Charge vs Save in steady-state driving

[ThudnBlundr]

On a long trip last weekend, I got to thinking about the relative merits of just leaving the PHEV to do its own thing vs managing the charging via the buttons while on a motorway.

Once the battery is empty, it goes into the hysteresis loop, constantly charging and emptying the battery. I wondered if I could get similar economy just by running the car in Charge mode for longer, and then emptying the battery as normal. It would be a similar hysteresis loop, but just longer in duration, so the economy should be similar. Or am I missing something?

The reason I was wondering was recharging while on the motorway for a slower drive later on, such as into town. I'm not sure how efficient the hysteresis loop would be in town, and wondered if having a battery charged on the motorway might actually be more efficient use of energy if the ICE would be running anyway. It could use spare capacity rather than firing up just to charge the drive battery around town.

Any thoughts?

 

[anko]

This is what many of us do. And this is what many of us believe to be more efficient. Two notes:

- Make sure you do not overdo it causing you to return home with a non-empty battery. That would be defeating the purpose.

- Myself and a few others are convinced that the efficiency of the hysteresis cycle suffers from high SOC, because at SOC above 65% real (50% on the gauge) the charge current is limited (compare with DC charging tapering off) and then engine can no longer operate in its sweetspot. Not everybody agrees or believe it is worth worrying about. But then again, if you didn't want to worry, it would probably be best to leave all buttons be ;-)

 

[elm70]

On a long trip last weekend, I got to thinking about the relative merits of just leaving the PHEV to do its own thing vs managing the charging via the buttons while on a motorway.

Once the battery is empty, it goes into the hysteresis loop, constantly charging and emptying the battery. I wondered if I could get similar economy just by running the car in Charge mode for longer, and then emptying the battery as normal. It would be a similar hysteresis loop, but just longer in duration, so the economy should be similar. Or am I missing something?

The reason I was wondering was recharging while on the motorway for a slower drive later on, such as into town. I'm not sure how efficient the hysteresis loop would be in town, and wondered if having a battery charged on the motorway might actually be more efficient use of energy if the ICE would be running anyway. It could use spare capacity rather than firing up just to charge the drive battery around town.

Any thoughts?

I plan my trip on motorway to have enough battery charged for drive in EV mode outside the motorway (if this is my final destination with a charging option, I need to charge the exact amount of EV range since having left EV range before charge the car it is a waste of fuel) ... I can't prove if this is more or less efficient ... but it is logically more efficient and logically more ecological .. also is more cool to drive in a city in pure EV

I was also trying to make manual but longer "hysteresis loop" ... on long motorway trip ... like charging up to 10km EV range, and then doing 10km in pure EV mode ... but I believe this is just marginal more efficient, and possibly more a stress for the battery ... so I'm not doing this anymore (I don't know if this is a coincidence, but after 2 weeks of ICE driving and some manual charge via ICE and no access to J1772 charging, my PHEVwhatchDog report my record battery lost of 0.5Ah in one single shot .. it also 3k km in 2 weeks and very hot climate ... still I was not expecting this massive battery degradation after this trip) .. or better ... I just discharge at the beginning my EV battery .. and then slowly charging (by changing from save to charge intermittently) in the motorway for achieve the needed km in EV mode outside motorway

 

[maby]

Trex ran some very detailed tests a couple of years ago which indicated a small improvement in fuel economy from letting the battery run right down. The theory is that the battery will accept charge more efficiently when flat and hence the hysteresis loop operates better. Trex is in Australia - long, flat, empty roads where he could just set the cruise control and drive fifty miles at a steady speed. I tried repeating his tests on UK motorways and could detect no difference - the few percent improvement he claimed gets swamped under the noise caused by hills and traffic jams.

Personally, I like my battery fully charged so that it can give me the maximum acceleration boost when I need it. I drive on "Save" with an almost full battery on any long journey - once you are doing a hundred miles or more at motorway speeds, the improvement in fuel consumption achievable from fiddling with the controls is just too small to be worth it.

 

[anko]

Personally, I like my battery fully charged so that it can give me the maximum acceleration boost when I need it.

I believe we agreed that the reason was so much not performance, because on an 'empty' battery, the car will perform the same as on a charged battery. If I am not mistaken, the reason was attempting to increase comfort by preventing serial mode and the associated (occasional) high revving?

I have presented diagrams here some time ago, showing the two e-motors of the car delivering full power at an SOC well below 30%.

 

[maby]

Personally, I like my battery fully charged so that it can give me the maximum acceleration boost when I need it.

I believe we agreed that the reason was so much not performance, because on an 'empty' battery, the car will perform the same as on a charged battery. If I am not mistaken, the reason was attempting to increase comfort by preventing serial mode and the associated (occasional) high revving?

I have presented diagrams here some time ago, showing the two e-motors of the car delivering full power at an SOC well below 30%.

I did say "battery fully charged so that it can give me the maximum acceleration boost when I need it" - in the absence of a significantly charged battery, more of the power has to come from the engine - resulting in the high engine revs. It happens at lower speeds when the car is in serial mode all the time - I have several reasonably steep hills around my house - trying to accelerate up them with a flat battery makes the engine scream like a banshee whereas I can pull away from stationary and accelerate to 40mph with the engine maintaining a relatively low speed provided I have a full battery.

 

[anko]

in the absence of a significantly charged battery, more of the power has to come from the engine - resulting in the high engine revs.

IMHO, the difference is not high or low SOC. The difference is the fact that you are already in serial mode. Once the engine is running, the car will get as much power as needed / available from the engine and only use the battery when the engine can't handle the load. Whether the battery if full or empty doesn't make a difference. Even with a full battery, if you need more power than the battery can provide, you will go into serial mode and are likely experience high revving. But regardless of SOC, the maximum amount of power available is the same (unless you manage to get into Turtle mode, of course).

I seriously thought we agreed on this earlier :?:

 

[maby]

in the absence of a significantly charged battery, more of the power has to come from the engine - resulting in the high engine revs.

IMHO, the difference is not high or low SOC. The difference is the fact that you are already in serial mode. Once the engine is running, the car will get as much power as needed / available from the engine and only use the battery when the engine can't handle the load. Whether the battery if full or empty doesn't make a difference. Even with a full battery, if you need more power than the battery can provide, you will go into serial mode and are likely experience high revving. But regardless of SOC, the maximum amount of power available is the same (unless you manage to get into Turtle mode, of course).

I seriously thought we agreed on this earlier :?:

We may have thought that we agreed, but my experience of my car does not correspond to your description above. The location of my home is such that I often have to accelerate up a moderately steep hill from stationary at the bottom. With a full battery, I can accelerate from stationary to 40mph reasonably quickly without the engine racing - with a flat battery, it is screaming all the way up. With my driving style, it is rare for the car to drop out of parallel mode into serial for acceleration - most of my mileage is on motorways and I generally accelerate to about 70mph, turn on the cruise control, and continue at 70 to my destination. I like to get from stationary to my target speed quickly, but then drive in a pretty relaxed style till I stop.

 

[anko]

With a full battery, I can accelerate from stationary to 40mph reasonably quickly without the engine racing - with a flat battery, it is screaming all the way up.

So, it is more comfortable. I had already granted you that one. But I still think that your conclusion that with low SOC the car does not have enough power to provide maximum acceleration is misguided. And apart from the statement itself, I have not heard anything from you (or anybody else) that suggests it might be true.

As most people know by now, I regularly tow a 1500 kg caravan. To Croatia, to the south of France (A75 north bound will take care of your SOC, like it or not), etc. I have experienced a revving engine many many times. But nly once I have experienced reduced power, and this was when I had indeed ended up in Turtle mode after a long 'high' speed climb. Other times I saw the Turtle, it was just a warning and power was not reduced.

 

[maby]

With a full battery, I can accelerate from stationary to 40mph reasonably quickly without the engine racing - with a flat battery, it is screaming all the way up.

So, it is more comfortable. I had already granted you that one. But I still think that your conclusion that with low SOC the car does not have enough power to provide maximum acceleration is misguided. And apart from the statement itself, I have not heard anything from you (or anybody else) that suggests it might be true.

As most people know by now, I regularly tow a 1500 kg caravan. To Croatia, to the south of France (A75 north bound will take care of your SOC, like it or not), etc. I have experienced a revving engine many many times. But nly once I have experienced reduced power, and this was when I had indeed ended up in Turtle mode after a long 'high' speed climb. Other times I saw the Turtle, it was just a warning and power was not reduced.

We are talking at cross-purposes - as is often the case - I don't disagree that the car is able to meet its stated performance on a flat battery, but only by racing the engine far more than I would consider acceptable. The poor little petrol engine in the PHEV is only two litres and normally aspirated - nothing high-tech or high performance. It is also having to move a heavy battery that becomes dead-weight as soon as it is flat. If Mitsubishi had simply taken the diesel engine out of a standard Outlander, shoved a large bag of sand under the floor and installed a two litre petrol engine, it would have been laughed out of existence. On the other hand, you seem to claim that there is nothing wrong with running a PHEV on a flat battery - that really does not make sense.

 

[anko]

I don't disagree that the car is able to meet its stated performance on a flat battery, but only by racing the engine far more than I would consider acceptable.

Regardless of whether the battery is full or empty (with an exception for 'extremely' empty) max output of the drive train at speeds below 125 km/h is 160 kW. Regardless of whether the battery is full or empty it requires 4100 RPM from the engine to achieve that 160 kW.

 

[ThudnBlundr]

Thanks for your thoughts. I hadn't considered the slower charging at higher SOC, so leaving it charging at higher SOC may be less efficient. And I can understand why the theoretical efficiency could be lost in the "noise" of normal UK use. Having been told that using Charge was inefficient fairly regularly, I can see why it might be better to use it occasionally, especially if you've got an urban trip at the end, but only to charge to roughly 50% range

I am not at all clear why a battery with a higher SOC should be able to produce the "better" peak power than an empty battery at 30%. Obviously you can cause problems if you continue to empty it, but the peak power should be fairly constant across the SOC.

 

[elm70]

..

I am not at all clear why a battery with a higher SOC should be able to produce the "better" peak power than an empty battery at 30%. Obviously you can cause problems if you continue to empty it, but the peak power should be fairly constant across the SOC.

A (/any) battery with Higher SOC can deliver more peak power , compared to low SOC

And this is true on Tesla in ludicrous mode.

But, in our PHEV the max power is looking designed/configured .. this means at high SOC the current draw from the battery is low, and at low SOC this current is higher ... it does not make much sense .. but this is what they design in Japan.

The limitation for the battery is always in amount of current that it can provide .. and same apply for the cabling

Possibly in Japan , they must have decided that the car should behave/perform equally independently by the SOC
So .. it is a design decision to reduce the max power possible at high SOC ... and limit the experience to the lowest safe max power level