Speak EV - Electric Car Forums banner
1 - 14 of 14 Posts

·
Super Moderator
Joined
·
7,610 Posts
Discussion Starter · #1 ·
An interesting observation this afternoon, I was down somewhere around 12-15% SOC and wanted to overtake someone. Foot to the floor and very little happened. Power meter in the dash only went about half full, and in the EV screen motor power seemed pinned at 80kw max. Not what I’d expect with 6-10kwh still in the tank. Anyone else experienced this?
 

·
Registered
E-Niro 64kWh '4' since 9/20 (was Prius)
Joined
·
1,157 Posts
I’ve not experienced it. As yet I’ve never been anywhere near so low with the SOC. However, it is exactly what I would expect it to do.

Lithium Ion batteries suffer from considerably increased internal resistance at lower SOC (in fact so also does most battery chemistries). This effect will be made even worse at lower temperatures.

The battery management system will be reducing the maximum current permitted to be drawn in order to protect the battery cells from internal damage or premature longevity reduction. That is a good thing. I expect if we were in midsummer temperatures, that max power limit threshold would be increased and become rather less noticeable for the same SOC.

The same sort of thing should also happen if trying to do rapid charging to a well depleted battery (again even more so if it’s also cold). The charge current should be limited until the SOC has risen above a certain level. The reasons are exactly the same, raised internal cell resistance.
Peter
 

·
Registered
Kia Soul EV 2020
Joined
·
2,861 Posts
Do you know what was outside or battery temp, by any chance?

After watching a recent video on YT about a guy testing SoulEV and getting a turtle mode limited to 5mph at 2% SOC, I would say, it is possible.

The way I think about it is: the combination of both cold temps and low battery, is a double whammy on your battery performance. Tesla have a visualisation for the cold temp on their battery, but the way I understand it Kia views SOC as fixed, but in really in very cold conditions your 12% are only actual 7 or 8%SOC. Combine that with reaching low SOC for the battery, which also brings additional increased performance...

It is surprising, but not shocking.
 

·
Super Moderator
Joined
·
7,610 Posts
Discussion Starter · #4 ·
Oh I understand the principle of why, just don’t expect it so far up the SOC range - I’ve been driving a leaf for 7 years and it’s power limit comes when there’s very little energy left in the battery (around 2kwh or so)

Ambient temp today was 5C, battery temp no idea but I’d done a gentle ~1 hour drive.
 

·
Registered
Kia Soul EV 2020
Joined
·
2,861 Posts
Oh I understand the principle of why, just don’t expect it so far up the SOC range - I’ve been driving a leaf for 7 years and it’s power limit comes when there’s very little energy left in the battery (around 2kwh or so)

Ambient temp today was 5C, battery temp no idea but I’d done a gentle ~1 hour drive.
Yes, the temp was reasonable. For me, after an hours drive the battery temp would be 12-13degC, depending on speed/acceleration.

The other thing I would consider is that you were at speed? So, the car was delivering power, but you wanted more? Maybe you hit some other limit at low SOC? That is not that clearly understood by us... 80kW is a very reasonable power output of a low battery.

I remember now the visuals in my previous GTE: there was a gray bar, demonstrating what kind of power I have available and a blue demand bar would be "crawling" up the gray as I stepped on the go pedal. But the important bit was that the gray bar would get shorter as the battery depleted. At about 2-3miles range the ICE would jump in, but the gray bar was almost gone by then.
 

·
Registered
Joined
·
127 Posts
An interesting observation this afternoon, I was down somewhere around 12-15% SOC and wanted to overtake someone. Foot to the floor and very little happened. Power meter in the dash only went about half full, and in the EV screen motor power seemed pinned at 80kw max. Not what I’d expect with 6-10kwh still in the tank. Anyone else experienced this?
Surprised it was at that high a level. Would have expected that around 5% from previous EVing. Has the battery not been charged to 100% recently thus allowing the BMW to calibrate and therefore being extra cautious?
 

·
Registered
E-Niro 64kWh '4' since 9/20 (was Prius)
Joined
·
1,157 Posts
Sorry, but at the risk of sounding like a smart ass, I’m not at all surprised. The ambient may be 5°, but if the car was outside all night (cold), the very large thermal mass of the battery could still be at considerably less than the daytime ambient.
Gentle 1 hour driving doesn’t warm the battery that much at all. Maybe just a couple of degrees?
I reckon it’s a combination of lowish SOC, lowish battery core temperature, and a sudden very high power demand (that you perhaps wouldn’t normally have made so therefore wouldn’t normally notice the enforced power limit even if it was there).

I bet if you repeat the same test, at the same SOC on a warm summer afternoon, things would be rather different.
Peter
 
  • Like
Reactions: Petriix

·
Registered
Joined
·
1,907 Posts
Oh I understand the principle of why, just don’t expect it so far up the SOC range - I’ve been driving a leaf for 7 years and it’s power limit comes when there’s very little energy left in the battery (around 2kwh or so)

Ambient temp today was 5C, battery temp no idea but I’d done a gentle ~1 hour drive.
I guess it's a little bit of a strange feeling to be restricted to merely the same as the same power of a leaf at that level :)
Useful to note though as I rarely drop into such a low SoC given the range.
 

·
Super Moderator
Joined
·
7,610 Posts
Discussion Starter · #10 ·
I guess it's a little bit of a strange feeling to be restricted to merely the same as the same power of a leaf at that level :)
Useful to note though as I rarely drop into such a low SoC given the range.
Yes it felt exactly like being in the Leaf, a sort of gutless attempt at speeding up from 40mph rather than the normal firm push the Niro gives up to 70!
 
  • Like
Reactions: MetalHead

·
Super Moderator
Joined
·
7,610 Posts
Discussion Starter · #11 ·
You should try the e-Golf. At current temperatures it starts to restrict the power slightly at around 40% and by 20% it's quite reduced.
At around 10 miles left it switches off the heating or aircon and the power is quite restricted.
Very annoying if I'm only 2-3 miles from home.
Oh that sounds horrible! Does it at least give an indication power is reduced? The Leaf does so with some power “rings” on the dash but I didn’t notice anything on the Niro dashboard had changed.
 

·
Registered
Joined
·
721 Posts
An interesting observation this afternoon, I was down somewhere around 12-15% SOC and wanted to overtake someone. Foot to the floor and very little happened. Power meter in the dash only went about half full, and in the EV screen motor power seemed pinned at 80kw max. Not what I’d expect with 6-10kwh still in the tank. Anyone else experienced this?
I have read this a few times now, usually the poster says they have 10-15 miles on the SOC when it happens though, and speed is restricted to about 15 mph or lower, I just thought it was a Hyundai/Kia thing, and sounds quite dangerous when your 10 miles from home but still on a motorway for example.
 

·
Registered
E-Niro 64kWh '4' since 9/20 (was Prius)
Joined
·
1,157 Posts
I would imagine the maximum power allowed will gradually reduce on a continuous sliding scale dependant upon the battery total internal resistance value. Low SOC, low cells temperature, cell SOC balancing and battery age degradation could all be factors affecting just when this reduction starts to kick in. The 100% max motor power of 150kW could quite well start to be curtailed at a much higher SOC than we might typically expect.

I may not get to witness this effect myself as my intentions are to generally try to not go below 20-25% SOC. Deep discharging of the battery isn’t good for it, and I won’t often be needing to use the full range available.

I agree the car should have some warning or indication when this power reduction is coming into play. It could indeed be very dangerous if you try to do a quick overtake and only then discover the normal brisk acceleration power suddenly isn’t available. It’s certainly something to be mindful of of going forwards! Peter.
 

·
Registered
Joined
·
365 Posts
I would imagine the maximum power allowed will gradually reduce on a continuous sliding scale dependant upon the battery total internal resistance value. Low SOC, low cells temperature, cell SOC balancing and battery age degradation could all be factors affecting just when this reduction starts to kick in. The 100% max motor power of 150kW could quite well start to be curtailed at a much higher SOC than we might typically expect.

I may not get to witness this effect myself as my intentions are to generally try to not go below 20-25% SOC. Deep discharging of the battery isn’t good for it, and I won’t often be needing to use the full range available.

I agree the car should have some warning or indication when this power reduction is coming into play. It could indeed be very dangerous if you try to do a quick overtake and only then discover the normal brisk acceleration power suddenly isn’t available. It’s certainly something to be mindful of of going forwards! Peter.
For what it's worth, I was doing some uphill/downhill potential energy tests the other day, taking readings through the OBD. Looking back at the records, it seems battery temperature is indeed a really important factor here:
Reading 1: SoC 86%, battery temp 5°C, available charge power 85.82kW, available discharge power 159kW
Reading 3: SoC 83%, battery temp 6°C, available charge power 95.12kW, available discharge power 163kW

So despite the SoC being near full, even a 1K temperature increase was quite significant. Indeed, you wouldn't get all 150kW of motor power output if you could only draw 159kW from the battery.
 
1 - 14 of 14 Posts
Top