Supercharging a a low capacity battery

[Saghost]

Volt 1/3 of capacity reserved i.e. not available to use.
Its battery capacity will need to degrade under 70% for theoretical chance to measure a difference in cars behavior. Volt is a hybrid that automatically starts the ICE when it sees fit so the driver is even hardly pressed to notice the difference.
So, volt is not instructive here at all.

This would only be true if GM had algorithms adjusting the SoC window to compensate for the decreased capacity. Our GM technical contacts assure us this isn't the case, and I know for a fact that my four year old Volt has not made any such adjustments (OBDII data includes absolute SoC, which I've been monitoring.)

I'm not sure what the ICE part of your argument is about - unless you think the Volt starts the engine in response to hard acceleration (it doesn't.)

 

[SageBrush]

I don't think you can assume the same C rate for charge and discharge. In other words a battery that has a high discharge C rate does not mean it will have a high charging C rate. As I said above I think when talking recharge the anode drives it while in discharge the cathode drives it.

Informative, thanks.

But I was not saying the peak current in either direction is the same, I was saying that a high current in one direction would have the same affect on the battery had the current been reversed.

 

[gregincal]

Informative, thanks.

But I was not saying the peak current in either direction is the same, I was saying that a high current in one direction would have the same affect on the battery had the current been reversed.

I'm not quite sure what the difference is, and pretty sure that it's still not true. A given current charging the battery is harder on the battery than the same current discharging the battery.

 

[SageBrush]

A given current charging the battery is harder on the battery than the same current discharging the battery.

If true then I stand corrected.

 

[apacheguy]

Efficient cars regain range faster, by virtue of driving more miles kwh per kwh. While the efficiency gains probably won't counteract the larger battery, it will help out in some manner.

The LEAF is more efficient than a MS but last I checked it regains range more slowly. Same is true of the 60 kWh vs 85 kWh MS. However, 85 kWh MS is more efficient than 90 kWh and it does regain range faster (although not because of efficiency, just cell chemistry differences).

 

[Saghost]

The LEAF is more efficient than a MS but last I checked it regains range more slowly. Same is true of the 60 kWh vs 85 kWh MS. However, 85 kWh MS is more efficient than 90 kWh and it does regain range faster (although not because of efficiency, just cell chemistry differences).

This is true. It's also ignoring or willfully distorting his point - which was that if you charge two cars at the same rate in kW, the more efficient car gains more miles in the same time. Thus, the Model 3's greater efficiency can reasonably be expected to offset some portion of its presumed slightly slower charge rate in kW.

 

[Mark C]

It sounds like I'm throwing a comment into a room full of battery experts of which I don't qualify. But I would think the rate the Model 3 charges would be determined by how Tesla sets the software to control the charger output into the battery. I leave it to their capable hands to not charge faster than what the battery can reasonable accept and that issues such as pack temperature / humidity are appropriately compensated for.

 

[diamond.g]

This is true. It's also ignoring or willfully distorting his point - which was that if you charge two cars at the same rate in kW, the more efficient car gains more miles in the same time. Thus, the Model 3's greater efficiency can reasonably be expected to offset some portion of its presumed slightly slower charge rate in kW.

As evidenced in the miles per hour charge rate difference between the Model S and the Model X.

 

[apacheguy]

This is true. It's also ignoring or willfully distorting his point - which was that if you charge two cars at the same rate in kW, the more efficient car gains more miles in the same time. Thus, the Model 3's greater efficiency can reasonably be expected to offset some portion of its presumed slightly slower charge rate in kW.

Yeah maybe, but I'd doubt it. Hopefully they have great new battery tech at that point to enable it to see 120 kW rates. But if it's less than 60 kWh, it's going to be a slow charge. Doesn't much matter if it's 10% more efficient or whatever. The taper will kill you on road trips. I really hope Tesla will publish these stats for the various sizes.

 

[SageBrush]

It sounds like I'm throwing a comment into a room full of battery experts of which I don't qualify.

If it makes you feel any better, you are not alone. I'm here too.

 

[Johan]

It sounds like I'm throwing a comment into a room full of battery experts of which I don't qualify. But I would think the rate the Model 3 charges would be determined by how Tesla sets the software to control the charger output into the battery. I leave it to their capable hands to not charge faster than what the battery can reasonable accept and that issues such as pack temperature / humidity are appropriately compensated for.

You're correct in the sense that yes, the charge will be controlled by software. But the underlying determinators are acceptable C-rate with regard to battery longevity at a given voltage (in pay determined by cooling capability) and power available from charger + current limitations of cabling and charge inlet.

 

[diamond.g]

Yeah maybe, but I'd doubt it. Hopefully they have great new battery tech at that point to enable it to see 120 kW rates. But if it's less than 60 kWh, it's going to be a slow charge. Doesn't much matter if it's 10% more efficient or whatever. The taper will kill you on road trips. I really hope Tesla will publish these stats for the various sizes.

Well 80-100% shouldn't be needed to get from SC to SC (once Tesla finish filling them in). Destination charging should help, though I guess that only matters if your destination uses DCFC @>100kW. Which isn't common at all at this point (other than Tesla SCs).

 

[jkk_]

Well 80-100% shouldn't be needed to get from SC to SC (once Tesla finish filling them in). Destination charging should help, though I guess that only matters if your destination uses DCFC @>100kW. Which isn't common at all at this point (other than Tesla SCs).

I'd wager that if someone needs to go 200km without charging in the winter in the base model, there will be need to charge to at least 90% at a supercharger. For >95% of the cases, I'm sure you are right but there are valid cases where one needs to charge >80% at a supercharger.

 

[Johan]

Rocky: since you're disliking my posts on the subject of C rates why don't you share you view of what's correct.

 

[Northrop]

Charge rate is best thought of as [rated] miles per minute/hour rather than kW (or kWh/h which is the same as kW). Since the Model 3 will have better efficiency (Wh/mile) that effect will likely fully counteract the fact that charge rates in kW may be lower. In fact I believe the Model 3 will supercharge quicker on average than Model S or X when measured in miles restored power hour of charging.

That said, between different Model 3 battery sizes the one with the larger battery will charge faster.

I agree! kW are not important, rather charging speed in mph. Also pack size does not affect charging speed in kW that much. Cooling does, more or less alone. Cell chemistry and size are things that help cool. A model 3 with modern chemistry might charge faster in kW and WAY faster in mph then a current S/X.

 

[Rocky_H]

Rocky: since you're disliking my posts on the subject of California rates why don't you share you view of what's correct.

I do apologize for this, and I went back and removed the dislikes after doing a bit more research. You seemed to be saying that the definition of C rate changed with chemistry, rather than pack size, which would not be correct, hence my ratings for what seemed to be incorrect information. Also, I have usually seen before the C rate expressed in the simplified terms JeffK was using, where it's an instantaneous power level (60kwh pack means 1C is 60kW). However, after looking it up in a few sources, I found that it is not an instantaneous power rate. It is defined by the total behavior over 1 hour. So the kW levels through the charging time and tapering rates could give pretty different values for different chemistry/design batteries, even if they are still achieving the same overall C behavior.

 

[Johan]

I do apologize for this, and I went back and removed the dislikes after doing a bit more research. You seemed to be saying that the definition of C rate changed with chemistry, rather than pack size, which would not be correct, hence my ratings for what seemed to be incorrect information. Also, I have usually seen before the C rate expressed in the simplified terms JeffK was using, where it's an instantaneous power level (60kwh pack means 1C is 60kW). However, after looking it up in a few sources, I found that it is not an instantaneous power rate. It is defined by the total behavior over 1 hour. So the kW levels through the charging time and tapering rates could give pretty different values for different chemistry/design batteries, even if they are still achieving the same overall C behavior.

Thanks. It can be a somewhat confusing subject. And there are many different angles. And I meant C rates (my phone corrected it to California rates).

My general point is that different battery chemistries are able to charge and discharge safely and without unacceptable degradation at different C rates, something that to a large degree decides how useful that particular chemistry is given a particular use case. In constructing a pack one can, in addition, connect individual cells in different arrangements (in parallel and serial or combinations thereof) to achieve the desired voltages and peak currents. But the ability of the pack to charge or discharge (the achievable C rates) does not change because it's still every single cell in the pack being charged and discharged together regardless of there are 10 cells or 8000 cells and regardless of their serial and/or parallel arrangement.

 

[JeffK]

yes, c-rate is capacity / hour not instantaneous.

It's been said the cells Tesla is using are good to a 10 C discharge rate.

 

[Northrop]

yes, c-rate is capacity / hour not instantaneous.

It's been said the cells Tesla is using are good to a 10 C discharge rate.

Again cooling is the key. As long as they are withing the voltage span and within the temperature spec you can do almost whatever. Tesla wants to provide a smooth ride so backing of a bit to keep things more consistent over time and different conditions. Remember the P90DL have an option to put the batteries in a race mode. It probably includes getting the cells to the proper temperature.

Also there are no point in chasing cells capable of 20C or 30C if you only are looking at 6C burst for the P90DL. Higher C capability tends to decrease capacity per volume and weight.

If you drive your car hard, you get lets say 125miles of range with an average speed of closer to 100mph? 100/125 = 0.8C discharge in average!

 

[stopcrazypp]

Also, I have usually seen before the C rate expressed in the simplified terms JeffK was using, where it's an instantaneous power level (60kwh pack means 1C is 60kW). However, after looking it up in a few sources, I found that it is not an instantaneous power rate. It is defined by the total behavior over 1 hour. So the kW levels through the charging time and tapering rates could give pretty different values for different chemistry/design batteries, even if they are still achieving the same overall C behavior.

yes, c-rate is capacity / hour not instantaneous.

It's been said the cells Tesla is using are good to a 10 C discharge rate.

C-rate can be used to describe instantaneous behavior too (peak C-rate). It is simply a measure of power normalized to battery capacity (proper method is actually using Ah and A, but usually kWh and kW is more available).

The S60 peaks at around 105kW or about 1.75C.