Does 90-100% hold more kWh?

[devmach-e]

The app

The Ford app shows what is delivered to the battery, not what is drawn from the wall. The charging stations we have at work are 30A units on commercial electricity, so it is 208V instead of 240V. So they provide about 6.1 kW, but the Ford app shows the charge rate as 5.6 kW being delivered to the battery. 19.280 kWh pulled from the station according to ChargePoint,, but only 17.9 kWh added to the battery according to the Ford app.

At home, I have a 32A unit running at 248V, so I get about 7.8 kW drawn from the wall, but only about 7.22 kW makes it to the battery.

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[raijinmach]

The Ford app shows what is delivered to the battery, not what is drawn from the wall. The charging stations we have at work are 30A units on commercial electricity, so it is 208V instead of 240V. So they provide about 6.1 kW, but the Ford app shows the charge rate as 5.6 kW being delivered to the battery. 19.280 kWh pulled from the station according to ChargePoint,, but only 17.9 kWh added to the battery according to the Ford app.

At home, I have a 32A unit running at 248V, so I get about 7.8 kW drawn from the wall, but only about 7.22 kW makes it to the battery.

So in my case, it shows 5 kw all the way until 100% but 90-100% takes 3x longer

 

[Teslaeata]

All you really need to know is the charge rate does slow towards the end of charging the HVB so live and work with it.

It’s designed that way to protect the battery.

 

[Mache_Nor]

While I believe what other say is true about it generally taking longer time to charger a close-to-full battery, we also have to take into consideration that it seems like the SOC / % estimate of the battery is not linear. When driving it takes longer (driving) time doing 90%-80%, than say 30%-20%. Also, when at 100%, the car is actually at 96.5% (verified with scanner), thus from 100-99% takes much longer than all other percentages regardless of the very top cell balancing.

Edit: If it was a bit confusing my example are just reversed to show that the SOC / % acts differently on different stages of charge, and that 100%-99% is not the same as 0%-1% (which then agian likely also affects how charging seemingly behaves).

 

[OH2AZ2OH]

The data from the app can be, and often is, wrong. The current definitely drops down at the end of the charge (I can monitor real-time load on my electrical system, and I have watched it multiple times). I think it drops at 95% charge, and the last 1% charge is definitely slower as the cells rebalance. The longer it has been since I last charged to 100%, the longer that last 1% takes.

 

[Mache_Nor]

The data from the app can be, and often is, wrong. The current definitely drops down at the end of the charge (I can monitor real-time load on my electrical system, and I have watched it multiple times). I think it drops at 95% charge, and the last 1% charge is definitely slower as the cells rebalance. The longer it has been since I last charged to 100%, the longer that last 1% takes.

Forgot to mention, yes, app is usually wrong. When I L2 charge it roughly is 10% off most of the time. Guess it charging losses and whatnot (charger will pull roughly 11.3 kwh, car puts right above 10 kwh into battery). This regardless of the top charge cell balancing.

 

[OH2AZ2OH]

Yeah, the car can see what goes into the battery, but it doesn't know what came out of the panel. For 240V charging, charging losses should be around 7 - 8 % or so. I haven't paid attention to that part of the app in a long time, but it used to be that the math didn't work, meaning if you taok the time on charger and the charge rate, it wouldn't multiply to give you the KWh added, especially when the car stayed on plug after reaching target charge.

 

[devmach-e]

So in my case, it shows 5 kw all the way until 100% but 90-100% takes 3x longer

You are conflating DC fast charging rates with AC L2 charging rates. With AC charging, the charge rate is pretty consistent throughout the entire session, which is 5 kW in your case. It will do that rate all the way to 99%.

With DC fast charging, it is constantly being ramped down to avoid cooking the battery. I.e starts out at a rate of 150 kW, then drops to 100 kW for a while, and then when the car hits 80%, drops to 40 kW or so.

 

[devmach-e]

The data from the app can be, and often is, wrong. The current definitely drops down at the end of the charge (I can monitor real-time load on my electrical system, and I have watched it multiple times). I think it drops at 95% charge, and the last 1% charge is definitely slower as the cells rebalance. The longer it has been since I last charged to 100%, the longer that last 1% takes.

On AC charging, for my vehicle it doesn’t drop until 99%.

 

[Blue highway]

So in my case, it shows 5 kw all the way until 100% but 90-100% takes 3x longer

The 5KW shown in the app is a simplification... not what is actually happening. The charge rate is indeed capped at 5KW for most of the charge process but as the cells fill up to near full state of charge, the actual charge rate (current) slows down as the cell voltage rises...

So yeah, going from 90% to 100% takes longer because the charge current is ramping down as the cells approach their final charge voltage.

A bit more detail in terms of what is happening. Lithium batteries use a two-stage Constant Current-Constant Voltage (CC-CV) method for safety and efficiency, starting with a steady current (CC) (this is where the 5KW comes from) until a set voltage is reached, then switching to a constant voltage (CV) as the current tapers off to fully charge the cells without any of the cells exceeding a safe charge voltage.

Another item that affects charge time near full charge is cell balancing. The cells are not all exactly at the same charge voltage. As they are charged to near 100% (4.2V per cell lets say) some cells are going to hit that voltage while others are still at a lower voltage (4.05V lets say)... what happens is that the cells that are at or near 100% have a bleed resistor connected across them to draw down their charge as the other cells slowly get to the desired full state of charge. This prevents any cells being charged to a voltage at which they break down and catch fire... and at the same time, all cells in the pack are brought to the same final charge voltage. Depending on how far out of balance the cells are, the longer the balance process takes.

I periodically (about once a month) charge my cars to 100% to allow the cell balancing to take place. Otherwise they spend their lives between 40-70% charge and the state of charge of individual cells can vary if the pack is never allowed to balance.

BTW, all this takes place in any Lithium battery charger charging more than one cell... phone, PC, model plane etc.

 

[MadMatt]

Charging rates aside,

I too notice the first 10-15% drops slower than the rest (assuming you've done a 100% charge)

example, I charged to 100% the other day, and did a 57km drive. arrived at like 78% meaning i used 22%.

last night, i did a 19km, parked for 2-3 hours then drive home for another 19km to make 38km total. when arrived i was down to 54%, meaning i used 26%.

in other words, i did 19km more using 4% less battery when leaving at 100%.

Now, i realize things like ambient temp (it was colder on the second trip and the car parked for 2-3h meaning the battery/vehicle cooled down) affects this.

Just generally speaking, I've noticed this pattern a lot. that top 10-15% holds more juice than it should. Likely just the HV BMS calculation being slightly un-calibrated, just worth mentioning.

 

[devmach-e]

Something to note, when DC fast charging, the lowest rate you will get will be in excess of the highest rate of L2 AC charging possible for the car.

 

[devmach-e]

The car might accept the full 48A @ 240VAC (11.52 kW), but what gets into the battery is less than that due to various parasitic losses. The biggest one is the AC to DC conversion process which results in about an 7 to 8 percent loss (which is actually quite good). The next bigger loss is the power needed to run the various battery thermal controls (AC compressor, pumps, fans), and then the underlying electronics, and charging of the 12V battery. The car does not ramp down the charging rate until it hits 99%.

 

[cheerioboy26]

On AC charging, for my vehicle it doesn’t drop until 99%.

Agree, but that last 1% can take an hour.

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