Best speed to charge battery during long journeys?

[maby]

The benefit I find is the reduced series hybrid operation as a result of saving some battery.

I would have thought that achieving similar fuel consumption equates to similar amounts of time with the ICE operating. What am I missing?

I have a particular section of road with a transition from 80kph down a hill section to a 100kph section with an uphill grade, that I usually have SAVE mode engaged. My PHEV behaves the same as my mates, and drops out of parallel hybrid to series hybrid in the same way when the power is applied to accelerate in the 100kph section. ICE transitions from pleasant to drive, to ICE screaming.

My observations over almost 2 years ownership is biased with many tens of thousands of km with ICE operations. Soft pedaling at speeds under 70kph gives a quiet drive, when the PHEV operates series hybrid and parallel hybrid operation above 80kph has a similar quiet drive effect. I have found that consuming the electricity at high speed to deplete the battery, in NORMAL mode, leaves the computer less options for parallel mode operation at higher speeds [above 80kph], and the series hybrid kicks in for additional power needs, and this results in a less pleasant drive overall. There is not enough in it for economy savings for me to run with the depleted battery compared to keeping some additional reserve in it.

WRT best speed for recharging, 90-100kph, for the times I have needed to do it. Never tried to recharge at lower speeds, in series hybrid, as long journeys would typically be at higher speeds anyway.

I fully agree, gwatpe. While there are theoretical fuel savings to be achieved from running on a flat battery, and the ICE alone can supply sufficient power to drive the car, the real-world savings in fuel consumption are too small to reliably measure against the background noise and the car with a flat battery is just not very much fun to drive. If I set out on a 200 mile journey with a full battery, 180 of those miles is going to be driven on petrol - I may as well make them the first 180 miles and have charge in the battery to give me the extra boost.

 

[ChrisMiller]

If the ICE starts it should run at least 15 minutes or longer depending on temperature.

My impression is that the first time the ICE starts it runs until it has warmed up (particularly if it's starting in order to provide heating on a cold day). But I'm sure others can give you a more definitive answer.

 

[jaapv]

You will not feel a difference between a "flat" battery and a charged one. When the car tells you it is flat it is actually keeping a considerable reserve for "extra boost" .
In effect the car is running on "Save" around the 30% charge mark when you think that it is flat. That accounts for the bursts of ICE mentioned. It is exactly the same running it at "save" on a higher battery level.

We had this discussion before I seem to recall everybody agreed to disagree.

 

[maby]

You will not feel a difference between a "flat" battery and a charged one. When the car tells you it is flat it is actually keeping a considerable reserve for "extra boost" .
In effect the car is running on "Save" around the 30% charge mark when you think that it is flat. That accounts for the bursts of ICE mentioned. It is exactly the same running it at "save" on a higher battery level.

I'm not convinced of this, you know. In the same way that anko et. al. argue that better fuel economy will be achieved by running on a flat battery because it will accept a higher charge current, it would seem likely that the same flat battery cannot provide as much power
boost as a relatively charged battery because the voltage is lower and the available discharge current is lower. It's not so much a case of an overall reduction in acceleration as an increase in engine revs required to achieve it.

 

[jaapv]

As a Li-Ion battery cell only shows a 0.2 V drop between 80% and 30% I doubt that this would make a measurable difference.

 

[maby]

As a Li-Ion battery cell only shows a 0.2 V drop between 80% and 30% I doubt that this would make a measurable difference.

So why does anko seem to believe that he can detect a meaningful difference in charging current? Is it unreasonable to believe that there is a corresponding difference in discharge current available across the charge level spectrum?

 

[Kim]

With Li-batterys the voltage drop under high output is much higher at a lower SOC.
For example:
When you draw 50kW at 90% SOC the cell voltage will for that short time drop let's say 0.3 V (each cell!)
at 30% SOC the drop will be at least twice as high, 0.6 V

 

[jaapv]

As a Li-Ion battery cell only shows a 0.2 V drop between 80% and 30% I doubt that this would make a measurable difference.

So why does anko seem to believe that he can detect a meaningful difference in charging current? Is it unreasonable to believe that there is a corresponding difference in discharge current available across the charge level spectrum?

No. I do not observe the effect in engine response, though. YMMV.

 

[maby]

With Li-batterys the voltage drop under high output is much higher at a lower SOC.
For example:
When you draw 50kW at 90% SOC the cell voltage will for that short time drop let's say 0.3 V (each cell!)
at 30% SOC the drop will be at least twice as high, 0.6 V

ok - that is useful information and could go a long way towards explaining what I have always believed to be the case. With a (notionally) flat battery, if you demand significant amounts of power as in hard acceleration or a steep hill climb, the petrol engine will tend to race.

 

[anko]

You will not feel a difference between a "flat" battery and a charged one. When the car tells you it is flat it is actually keeping a considerable reserve for "extra boost" .
In effect the car is running on "Save" around the 30% charge mark when you think that it is flat. That accounts for the bursts of ICE mentioned. It is exactly the same running it at "save" on a higher battery level.

I'm not convinced of this, you know. In the same way that anko et. al. argue that better fuel economy will be achieved by running on a flat battery because it will accept a higher charge current, it would seem likely that the same flat battery cannot provide as much power
boost as a relatively charged battery because the voltage is lower and the available discharge current is lower. It's not so much a case of an overall reduction in acceleration as an increase in engine revs required to achieve it.

Hang on, I thought we had a more sophisticated view on this by now .... It is not so much how much power the battery can provide that makes the difference, it is the low SOC that makes it switch from EV mode to Serial mode, which causes the 'issue'.

Imagine you need 40 kW for driving. Even at an extremely low SOC, the battery can easily produce this amount, as I have proven with my graphs. That is not the problem. But if SOC is lower than (approx) 28% it will simply prefer not to do so. It will prefer to switch to Serial mode in the normal hysteresis cycle. And an engine producing 40 kW in Serial mode at relatively low speed is not very comfortable, as we know.

Even when driving very relaxed, without any climbing, I prefer to use the engine in parallel mode rather than serial mode. As it is less disturbing the peace in parallel mode. When driving hard, this effect gets bigger. Nothing to do with available power. IMHO.

 

[maby]

...

Hang on, I thought we had a more sophisticated view on this by now .... It is not so much how much power the battery can provide that makes the difference, it is the low SOC that makes it switch from EV mode to Serial mode, which causes the 'issue'.

....

I'm more concerned about the behaviour of the car at sub-parallel speeds - acceleration with the car already in serial mode. Under these circumstances, any demand for significant power levels on a flat battery seems to be met with high engine revs.

 

[jaapv]

How does this differ from running @ say 40 % SOC on save?

 

[anko]

How does this differ from running @ say 40 % SOC on save?

It doesn't. I guess you should not use Save mode in a low speed zone. Or when power demand is more than the engine can provide in parallel mode. Problem solved.

Maby, do you have to disengage Save mode to prevent the screaming engine?

 

[anko]

...

Hang on, I thought we had a more sophisticated view on this by now .... It is not so much how much power the battery can provide that makes the difference, it is the low SOC that makes it switch from EV mode to Serial mode, which causes the 'issue'.

....

I'm more concerned about the behaviour of the car at sub-parallel speeds - acceleration with the car already in serial mode. Under these circumstances, any demand for significant power levels on a flat battery seems to be met with high engine revs.

But this is exactly what I was trying to say! Due to the low SOC, the car has switched from EV mode to Serial mode and a s a consequence, the engine responds to every little move of the accelerator pedal. The screaming engine is not because the battery cannot provide 60 kW at low SOC, it is because the car has selected Serial mode because of the low SOC.

Performance is not impacted. Comfort is.

 

[maby]

...

Hang on, I thought we had a more sophisticated view on this by now .... It is not so much how much power the battery can provide that makes the difference, it is the low SOC that makes it switch from EV mode to Serial mode, which causes the 'issue'.

....

I'm more concerned about the behaviour of the car at sub-parallel speeds - acceleration with the car already in serial mode. Under these circumstances, any demand for significant power levels on a flat battery seems to be met with high engine revs.

But this is exactly what I was trying to say! Due to the low SOC, the car has switched from EV mode to Serial mode and a s a consequence, the engine responds to every little move of the accelerator pedal. The screaming engine is not because the battery cannot provide 60 kW at low SOC, it is because the car has selected Serial mode because of the low SOC.

Performance is not impacted. Comfort is.

OK - difference in terminology - as far as I'm concerned, once the battery has gone flat it is never in EV mode - it's either serial or parallel and may turn the engine off from time to time if it's managed to build up sufficient buffer in the battery. I'll take your word on performance - if my engine is racing, I automatically back off the accelerator and performance does effectively suffer.

I've kept out of the discussions of the pure EV mode mods that are being tested because they are not appropriate to my driving style. If our chipper would come up with a "Prius Mode" mod that would move the hysteresis loop up so that it oscillated around 50 or 60% and, hence, protected us from the racing engine, then I would be seriously interested.

 

[anko]

OK - difference in terminology - as far as I'm concerned, once the battery has gone flat it is never in EV mode - it's either serial or parallel and may turn the engine off from time to time if it's managed to build up sufficient buffer in the battery. I'll take your word on performance - if my engine is racing, I automatically back off the accelerator and performance does effectively suffer.

It is your performance than, that suffers

I've kept out of the discussions of the pure EV mode mods that are being tested because they are not appropriate to my driving style. If our chipper would come up with a "Prius Mode" mod that would move the hysteresis loop up so that it oscillated around 50 or 60% and, hence, protected us from the racing engine, then I would be seriously interested.

:shock: You would have the exact same problem. But than with a 50% or 60% charged battery instead of with a 30% charged battery. The point is, for what you want, you need to keep SOC above the normal hysteresis level.

 

[jaapv]

How does this differ from running @ say 40 % SOC on save?

It doesn't. I guess you should not use Save mode in a low speed zone. Or when power demand is more than the engine can provide in parallel mode. Problem solved.

I see we agree.

 

[jaapv]

...

Hang on, I thought we had a more sophisticated view on this by now .... It is not so much how much power the battery can provide that makes the difference, it is the low SOC that makes it switch from EV mode to Serial mode, which causes the 'issue'.

....

I'm more concerned about the behaviour of the car at sub-parallel speeds - acceleration with the car already in serial mode. Under these circumstances, any demand for significant power levels on a flat battery seems to be met with high engine revs.

But this is exactly what I was trying to say! Due to the low SOC, the car has switched from EV mode to Serial mode and a s a consequence, the engine responds to every little move of the accelerator pedal. The screaming engine is not because the battery cannot provide 60 kW at low SOC, it is because the car has selected Serial mode because of the low SOC.

Performance is not impacted. Comfort is.

Which is why the VTech box modifies pedal response, I guess.

 

[Claymore]

So why does anko seem to believe that he can detect a meaningful difference in charging current? Is it unreasonable to believe that there is a corresponding difference in discharge current available across the charge level spectrum?

As the SOC gets closer to 100% a good charging system will always reduce the charging current to a multi cell lithium pack in order to ensure that any wayward cells are not pushed beyond their safe maximum voltage during the period of the charge when the charger is balancing the cells and attempting to get them all to as close as 100% as possible simultaneously and in doing that it will stop charging some cells whilst others catch up. So the charger will put much more current in at low levels of SOC than can be done at high levels of SOC - irrespective of how much current the generator might be capable of giving at any given moment.

Whether that restriction is fed back to the ICE motor so it doesn't thrash itself to death for no result I have no idea.

At the other end of the process when the drive pack is depleted the car's circuitry should also stop energy flowing out of the pack when one or more cells are nearing their minimum safe voltage irrespective of the overall SOC of the whole pack.

JimB

 

[maby]

So why does anko seem to believe that he can detect a meaningful difference in charging current? Is it unreasonable to believe that there is a corresponding difference in discharge current available across the charge level spectrum?

As the SOC gets closer to 100% a good charging system will always reduce the charging current to a multi cell lithium pack in order to ensure that any wayward cells are not pushed beyond their safe maximum voltage during the period of the charge when the charger is balancing the cells and attempting to get them all to as close as 100% as possible simultaneously and in doing that it will stop charging some cells whilst others catch up. So the charger will put much more current in at low levels of SOC than can be done at high levels of SOC - irrespective of how much current the generator might be capable of giving at any given moment.

Whether that restriction is fed back to the ICE motor so it doesn't thrash itself to death for no result I have no idea.

At the other end of the process when the drive pack is depleted the car's circuitry should also stop energy flowing out of the pack when one or more cells are nearing their minimum safe voltage irrespective of the overall SOC of the whole pack.

JimB

So, I think what I would like is a mode that holds the SOC around 50% with a lazy hysteresis policy such that the battery can source big surges in demand without thrashing the engine. I would effectively be telling the car that it can expect to stay running for a long time, so be prepared to such the battery down quite hard and be relaxed about recharging it. Just make use of the battery to avoid thrashing the engine and don't then push the revs up high to recharge it - it will have another hour or more to recharge.