[Teslarati] "Auto experts reveal why Tesla’s batteries hold a comfortable lead ..."
09-19-2019, 10:19 AM
#16
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In addition to needing the RPM vs. efficiency curve for the motors involved, you also need to consider the efficiency loss within a two-speed gearbox versus a simple fixed gear reduction.
The Porsche two-speed gearbox is surprisingly complex. It contains a wet clutch, it seems, which would likely require a 40,000 or 60,000 mile change as in PDKs. And oddly, it includes a reverse gear - there must be something about how it operates that doesn't allow simply running the motor backwards. Perhaps the pump(s) for its controls.
If it's an option on the lesser models, as the configurator seems to suggest, I wouldn't want it.
The Porsche two-speed gearbox is surprisingly complex. It contains a wet clutch, it seems, which would likely require a 40,000 or 60,000 mile change as in PDKs. And oddly, it includes a reverse gear - there must be something about how it operates that doesn't allow simply running the motor backwards. Perhaps the pump(s) for its controls.
If it's an option on the lesser models, as the configurator seems to suggest, I wouldn't want it.
09-19-2019, 10:35 AM
#17
If I'm really short, a 45 minute lunch break while supercharging will get me back to almost 80% charge which is plenty to get me to my destination. We've stopped using our ICE cars for the most part since we got the M3. Plus the ICE cars are absolutely boring to drive compared to EV torque monster.
09-19-2019, 10:51 AM
#18
Burning Brakes
because there isn’t that much spread on efficiency in an electric motor - we are talking about moving from like 86/87% efficient to 90% efficient based on dropping RPMs - simple put EV motors don’t have wide efficiency variation that ICE motors have - there isn’t that much to gain - the torque curve has a bit more to gain which is why i suspect porsche did it - better 50-100 mph behavior - formula-e has transmissions i believe - because they are chasing those single digit performance gains
changing rpms in an EV does not dramatically alter efficiency like it does in a ICE - it has some effect - but not what you are used to.
transmission was more about performance than range - extra weight/complexity probably made range worse - best case a wash in certain circumstances.
ICE motors have efficiency ranges from like 7-30% - if you are in an RPM range where it’s 10% efficiency you can double efficiency by dropping RPM’s and moving to the 20% efficiency range, or even triple it by moving to the top 30% - there is no doubling/tripling efficiency by shifting RPM’s in an EV motor - I found one table that showed 84% to 93% efficiency range for a static load EV motor…that’s a spread of 9% difference across the entire RPM range - with most values being close to 90% for MOST of the RPM range - it’s only at the extreme ends of the RPM range (near zero and near max) that you get the spread...
porsche is a performance brand - I can’t believe they did themselves any major favors with the transmission regarding range - I’m 100% positive they did work to minimize or mitigate the overhead of the transmission when cruising and even if there is only say a 9% spread it’s worth chasing when you need it - but I see the transmission as more trouble than it’s worth and as @Adk46 points out below there now may be a maintainence schedule which undermines ones of the main EV advantages…
EV’s can be made very simple mechanically - Porsche added complexity for some reason - most likely performance - because it wasn’t for complexity or cost reduction - range is a stretch (I can lose 9% efficiency given a stiff head wind or simply driving slightly faster).
changing rpms in an EV does not dramatically alter efficiency like it does in a ICE - it has some effect - but not what you are used to.
transmission was more about performance than range - extra weight/complexity probably made range worse - best case a wash in certain circumstances.
ICE motors have efficiency ranges from like 7-30% - if you are in an RPM range where it’s 10% efficiency you can double efficiency by dropping RPM’s and moving to the 20% efficiency range, or even triple it by moving to the top 30% - there is no doubling/tripling efficiency by shifting RPM’s in an EV motor - I found one table that showed 84% to 93% efficiency range for a static load EV motor…that’s a spread of 9% difference across the entire RPM range - with most values being close to 90% for MOST of the RPM range - it’s only at the extreme ends of the RPM range (near zero and near max) that you get the spread...
porsche is a performance brand - I can’t believe they did themselves any major favors with the transmission regarding range - I’m 100% positive they did work to minimize or mitigate the overhead of the transmission when cruising and even if there is only say a 9% spread it’s worth chasing when you need it - but I see the transmission as more trouble than it’s worth and as @Adk46 points out below there now may be a maintainence schedule which undermines ones of the main EV advantages…
EV’s can be made very simple mechanically - Porsche added complexity for some reason - most likely performance - because it wasn’t for complexity or cost reduction - range is a stretch (I can lose 9% efficiency given a stiff head wind or simply driving slightly faster).
09-19-2019, 12:52 PM
#19
Rennlist Member
I thought I read somewhere that Porsche is very deliberately using less than 100% of the battery capacity to ensure longevity. I suppose this accounts for some part of the difference in range.
cheers!
cheers!
09-19-2019, 01:10 PM
#20
Burning Brakes
Same can be said of the lead-acid 12V starting batteries we are all used to.
In fact one of the nuances about regenerative braking is that if the battery is charged to 100%, regen is necessarily limited because there is no place to store the energy. It is one reason why most Tesla owners only charge their cars to 80-90%, GM's Bolt EV has a 'hilltop' charging mode that doesn't charge the battery to 100%, etc. More efficient to do so due to less use of the friction brakes.
09-19-2019, 03:37 PM
#21
Its right in our owners manual to not charge the car to 100% all the time.
With model S having over 300 000 miles on them, I'm not too concerned about the longevity of Telsas batteries at all.
With model S having over 300 000 miles on them, I'm not too concerned about the longevity of Telsas batteries at all.
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daveo4porsche (09-19-2019)