Benefits of onboard 6.6 kW versus 3.3 kW charger?

[Olagon]

Of course it charges much faster but are there other benefits? Convert more wall power into stored energy than 3.3 (more efficient charging)? Less wear and tear on battery pack? Able to utilize additional braking regen? Less heat created when charging due to faster charge times? Curious if there are other advantages over just faster charging rates.

 

[jmueller065]

The TMS operates better with the Level 2 EVSE. It has been observed that with a Level 1 the car switches between TMS operation and charging. With a Level 2 it can run the TMS and charge at the same time.

 

[michael]

The biggest advantage is that 3 kW charging is a PITA, even with PHEV size (7 - 10 kWh) batteries and especially with 20 kWh class batteries. If you are charging at work, this is especially important (needs a full work day to refill the FFE battery at 3 kW)

A side benefit of 6 kW charging is that it's better on the battery if your use it optimally. The battery can stay at a lower SOC longer and then charge up right before it's needed. The average SOC and in most cases the average battery temperature are lower than with slow, early charging.

 

[dmen]

I have not plugged in to 3.3kW; but I would expect preheating the cabin to not work as well as on 6.6kW. Since the cabin heater draws 5+kW, I would expect cabin heating by go-time and/or remote starting to take longer, result in a suboptimally warmed cabin, and use up some of the battery energy- based on how it works on 1.4kW. But if you don't need cabin preheating, then the main thing as you know would just be taking 7 hours to charge from empty on 3.3kW vs 3.5 hours on 6.6.
The effect on battery temp/life expectancy may be a wash. Either you're generating more heat over a shorter charge cycle, or less heat over a longer charge cycle. Pretty sure at modest temps the TMS will kick in either way, so if you trust that it works, I wouldn't consider this in the decision on which charger to use.

 

[michael]

I have not plugged in to 3.3kW; but I would expect preheating the cabin to not work as well as on 6.6kW. Since the cabin heater draws 5+kW, I would expect cabin heating by go-time and/or remote starting to take longer, result in a suboptimally warmed cabin, and use up some of the battery energy- based on how it works on 1.4kW. But if you don't need cabin preheating, then the main thing as you know would just be taking 7 hours to charge from empty on 3.3kW vs 3.5 hours on 6.6.
The effect on battery temp/life expectancy may be a wash. Either you're generating more heat over a shorter charge cycle, or less heat over a longer charge cycle. Pretty sure at modest temps the TMS will kick in either way, so if you trust that it works, I wouldn't consider this in the decision on which charger to use.

This is a subtle concept.

The numbers below are rough approximations, to give the idea. Don't focus on the exact numbers used. Lets assume for the sake of this example that a full charge take 4 hours at 6 kW and 8 hours at 3 kW.


Now let's consider a battery needing 3 hours of charge at 6 kW or 6 hours at 3 kW (i.e, starting at 25%, ending at 100% approximately)

Let's also use an example where after 1 hour it hits 98 degrees F using a 6 kW charge rate. It will take approximately 2 hours to hit that same temp at 3 kW. Temperature will then remain stable at 98 F due to the TMS.

With the 6 kW charge, it will be at 98 degrees for 2 hours before charge ends. With the 3 kW charge, it will be at that temperature for 4 hours. The first case is definitely easier on the battery.

Same idea with charge level. With 6 kW charger, the battery spends one hours between 75 and 100%. With the 3 kW charger, it spends 2 hours between 75 and 100%, and it spends an hour between 87 and 100 percent. Again, the first case (6 kW) is easier on the battery.

The benefits of faster charging are wasted if you let the battery sit for hours fully charged and at 98 degrees. In that case it matters less how long it took to get to 100% charge and 98 degrees, that battery degradation happens while sitting at full charge and temperature.

So again, charge as late as possible and charge as fast as possible for best battery life.

How much does it really matter? According to recent papers on the subject, it does extend battery life. One recent NREL paper suggested life increase from 5 to 8 years comparing charge-on-arrival to charge-just-in-time.

 

[dmen]

This is a subtle concept.

The numbers below are rough approximations, to give the idea. Don't focus on the exact numbers used. Lets assume for the sake of this example that a full charge take 4 hours at 6 kW and 8 hours at 3 kW.


Now let's consider a battery needing 3 hours of charge at 6 kW or 6 hours at 3 kW (i.e, starting at 25%, ending at 100% approximately)

Let's also use an example where after 1 hour it hits 98 degrees F using a 6 kW charge rate. It will take approximately 2 hours to hit that same temp at 3 kW. Temperature will then remain stable at 98 F due to the TMS.

With the 6 kW charge, it will be at 98 degrees for 2 hours before charge ends. With the 3 kW charge, it will be at that temperature for 4 hours. The first case is definitely easier on the battery.

But you don't know that at 3kW the battery temp will hit 98F at all, let alone in 2 hrs vs 1 in 1 hr at 6kW. You made up those numbers and that 2:1 ratio for illustrative purposes only so you can't draw conclusions from them as if they are fact. If it is very warm out, 3kW charging will hit 98 almost as fast as 6kW charging, and your argument is valid. But it might not hit 98F at all in 6 hrs if ambient temperature is moderate or cold. Battery temp is not necessarily going to rise indefinitely. I know at 1.4kW the battery only gets hot enough to engage TMS at very warm ambient temps, like in the 90s. For you in SoCal this is a frequent occurrence; for me in IL this happened maybe twice in 2014. Now that I think about it, I once charged at a 2.8kW unit for 3 hours at ambient temps in the 70s, and the TMS did not appear to be running.

Same idea with charge level. With 6 kW charger, the battery spends one hours between 75 and 100%. With the 3 kW charger, it spends 2 hours between 75 and 100%, and it spends an hour between 87 and 100 percent. Again, the first case (6 kW) is easier on the battery.

As far as I can tell (which admittedly is not all that far), the issues with battery degradation due to remaining at a high state of charge would occur with days or weeks sitting at that state, not hours. That fits with the owner's manual recommending a 50% charge if the car will be garaged for an extended period, vs recommending plugging in whenever the opportunity exists for normal use. Do you really think being fully charged for one hour vs 2 or even 6 hours will prolong the battery life? I would not expect Ford to encourage plugging in at every opportunity if that were the case.

How much does it really matter? According to recent papers on the subject, it does extend battery life. One recent NREL paper suggested life increase from 5 to 8 years comparing charge-on-arrival to charge-just-in-time.

Was that paper EV specific or Li batteries in general? Was it based on models or on actual user data? Did they break down the amount of time spent at different states of charge? Do you know if that paper looked at actively cooled batteries?

I agree charging just in time is a prudent approach, so long as your driving needs are predictable. But I would guess that most FFE drivers do not do this. My car has to be ready to go for 2 adults and 2 kids with plenty of unpredictability, so I generally plug in right away. If I didn't, I'd have to take the backup car more often, which would be defeating the purpose of owning this car in the first place. Whatever loss of life my battery sees is justified by being able to get the most out of it while it has life.