Regen question

abasile said:

According to my gid meter's "power" readout, when my LEAF's regen reaches zero or close to it, the car is actually drawing power from the battery pack. At the same time, I'm going downhill and having to use the friction brakes. Running the heater at full blast doesn't seem to help in this case (other than by slowly reducing SOC); it simply draws more power from the battery. This makes no practical sense.

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O.K. I did not previously understand that you were consuming energy from the battery while going downhill. I agree that makes no sense!

Can you give us an idea how much regeneration occurs, in kWh, before this condition sets in? Is it 1 kWh? 5 kWh? More?

abasile said:

In general, my expectation is that, for a given set of battery conditions, available regen should be equal to the allowed Quick Charge power, or perhaps somewhat less so as to treat the battery more conservatively. Only when "user SOC" approaches 100% does QC taper all the way down to zero.

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Agreed that sounds very reasonable. In fact, regeneration already *is* more conservative since there is airflow available to cool the battery which does not exist during QC. OTOH, it seems to me that QC is currently overly aggressive, since it is possible to heat the battery to a rather high temperature.

But as my test yesterday showed, we only get about half the power in regeneration as is available during a quick charge. I suppose there could be a driving scenario up and down steep hills which come into consideration here. There are some sections of interstate that I have driven (not in the LEAF) which could create a LOT of battery heating for a sustained period of time. Or perhaps they did not want to bring the issue of activating the brake lights into the equation? (Although, as I have previously stated, IMO 20kW of regen should result in brake lights coming on!)

abasile said:

I'm hoping the 2013 LEAF's 'B' mode regen will be a bit more generous...

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I've seen mention of this, but I do not know what it implies. Maybe it includes brake lights!

abasile said:

The regen behavior that I described above is something I see almost daily, i.e., every time I drive down the mountain. Lesser descents aren't really enough to bring this bug to light; normally I have to do at least a few hundred feet of descending, with regen, before it becomes an issue. Yes, I consider it a bug, because I don't see why speed should have anything to do with available regen kW.

Again, to maximize available regen power on big descents in the cold or at somewhat high SOC, I have to keep my speed way down. To be clear, this is independent of the fact that more energy is lost to wind drag at higher speeds; I am talking about the amount of regen that the car's firmware allows.

Also, it's clear to me that the relevant temperature is that of the battery pack, not the ambient temperature. On occasion, our LEAF makes two round trips to the Valley within one day. This heats the pack quite noticeably. On the second descent, substantially more regen is available, even if the ambient temperature hasn't risen much.

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I also just noticed this limited regen behavior for the first time this evening, and also (not so?) coincidentally in the coldest temperatures I've seen since I started driving the LEAF. I had just started my drive home from my kids' house and I got my first ever "cold outside temperature" alert on the dash. The ambient temperature gauge on the dash read about 35 degrees F. SOC was 7 bars and my Gid meter showed about 57% Gids. I neglected to look at my battery temp gauge. As I glanced at my regen bubbles, I noticed that only the top 3 of the 4 were double rimmed while I was driving. This continued throughout the 15 mile drive, which has a varying degree of mostly gentle downhill slope, dropping perhaps 700 feet in all. Every time that I slowed below 20 mph and while I was sitting at stop lights, I had all 4 regen bubbles available. When accelerated again, I would lose the last regen bubble as soon as I hit about 40 mph. My SOC bars ranged from 7 at the start of the trip to 5 at the end of the trip, and the bubble behavior didn't change except that at one point in the drive, probably at the fastest speed going downhill, I had only 2 available regen bubbles.

I did a search to find this thread, since I had never seen this behavior before. Glad I'm not the only one. Since abasile, edatoakrun and I have some of the older 2011 cars, I'm wondering if this behavior is characteristic of the older batteries, since I haven't seen this reported from the cold winter states before.

Boomer23 said:

I also just noticed this limited regen behavior for the first time this evening, and also (not so?) coincidentally in the coldest temperatures I've seen since I started driving the LEAF. I had just started my drive home from my kids' house and I got my first ever "cold outside temperature" alert on the dash. The ambient temperature gauge on the dash read about 35 degrees F. SOC was 7 bars and my Gid meter showed about 57% Gids. I neglected to look at my battery temp gauge. As I glanced at my regen bubbles, I noticed that only the top 3 of the 4 were double rimmed while I was driving. This continued throughout the 15 mile drive, which has a varying degree of mostly gentle downhill slope, dropping perhaps 700 feet in all. Every time that I slowed below 20 mph and while I was sitting at stop lights, I had all 4 regen bubbles available. When accelerated again, I would lose the last regen bubble as soon as I hit about 40 mph. My SOC bars ranged from 7 at the start of the trip to 5 at the end of the trip, and the bubble behavior didn't change except that at one point in the drive, probably at the fastest speed going downhill, I had only 2 available regen bubbles.

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Except for this very last point, your bubble behavior matches what I see very closely. I will watch to see if I ever drop to only two bubbles at "higher speeds" in cold temps. It won't happen this weekend, as we are supposed to be up around 65F!

Please note that two bubbles of regen still will get me about 15kW of regen normally. That is WAY more than what abasile is seeing, which is essentially none. Also note that I have a drop of about 650 feet in about one mile and that does not trigger the "no regen" behavior in our car. One day when it is below 30F I will drive up there with 9 bars and see if I can trigger this. (I made it there with 10 bars on Tuesday, but it was 50F outside.)

Boomer23 said:

I did a search to find this thread, since I had never seen this behavior before. Glad I'm not the only one. Since abasile, edatoakrun and I have some of the older 2011 cars, I'm wondering if this behavior is characteristic of the older batteries, since I haven't seen this reported from the cold winter states before.

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I have also suggested this possibility, but I didn't get a nibble. Please note, however, that our car is only slightly newer: It was built in June 2011.

An update from today. I'm still seeing the same behavior, even though today's drive was in the afternoon, with warmer ambient temperature of 50 F, but still 4 battery temp bars because of last night's cold weather. I started out after an 80% charge with 10 SOC bars. At rest and at low speeds, I had all four regen bubbles, but as soon as I reached about 35 mph, I would lose the leftmost bubble. We drove a freeway route, and above about 60 mph, I would lose the left TWO regen bubbles. After seeing a movie, I had 5 battery temp bars, but the regen behavior was the same.

I have never noticed this behavior before, and after last night's experience in very cold (35 degree) weather, I thought that it might be limited to such temperatures. It's still unusually cold for So Calif, so this is likely still temperature related, and I'll be very interested in watching this over the next week, as temperatures are forecast to rise a bit. I'm still a bit concerned that this might be symptomatic of a larger problem.

RegGuheert said:

abasile said:

According to my gid meter's "power" readout, when my LEAF's regen reaches zero or close to it, the car is actually drawing power from the battery pack. At the same time, I'm going downhill and having to use the friction brakes. Running the heater at full blast doesn't seem to help in this case (other than by slowly reducing SOC); it simply draws more power from the battery. This makes no practical sense.

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O.K. I did not previously understand that you were consuming energy from the battery while going downhill. I agree that makes no sense! Can you give us an idea how much regeneration occurs, in kWh, before this condition sets in?

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On a "normal" winter morning, I might leave the house with about 67% SOC (according to the gid meter) and four battery temperature bars. After two miles of down and up, I begin the descent down CA-330 with 65%. After about 2200 feet of descending over seven miles (nine miles from home), I reach a relatively fast portion of the downhill (not steeper, just straighter) where traffic compels me to go closer to 55 mph. By then, my SOC is close to 70% (give or take, and my "80%" is more like 76-77% these days), and regen is quite limited. As I go faster, I lose it completely. Further down, traffic slows for some sharper curves, and I get some regen back.

In terms of kWh, going from 65% to about 70% is roughly 5% of the usable capacity of a new battery (~ 21 kWh), or about 1 kWh.

Also, the sort of regen behavior observed by Boomer23 has long been quite typical for us up here, especially on cold days like today. We drove to Big Bear Lake and back, with the ambient temperature in the low to mid 20s the whole time. Our nighttime temps are in the teens in this cold snap.

All in all, the reduced regen is hardly an issue when driving around the mountain communities where the elevation changes are more modest. It's more of an issue on the big descent down to the Valley, where I need to gain and maintain enough charge to come back up.

abasile said:

In terms of kWh, going from 65% to about 70% is roughly 5% of the usable capacity of a new battery (~ 21 kWh), or about 1 kWh.

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Thanks for helping me understand better! I don't think I can ever regain that much energy around here. I figure I might be able to add about 300 Wh at the most. That's probably why I have never seen this.

abasile said:

Also, the sort of regen behavior observed by Boomer23 has long been quite typical for us up here, especially on cold days like today. We drove to Big Bear Lake and back, with the ambient temperature in the low to mid 20s the whole time.

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Can you please give us an idea how far this was and how much charge remined when you returned? I'm just curious.

abasile said:

Our nighttime temps are in the teens in this cold snap.

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We normally have a month or so each winter when it gets into the teens every night. Not this winter! We've only seen the teens a few nights. As mentioned previously, we're expecting 65F today!

abasile said:

All in all, the reduced regen is hardly an issue when driving around the mountain communities where the elevation changes are more modest. It's more of an issue on the big descent down to the Valley, where I need to gain and maintain enough charge to come back up.

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Understood. And I can see how it would be frustrating since we all know that the battery can be charged to very near full at *at least* a 3 kW rate.

As you say, perhaps Nissan will improve things with the new "B" mode regen in the 2013s. We should know more about them soon.

RegGuheert said:

abasile said:

Also, the sort of regen behavior observed by Boomer23 has long been quite typical for us up here, especially on cold days like today. We drove to Big Bear Lake and back, with the ambient temperature in the low to mid 20s the whole time.

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Can you please give us an idea how far this was and how much charge remined when you returned? I'm just curious.

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We drove a bit over 32 miles in total, starting with a 1000' climb, a 400' descent, lots of smaller ups and downs, and the same route in the opposite direction. Sometimes traffic forced us to slow to 20 mph or slower, and in the passing lanes we did up to 50 mph. We were not range limited, so I accelerated when I felt like it and passed cars whenever I could. Still, our average speed could not have been much more than 30 mph. We also ran the climate control intermittently, mainly to keep the windows clear. The starting charge was 72.2% and we had about 33% remaining upon return home.

Also, on the 1000' descent on the return home, we had ample regen available, 20+ kW. With the SOC on the low side and a pack warmed from driving, however, that was expected. Even then, we never did get the leftmost regen circle.

RegGuheert said:

abasile said:

In terms of kWh, going from 65% to about 70% is roughly 5% of the usable capacity of a new battery (~ 21 kWh), or about 1 kWh.

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Thanks for helping me understand better! I don't think I can ever regain that much energy around here. I figure I might be able to add about 300 Wh at the most. That's probably why I have never seen this.

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In summer, if I really try to maximize regen and start at a lower SOC, I can pick up as much as 15% charge on the entire descent, or about 3 kWh!