Tuesday, November 24, 2015

Regen Or Not To Regen

Its cold out! And first thing people are starting to notice is that regen simply is not working as well as before.  Now why is this happening?  Well, I can only comment based on observations in my own LEAF.  I have been LEAFing it nearly 5 years and have tried nearly everything to find what works best for me as far as gaining a few more miles of range.  So before I get going, I have to say all I can offer is my personal experiences.  If you have something that you think is better, please let me know! I have 8 of the next 10 days off so I have time!!

I have always been a fan of neutral driving. Coasting in neutral helps me maintain speed when slowing for a traffic light that is still several blocks away but it also allows me to get more out of regen.  Now again, I have no scientific proof of this, only things I have tried and observed.

One trip I make frequently is driving down the Highway 512 hill going into Puyallup, WA. This is a relatively steep but short hill but it is steep enough that I can stay in eco mode and not really lose a lot of speed. And I was happy to do this but then I noticed that I was not getting the full regen and at 60 mph, I was more than a bit disappointed.  Me being the cheap bastard that I am did not have a LEAF with B mode so eco was it (Back when I was a "wild spender" my 2011 SL simply did not have the option...) Now all would be fine except that at the bottom of the hill was a pretty sharp curve and I found myself having to perform the ultimate of sins...friction braking.

Well, I was shocked.  After glancing around to make sure no other LEAFers saw me, I was determined to fix the problem!   Well we all know that good things do not come easy so naturally Nissan issued some sort of fix for something (probably something that wasn't broke) and the first thing people noticed is their regen wasn't working as well, on FLAT GROUND!

Another reason this needed to be addressed was simply maintaining my comfort zone.  I use my friction brakes every day (as much as I hate to admit that) but it has always been at like 5-10 mph when I had to stop.  I found the feeling of friction brakes at high speeds  to be a feeling I was completely uncomfortable with.  It was just a feeling that I knew I would never get used to much less accept.

Being in Western WA means you are either going up or going down. No huge changes in elevation mind you. Just a few hundred feet here and there. Just a few miles from my house is the Nisqually Flats that is bisected by I-5. Again a steep hill but less than half the length of the Puyallup Hill.  So what I was doing is shifting into neutral a few hundred yards from the crest starting around 60sih mph.  Generally I would drop down to about 55 mph before gaining speed on the downslope. The LEAF coasts very well! Now I would get up to around 70 at which time I would shift into Eco and slowly drop in speed to near 60 at which time I would be at the bottom or just past the bottom of the hill.  IOW; it worked perfectly!

So why wasn't the Puyallup Hill working? Was it steeper? That could be although my eye thought they were about the same. The speed increase in neutral seemed about even. So I decided to run the hill using different methods.  The original method I used was being in neutral until about 65 mph then shifting to eco. The steepness of the hill would maintain my speed well enough until I hit the sharp curve at the bottom where I wanted to be around 55 mph. I think there is a 45 mph sign posted there (very few people slow down that much btw...)

Anyway I tried shifting back to eco at a lower speed. This was tricky. Doing it too soon meant losing speed too fast which caused me to be a bit of a "slowbie"  (kinda like a Furbie but bluer... :) )  So I adjusted my timing a bit and it started to work!!  Well, for a minute.  I began to notice that even when at the same speed, my regen was lessening and eventually causing me to have to brake at the bottom.

Finally I found that my only real option was to shift back and forth from neutral to regen keeping speeds below about 62ish (easy to do as a lot of people drive rather slowly down the hill)  I then began to realize that by the time I got to the bottom of the hill, my regen capabilities were about half gone.  Even slight pressure on the brake pedal would not restore it.

So the next thing I figured was maybe batteries were getting too hot. This did start during a rare "6 TB" day.  But even during the coldest of Winter days, I was not getting any better regen.  But that kinda made sense. Batteries are restricted by the amount of charge they will take by both cold and heat.  IOW; they are like us. They function best in a fairly narrow temperature range.  But the inverter is a bit different. It only goes from hot to hotter.  So goes the conundrum.  It appeared my inverter was heating up and restricting the regen to the cold batteries who needed to regen to heat up to realize their full capabilities.  In run after run, it was the same result. I would start out at 4 regen circles but by the time I got to the bottom, it was 3 at the most and sometimes only 2 while the batteries started cold and stayed that way. This made it pretty apparent that the batteries were only a part of the problem... the small part.

At first this did not make sense to me.  After all, the LEAF is designed to take a lot of charge and be ok. But then I realized that regen is AC and fast charging is DC.  Normally, AC is not being taken in any faster than 6.6 KW but regen can have bursts up to 30 KW. This got me thinking that maybe Nissan did alter the regen profile because of issues that had  been cropping up when regen was combined by the heat of Summer?

Either way I discovered that my regen seemed to be the most beneficial if done in shorter bursts instead of long gradual ones.   Now I recently took a trip with a lot of much longer hills including a few 7-8% grades 3 miles long.  On the 140 mile trip, I still managed 4.9 miles per kwh shifting to neutral for any downhill stretch that lasted more than a few hundred yards.  I never got out of the 4 TB range despite batt temp readings of  68º from LEAF Spy a few minutes after a short (roughly 20 min) fast charge session.  So I probably have to call it 4½ TBs!


  1. I seem to have noticed the benefit of neutral driving / I too think the "short burst" is the way to go... Check it out at TexasLeaf.com or Everafterimages.com

  2. I'm surprised you didn't mention the state of charge of the battery. In my experience the largest determinant of the effectiveness of regen is the SOC. At 100% it is of course nearly non-existent and at about 90% it is nearly fully functional (up to 30kW).

    I notice that on long downhill runs near 90% the regen capacitiy will gradually reduce. I have always suspected this is the battery management system protecting the battery. In general, I have found that I use a lot of neutral coasting, exactly the same hill-crest technique you are are using and I use the D, D with ECO and B mode to create 3-speed regen. I switch liberally between them while "braking".

    I think this is both fun and seems to create a highly efficient ride. I live in the Seattle area and get monthly averages peaking around 5.1 m / kWh in the summer and dropping to as low as 4.0 m kW/h in the winter. It is my belief that I rarely end up using the friction brakes except for hills with when I have high SOC and hard stops as necessary.

    1. sorry for the delayed reply! Before the SW update for the 2011-12's the SOC greatly affected regen levels but that has changed. Frequently (despite all 4 regen circles being available) I will have a hard time lighting up the last 1-2 circles even with SOC well below 80%!

      As to why this is happening I can only guess. Starting with the 2013 MY, Nissan modified the power profile to increase efficiency but I also think they put in algorithms to lower regen in certain situations to reduce the rate of cycle degradation. I think they went a bit overboard on this. Just as their warnings about fast charging more than once a day was too conservative, I also think the ills of regen is overblown as well