSE complies.

3) Is it possible to set the limit for DC charging to 85% since the manual says both profile and timer are not applicable to DC charging.

Good question and I would like to know the answer myself.

 

[iten]

Yes the CCS connector provides two-way communication. The car sets the charge rate and the EVSE complies.

Good question and I would like to know the answer myself.

I tried again today and the car was still taking 47kwh at 89%...I was too worried to continue...

 

[Kingske]

Yes the CCS connector provides two-way communication. The car sets the charge rate and the EVSE complies.

Good question and I would like to know the answer myself.

Question 3: I don't think so. Maybe with the new OTA "battery protection" feature that was promised earlier?

 

[evanevery]

Charging at 50KW chargers is pretty painful I think...

At higher power chargers (150KW, 350KW), 85% is pretty much where you will start to see your charging rate really start to taper. I will typically see about 125KW at 80% and then 100KW at about 85% and then it really starts to drop. If you are at a 50KW charger you obviously won't see those peaks and you can charge at the 50KW "max rate" further into your SOC.

I typically charge to 85% regardless of how much charge I actually need to get to my next charging stop. Even if ABRP tells me I only need to charge to say 65% (to reach my next stop at 10%), I still charge all the way to at least 85% and then "bank" the balance. Given the current reliability of charging stations, and their relative sparsity on the open road, there is no way I'm allowing my car to get down to only 10% on a long road trip. 80-85% is specifically where I typically stop my charging session (unless I REALLY need more) as it is at that point where the charging rate starts to taper significantly...

 

[evanevery]

Sorry, but seems like we are getting a bit off topic. Just want to know:

1) if anyone else are experiencing this issue?
2) It seems that the Car can actually communicate with a DC charger through the CCS plug...Is the charge rate determined by how much the charger is feeding the car or how much the car is drawing from the charger?
3) Is it possible to set the limit for DC charging to 85% since the manual says both profile and timer are not applicable to DC charging.

Thanks!

I'm curious why you would want to set max charge at a DC charger to 85%? Do you have one at home? Are you using it on a nightly basis?

There is absolutely no worries about charging your battery to 100% as long as you are going to drive it off. (I believe consensus currently recommends driving it off "within 24 hrs"). You are NOT going to damage your battery by charging it to 100%. That is exactly why you have 100% to work with! Otherwise, what's the point?

(Not that I'm suggesting this, but there is even some debate that you could even charge your battery to 100% every night and not notice an appreciable decrease in range for a very long time. Porsche is only letting you use about 90% of the total battery capacity in any case. 93.4KW capacity but only 83.7KW usable.)

Why are you worried about charging to 100% at a DC charger?

 

[NC_Taycan]

I'm curious why you would want to set max charge at a DC charger to 85%? Do you have one at home? Are you using it on a nightly basis?

There is absolutely no worries about charging your battery to 100% as long as you are going to drive it off. (I believe consensus currently recommends driving it off "within 24 hrs"). You are NOT going to damage your battery by charging it to 100%. That is exactly why you have 100% to work with! Otherwise, what's the point?

(Not that I'm suggesting this, but there is even some debate that you could even charge your battery to 100% every night and not notice an appreciable decrease in range for a very long time. Porsche is only letting you use about 90% of the total battery capacity in any case. 93.4KW capacity but only 83.7KW usable.)

Why are you worried about charging to 100% at a DC charger?

I think this is a good point. If you are on a road trip, charge to 100%. Assuming you are grabbing a snack, nature break or whatever while charging, leave the car and don't worry about it. If it's convenient to do so and some SOC < 100% is good enough for your remaining travel home, stop it before 100% and don't worry about it. In either case, as pointed out if you aren't leaving the car at 100% for a long period and you aren't doing this frequently, don't worry about it. My $0.02.

Sponsored