HVB Tests C-Max Hybrid Idaho National Lab

[plus 3 golfer]

As many will likely recall, INL has / had four C-Max Hybrid under tests.   I recently looked at the the test reports / summaries and graphed the HVB kWh of energy storage vs miles driven as shown in the two attachments below.  One attachment is a graph of the average capacity decline / capacity loss of the nominal 1.4 kWh HVB of the four C-Max Hybrid test vehicles.  The second attachment is similar to the first except each data point is shown for the four test vehicles.  The last graph is similar to the first graph except it if for the Fusion and C-Max Energi test vehicles. 

 

The conclusion I draw from the graphs is that the capacity loss for the Hybrid is minimal especially when compared with the Energi at various mileages.  The Energis show a capacity loss of about 20% at around 160,000 miles while the Hybrids show about 10% loss at 160,000 miles. A 20% capacity loss (say 1.5 kWh) significantly reduces EV range in the Energi as it directly affects the usable kWh for operation in EV mode.

 

I'm going to look at ForScan to see if there is a way to quantify capacity loss for our Hybrids.  Does anyone believe they can "see" a loss of capacity in the Hybrid through some performance measure like miles on EV only, more ICE cycling and so forth.

 

When I was looking to buy a C-Max, I considered the Energi but I was somewhat worried about capacity loss in the Energi given what the Leaf owner's were seeing at that time as it would significantly affect overall FE and thus payback of the additional cost of the Energi over the Hybrid in 2012 when I purchased my C-Max.

 

Edited March 23, 2018 by Plus 3 Golfer

[ptjones]

The only thing I've noticed is the HVB charges up quicker going down hill with regen. When the car was newer the highest HVB % charge was 65% going down hill, but now I have seen 70.5% a number of times. :headscratch:   I'm guessing that I don't go as far in EV, but it isn't really noticeable and I'm getting as good as gas mileage as I have ever gotten. :)  My EV to ICE usage is 51.7% which I think is very good considering 80% HWY miles.

From my experience I have found the best use of the HVB is between 38% and 50% battery capacity to get the best MPG's. So I don't think loss of HVB capacity is going to hurt MPG's.

 

Paul 

Edited March 23, 2018 by ptjones

[plus 3 golfer]

Yes, below is a graph that shows I've recorded about 71% SOC a few years ago.  I wonder if the usable energy (kWh) is held virtually the same as the HBV storage capacity diminishes from the 1.4 kWh.

 

IMO, it would make sense to allow the algorithms to use the same storage range in kWh over the life of the battery instead of removing the lost capacity from the normal operations. I agree that a normal "good" operating range is in the 38-50% range.  That is only about 0.17 kWh when the capacity was at 1.4 kWh.  The curve in my initial post shows an average capacity loss of about 0.11 kWh at 160k miles which would equate to about a 8% reduction in the capacity in the 38-50% range. So, the 12 % range would need to be increased by 8% to 13% of the current capacity so that one would not notice any performance differences.

 

At the max storage of around 70%, it would seem that one may not want to add the full 8% as battery degradation would likely accelerate as one would be cycling to a higher capacity if the full 8% were added.  So, perhaps the algrorithm makes a more modest adjustment instead of adding the 8% to the max. storage.  That may be why the battery fills quicker as the battery degrades.  Instead of adding 8% perhaps only half is added and why we see over 70% now on occasion where prior we were seeing upper 60s on occasion. 

 

Paul, your car is testament to my hypothesis above as unlike the Energi which looses usable capacity when the battery degrades, our Hybrids apparently do not suffer (performance wise) when the battery degrades.

 

[ptjones]

I would have to try out a new CMAX to see if I noticed a difference, I don't remember any noticeable difference when I drove the 2017 CMAX, I think I got 46mpg on 20 miles trip.

 

Paul

[fbov]

It's not surprising that Energi's HVB would suffer greater battery loss over time.It's being used in a more stressful application. 

- when plugged in, they are always charge to "full"

- when used in EV mode, they discharge very deeply before starting the ICE in hybrid mode

- the hybrid mode only uses 20% of HVB capacity, so 80% stays discharged until plugged in.

 

The hybrid HVB may have similar charge/discharge limits, but it's SOC is in constant flux because it's being used as an energy buffer, not a source of energy. We rarely hit "empty" because the ICE intervenes, and I don't have the hills to hit full charge. 

 

And there's nothing a Li-ion battery likes more than to be held at mid-capacity. 

 

Have fun,

Frank

[plus 3 golfer]

Agreed. 

 

I've been on the Energi forum recently and note there are many losing energy capacity as their miles accumulate.  Usable EV only energy starts out at around 5.5 kWh when new and has dropped to around 4 kWh and lower for some that apparently Ford calls normal wear and tear and is not covered under warranty.    The solutions to lessen the continual loss of battery capacity are practices such as: charge only to 80%, charge no more than once a day, charge only when battery is cool, minimize use of electrical loads, drive slower and so forth.  IMO, all reasons NOT to buy a limited range PHEVs or EVs (those where one would need to charge frequently to 100% to get the cost savings benefit of using the HVB).  I understand there are those that want to be "green."

 

There is supposedly a class action suit pending similar to the Leaf suit of years ago about warranty coverage of lost capacity.  I am happy that I purchased a Hybrid not an Energi in December 2012. :)

Edited March 24, 2018 by Plus 3 Golfer

[NRGTi]

That's a good point. I'm no electrical engineer (and I suspect some of you are), but I do notice that every warning about good battery-saving practice is violated by the uses that support the use of Teslas and other EVs. They expect you to charge fast & to the brim, in every kind of weather, drive it till almost empty, then recharge at 400+ watts. What could go wrong with that?

[SnowStorm]

Just because an EV can go 250 miles and recharge quickly doesn't mean it will be operated that way all the time.  Most use cases will be charging at home overnight at a "slow" rate and then going out for a daily commute of far less than 250 miles.  So, most charge/discharge cycles will be fairly easy on the battery.

[raadsel]

That's a good point. I'm no electrical engineer (and I suspect some of you are), but I do notice that every warning about good battery-saving practice is violated by the uses that support the use of Teslas and other EVs. They expect you to charge fast & to the brim, in every kind of weather, drive it till almost empty, then recharge at 400+ watts. What could go wrong with that?

 

From what I've seen, Tesla advises their owners that they should typically only charge to about 80%, only fully charging to 100% if they absolutely need the range. I also believe, from videos I've seen, that the last 20% the charger slows down (also at the start, if the battery has a very low state of charge) to further protect the battery from the excess heat generated when you fully charge it -- much as most modern smartphones also slow down the charging when the battery gets up to about 80%. From what I've seen, it is most EVs that do this, not only Teslas -- and some even "block" the top 20% from being used; they'll claim the car comes with an 80 KWh battery, and that is all that is usable, but it actually has a 100 KWh battery. 

 

Of course, this is not solely to protect the battery life but also helps to prevent "explosions," such as happened with the Note 7 phones.

[plus 3 golfer]

IMO, the fundamental issue with EVs (and PHEVs) is range vs. battery size (cost) and life.  So, if you buy a Tesla 3 with a 50 kWh battery you get 220 mile range. But charging to only 80% reduces range to about 176 miles.  So you can select the 75 kWh battery as an option at a price of $9,000 for a range of 310 miles but only 248 miles at 80% charge.  Do you opt for the larger battery to extend battery life so that you can drive 220 miles?  And you better not drive at 75 mph as the Telsa 3 range with the 75 kWh battery @ 80% charge will likely be around 160 miles (C&D review 200 miles at 100%).  $9k buys over 3000 gallons of gas or in our C-Max around 120 k miles of driving. Of course you can always "waste" time charging more often. :)

Edited April 9, 2018 by Plus 3 Golfer

[fbov]

Actually, I see less problem with an EV-only vehicle. The far larger battery is less likely to be substantially depleted every day, so it won't need to be charged every day. With a 200 mile range, my 30 mile/day commute would require charging about once a week. I wonder how many users do that... 

 

Have fun,

Frank

[ptjones]

Actually, I see less problem with an EV-only vehicle. The far larger battery is less likely to be substantially depleted every day, so it won't need to be charged every day. With a 200 mile range, my 30 mile/day commute would require charging about once a week. I wonder how many users do that... 

 

Have fun,

Frank

It would seem you wouldn't need to get a EV with that much range in that case and save money with less expensive EV car. :)

 

Paul