Interesting that you have noticed a difference at various SOC, do you think the 0-60 is worse at 10% and in what modes?

 

Well, I pretty much exclusively drive in ECO mode, but the other day I went down to 11% SOC on the way to work (we have very cheap chargers, 11kw 1p/min) and then on the way home at 80% SOC the car felt a lot more responsive from a stop. Maybe it's psychological (I swear I had that with premium fuels in my last ICE), but it's interesting to see the responses here, seems like it does make a difference! Thanks for all the input guys!

 

The pack voltage dictates the ‘base speed’ or constant torque region of the motor. Available torque drops off above the base speed.

As you discharge the pack, your base speed will decline.

You may notice a difference in available torque at cruising speed, depending on SOC. Particularly under load (eg towing).

At low speeds, no real difference!

 

You are correct. Bjorn Nyland takes this into account on his acceleration tests where he takes the 0-100kmh times from 100% to 10% and then plots the change over the different SOC. With a M3 LR he saw 0-60 of 4.4s at 90%, reducing to 4.92s at 20% and then 6.15s at 10%. At the time there was an issue with the refresh 2021 M3 performance and it was going really slow at lower SOC (like 14s 0-100 at 10%). Tesla sorted it after a month or two.

 

I wondered in a similar vein. However with my Leaf 62, I found that even with less than 10% Soc, the power gauge would still shoot round to 160kw. I never did discover at what SoC the power is actually reduced.

The only time I did observe a drop from 160 to about 120 was above 80, on the way to max speed (private road of course)

 

I'm not sure the power guage itself would be calibrated accurately enough to show that it wasn't achieving its maximum output. Think of it more like a percentage duty cycle that's multiplied by theoretical maximum output as a convenience for the consumer. It would probably only show reductions of output when its deliberately limiting output power.
Fact of the matter is that when the battery is at lower SOC there's fewer kw able to be drawn from the pack, regardless of what the dashboard says.

 

Not necessarily because the battery output does not go directly to the motor(s).

Most motors are multiphase AC so the motor control until will adjust the input current to generate the demanded motor power. It is designed to operate regardless of the battery voltage because otherwise, the power delivery would only be max potentially with a full battery.

 

I do notice this effect in my i3. Used to think I was imagining it but definitely not. Noticeably (but only slightly, in reality) more responsive with high battery % (>90%), and similarly less responsive at low soc (say, less than 30%). The rest of the time it seems consistent. I guess the electronics compensates over most of the range but not at the extremes...

 

Certainly on my Ioniq 38 the power is restricted when the battery depletes.
Looking at the power table in the console screen, full throttle would usually be 99kW
However at around 20% this seems to max at around 90kW, and at around 10-15% at about 80kW. Below 10% it will restrict further as you approach turtle mode, but it will give a warning of restricted power.
It also restricts power when battery is cold, by which I mean around 0Cor less. That is actually more noticeable, as I have a short slip road to join a dual carriageway out of my village, and in winter the car is noticeably slower to accelerate.

 

You would need to clarify if reduced performance is part of the software and designed to conserve energy i.e. it is possible that some cars could accelerate just as faster at lower %, but are programmed not to do so to stop the battery running out. I think my Ioniq 28 has a sudden reduction at a certain % (maybe 2%, 3% or 5%, but I can't remember, which might be programmed).

I'm guessing this is mostly not what's going on here, but it could be in some cases.

 

Sure, but e.g. the performance change of a few tenths of a second consistently measured by folks when they compare full batteries to "less full" batteries would be nowhere near the same as the difference between 160kw and 120kw, it would be the difference between 160 and ~158 .. or it could even maybe just be that the system takes longer to put the output up to 160 because the input voltage sags more under the higher current load when the battery is less charged ..

And all of this would be equivalent to less than the difference in output between driving a just-warming-up ICE and driving a heat-soaked ICE...

 

Several obd2 apps show battery peak power (kW and amps) and even motor torque Nm - you can watch and record max power at various levels of SOC.

Here is Car Scanner Elm Obd2 in EV6 GT:

 

Several obd2 apps show battery peak power (kW and amps) and even motor torque Nm - you can watch and record max power at various levels of SOC.

Indeed, but realise that a torque value is not directly measured it is calculated based on a mathematical model of the motor RPM, possibly its temperature, and the current and voltage applied by the motor controller. There may be more required to get this right, such as magnet ageing parameters, but I'd guess they are unlikely to be so complicated for an internal estimated value.

 

Hello everyone,

This is just a thought that came to mind and I'm no electrician so please forgive me if this sounds like a silly question, but since the battery voltage at the cell level and the battery as a whole will differ quite significantly between say 100% and 10% SoC, does this mean that the performance would too?
Or is the BMS somehow able to smooth this out?

I searched the forum and couldn't find a similar thread, however if it's a duplicate please let me know and I'll close it out!

I've wondered this since I got my Ioniq 5 and I'm not sure whether it's psychological or actually there but I feel like there's a difference between say when I'm at 80% charge and 20%.

If so it's quite interesting that an EV would work in the opposite way to an ICE, i.e more fuel = higher voltage = maybe higher performance, but no extra weight, whereas an ICE would be significantly heavier with a full tank.

These are just my ramblings, but interested to know the thoughts of others

Thanks!

Battery voltage isn’t proportional to SoC.

Using LiFePO4 as an example (because I can remember the values) 3.00V is 10% and 3.33V is 90%. So from “full” to “empty” the voltage drops only 10%.

 

Battery voltage isn’t proportional to SoC.

I don't think anyone suggested it was proportional to SoC. That would make it a capacitor. But it does change, as in your example.
It's still valid that as the battery voltage drops, the available power might be reduced.
In particular, it will drop if power is limited by a maximum current rating (which is quite likely). A 10% drop in voltage would result in a 10% drop in power if the current cannot increase.

 

Can’t say I’ve noticed any difference in performance from low 20% ish battery to high battery around 90%. I always drive in normal mode observing speed limits but keeping up with traffic hovering around 60mph on motorways.