The myth of inefficent petrol motor charging on the PHEV.

[anko]

Some [most ?] people..... use Save mode

Flyer34, that is a good example of poor quoting. I wrote: "Some people play with Save mode to come by: ...", referring to the apparent wish for having a 50% er even higher 'baseline SOC' instead of the standard 30%. By removing to come by you separated my statement from its context. Also you added something to the quote that I did not write. Please be careful with that / don't do that ;-)

I do think / agree that there are good reasons to arrange for some additional SOC:
- To allow for EV driving on upcoming below-parallel-speed stretches
- To allow for smooth climbing / towing and such

Waiting to be within EV range of the next charge point before letting the SOC drop below, say, 50 % seems good politcs.

I think that, in general and when possible, it would be better to allow the battery to drain and rebuild the needed SOC from '0' by engaging Charge in due time, rather than to hang on to the required SOC by using Save all the time.

 

[anko]

My typical drives have hills, and 2-3 battery bars may be used in addition to the ICE on the way up some, which is replaced on flatter sections when in SAVE mode.

I was pretty sure Save will not recover any charge lost beyond the normal zigzag pattern?

 

[Grigou]

I was pretty sure Save will not recover any charge lost beyond the normal zigzag pattern?

Agree. In Save mode there is no chance to recharge on flat sections and to recover 2-3 bars.
Maybe 1 bar on particular circumstances (if you slow down with regen just after this bar as disappeared for example).

 

[FLYER34]

I think that, in general and when possible, it would be better to allow the battery to drain and rebuild the needed SOC from '0' by engaging Charge in due time, rather than to hang on to the required SOC by using Save all the time.

Sorry for mis-quoting your previous post.

As long as you reach your charging point with "---" EV range, I fail to see the difference in cost/efficiency between :
- keeping SOC at 50 % / 70 % in "save" mode ;
- staying in "normal" mode.

I did see a (big) difference in climbing an unexpected steep hill with "---" EV range rather than with a decent SOC reserve.
Switching to "Charge" in this kind of circumstance will not be of great help.

As long as you do not spoil valuable EV range by reaching the charge point with remaining SOC, zigzaging around 50 % SOC or around 27 % SOC does not make any difference at the end of the day.
Imho, facing an unexpected power demand will cost you more petrol + engine wear/noise with "---" EV range than with a comfortable SOC reserve.

After one or two bad experiences, I decided never to let the SOC drop below 50 % before the end of the planned trip :idea:

 

[Grigou]

It seems to be a wise decision, especially if we consider that 50 % SOC corresponds to less of 5 bars on the monitor, and less of 30 % of the useful capacity. Not a huge reserve btw ...

 

[anko]

As long as you reach your charging point with "---" EV range, I fail to see the difference in cost/efficiency between :
- keeping SOC at 50 % / 70 % in "save" mode ;
- staying in "normal" mode.

When SOC goes over 50% the charge current is reduced. And at higher SOC's more so. This means that the load on the engine is reduced and it is running less efficient, when it is running. In parallel hybrid mode there will be more or longer periods of parallel mode driving and less or shorter periods of EV driving.

Switching to "Charge" in this kind of circumstance will not be of great help.

True. This is why I wrote in due time

 

[gwatpe]

The only time a driver would want to drain the battery fully, is if before the next drive the battery could be fully recharged. Any other time, the battery capacity should be SAVEd. As has been mentioned before, the battery range in a longer mainly ICE driven trip, is insignificant and considering the possible terrain that my be driven through as a variable, having around 50% battery capacity available, covers high power needs as well as high REGEN needs. Lithium batteries are normally stored with 50% charge. I don't recharge my PHEV unless the battery shows under 50% remaining. For those short city drives by all means drive in normal mode and recharge as needed.

 

[maby]

The only time a driver would want to drain the battery fully, is if before the next drive the battery could be fully recharged. Any other time, the battery capacity should be SAVEd. As has been mentioned before, the battery range in a longer mainly ICE driven trip, is insignificant and considering the possible terrain that my be driven through as a variable, having around 50% battery capacity available, covers high power needs as well as high REGEN needs. Lithium batteries are normally stored with 50% charge. I don't recharge my PHEV unless the battery shows under 50% remaining. For those short city drives by all means drive in normal mode and recharge as needed.

Exactly what I've been saying for months! The car should have a "Prius mode" for long range use.

 

[FLYER34]

When SOC goes over 50% the charge current is reduced. And at higher SOC's more so. This means that the load on the engine is reduced and it is running less efficient, when it is running. In parallel hybrid mode there will be more or longer periods of parallel mode driving and less or shorter periods of EV driving.

Imho, the reduction in "charge current" you mention starts at a much higher SOC than 50 %. (80 % ??).
Look at the regen power : do you see a difference between regen at 50 % SOC ant regen at 70/80 % SOC ?
Imho again, as soon as the max regen is reached (3 bars missing), you can switch to "save". The loss you mention should be marginal.

I just saw, on another forum, reports that the Golf GTE has a "Hybrid Auto" mode :
- initially, only EV (to drain the battery for max regen) ;
then :
- more EV at low speeds (below 40 mph) ;
- more ICE at higher speeds.
Essentially what we do on our PHEV by switching manually between "save" and "normal" after an initial battery drain in EV.

True. This is why I wrote in due time

I did not understand what you meant by "in due time" : this is precisely the very reason for my previous mis-quotation.
Now, it is clear.
Sorry again

 

[kentphev]

The only time a driver would want to drain the battery fully, is if before the next drive the battery could be fully recharged. Any other time, the battery capacity should be SAVEd. As has been mentioned before, the battery range in a longer mainly ICE driven trip, is insignificant and considering the possible terrain that my be driven through as a variable, having around 50% battery capacity available, covers high power needs as well as high REGEN needs. Lithium batteries are normally stored with 50% charge. I don't recharge my PHEV unless the battery shows under 50% remaining. For those short city drives by all means drive in normal mode and recharge as needed.

Exactly what I've been saying for months! The car should have a "Prius mode" for long range use.

I agree. Previously I had a Peugeot 3008 diesel hybrid which (rightly or wrongly) in the manual said hydrid power was best used in stop/start or low speed driving when the ICE would be at its least efficient.

Conversely, if you let you battery drain to empty while, for example driving at a steady 50-60mph and then have nothing left for start/stop town driving after you wouldnt have made best use of the batts. Additionally once the range-to-destination matches the ev-range I flip back into EV.

On charge levels.... lots of 'experts' seem to agree with phone batteries keeping them around the 80% charge level with periodic deep discharge is supposed to be best. I'd assume that when the Phev says they are 100% charged they are probably not actually at full capacity physically. That way you could suffer some degradation of cells before you'd even notice.

 

[anko]

When SOC goes over 50% the charge current is reduced. And at higher SOC's more so. This means that the load on the engine is reduced and it is running less efficient, when it is running. In parallel hybrid mode there will be more or longer periods of parallel mode driving and less or shorter periods of EV driving.

Imho, the reduction in "charge current" you mention starts at a much higher SOC than 50 %. (80 % ??).
Look at the regen power : do you see a difference between regen at 50 % SOC ant regen at 70/80 % SOC ?
Imho again, as soon as the max regen is reached (3 bars missing), you can switch to "save". The loss you mention should be marginal.

Very true, when it comes to regen breaking. But my statement was (in line of this very topic) about charging from the petrol engine. What I have noticed more than once is that while driving at a constant pace, the instantaneous full consumption is reduced when SOC reaches about 50%. And a couple of times thereafter at even higher SOC's. IMHO this can only be explained by a reduction in charge current. One would expect a reduced load on the engine to result in a reduced efficiency.

I just saw, on another forum, reports that the Golf GTE has a "Hybrid Auto" mode :
- initially, only EV (to drain the battery for max regen) ;
then :
- more EV at low speeds (below 40 mph) ;
- more ICE at higher speeds.
Essentially what we do on our PHEV by switching manually between "save" and "normal" after an initial battery drain in EV.

Makes sense. I can see some added value there. But the question is: when driving on high speeds, how does the Golf know if we happen to have sufficient EV range left to make it to the next charging point? I assume it doesn't. So, it will keep using the ICE where we want it to go in EV mode. In order to use up all of your EV range, you may have to switch it off in time.

BTW: We have something similar in the PHEV, although the threshold is set to 130 km/h with us :mrgreen:

I did not understand what you meant by "in due time" : this is precisely the very reason for my previous mis-quotation.
Now, it is clear.
Sorry again

No problem

 

[maby]

It is possible to get too hung up on fuel efficiency, you know! I'm more interested in having a performant car that is pleasant to drive than squeezing the last couple of mpg out of it. The PHEV has a decent turn of acceleration but it does drag the battery down a fair bit.

 

[anko]

Interesting: the 3008 is a Diesel and would probably have been a much better match to gwatpe's driving profile (long trips with long periods without external charging). Is that something worthwhile thinking over?

Guy's, I do use Save to save a little bit of SOC for the last part of my trip, in many cases. All I am saying is: don't overdue it. If you drive around with more than 50% SOC, you hurt the efficiency of the car. Plus, you risk forgetting to disable Save mode in time and ending up at your next charge point with lot's of battery power left.

If you care for (prolonged) performance, more than efficiency (like I do while towing my caravan), then by all means, hang on to your SOC as much as you can.

Edit: Like maby

I think that for many people / driving conditions (like myself during day-by-day driving), performance is not so much an issue, and you would be better off allowing the car to use the full SOC bandwidth.

 

[anko]

It is possible to get too hung up on fuel efficiency, you know! I'm more interested in having a performant car that is pleasant to drive than squeezing the last couple of mpg out of it. The PHEV has a decent turn of acceleration but it does drag the battery down a fair bit.

I think this goes both ways. You can be so hung up on performance that you forget about efficiency. Everybody is entitled to his own view. I know that I bought the car because it was more fuel efficient then the next car, plus it had incentives associated with that.

 

[FLYER34]

... One would expect a reduced load on the engine to result in a reduced efficiency.
...
If you drive around with more than 50% SOC, you hurt the efficiency of the car. Plus, you risk forgetting to disable Save mode in time and ending up at your next charge point with lot's of battery power left.

I do not dispute these points.
Imho, the alleged "reduced efficiency" of the save mode at, or above, 50 % SOC must be balanced with the risks of :
1) running the ICE, due to low SOC, when stopped in traffic (you have no way to choose when the "zig" part of the hybrid mode starts) ;
2) running out of steam in an unexpected steep climb.

...how does the Golf know if we happen to have sufficient EV range left to make it to the next charging point? I assume it doesn't...

Of course, it does not, but the GTE also has a "save for later" mode for smart(er) drivers

 

[maby]

It is possible to get too hung up on fuel efficiency, you know! I'm more interested in having a performant car that is pleasant to drive than squeezing the last couple of mpg out of it. The PHEV has a decent turn of acceleration but it does drag the battery down a fair bit.

I think this goes both ways. You can be so hung up on performance that you forget about efficiency. Everybody is entitled to his own view. I know that I bought the car because it was more fuel efficient then the next car, plus it had incentives associated with that.

Quite true, but almost all the fuel efficiency comes from running in EV mode for short journeys, not from devising complex strategies to minimise petrol consumption on long journeys. I view it as two cars in a single body shell - up to the EV range of around 25 miles, it's an electric car and turns in figures of something in the region of 130mpg equivalent - depending on your electricity tariff. As soon as you go far beyond the EV range, the running costs on petrol start to dominate and once your journey gets up to a couple of hundred miles, you may as well consider it as a petrol car which gives you something between 35 and 40mpg. Given that the difference in fuel economy between the two modes is so very high, the way to minimise your running costs is to develop strategies for maximising your EV range. Once you are into petrol driven mode, I don't think that any amount of tinkering with Charge and Save is going to change your fuel consumption by more than a few percent - but letting the battery run completely flat (accepting that the control algorithms always save something close to 20%) does impact on performance and driveability.

 

[gwatpe]

+1

My driving needs are an EV car for the local runs, and essentially a petrol car for the long runs. Having both options now on how my PHEV powers ON, I find my PHEV much easier to drive with SAVE automatically selected for all drives. As soon as I hear the ICE start on a shorter drive, if I have forgotten to cancel SAVE mode, I just push the save button and cancel SAVE mode. ICE shuts down almost immediately. Might use 20-50ml of petrol. Not a big deal and probably helps to flush stale fuel from the injectors. AUS weather conditions where I live means preheating is not needed. The ICE only starts in normal mode if I put my boot into the accelerator, so essentially normal mode is EV mode for local driving. Don't have too much traffic to deal with in regional AUS.

We may waste more petrol trying to work it out by ourselves individually, than we may gain through any saved petrol later, so we need a thorough scientific study by an expert with the right tools to add a section to the manual.

PS: Trex has a PM :?:

 

[markogts]

Hello,

just came back from two relatively longer trips on highways (2x400km @110km/h true speed) without possibility to charge along them.

Let's make a premise: "charge" button pressed below 70km/h (i.e. serial mode) is different from "charge" button pressed above it (i.e. in parallel mode). In parallel mode, the engine is bond to the wheel speed, that is, it is limited in the power it can deliver. Any increase of demand in such a situation leads to the throttle opening, which is a good thing for the efficiency.

Now, while driving, I was wondering: if the save button is doing "zig-zag" sawtooth, with no clue of what is coming next, then, isn't it wiser to have the "zig" phase (engine running and charging) on high-power-demand parts of the trip and the "zag" (ev mode) on downhills and low-power-demand parts of the trip? In other words, to "steer" the zig-zag and fit it to the road. In this way you should have two advantages: the engine is always near the sweet spot and the current to and from the battery is always "small".

Therefore, what I did on the second trip, (with plenty of highway climbs and descents), was to push "charge" every time the road was going flat or up and reverting to normal when running downhill or along roadworks with lower speed limits.

I averaged 7,5l/100km plus the usual 10 kWh "dispersed" over 453km, of which 374 of highway and the remaining 79 mountain (and there it was painful, about 10 l/100km according to the board computer so the highway part should be around 7l/100km net)

I didn't know about Anko's advice to run below 50% SOC, which seems logical, but I quickly reached it anyway.

PS I did a stretch at full power on a steep highway uphill, 2 km with 8% incline: I was delighted by the ease with which the car was gaining speed, much better than my former V6 2.5 litre petrol sedan. Wifey light came on before the turtle... :?

 

[anko]

I do not dispute these points.
Imho, the alleged "reduced efficiency" of the save mode at, or above, 50 % SOC ...:/quote]
You don't dispute the alleged reduced efficiency? That's funny

1) running the ICE, due to low SOC, when stopped in traffic (you have no way to choose when the "zig" part of the hybrid mode starts) ;

But, I don't think the car will start to zig while stopped in in traffic. As a matter of fact, even if the car was zigging, it would stop zigging closely before coming to a full stop.

 

[anko]

In parallel mode, the engine is bond to the wheel speed, that is, it is limited in the power it can deliver. Any increase of demand in such a situation leads to the throttle opening, ...

Assumption? Or verified fact? It is my experience that with the first increase of demand, the fuel consumption doesn't change, but charging is reduced. Only after charging has been reduced to 0 (the blue charge arrow has dimmed) and demand further increases, fuel consumption increases.