Tru's thoughts on the Mach-E from second driving experience

[SnBGC]

I am curious. Why wouldn't you want the faster charge rate?

When DC Fast Charging, a higher charge rate is more harmful to the battery compared to a slower rate.
Higher charge rates also generate more heat (all else being equal).

Then you have the issue of potential damage to the switch gear. The vehicle actually performs a weld check after each DCFC session to check for damage. The higher the voltage, the more chance for an arc that could weld stuff together.

The reason charge rates vary is because the vehicle is busy managing all sorts of data from various sensors and using that information to protect itself.

And.....
The charging station is doing the same thing. It regulates it's output based on a self preservation strategy just like the car does.

In some ways, not all that different from a redline on the tachometer of an ICE. If the safe operating RPM is 5500 then why would we ask the manufacturer to raise the limiter to 6500? Yet that appears to be what people are asking for.
???

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[ajmartineau]

I think being able to set maximum A/C and D/C charge rate should be a basic part of all EVs. If I'm visiting a friend or at an RV park or using a dryer plug splitter, I might want to limit it to 20 or 25 amps.

If I know I'm going to be ten minutes late getting back to my car while charging at a DCFC. It'll be better to charge a little slower and have it finish as you get back. A person waiting to charge might charger(road) rage because your car finished ten minutes ago and they had to be inconvenienced by you. Or to save on Idle fees. Or yeah to save the health of your battery. It would be even better if that setting made it so the BMS told the DCFC that (99kW for example), was your maximum so you weren't charged in the next higher tier.

 

[DaveRuns]

Thanks for these videos, the Rapid Red is looking great.

I read something sort of crazy about the Model Y yesterday. Apparently some owners are experiencing substantial ear pain while driving, and people aren’t sure if something in the car is giving off a barely perceptible noise (infrasound), if it’s the hatch shaking while driving causing percussion, hallucination (psychosomatic), or something else.

Not sure if this link from the Tesla Motors Club will work, but the discussion is wild. If the link doesn’t work, it’s the top hit if you Google ‘Model Y ear pain’.

In the off-chance this is something BEVs are susceptible to (that TMC discussion has people talking how their Model S’s and E-Trons do the same thing), I definitely will be on the look out when testing the MME, but glad so far that neither you nor anyone else has mentioned any sort of similar thing as those unlucky MY owners who are experiencing ear pain while driving their cars.

Granted it's only been 6 days with the Model Y, but I haven't experienced any ear pain while driving. Now that you mention it though, I'm going to be looking out for it.

 

[jhalkias]

When DC Fast Charging, a higher charge rate is more harmful to the battery compared to a slower rate.
Higher charge rates also generate more heat (all else being equal).

Then you have the issue of potential damage to the switch gear. The vehicle actually performs a weld check after each DCFC session to check for damage. The higher the voltage, the more chance for an arc that could weld stuff together.

The reason charge rates vary is because the vehicle is busy managing all sorts of data from various sensors and using that information to protect itself.

And.....
The charging station is doing the same thing. It regulates it's output based on a self preservation strategy just like the car does.

In some ways, not all that different from a redline on the tachometer of an ICE. If the safe operating RPM is 5500 then why would we ask the manufacturer to raise the limiter to 6500? Yet that appears to be what people are asking for.
???

I am fine with the max charge rate. 150KW is adequate.

However, I would like to see them have a good charging curve. Maintain that 150 from 0 to 80%. If they did that you could go from 0% to 80% in less than 30 minutes.

 

[dbsb3233]

In some ways, not all that different from a redline on the tachometer of an ICE. If the safe operating RPM is 5500 then why would we ask the manufacturer to raise the limiter to 6500? Yet that appears to be what people are asking for.
???

I don't think people want unsafe 6500, I think they just expect the "safe 5500" to be at or near the advertised rate of 150 kW.

In other words, I think people expect the advertised rate to be safe and achievable.

 

[ARK]

When DC Fast Charging, a higher charge rate is more harmful to the battery compared to a slower rate.
Higher charge rates also generate more heat (all else being equal).

Then you have the issue of potential damage to the switch gear. The vehicle actually performs a weld check after each DCFC session to check for damage. The higher the voltage, the more chance for an arc that could weld stuff together.

The reason charge rates vary is because the vehicle is busy managing all sorts of data from various sensors and using that information to protect itself.

And.....
The charging station is doing the same thing. It regulates it's output based on a self preservation strategy just like the car does.

In some ways, not all that different from a redline on the tachometer of an ICE. If the safe operating RPM is 5500 then why would we ask the manufacturer to raise the limiter to 6500? Yet that appears to be what people are asking for.
???

Do you have an opinion on the highest maximum charge rate to use to avoid battery degradation over time? I’m guessing this number might be different (lower) for the standard range battery as opposed to the extended range?

 

[phidauex]

? Well, if I remember my High School Physics class, slowing down is really just acceleration in the opposite direction.

True! This would also mean the brake pedal could also be called an accelerator pedal (negative accelerator?). But I do like the term accelerator pedal, accurate with no left over ice terminology like throttle (combustion air supply) or gas (fuel supply).

 

[phidauex]

Do you have an opinion on the highest maximum charge rate to use to avoid battery degradation over time? I’m guessing this number might be different (lower) for the standard range battery as opposed to the extended range?

Charge and discharge rates on batteries are often reported as a “C rate”, which is a ratio of the charging or discharging power over the total capacity of the battery. A C rate of 1.0 is the power at which you would fully discharge the battery in one hour exactly. C rate of 2.0 is the power at which the battery would be discharged in 30 minutes.

All charges and discharges will degrade a battery. You can imagine that every hour of a batteries life, it loses a small percentage of its state of health. Sitting at 30% soc it loses very little. Sitting at 95% it loses more. Charging at 0.5 C it loses a bit more, and charging at 1.5 C it loses a lot.

This is a generalization, but this type of battery likes to be charged under 0.5 C, accepts charging up to 1.0C, and does not like charging much higher. 2.0C is right out, you would need to change cell chemistry.

You are right that the ideal charge rates depends on the full size of the battery, so the sr and er will have different preferred charge powers.

SR -76 kWhs
0.15C = 11.5 kW (48A home chargers)
0.5C = 38 kW
1.0C = 76 kW
1.5C = 114 kW
2.0C = 152 kW

ER - 99 kWhs
0.12C = 11.5 kW (48A home chargers)
0.5C = 49.5 kW
1.0C = 99 kW
1.5C = 148.5 kW
2.0C = 198 kW

You can see how the larger battery allows higher max charge rates, and sees less degradation at the same charge rates. That is one reason the overbuild is wise. We do the same thing, for the same reason, on grid connected storage, though our overbuilds tend to be more like 15-35% for daily cycling systems.

 

[ARK]

Charge and discharge rates on batteries are often reported as a “C rate”, which is a ratio of the charging or discharging power over the total capacity of the battery. A C rate of 1.0 is the power at which you would fully discharge the battery in one hour exactly. C rate of 2.0 is the power at which the battery would be discharged in 30 minutes.

All charges and discharges will degrade a battery. You can imagine that every hour of a batteries life, it loses a small percentage of its state of health. Sitting at 30% soc it loses very little. Sitting at 95% it loses more. Charging at 0.5 C it loses a bit more, and charging at 1.5 C it loses a lot.

This is a generalization, but this type of battery likes to be charged under 0.5 C, accepts charging up to 1.0C, and does not like charging much higher. 2.0C is right out, you would need to change cell chemistry.

You are right that the ideal charge rates depends on the full size of the battery, so the sr and er will have different preferred charge powers.

SR -76 kWhs
0.15C = 11.5 kW (48A home chargers)
0.5C = 38 kW
1.0C = 76 kW
1.5C = 114 kW
2.0C = 152 kW

ER - 99 kWhs
0.12C = 11.5 kW (48A home chargers)
0.5C = 49.5 kW
1.0C = 99 kW
1.5C = 148.5 kW
2.0C = 198 kW

You can see how the larger battery allows higher max charge rates, and sees less degradation at the same charge rates. That is one reason the overbuild is wise. We do the same thing, for the same reason, on grid connected storage, though our overbuilds tend to be more like 15-35% for daily cycling systems.

Thank you, I appreciate this detailed explanation.

Would it be fair to say then that charge rate on any type of L2 charger (e.g., 32 amp vs 40 amp vs 48 amp) won’t be meaningfully different in terms of impact on long-term battery life, and the potential concern is limited to L3 chargers, particularly the very fast L3 chargers?

 

[phidauex]

Thank you, I appreciate this detailed explanation.

Would it be fair to say then that charge rate on any type of L2 charger (e.g., 32 amp vs 40 amp vs 48 amp) won’t be meaningfully different in terms of impact on long-term battery life, and the potential concern is limited to L3 chargers, particularly the very fast L3 chargers?

I don't think there will be a big difference. Technically there still is a little difference in degradation, but while we calculate meaningful differences (over 20 years) between 0.25C and 0.15C, anything less than 0.15C sort of disappears into the noise in terms of separating out any real change in degradation.

There is also charging efficiency to keep in mind - in general lower charge rates are more efficient (since heat losses increase with the square of current flow), but there is also a "fixed cost" of having the charging infrastructure running, power electronics operating, etc. Charging at 1 amp, for instance, would be very efficient for the battery itself, but the overhead to keep the whole system online would probably mean your actual "kWhs in vs. kWhs out" efficiency would be extremely low, maybe less than 50%.

For myself, I'll install a 48A hardwired charger, and dial it back a bit to 35 amps or so (8.4kW, 0.08C) unless I need it faster for a particular trip, and not worry about it. Over time we'll get more data on actual charging efficiency, and we can make some more precise choices. For most people it will probably be some balance of cost effectiveness (lower powers if you are on a residential demand rate), total efficiency, and battery longevity. However, I think that people who mostly charge at home don't need to worry much about degradation. If you are DCFC daily or weekly, or if you were a fleet operator where the vehicles are running full cycles every single day, then you'd have to put a lot more thought into it.

 

[back_at_it_19]

I don't think there will be a big difference. Technically there still is a little difference in degradation, but while we calculate meaningful differences (over 20 years) between 0.25C and 0.15C, anything less than 0.15C sort of disappears into the noise in terms of separating out any real change in degradation.

There is also charging efficiency to keep in mind - in general lower charge rates are more efficient (since heat losses increase with the square of current flow), but there is also a "fixed cost" of having the charging infrastructure running, power electronics operating, etc. Charging at 1 amp, for instance, would be very efficient for the battery itself, but the overhead to keep the whole system online would probably mean your actual "kWhs in vs. kWhs out" efficiency would be extremely low, maybe less than 50%.

For myself, I'll install a 48A hardwired charger, and dial it back a bit to 35 amps or so (8.4kW, 0.08C) unless I need it faster for a particular trip, and not worry about it. Over time we'll get more data on actual charging efficiency, and we can make some more precise choices. For most people it will probably be some balance of cost effectiveness (lower powers if you are on a residential demand rate), total efficiency, and battery longevity. However, I think that people who mostly charge at home don't need to worry much about degradation. If you are DCFC daily or weekly, or if you were a fleet operator where the vehicles are running full cycles every single day, then you'd have to put a lot more thought into it.

Never thought of that. I have a hardwired 48a charger also. Long commute and short enough overnights sometimes when I’ll prefer a full charge. But it’s easy to reduce output so might as well when time doesn’t matter.

 

[ARK]

I don't think there will be a big difference. Technically there still is a little difference in degradation, but while we calculate meaningful differences (over 20 years) between 0.25C and 0.15C, anything less than 0.15C sort of disappears into the noise in terms of separating out any real change in degradation.

There is also charging efficiency to keep in mind - in general lower charge rates are more efficient (since heat losses increase with the square of current flow), but there is also a "fixed cost" of having the charging infrastructure running, power electronics operating, etc. Charging at 1 amp, for instance, would be very efficient for the battery itself, but the overhead to keep the whole system online would probably mean your actual "kWhs in vs. kWhs out" efficiency would be extremely low, maybe less than 50%.

For myself, I'll install a 48A hardwired charger, and dial it back a bit to 35 amps or so (8.4kW, 0.08C) unless I need it faster for a particular trip, and not worry about it. Over time we'll get more data on actual charging efficiency, and we can make some more precise choices. For most people it will probably be some balance of cost effectiveness (lower powers if you are on a residential demand rate), total efficiency, and battery longevity. However, I think that people who mostly charge at home don't need to worry much about degradation. If you are DCFC daily or weekly, or if you were a fleet operator where the vehicles are running full cycles every single day, then you'd have to put a lot more thought into it.

Thank you, again, I really appreciate this. I will likely set my 48amp charger to 32 amp then for my standard range Mach E as charging speed is not a concern for me and the issue is battery preservation and efficiency in charging, as you detailed.

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