Topic: State of Charge: Year 3 of Nissan Leaf Ownership

[JohnM]

Let me re-phrase the question.  Can you totally load the battery up at a low temperature and then take advantage of the increased output as it warms?

ie will it tolerate overcharging more if the temperature is low?

Cheers,
John M.

[Sir Osis of Liver]

Let me re-phrase the question.  Can you totally load the battery up at a low temperature and then take advantage of the increased output as it warms?

ie will it tolerate overcharging more if the temperature is low?

Cheers,
John M.

No. The capacity that the battery will hold is lower at low temperatures. If you warm the battery, you still have the same amount of stored charge, it's just that the battery will have unused storage capacity.

[X-Traction]

When the Leaf battery is fully charged or close to, even in B mode, you barely get any regen. That's because you have to reduce charging on LI-Ion batteries above 80% charge.

I'm wondering if the batteries in EV's are managed so that they are never 100% full or completely discharged.

The hybrid setups I'm familiar with don't go much below 40%m or above 63% of a full charge, and the NiMH battery longevity is partly due to that. But it also means much of the battery capacity is "wasted".

Is the Lithium-ion battery technology in EV's such that they can be completely charged and discharged without losing capacity over time?  If not, what range within their total capacity is being used?

As Guy touched on, things start changing on hybrids and EV's when the battery is at the discharge or full charge limits.

If it's at the full charge limit, it will not accept any more charge from regeneration, and the braking will revert to fully using the mechanical brakes.  Obviously this happens sooner and more often on hybrids than EV's.  It may also be a reason why hybrids have a lower towing weight limit than non-hybrids.  If you're towing a trailer through mountains, there is so much kinetic energy to be dissipated that the battery soon fills up and you're completely on the mechanical brakes.  Plus whatever mechanical engine braking is available.

It's unlikely you'd exceed the full charge limit with an EV, but you could.  Say you overnighted and charged up at a ski resort, and started down a big descent to go home.  It's entirely possible that with the full battery, all braking on the descent would be with the mechanical brakes.

I often drive down 10km grades averaging 8%.  Whether I use the brakes (all regen at first) or downshift to Low, the Escape Hybrid fills up the traction battery long before the bottom.  In Low, you can feel the speed start to increase at the point where the battery is full.  The charge gauge indicates no more charging.  For a hill of this length, I use Low because it wastes additional energy flailing the engine parts around at a higher rpm.  This saves some use of the mechanical brakes.

EV's don't have a problem at the low discharge level, except that they won't move at all.  Hybrids at the low end then lack the extra "oomph" that you may need.  A couple of weeks ago I drove up a long steep hill, and where it leveled at the top I had reason to floor it.  Nothing much happened because there was no electrical energy available to augment the gas engine.

[X-Traction]

The Leaf is a little different than traditional hybrids.  I read the article a while ago detailing what the 'B' mode on the Prius works, and how it relates to engine braking and regen.  Seeing as the Leaf is electric only, there's obviously no engine to compression brake.  What's more, unless you've unplugged the car from a full charge mere minutes ago, almost any amount of operation will ensure that you don't have a full battery anymore, almost guaranteeing potential regeneration.  Battery temperature may still play a part in this, I don't know.

Driving the Leaf, there are three 'regen' settings.  The first is normal mode, and the lowest regen setting.  When releasing the gas (amp?) pedal regen kicks in and simulates engine braking in high gear.  Next there's Econ mode, which simulates engine braking in a low gear.  This is activated by a button on the dash, and the drive selector in 'D'.  Finally, we have 'B' mode.  When you release the gas pedal, the deceleration is drastic and noticeable.  It really is like stepping fairly hard on the brakes.  This is why I suspect the brake lights must come on in 'B' mode, as anybody behind you would be surprised by your level of deceleration.

I like the availability of the three regen settings.  The Prius and Escape Hybrid can be thought of as having "two".

The Escape Hybrid's earlier generation was set up differently from the '09-'12.  On the '05-'08, when you lift of the gas, I understand you get definite regeneration and loss of speed without touching the brakes.  This is similar to the Leaf.  So far no one has told me whether the gas engine revs faster in that mode.

On the '09-'12, lifting off the gas in "Drive" has little to no effect on speed. It seems that if you lift off suddenly, the system is set up to interpret that as a need to reduce speed, so it although it gives a bit of regen and loss of speed, there's no effect if you lift off more gradually.  If you're coasting and downshift to Low, there's definite loss of speed and significant regeneration happens.  But, the engine also revs faster, so some of the available energy is being lost to engine braking. Sometimes that's useful, but usually not.  For the '09-'12 it's better to slow down by remaining in Drive and using the brake pedal, since this does not rev up the engine and so recaptures all the available energy.

While the Escape Hybrid has a "Low" gear, the Prius has a "B" gear position.
 
The Prius works similarly, but since I don't own one I can't say exactly how it works.  A friend who has one describes the "B" gear selection as being similar to the jake brake on big trucks.  I suppose the Escape's "Low" position could be seen the same way.  I test drove a few Prii a couple of years ago, and I don't recall them slowing noticeably when I lifted off the gas in "Drive".

[Guy]

I'm wondering if the batteries in EV's are managed so that they are never 100% full or completely discharged.

Yes, The Leaf Battery is 24 KW but the car uses only 20. It's never "fully charged" even tough the dashboard says 100%. It will not let the battery to become completely depleted either.

[jimgord]

A couple of notes
1) The EPA rated range for a Leaf is 34 kWh/100 miles or 21.25 kWh/100 km
At this rate the Leaf would have used about 2,550 kWh or about 15% less than observed. As Toronto is fairly flat, the difference could be the cold winter weather. Given that this is a Generation 1 Leaf (pre 2013) with the resistance heater, mileage would be better with a Generation 2 SV or SL Leaf.

2) I am curious about what measures people find they have to take to keep their Leaf batteries from freezing in very cold weather conditions. The manual advises that the Leaf cannot be left (stored) for extended periods in very cold weather without risk of the electrolyte freezing.