Tag: PHEV

Post #1707: Nobody offers a warranty on the electric range of their plug-in hybrid vehicles?

 

Edit 2/11/2023:  I grossly underestimate the replacement cost for a Prius Prime lithium-ion battery.  Per this thread on Priuschat, the cost of new Prius Prime battery, from the dealer, is $12,595.  Others suggested the dealer took some markup, as the list price from Toyota is just under $10,000.  I say, potato, potahto.

In round numbers, the cost of a new replacement battery is 43% of the cost of a brand-new Prius Prime, base model, current MSRP $28,770.  As a footnote, literally none were available in North America, and the battery has to be shipped directly from Japan.

I should put in the usual EV-weasel-wording:  By the time the battery dies, there will be plenty of good-used batteries in junkyards, from wrecks.  That did, in fact, happen with the original Prius NiMH hybrid battery.  Plus, there may be much cheaper aftermarket replacements at some point.  And so on.  But right here, right now, what I cited are the hard numbers for battery replacement cost.

Original post follows.

Only Volvo offers any warranty on your plug-in hybrid electric range, near as I can tell.

And I think I have finally nailed down why that is.

A typical battery guarantee for a fully electric vehicle (EV) is that a car will lose no more than 25% of range in 8 years/100,000 miles.

Based on research shown below, using actual driving behavior, for a Prius-Prime-like plug-in hybrid electric vehicle (PHEV), you would expect about 5% of batteries to fail, under that 8-year, no-more-than-25% loss definition.  Just from normal wear-and-tear, as-typically-driven.

So, my guess is that PHEVs don’t get those guarantees because manufacturers would end up replacing too many batteries.

All the more reason to treat your battery gently.

Background

Last week, I found out that my wife’s Prius Prime had no warranty on its electrical range.  Currently, as we drive it, we get mid-30-miles on a charge.  But if that drops to zero, tough.  As long as the car will still run as a hybrid, they battery has not “failed” under Toyota’s 10-year/150,000 mile warranty.

So I got curious.  I already have a list of all 2022 plug-in hybrid electric vehicles (PHEVs), from a just-prior post.   I decided to look up the warranty information for as many manufacturers as I could find.

Here’s the results.

Volvo offers a 30% loss-of-range warranty.  If you lose more than that, during the eight-year warranty period, they’ll fix it.

Near as I can tell, none of these other manufacturers offer any warranty whatsoever, on the electrical range of their PHEVs.

Toyota
Kia
Porsche
MINI
Ford
Chrysler
Mitsubishi
Jeep
Hyundai (I think)
BMW (but maybe they decide case-by-case?)

The Hyundai warranty covers EVs, PHEVs, and hybrids, and in separate places says that it definitely covers loss of range, and that it definitely does not cover loss of range.  Your guess is as good as mine, but I’m guessing they cover range for EVs (as required by law) but not for PHEVs.

Originally, I could not understand why Toyota offered no PHEV range warranty.  That situation has now improved.  I’m now baffled why almost nobody offers a PHEV range warranty.

Unfortunately, I think that “no PHEV range warranty” is the industry norm  for precisely the reason stated in the Toyota warranty documents:

 

I’m an economist by training, and I find it this interesting, I guess. When there’s a de-facto industry standard, there’s usually a reason for that.

And I think I understand why no-PHEV-range-warranty is the industry standard.

How many would “fail” under normal driving conditions?

I’ve been searching for an answer for this for the better part of a week.  I posted my thoughts on preserving battery capacity on a chat side dedicted to the Prius (PriusChat), and with a few exceptions, got met with derision.  For sure, nobody there had ever heard of a Prime or the prior version (Plug-in Prius) showing any signs of premature loss of range.  Almost nobody thought that any sort of battery-protecting behavior was necessary.

I finally came across what I believe is a realistic projection of the fraction of Prius-Prime-like vehicles that would fail under the typical EV warranty of no more than 25% range loss in eight years/100,000 miles.

That’s:  Comparison of Plug-In Hybrid Electric Vehicle Battery Life Across Geographies and Drive Cycles, 2012-01-0666, Published 04/16/2012, Kandler Smith, Matthew Earleywine, Eric Wood, Jeremy Neubauer and Ahmad Pesaran
National Renewable Energy Laboratory, doi:10.4271/2012-01-0666

They used actual driving data from about 800 trips taken by Texans in PHEVs.  The then extrapolated that to eight years of driving behavior.  Their model is not quite perfect, as the modeled vehicle only provides a 10% “buffer” at maximum allowable charge, while the Prius Prime provides 15%.  On the other hand, for the key chart, they did not include (e.g.) the effects of high temperatures on battery life.  (So, no parking your car in the sun in this model, so to speak).

Here’s the key graph, where the most Prius-Prime-like vehicles is the PHEV40.

Source:  Cited above.

In a nutshell, only counting the wear-and-tear from normal driving and charging, they expect the average user to lose 20% of range by the end of the eighth year.  And about 5% of users would experience in-the-neighborhood-of 25% range loss.

If they were to throw in the effects of variation in climate (hot climates kill batteries quicker), and variation in practices regarding storing the car fully charged (which also kills batteries quicker), I might guess that around 10% of drivers might exceed that 25% loss threshold within an eight-year warranty window.

To put that in perspective, car manufacturers as a whole spend about 2.5% of their total revenues on warranty repairs (reference).  A ten percent failure rate of this part, replaced at new-battery cost shown above, would by itself account for (roughly) 4 percent of Toyota revenues from Prius Prime sales.

As far as I’m concerned, this solves the mystery of the missing warranty.  (Almost) nobody offers anything like the standard EV warranty, because if they did, they’d have to replace an unacceptably large fraction of batteries under warranty.  And that would lead to an unacceptably high warranty cost.

All the more reason to avoid unnecessary wear-and-tear on a PHEV battery.

Post #1618: There ain’t no disputin’ Sir Isaac Newton: Efficient driving in an EV.



Driving an electric vehicle (EV) efficiently is forcing me to learn some new driving habits.  And, in particular, I have to un-learn some cherished techniques used for driving a gas-powered car efficiently.


When I look for advice on driving an EV efficiently, all I get is a rehash of standard advice for driving a gas car.  But the more I ponder it, and the more I pay attention to the instrumentation on my wife’s Prius Prime, the more I’m convinced that’s basically wrong.


An electric motor is fundamentally different from a gas engine.  With an electric motor, you want to avoid turning your electricity into heat, rather than motion.  That boils down to avoiding “ohmic heating”, also known as I-squared-R losses.


To minimize those heating losses, you want to accomplish any given task using or generating constant power.  That task might be getting up to speed after stopping at a red light, or coming to a stop for a red light, in some given length of roadway.


Here’s the weird thing.  Assuming I have that right — assuming that an efficient EV driving style focuses on providing or generating constant power over the course of an acceleration or deceleration — that implies a completely different driving style, compared to what is recommended for efficient driving of a gas-powered vehicle.


In particular, the standard advice for gas cars boils down to accelerating and decelerating with constant force.  When you take off from a stop light, aim for a constant moderate rate of acceleration.  When you are coming to a stop, aim for a steady rate of deceleration.  Constant acceleration or deceleration boils down to constant force on the wheels, courtesy of Sir Isaac Newton’s F = MA (force is mass times acceleration).


But power is not force.  As I show briefly, in the next section.  In a car, power depends on speed.  Constant force on the brake pedal (and so, on the brake rotors in a traditional car) generates far more power at high speed than at low speed.  Similarly, a constant rate of acceleration consumes more power at high speed than at low speed.


And so, there seems to be a fundamental conflict between the way I was taught to drive a gas car efficiently, and what seems to be the right way to drive an EV efficiently.


In a nutshell, to drive an EV efficiently, you should be more of a lead-footed driver at low speeds.  And taper off as the car speeds up.   Conversely, hit the brakes lightly at high speed.  And press the brakes harder as the car slows.


That’s the driving style that aims for production and consumption of power at a constant rate, over the length of each acceleration or deceleration. And that’s completely contrary to the way I was taught to drive a gas vehicle.


Think of it this way.  Suppose you apply a certain level of force to the brake pedal of a traditional car.  The resulting friction between brake pads and rotors will generate heat.  That rate of heat production is, by definition, power, as physicists define it.  You’re going to generate a lot more heat per second at 80 MPH than you are at 4 MPH.  (In fact, 20 times as much.)  Restated, for a given level of force, you are bleeding a lot more power off the car’s momentum at 80 MPH than at 4 MPH.  And those big differences in power, over the course of an acceleration or deceleration, are exactly what you want to avoid in an EV with regenerative braking, in order to avoid I-squared-R losses.


 




Force and power:  A brief bit of physics and algebra




1:  Two definitions or laws of physics


Work = Force x Distance


Power = Work/Time


2:  A bit of algebra


Substitute for the definition of work:


Power = (Force x Distance) / Time.


Re-arrange the terms:


Power = Force x (Distance/Time)


Distance/time = speed (definition)


Power = Force x speed.


For a constant level of force applied to or removed from the wheels, the rate of power consumption (or production) is proportional to the speed.


Upshot:  To accelerate or decelerate at constant power, the slower you are going, the heavier your foot should be.  The faster your are going, the lighter your foot should be.  For the gas pedal and the brake pedal.




Ohmic heating:  Why a long, hard acceleration trashes your battery reserve.




Anyone who drives a PHEV — with a relatively small battery — will eventually notice that one long, hard acceleration will consume a big chunk of your battery capacity.  On a drive where you might lose one percent of battery charge every few minutes, you can knock several percent off in ten seconds if you floor it.


Another way to say that is that getting from A to B by flooring it, then coasting, consumes much more electricity than just gradually getting the car up to speed.


I’m not exactly sure why that is.  But I am sure that it is universally attributed to I-squared-R or ohmic heating losses in the motors, batteries, and cables.


Any time you pass electric current through a wire or other substance, it heats it up.  From the standpoint of moving your car, that heating is a loss of efficiency.  The more current you pass, the more it heats up the wire.  And that heating is non-linear.  Watts of heat loss are proportional to I-squared-R, in the argot.  They go up with the square of the current that you pass through that wire.


Again, I’m not completely sure here, but my takeaway is that your heating losses, at very high power, are hugely disproportionate to your losses at low power.  At constant voltage, I believe those losses increase with the square of the power being produced by the electric motors.  In other words, ten times the power produced to move the car creates 100 times the ohmic heating losses.


And that’s how ten seconds of pedal-to-the-metal can use up as much electricity as 10 minutes of moderate driving.


That said, I have to admit that I’m relying on “what everybody says” for this.  For sure, hard acceleration seems to trash your battery capacity far in excess of the distance that you travel at that rate of acceleration.   Whether the root cause for that is I-squared-R losses, or something else about the car, I couldn’t say.


Either way, my takeaway is that if losses are proportional to the square of power consumed or generated, then to accomplish any given task (any fixed acceleration or deceleration episode), your aim should be to do that at constant power.  Because that’s what will minimize the overall energy loss from that acceleration or deceleration episode.




Drive like you are pressing on an egg — that was a real thing.  EV drivers should chuck the egg.




Source:  Duke University Libraries, via Internet Archive.


Those of us who grew up during the 1970s Energy Crisis will probably recall public service announcements that asked you to drive as if there were a raw egg between your foot and the gas pedal.  I managed to find a Texaco ad of roughly that era, laying out that egg-on-gas-pedal meme.  The picture above is from that video.


As kids, that was pretty much beaten into us.  Responsible driving means no jackrabbit starts, no tire-smoking stops.  Easy does it.  We’re in the middle of a prolonged gasoline shortage, after all.


So now I come to the part that is absolute heresy for someone of my generation.  If you’ve absorbed the prior two sections, you realize that this advice probably isn’t correct for an EV.  Why?  To consume power at a constant rate over the course of an acceleration, you should start off with a brisk rate of acceleration, then diminish that as the car speeds up.


In other words, if you drive an EV, drive with a lead foot.  Not all the time.  But at the start of every acceleration.  And the end of every deceleration.


If you drive an EV, chuck the egg.




The Prius Prime Eco display




Source:  Underlying picture is from Priuschat.


With that understanding in hand, I’m finally starting to make some sense of the “eco” display on my wife’s Prius Prime.


In theory, this little gauge is giving you guidance on how to drive the car most efficiently.  In practice, I could never make head or tail out of it, except that it seemed to be telling me to drive with a lead foot.


Which, I now understand, it was.


On this display, if you put your foot on the gas, it will show you your actual throttle (gas pedal) position, and the gas pedal position that will, in theory, give you greatest efficiency.


By contrast, when you put your foot on the brake, it doesn’t show you the brake pedal position.  Near as I can tell, it shows you the amount of power than you are generating.  That is, a constant brake pedal position will lead to a shrinking bar, as the car slows down and less energy is generated.


Watch what happens if I try to accelerate gently:




It’s possible that all the meter is actually telling me is that a very lightly-loaded electric motor will operate inefficiently.  I don’t think the Prius eco monitor is actually trying to get me to drive at constant power.


Edit 3/11/2024:  After driving around with a ScanGauge III, my conclusion is that accelerating at constant power is exactly what the eco-meter is trying to get you to do.  It wants you to start off with a heavy foot, and then, as you accelerate, it wants you to back off.  Near as I can tell, that bar is set up to keep you at around 23 HP of power output, or 50 amps of discharge current, or a “2 C” rate of discharge, for this battery.


In particular, my diagram above is labeled wrong. The two red arrows should be labeled “desired power output” and “actual power output”.  You will notice that if you don’t move the gas pedal, the “actual power output” line will creep up as you speed up.  The only way to keep that line in the same place is to back off the gas as your speed increases.  So that line isn’t the throttle position, it’s the power output (power = force x speed).


But no matter how I arrive at it — from theory, or from finally paying full attention to the Prius eco meter — the whole drive-like-there’s-an-egg-between-foot-and-gas-pedal is clearly obsolete.  Gentle acceleration may get you your best mileage in a gas-powered vehicle.  But it’s not the correct way to drive an EV.



	


	
	






	
	

		
	

		
Post #1310:  What does 30 electrical miles get you?
	


	

		
 


We haven’t bought gasoline since mid-August, owing to my wife’s purchase of a Prius Prime.  That’s a plug-in (PHEV) version of the Prius, with a battery that’s good for about 30 miles.


It’s not like we stumbled into that purchase.  We researched the offerings available and decided that hit the sweet spot for us.  No range anxiety, no need to rewire the garage, and no need to mortgage the house if that big battery wears out.


And, as you can guess, it’s working out well.  We’re not avoiding traveling, it’s just that most of what we do seems to fit into that 30-mile-a-day limit.  Or nearly.


Which got me to wondering: Is our experience all that unusual?


I mean, people seen to think that little 30-mile battery isn’t much.  It’s certainly no Tesla, either for distance or acceleration, for sure.  But it’s not intended to be, and, from my perspective, that smaller battery is efficient.  Most people who drive a full EV aren’t going to use the full capacity of their battery on most days.


But with this PHEV setup — where the first 30 miles is electric, then it switches to gas — just how much gas would the average American save?


More precisely, how much would total U.S. private passenger vehicle gasoline consumption decline if the first 30 miles of everybody’s driving day were done on electricity?  As if everybody had a Prius Prime, but nobody could recharge mid-day.  And with no change in behavior otherwise.


Turns out that you can’t just look that up.


You can find some glib statistics on (e.g.) the fraction of individual car trips that are short.  And yeah, sure, most car trips are for just a few miles.  I don’t think anybody’s shocked by that. But that’s not the question.


So I turned to the National Household Travel Survey (NHTS) to get an answer.  If you ever want to know anything about how Americans get from A to B, that’s the place to look.


I took their file of vehicle trips, reduced it to travel by private passenger vehicle (car, SUV, van, pickup), focused on the vehicle driver only (to avoid duplicating drivers and passengers), and summed up the total miles that each driver drove, each driving day.   That yielded about 150,000 distinct person-days of vehicle driving.  At that point, I (arithmetically) substituted up to 30 miles of that with electricity, and tabulated the results.




Source:  Calculated from 2017 NHTS trip file, weighted estimate.


And there’s your answer.  If you were to substitute the first 30 miles of everybody’s private vehicle driving-day with electrical transport, you’d reduce gasoline-powered miles by 55%.  That’s all the miles on days under 30 miles, and 41 percent of the miles on days over 30 miles.


The upshot is that with PHEV, that 30-mile battery is enough to cut average private-vehicle gasoline consumption more than in half.  All of that, without the truly huge batteries required for full EVs.  And without a whole new electrical infrastructure required to keep EVs going, at least for those of us who can recharge at home out of a standard wall socket.


So I’m back to where I ended up in my last post about electrical transport.  People seem to get all caught up in their underwear about this huge, dramatic, risky blah-blah-blah.


And it’s all nonsense.  If you have a standard outlet available, you have the option to shift most of your personal transportation to electricity.  Right now.  With absolutely no other change in your lifestyle.  And a Federal tax credit, to boot, depending on what you choose.


Well, OK, in truth, we have made a few lifestyle changes.  I buy fewer lottery tickets now.  But that’s probably a good thing.  Otherwise, except for remembering to plug it in, there’s no practical difference between our last (all-gas) car, and our current (nearly-all-electric) car.


And now, judging from the U.S. numbers, we’re probably not alone in terms of the advantages from that small PHEV battery.


Think of it as a case of diminishing returns.  Your first few miles of electric capability get the most bang-for-the-battery-buck.  Here’s the picture, same data source and analysis above, just plotted for PHEV batteries of various sizes.




Source:  Calculated from 2017 NHTS trip file, weighted estimate.


Sure, you can be a purist and insist on nothing but electrical travel.  And more power to you.  But even with zero change in behavior, and no mid-day charging, a PHEV with a modest battery size can get you a long way toward that goal.