Odd 60% loss in SoC during acceleration

[chaz]

Hi all,
I am wondering if anyone has had a massive loss in SOC due to accelerating in cold weather.
Background:
My wife has a march 2013 leaf missing 3 bars. We bought in UT used in july. It was originally from southern CA.
We drove to dinner the other day and drew it down to about 80% SoC. The car sat at about 20 deg F for a few hours and then we went to go home. While hopping on the highway and getting up to 80 the SoC dropped to 22% and we freaked out and drove home in eco.
On the trip back the SoC slowly ramped up and we ended the night with a little more than 25%.
I looked up DTC with leaf spy pro and there were none recorded.

Anyone ever experience this? With no DTC codes recorded I am worried the battery is going to get flaky but the dealer won't be able to do anything to help. I am nearing the end with the battery lottery also, I would hate to not loose the last bar and be stuck with a flaky battery.

Thanks.
-Chaz

 

[DNAinaGoodWay]

Can you post a shot of your cell balance?

 

[chaz]

Sure thing, in what specific situation? 100% SoC at rest or pulling 80Kw up a canyon?

 

[DNAinaGoodWay]

Any and/or all. Just curious if you have a bad cell. A sharp drop in the GOM is normal in what you described, but not a sharp drop in SOC.

 

[LeftieBiker]

It sounds like you have a bad cell. Even if you still have only (!) three bars gone you may qualify for a new pack under the 8 years defect warranty.

I'll bet anyone serious money that this car was built before April of 2013.

 

[DaveinOlyWA]

It sounds like you have a bad cell. Even if you still have only (!) three bars gone you may qualify for a new pack under the 8 years defect warranty.

I'll bet anyone serious money that this car was built before April of 2013.

OP states mar 2013, so you win the bet...if you can find any takers

 

[LeftieBiker]

Oh yeah, didn't read the tiny signature print.

 

[DaveinOlyWA]

I think its a bad cell. I kinda pretty sure I read about someone else who had like 60 miles on GOM and then suddenly went to Turtle mode skipping the normal warnings. It turned out to be a bad cell.

Remember your pack is only as good as its weakest cell.... *spoken with an english accent*

 

[chaz]

Here are some images of the cells: only a 59mv difference under full load but again the cells are fairly full. I'll try again when it is almost empty.

Full:

Under Load:

I sure hope it is a bad cell, that would be grand.

 

[GerryAZ]

Since the voltage drops to 360 under full load when the battery is near full charge, you are seeing the effects of high internal resistance. The internal resistance of the battery (or each cell if you want to look at it that way) goes up as the battery deteriorates. The 60 mV difference between highest and lowest cells is reasonable so I doubt that you have a bad cell. I think the LBC (lithium battery controller, also called battery management system or BMS) sees the severe voltage drop under acceleration as an indication of low SOC even though the energy stored in the battery is not low. The high internal resistance is more noticeable during cold temperatures. Eventually, the internal resistance when cold will increase to the point where the battery cannot supply 80 kW for maximum acceleration. The 8-year, 100,000-mile warranty should cover repair at that point, but it may take quite a while and many miles to get there.

Gerry

 

[LeftieBiker]

Since the voltage drops to 360 under full load when the battery is near full charge, you are seeing the effects of high internal resistance. The internal resistance of the battery (or each cell if you want to look at it that way) goes up as the battery deteriorates. The 60 mV difference between highest and lowest cells is reasonable so I doubt that you have a bad cell. I think the LBC (lithium battery controller, also called battery management system or BMS) sees the severe voltage drop under acceleration as an indication of low SOC even though the energy stored in the battery is not low. The high internal resistance is more noticeable during cold temperatures. Eventually, the internal resistance when cold will increase to the point where the battery cannot supply 80 kW for maximum acceleration. The 8-year, 100,000-mile warranty should cover repair at that point, but it may take quite a while and many miles to get there.

Gerry

That would be like the severe voltage "sag" that occurs with SLA-powered EVs, and worsens with low SOC and increasing age. The LeafSpy shot sure looks ok, in my limited expertise. The question is, if this is normal deterioration, why doesn't this symptom show up much more often in aging Leaf Packs...? The OP needs to gte a look at (and video record) the pack voltage in realtime, over maybe 30 seconds of high load. If it's a short or open that only happens at high loads, a regular snap might not show it.

 

[DaveinOlyWA]

59 mV difference at high SOC is a concern to me. If looking for a weak cell, you should be monitoring your pack when SOC gets below 20%. This is where the separation happens.

The other thing to consider; After a bit of playing around (for the sake of science!) I have to think that there is a delay with Nissan instrumentation and LEAF Spy readings. I also see random spikes where only half the cells' voltage drops 3-4X more than the other half. Granted only lasts a second or two but in general, I rarely saw more than 30-40 mV delta. rest or low power draws showed 10 to 15 mV when SOC was over 80%.

But when getting down to 18% yesterday, rest was 11 mV but under power I was seeing 50-75 mV ranges with most of that being random single cells (about 4 to 5 different ones) dropping momentarily but then bouncing back. so nothing consistent.

 

[chaz]

Well I drove it down to around 20% SOC and under full load saw 70mv differential.
However when I plugged it in to charge the change jumped to 106mv. I wonder what to make of that.
Why would there be more change once charging at 17A occured vs drawing 275A?

 

[sendler2112]

I sure hope it is a bad cell, that would be grand.

Nissan won't replace a battery for a "bad cell" unless there is a malfunction indicator light on. Which you are nowhere near that. The other car got as far as 700mv out on one cell and still no warning. Your 250 amp screen shot shows nothing even close to that.
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http://www.mynissanleaf.com/viewtopic.php?f=27&t=23250&start=10#p481485
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[DaveinOlyWA]

Well I drove it down to around 20% SOC and under full load saw 70mv differential.
However when I plugged it in to charge the change jumped to 106mv. I wonder what to make of that.
Why would there be more change once charging at 17A occured vs drawing 275A?

weak cells have a much greater swing so wild numbers are to be expected. As many have mentioned, Nissan can't do anything until the car starts throwing codes and your best chance of that happening is pushing the low end. With balancing going on all the time, you might want to drive to near Turtle (watch your power circles) then let it sit for a while. the balancing is pretty weak, so might have to sit at least an hour, then start it up and drive it until near Turtle again.

This will put more pressure on the weak cell as its voltage swings should exceed the rest of the pack

 

[chaz]

whoo, that is bad! i had it in turtle last night and it was 200mv max. 600mv is nuts.

 

[sendler2112]

That car was like that from new. The bad cell was robbing him of 24% of his capacity and Nissan refused to do anything about it even after several dealer visits and calls to Nissan corporate. Until he started legal action. He must be under gag order now because we have never heard anything more about how it turned out.