Always Shunting?

Every time after I unplug my car following a 100% charge (and sitting overnight), Leaf Spy shows images like this:



It APPEARS that all of the cells except one (the first one) are being shunted. But the pack isn't particular imbalanced, and the car is on, so why would it be doing this? It doesn't make any sense. One person is insisting to me that the LEAF does not do balancing except after charging, so it can't possibly be balancing here. But Leaf Spy shows the shunts! If Leaf Spy wrong? Or what?

I saw this with my previous car as well (though it was a different cell that was always lower), but I haven't seen it on my wife's.

Thoughts?

My LEAF has most of its pairs shunting all the time. Guessing maybe they lowered the delta voltage to initiate?

This has been normal for me during the (very cold, even for here) Winter. Through the Summer and Fall it was relatively rare.

Within a few seconds of turning on the car or plugging in, the shunts will turn on if they've previously been instructed to do so.
Why all but cell #2 are being shunted here (correct order is 8421, not 4812) is unclear but likely due to it being abnormally low at some point in the past.

Hopefully this is not a self discharge issue which we encountered with LiFePo4 cells in the past. Very annoying. One cell would (sometimes after hundreds or thousands of miles of use) develop a high internal self discharge. Over time the BMS tries frantically to drain all the other cells to keep the pack in balance but on some of the early Prius PHEV conversions even aggressive balancing couldn't compensate for the lone cell with the high self discharge. Again, hopefully that's not the issue here.. but if a screen like this is common on LeafSpy or LeafDD it could be signs of a bigger problem...

It's always the exact same cell pair not being shunted (either 1 or 2, depending on whether you believe GregH or not), both with this 2013 and my old 2012. It's been like this since the first moment I sat in the car (and immediately plugged in my OBD-II adapter, of course).

If there is something wrong with that cell pair, how do I convince Nissan of this? Is the car recording some data that would show up on one of their tools? Is this something the warranty would cover?

Are we even sure those bits mean what we think they mean? It's not like we were given documentation.

Could you provide a LeafSpy screenshot just before the end of charging (to full, not 80%).. for example when the pack voltage is 393 or more and the current has started to ramp down. Also a screenshot somewhere close to turtle (say 8-12 Gids).

These might provide some insight..

Both cars? Same cell you say? I'm assuming (other than the shunt order) that LeafSpy is reading the same thing I'd see on LeafDD..

Here's a far out idea... It looks like your battery is fairly cool (49F)... Cells 1 and 2 are right next to the LBC. If 95/96 shunts are on then the LBC is probably generating a bit of heat. Would warming the closest cell cause the voltage of that cell to read in a way that might make the LBC shunt everyone else in the pack? You'd think if this was in error and happened for too long, then things would get out of balance. On the other hand if this cell is consistently warmer than the rest then during normal driving it will lose less charge due to a lower impedance.. ?!?!

GregH said:

Could you provide a LeafSpy screenshot just before the end of charging (to full, not 80%).. for example when the pack voltage is 393 or more and the current has started to ramp down. Also a screenshot somewhere close to turtle (say 8-12 Gids).

These might provide some insight..

Click to expand...

Here's an actual screenshot just AFTER turtle. That's the closest I'm going to get to "somewhere close to turtle".



It might be a couple days before I can get that other shot for you -- I only need to charge every couple days and I just charged last night.

GregH said:

Both cars? Same cell you say? I'm assuming (other than the shunt order) that LeafSpy is reading the same thing I'd see on LeafDD..

Here's a far out idea... It looks like your battery is fairly cool (49F)... Cells 1 and 2 are right next to the LBC. If 95/96 shunts are on then the LBC is probably generating a bit of heat. Would warming the closest cell cause the voltage of that cell to read in a way that might make the LBC shunt everyone else in the pack? You'd think if this was in error and happened for too long, then things would get out of balance. On the other hand if this cell is consistently warmer than the rest then during normal driving it will lose less charge due to a lower impedance.. ?!?!

Click to expand...

It was a different cell on the other car, I think #47. Seen here (no shunting):

Computerizer said:

Here's an actual screenshot just AFTER turtle. That's the closest I'm going to get to "somewhere close to turtle".

Click to expand...

I'd say that's a pretty well balanced pack! Much better than mine.. I get >100mv deviation well before 3.3V avg..

what does changing the shunt order actually do? and is their shunts between cells inside a single module?

Not sure who here started using the word "shunt" to describe the cell balancing resistors.. At my work they call them "loads"... Whatever.
The shunt order selection was before we had proof that the correct order was 8421.. I posted a video here somewhere demonstrating it. But even if you're using the (incorrect) default of the pre-Leafspy beta software all it means is the highlighted cells in the graph are off by one.. No big deal.
The balancing resistors/shunts/loads are located in the lithium battery controller (LBC) that is located on the drivers (left) side of the rear battery stack and takes up about the space of a single module (2 cells, or cell-pairs as some around here call them.. There are actually 4 cells in a module, 2 series, 2 parallel). A monster harness connects every cell pair (ie discreet voltage) to the LBC. The LBC monitors the voltages of all 96 cell pairs and can also switch on small resistors shunted over any of the 96 discreet voltages. When a particular shunt is "on", the corresponding cell pair is bled down slowly through the resistors in the LBC, creating heat in the LBC. I would imagine having 95 of the shunts on would create a little heat.. Especially relative to a cool pack. Unfortunately none of the battery temp sensors are near the LBC. The last few battery management systems I've worked on used about 40 ohms for the balancing resistors. Not sure what the Leaf uses... But if was 40 ohms over 4.0v * 95 cells that would be 38 watts to dissipate in a package the size of a module. Again though, I don't know what size resistors Nissan is using.

Computerizer said:

It APPEARS that all of the cells except one (the first one) are being shunted. But the pack isn't particular imbalanced, and the car is on, so why would it be doing this? It doesn't make any sense. One person is insisting to me that the LEAF does not do balancing except after charging, so it can't possibly be balancing here. But Leaf Spy shows the shunts!

Click to expand...

It is believed that the car will only balance/shunt the pack for about 15-30 minutes after the charge is complete so that the LBC can go into low-power mode. Some claim it will balance for longer, I personally don't believe it because of data-points like this one - the car had plenty of time to finish balancing over night - should be done by now.

This leads me to believe that the best way to force the pack to balance would be to either trickle charge from say 80%-100% on an EVSE that can be dialed down to 6-8A, or perhaps just simply leave the car on for a few hours after the car is charged up. Anyone want to experiment?

The only cell-pair that isn't being shunted is the lowest one, so it definitely appears to be actually balancing the pack.

It would be interesting to see what your wife's pack looks like if it doesn't shunt like this after a 100% charge. My car usually shunts about 2/3rds of the cell-pairs right after a 100% charge, but it's not nearly as balanced as yours (30-35 mV difference between max/min).

I have been running LEAF Spy nearly 100% of the time since Tyrel posted his pix last week and its the same. At best, i might see 4 shunts not active. This includes a normal running time up to 40 minutes daily twice a day and the shunt status is always the same. always all shunting except a handful

**edit**

ok, figures this would happen the very next day. I get up in morning and take off and all is "normal" 284 GIDs all but 2 shunts active. after 15 minutes, I notice that I lost BT connect at 255 GIDs. I reconnect, am now at 245 GIDs and now have 26 shunts not active. first time ever on the 2013. So car sits at work most of the day. I take off in afternoon and now have 36 shunts not active. can't help but wonder what this signifies??

My experience has been:
Little balancing during charge if the previous commands had expired.
After a full charge (sometimes) select shunts will turn on within seconds of turning on the car.. Subsequent power ups (or even charge events) will bring on the same pattern of shunts. I haven't measured how long a particular pattern lasts, but I feel like its a few hours. Always off when the car is off then comes on after powering up. With LeafDD you can watch it turn on the shunts from left to right and as the shunts come on you can see the corresponding voltage dip as expected. (This is how we confirmed 8421 as the shunt order). Does Leafspy show the shunts turning on at power up or does it not sample the shunt settings until everything has settled?

http://www.mynissanleaf.com/viewtopic.php?f=44&t=11676&p=314207&hilit=ek98u2SBdzc#p314207

GregH said:

After a full charge (sometimes) select shunts will turn on within seconds of turning on the car.. Subsequent power ups (or even charge events) will bring on the same pattern of shunts.

Click to expand...

How long after the car turns off is LeafDD able to monitor the shunts?

LEAF Spy doesn't monitor anything unless the car is responding, which means the car has to be charging or on.

DaveinOlyWA said:

I have been running LEAF Spy nearly 100% of the time since Tyrel posted his pix last week and its the same. At best, i might see 4 shunts not active. This includes a normal running time up to 40 minutes daily twice a day and the shunt status is always the same. always all shunting except a handful

Click to expand...

Even when the battery is at a low SOC?

GregH said:

The shunt order selection was before we had proof that the correct order was 8421..

Click to expand...

It's pretty clear on my old LeafSpy shots from my 2012 that 4812 was the wrong order, as the one low cell was always right next to the one highlighted in blue:


However on our 2013s, whenever there's a low cell and the rest are shunting (here's a new one from this morning), it's clear that 4812 is the correct order. Perhaps the order has changed in 2013s?

drees said:

It would be interesting to see what your wife's pack looks like if it doesn't shunt like this after a 100% charge.

Click to expand...

My wife's looks like this:



Overall it's more out of balance than my pack, but there's not a single cell that's lower than the rest like mine. And, most notable, no shunting.

drees said:

GregH said:

After a full charge (sometimes) select shunts will turn on within seconds of turning on the car.. Subsequent power ups (or even charge events) will bring on the same pattern of shunts.

Click to expand...

How long after the car turns off is LeafDD able to monitor the shunts?

LEAF Spy doesn't monitor anything unless the car is responding, which means the car has to be charging or on.

DaveinOlyWA said:

I have been running LEAF Spy nearly 100% of the time since Tyrel posted his pix last week and its the same. At best, i might see 4 shunts not active. This includes a normal running time up to 40 minutes daily twice a day and the shunt status is always the same. always all shunting except a handful

Click to expand...

Even when the battery is at a low SOC?

Click to expand...

up until today, SOC has not mattered. I do notice when
SOC is generally below about 25%, all the shunts are active

check my edit. this morning i had 26 shunts not activated on morning drive at 85% SOC and 36 not active at 57% SOC... first time ever for that.

to be honest with ya, I seriously thought my color preferences were corrupt to the point where I changed the shunt color to something else long enough to check and then turned it back to red...

LeafDD only reads data when car is on or charging as well..
But when you're on the voltages page on LeafDD, I sample the shunt data several times a second so in the first few seconds after key-on, you can watch all the shunts turn on from left to right (as in the video above).. Also implies to me that they were off at the time of powering up thus no balancing when the car is off.