[WopOnTour]

One of the concerns we've heard expressed by some is the initial disabling of regenerative braking immediately after charging, when the owner lives (or charges) at near the top of steep grade.

Since with a fully charged battery there is no place to store the energy, the only option either to permit the system to brake the car using hydraulic/friction brakes, OR to manually stop charging so as to leave some room for the energy produced by regen during that initial descent.

Well the Bolt employs a a charging system feature that looks to mitigate this occurrence.

Hill-Top Reserve , when engaged in charging options and will automatically stop the charge slightly short of a full charge so that regen will be immediately available.

This feature also integrates with the Location Based Charging feature, allowing the system to be configured so it is enabled when at home (On - Home Only) or away (On - Away Only)

Problem Solved!

WopOnTour

 

[Fyodor]

Does this mean that the Bolt would ordinarily charge to 100%, or that the buffer at the top end is extended?

 

[WopOnTour]

Thanks! (a dull charge is not so sharp!)

The fully charged SOC is reduced in order to permit immediate regen on the next trip cycle

WOT

 

[Steverino]

Does the lip of my garage entrance count as a hill top? I live in the Chicago area. It's pretty flat around here.

 

[Michaelh310]

IMO everyone should use the hilltop setting (90%) as their normal charge target, reserve "full" charge for those occasions when additional range is needed. This should significantly increase battery lifespan.

I DO understand that "full charge" is not 100% SOC, it's probably something like 90%. So the hilltop setting should be perhaps 81% SOC, easier on the battery than full charge 90% (or whatever it is...)

 

[BAZINGA]

Does the lip of my garage entrance count as a hill top? I live in the Chicago area. It's pretty flat around here.

Us "flat landers" will never know the joy.

 

[bro1999]

Nice "workaround" of the EPA's blending rule. Now everyone can set max charge to 90% if they want....regardless of whether they live @ 3,000 feet or 0.3 feet above sea level.

 

[WopOnTour]

If we're doing spelling.......

decent - of an acceptable standard; satisfactory

descent - an action of moving downward, dropping, or falling

Nice, well OK then
WOT

 

[Fyodor]

Suppose you live halfway up (or down) a hill? Maybe the algorithm should look into your driving history and battery usage, as it does for the range guesser.

 

[ItsNotAboutTheMoney]

One of the concerns we've heard expressed by some is the initial disabling of regenerative braking immediately after charging, when the owner lives (or charges) at near the top of steep grade.

Since with a fully charged battery there is no place to store the energy, the only option either to permit the system to brake the car using hydraulic/friction brakes, OR to manually stop charging so as to leave some room for the energy produced by regen during that initial descent.

Well the Bolt employs a a charging system feature that looks to mitigate this occurrence.

Hill-Top Reserve , when engaged in charging options and will automatically stop the charge slightly short of a full charge so that regen will be immediately available.

This feature also integrates with the Location Based Charging feature, allowing the system to be configured so it is enabled when at home (On - Home Only) or away (On - Away Only)

Problem Solved!

WopOnTour

So, you can't just set a percentage or is that in addition to a percentage limit?

 

[Jeff N]

So, you can't just set a percentage or is that in addition to a percentage limit?

As far as I could tell from playing with the center charging screens at the LA Auto Show there is no Tesla-like "slider" to set a custom charge percentage upper limit. That's a bit absurd. It's such an obvious idea, gets past the EPA range calculation marketing concerns, and lets customers do what they want in an obvious way without having to "fake it" by magically knowing to set a single fixed "Hill Reserve" option.

It always amazes me when products get so many complex things right and then goof up the really easy things. I would hope this can be fixed with an over-the-air software update but I'm guessing that won't happen and any slider-type control will only be added in a future model year.

 

[Qinsp]

As far as I could tell from playing with the center charging screens at the LA Auto Show there is no Tesla-like "slider" to set a custom charge percentage upper limit. That's a bit absurd. It's such an obvious idea, gets past the EPA range calculation marketing concerns, and lets customers do what they want in an obvious way without having to "fake it" by magically knowing to set a single fixed "Hill Reserve" option.

It always amazes me when products get so many complex things right and then goof up the really easy things. I would hope this can be fixed with an over-the-air software update but I'm guessing that won't happen and any slider-type control will only be added in a future model year.

I can already to that with the Volt if I wish. Let's say I leave each morning at 6:30 am. I tell it I leave at 7:30 am, and it will leave about 2-3 kWh up top.

It's probably why they did "finish time" instead of start time, so you could leave a top buffer if you want, or only charge enough to get to work if you have free work charging.

 

[ItsNotAboutTheMoney]

I can already to that with the Volt if I wish. Let's say I leave each morning at 6:30 am. I tell it I leave at 7:30 am, and it will leave about 2-3 kWh up top.

It's probably why they did "finish time" instead of start time, so you could leave a top buffer if you want, or only charge enough to get to work if you have free work charging.

The problem with playing with time is that it depends on how much charge you had at the start, which means that you'd have to change your leave time a lot.

GM's idea is useful, but they're essentially saying that the only reason you'd not want to fill up is because you live or work on a hill. But with a BEV public charging is an obvious example where you would want the car to limit charging. I'd want to be able easily to set an upper limit.

 

[Fyodor]

The problem with playing with time is that it depends on how much charge you had at the start, which means that you'd have to change your leave time a lot.

GM's idea is useful, but they're essentially saying that the only reason you'd not want to fill up is because you live or work on a hill. But with a BEV public charging is an obvious example where you would want the car to limit charging. I'd want to be able easily to set an upper limit.

The car does limit charging. It just doesn't normally allow you to vary the limit. What this does is lower the limit in one situation.

 

[Jeff N]

I can already to that with the Volt if I wish. Let's say I leave each morning at 6:30 am. I tell it I leave at 7:30 am, and it will leave about 2-3 kWh up top.

It's probably why they did "finish time" instead of start time, so you could leave a top buffer if you want, or only charge enough to get to work if you have free work charging.

It's ridiculous that you cannot directly express what you want. You shouldn't have to play games to creatively coerce the car into doing what you want.

 

[Fyodor]

It's ridiculous that you cannot directly express what you want. You shouldn't have to play games to creatively coerce the car into doing what you want.

What would you actually gain if you could lower the upper limit to, say, 70%? Probably nothing in terms of battery life. Raising it beyond the set point might well do harm in the long run. So a fixed limit determined by GM makes sense to me.

WoT's hack leaves the actual upper limit where it is, but is intended to leave a little capacity unused below it that could absorb extra regeneration if needed.

 

[Jeff N]

What would you actually gain if you could lower the upper limit to, say, 70%? Probably nothing in terms of battery life. Raising it beyond the set point might well do harm in the long run. So a fixed limit determined by GM makes sense to me.

WoT's hack leaves the actual upper limit where it is, but is intended to leave a little capacity unused below it that could absorb extra regeneration if needed.

The rate of calendar aging of batteries similar to the ones in the Bolt TV is influenced by the combination of temperature and state of charge, especially when temperatures are hot and the state of charge is very high. You can find various studies and graphs if you Google around and the results differ for various Lithium battery chemistries but the general idea is broadly verified.

GM won't tell us what the precise nominal battery capacity is versus the usable capacity. In other words, when the car says it is charged to 100% of its usable capacity we don't how know that maps to the state of charge using the battery's actual capacity. Is 100% usable really 95% of the nominal capacity? We don't know yet.

Here are a couple of calendar time vs. temperature vs. state of nominal charge graphs.

This one shows the general idea:

The one below shows especially high capacity fade when the state of charge is over 95% nominal capacity at temperatures of 40C (104F) and higher. It also shows a substantial bump in capacity fade for charge levels above 60% or so versus charge levels up to 95%. So, perhaps 80% vs 90% is not so different but 55% versus 90% is substantial over the years:

Other studies show the best charging strategy is generally to charge shortly before you need to drive and charging at a typical L2 speed like 6-7 kW on 240V is somewhat better than 1.2 kW on 120V because it leaves the battery at lower charge levels on average.

In my case, with my long 45 mile commute each direction between work and home, it would appear to be ideal if I could set a weekday default charge level to about 70-75% reached in the morning before driving and then arrive at work with about a 50% charge. My return home would leave me with about a 30% charge and that gives me all of the extra flexibility I need if I make a side trip to the grocery store or to lunch at a restaurant during the day.

Today, the Bolt EV gives me no obvious and simple way to express my ideal charging configuration.

Of course, most people can happily ignore this level of detail but those of us who care (those prone to always change their gas engine oil on time etc. in the old times) do want simple ways of directly setting this up.

 

[WopOnTour]

The rate of calendar aging of batteries similar to the ones in the Bolt TV is influenced by the combination of temperature and state of charge, especially when temperatures are hot and the state of charge is very high. You can find various studies and graphs if you Google around and the results differ for various Lithium battery chemistries but the general idea is broadly verified.

GM won't tell us what the precise nominal battery capacity is versus the usable capacity. In other words, when the car says it is charged to 100% of its usable capacity we don't how know that maps to the state of charge using the battery's actual capacity. Is 100% usable really 95% of the nominal capacity? We don't know yet.

Here are a couple of calendar time vs. temperature vs. state of nominal charge graphs.

This one shows the general idea:



The one below shows especially high capacity fade when the state of charge is over 95% nominal capacity at temperatures of 40C (104F) and higher. It also shows a substantial bump in capacity fade for charge levels above 60% or so versus charge levels up to 95%. So, perhaps 80% vs 90% is not so different but 55% versus 90% is substantial over the years:



Other studies show the best charging strategy is generally to charge shortly before you need to drive and charging at a typical L2 speed like 6-7 kW on 240V is somewhat better than 1.2 kW on 120V because it leaves the battery at lower charge levels on average.

In my case, with my long 45 mile commute each direction between work and home, it would appear to be ideal if I could set a weekday default charge level to about 70-75% reached in the morning before driving and then arrive at work with about a 50% charge. My return home would leave me with about a 30% charge and that gives me all of the extra flexibility I need if I make a side trip to the grocery store or to lunch at a restaurant during the day.

Today, the Bolt EV gives me no obvious and simple way to express my ideal charging configuration.

Of course, most people can happily ignore this level of detail but those of us who care (those prone to always change their gas engine oil on time etc. in the old times) do want simple ways of directly setting this up.

I dont think Fyodor was referring to calendar aging, he was referring to charge-discharge cycle degradation that certainly can be minimized if the soft-stop for charging regularly occurs at a lower SOC. The Volt is a good example of that.

The negative effects of calendar aging at high cell temperatures, technically only takes place during periods where there is no charge or discharge taking place.
Attempting to optimize SOC for calendar aging over the course of those periods on a car that is in regular use is an exercise in futility. Especially so without data specific to the particular chemistry, and doubly so for an EV with a BMS that thermally maintains average cell temps during that period anyways. (providing you're plugged in)

Personally I think you're overthinking it
The average consumer is not interested in playing such games "tailoring" their resting SOCs in such a fashion
Fun for those with the inclination but for most people? Unnecessary
Just drive and smile!

WOT

 

[Steverino]

Personally I think you're overthinking it
The average consumer is not interested in playing such games "tailoring" their SOCs in such a fashion
Fun for those with the inclination but for most people? Unnecessary
Just drive and smile!

WOT

I tend to agree. While a number of enthusiasts may want the ability to fine tune, the vast majority just want to drive the car, not run a science experiment. Still, in an age of software controls, it would seem easy (?) to allow the driver to set their own level.

 

[Fyodor]

......

Of course, most people can happily ignore this level of detail but those of us who care (those prone to always change their gas engine oil on time etc. in the old times) do want simple ways of directly setting this up.

I am one of those who do care, but in this case I tend to think in more practical terms.

Suppose GM adds the capability to adjust buffer levels, and sells 500,000 Bolts. Perhaps 1% of the owners will have the inclination, and the understanding, to do this intelligently. You've demonstrated in detail how much goes into such a decision. Even for those few the actual benefits will be minimal.

That leaves 495,000 subject to the Spinal Tap Principle - if the knob goes to 11, that's where you set it. More always seems better, and for a significant number of those users there will be problems. GM does not want to deal with those problems, so they set fixed and conservative limits that work for everyone. It's just good business.