Is the reduction in power with low SOC a software design or is it a physical limitation?

[kadify]

It seems like when the car gets below ~60% SOC that it starts slowing down. I read somewhere that below 70% SOC the car slowly looses power. Is this a design limitation or is it a software limitation? Is it something that could be changed in the future?

Just curious because I know it is recommended to keep the battery between 20-80% charge but if you only have a 10% SOC delta where you actually get "full power", that seems a bit strange to me. If it is software limited, it would be nice to unlock the full potential at any SOC with the understanding that it will affect the efficiency. Similar to flooring it in a gas car, it isn't limited even if you're running on fumes, you just go through gas faster.

 

[SSedan]

You are likely seeing combine effects of low temp and SOC.
The heat pump is being reported as over scavenging heat from the pack keeping it cold.

 

[Battpower]

Since owners will have differing levels of interest and experience, it might be worth a reminder that lithium batteries fundamentally dislike low temperatures. Unlike a chemical fuel like gasoline or diesel where every drop of fuel behaves like any other drop of fuel, batteries and electric charge have conceptual differences. It might be easier to compare batteries with storing energy by winding up a spring or stretching an elastic band. As with any analogy there are limits, but with an elastic band it is easy to see that there is a middle range in which the stretchiness is effective at storing and releasing energy, while at the extremes it isn't.

In the case of lithium, temperatures between 20 and 50 Celcius put the battery in a better place to do its job at all SOC. The combination of low temp and low SOC puts the battery at a significant disadvantage as far as it's ability to release the remaining stored energy.

So while a pump and gas tank care little how full the tank is, and the fuel delivered to the engine is the same regardless, that is not the case with a battery. The battery IS the 'pump' in some respects, and it doesn't work well if its not warm enough.

The newer heat pump equipped cars can take heat from the battery, which with warmer ambient temperatures might not be a problem, but it does look as though the current software is not allowing sufficient heating of the battery in order to keep it working adequately at lower SOC.

Cars are programmed to heat up the battery before Supercharging, so setting a Supercharger as your destination should trick the car into heating the battery when needed. You are not producing extra energy by heating, but you are making the battery better able to deliver the remaining energy stored in it.

 

[Zoomit]

It seems like when the car gets below ~60% SOC that it starts slowing down. I read somewhere that below 70% SOC the car slowly looses power. Is this a design limitation or is it a software limitation? Is it something that could be changed in the future?

It’s a physical limitation of batteries. As the battery pack discharges, the voltage drops from about 400V at 100% SOC to around 300V at low SOC. This results in less available power to the motors. This can be compensated, to an extent, by increasing the amperage at low SOC, but the bottomline is that a BEV will always have this characteristic.

Here’s the now classic video showcasing this effect in the Model 3.

 

[Jan1076]

The latest car software will preheat the batteries when you either preheat the car interior using the app, or when using the planned departure option from within the car. This will allow the battery pack to have more range when you start using the car. Normally, when drivng at highway speed, the car draws enough current from the batteries to keep it warm.

 

[jcanoe]

The latest car software will preheat the batteries when you either preheat the car interior using the app, or when using the planned departure option from within the car. This will allow the battery pack to have more range when you start using the car. Normally, when drivng at highway speed, the car draws enough current from the batteries to keep it warm.

Warming the battery pack does not result in increased range (when compared to a cold battery pack) as the capacity and state of charge remain the same. Warming the battery pack will result in restoring some or most of the regenerative braking function and the battery pack will be able to deliver more peak power output on demand; also faster charging.

 

[MY-Y]

The graphs I've seen for the M3 show only mild power loss down to 20% or so. For sure, my boosted MY doesn’t share this behavior. It is way, way slower at 20% than normal. I'm pretty sure our minivan could beat it in a race at 20% at highway speed (seriously). I don't even like driving the car below 30%. (Somewhere around 30%, you see the dots appear on the power bar to indicate reduced power.)

 

[pt19713]

Warming the battery pack does not result in increased range (when compared to a cold battery pack) as the capacity and state of charge remain the same. Warming the battery pack will result in restoring some or most of the regenerative braking function and the battery pack will be able to deliver more peak power output on demand; also faster charging.

Bjorn's latest video shows the 2021 Model 3 being 20% more efficient when the battery is warm versus a "cold start." The drive was mostly highway so very little braking so regen wouldn't be a factor.

I've only done a few drives to test and I'm seeing 15% difference on my Y. I'm not as dedicated as Bjorn and prefer my car being warmed up before I drive so I'm not going to try doing more tests since his pretty much validates what I'm seeing.

 

[pt19713]

The graphs I've seen for the M3 show only mild power loss down to 20% or so. For sure, my boosted MY doesn’t share this behavior. It is way, way slower at 20% than normal. I'm pretty sure our minivan could beat it in a race at 20% at highway speed (seriously). I don't even like driving the car below 30%. (Somewhere around 30%, you see the dots appear on the power bar to indicate reduced power.)

On my LR I'm not seeing any power loss at 68% vs 85%, at least in the 0-60 runs I've done.

I just can't do any more testing until spring and warmer temps come back since grip & road conditions now is different than when I did the tests in late Sept and October. I still need to log the data of the motor output at lower SoC.

 

[SSedan]

TEMPERATURE is a factor.
Pack temp, heat pump vehicles are robbing pack heat.
Even for cars in the same climate, distance driven, speed driven, charging amperage are all going to play rolls in average pack temp.
Heck Denver being hilly with hard climbs followed by regen could net a warmer pack than same weather and same overall wh/m in a flatter place.

 

[LevelHeaded]

TEMPERATURE is a factor.
Pack temp, heat pump vehicles are robbing pack heat.
Even for cars in the same climate, distance driven, speed driven, charging amperage are all going to play rolls in average pack temp.
Heck Denver being hilly with hard climbs followed by regen could net a warmer pack than same weather and same overall wh/m in a flatter place.

Unrelated to the OPs question.

Power is reduced as SoC decreases as a result of characteristics of batteries themselves as described earlier as _well_ as software implementation not only in the name of efficiency but durability as well.

 

[Black306]

Unrelated to the OPs question.

Power is reduced as SoC decreases as a result of characteristics of batteries themselves as described earlier as _well_ as software implementation not only in the name of efficiency but durability as well.

Agreed; OP made no reference to temperature; only SoC.


OP, to your point, an ICE car could be on fumes and still have full power. That’s cause the quantity of a gas in the tank doesn’t affect power output of the engine.

EVs work differently and will be a bit of a learning curve to new EV owners. As others in this thread basically said, electric motor output (not just limited to EVs) will reduce when supply voltage (SoC) goes down.

 

[frankvb]

EVs work differently and will be a bit of a learning curve to new EV owners. As others in this thread basically said, electric motor output (not just limited to EVs) will reduce when supply voltage (SoC) goes down.

That's one thing that will happen, also I am sure that at very low SoC (state of charge) levels the software will reduce the maximum current going out of the battery to prevent damage. But that might only happen below maybe 10%, but really don't know as it would depend on the specific battery chemistry etc.

 

[SSedan]

Temp and SOC are used together to determine battery output limits.

 

[Battpower]

Temperature effects the battery's ability to maintain current flow. At low SOC the cell / battery voltage is lower so the only way to maintain power is to increase current. At low temperature, the chemistry of the battery is compromised, limiting its current capacity and also, I believe, the electro-chemical reaction that releases stored energy.

Certainly it is difficult to ignore the effect of temperature although the OP is clearly focused on SOC.

I am surprised though if a battery at above 10 Celcius and over 50% SOC is servely effected. As others have said, only sub 20% SOC would normally be the time to start paying close attention under normal driving.

 

[kadify]

The graphs I've seen for the M3 show only mild power loss down to 20% or so. For sure, my boosted MY doesn’t share this behavior. It is way, way slower at 20% than normal. I'm pretty sure our minivan could beat it in a race at 20% at highway speed (seriously). I don't even like driving the car below 30%. (Somewhere around 30%, you see the dots appear on the power bar to indicate reduced power.)

I have a MYP and went down to ~30% today and it was WAY slower than the vehicle is normally at 80%+. I wonder how the M3 is set up differently?

Unrelated to the OPs question.

Power is reduced as SoC decreases as a result of characteristics of batteries themselves as described earlier as _well_ as software implementation not only in the name of efficiency but durability as well.

Thank you this is what I was wondering.

Agreed; OP made no reference to temperature; only SoC.


OP, to your point, an ICE car could be on fumes and still have full power. That’s cause the quantity of a gas in the tank doesn’t affect power output of the engine.

EVs work differently and will be a bit of a learning curve to new EV owners. As others in this thread basically said, electric motor output (not just limited to EVs) will reduce when supply voltage (SoC) goes down.

This is what I was wondering. I was curious if it was a software setting or a physical characteristic of EVs which is seems to be.

 

[kadify]

Temperature effects the battery's ability to maintain current flow. At low SOC the cell / battery voltage is lower so the only way to maintain power is to increase current. At low temperature, the chemistry of the battery is compromised, limiting its current capacity and also, I believe, the electro-chemical reaction that releases stored energy.

Certainly it is difficult to ignore the effect of temperature although the OP is clearly focused on SOC.

I am surprised though if a battery at above 10 Celcius and over 50% SOC is servely effected. As others have said, only sub 20% SOC would normally be the time to start paying close attention under normal driving.

I was driving down to ~30% today because I really wanted to try going to a supercharger today and the car was WAY slower at 30% than it was at 80%+. Like two completely different cars almost. I was wondering if that was by design or just a characteristic of how EVs work.

 

[Battpower]

I was driving down to ~30% today because I really wanted to try going to a supercharger today and the car was WAY slower at 30% than it was at 80%+. Like two completely different cars almost. I was wondering if that was by design or just a characteristic of how EVs work.

Do you have any info on temperature of battery? Had you selected to navigate to the supercharger? (was battery heating?)

There is a physical element that this is how EV's work, but not to the extent you appear to be seeing.

 

[kadify]

Do you have any info on temperature of battery? Had you selected to navigate to the supercharger? (was battery heating?)

There is a physical element that this is how EV's work, but not to the extent you appear to be seeing.

I set a supercharger as the destination (started at roughly 34% charge) and just driving towards the supercharger (about 12-15 miles away) it was pretty slow. I wish I had timed the 0-60 or 0-30 just driving around when I noticed this because it was surprisingly slow compared to how it was immediately after charging up at the supercharger. Especially since I preheated the car and then navigated to the supercharger and had no region dots so I think the battery was up to normal operating temps when I started.

 

[DaveORD]

Navigating to SC means the car will try to heat up the battery as much as it can to speed up charging at the SC. The MY does not have a resistive heater for the battery so this is done by running the motors inefficiently, creating heat in the motors that can be used to heat the battery. So I'd expect less power available from those motors during this time, they would be operating at a lower efficiency. You could verify this by navigating to the SC when the charge is much higher, say 70 (?) percent and see if the power feels similarly reduced.