How to mitigate a badly out of balance pack?

[TomT]

Just buy an old Android phone on Ebay. It doesn't have to be activated so you can do it pretty cheaply that way...

Kinda makes me want to dump Apple and get an Android.

 

[DNAinaGoodWay]

Just buy an old Android phone on Ebay. It doesn't have to be activated so you can do it pretty cheaply that way...

Kinda makes me want to dump Apple and get an Android.

Oh, that's brilliant. Thanks.

What's the other thingy you have to have to go with it?

And, if the phone's not activated, how do I get the app into it?

 

[TomT]

You need the ELM 327 module, also available on Ebay, among other sources...
You can get the app on to it either via WiFi or a USB cable...

What's the other thingy you have to have to go with it?
And, if the phone's not activated, how do I get the app into it?

 

[Boomer23]

I remember Gary Gid writing that most of the balancing is done in like 45 minutes or so.

There's a bit of history involved, such that in the beginning, the only clues we had about balancing were a page in the service manual that mentioned shunts, and the fact that the charging tapered off at the end. Plus a few reports of the charge coming back on after awhile. Later on, ingineer mentioned that balancing could take place at times other than the 100% charge. Now, with the LEAF Spy, we can see what appears to be balancing (shunting) going on all the time. But we must remember most of what we know is gained empirically, since Nissan won't tell us what actually is going on.

Your results will vary with the charge turning itself back on. Mine never does this, so maybe this battery doesn't get too far out of balance.

One thing is for sure, on a 100% charge with no stop timer set, my 2013 SL definitely tapers down before it finally stops charging, unlike when I set it for an 80% charge, when it stops charging abruptly. I can see this clearly on the graphical plots on my TED energy monitor. I don't know whether this tapering behavior contributes to better balancing. I haven't seen evidence of the car drawing significant additional energy after it does finally taper down to zero charging.

 

[Nubo]

When the battery sits without charging or discharging, the cells should eventually get to about the same temperature. That allows for optimum balancing.

So, first it equalizes temperature, then the cell voltages equalize?

When I can get off this phone and to a desktop, I'll search old threads, I remember Gary Gid writing that most of the balancing is done in like 45 minutes or so. So maybe 2 hours is enough?

I use 4 hours as a rule of thumb; I think I originally got that from either Tony or Phil, who simply based it on empirical observations of what was the longest amount of time observed before witnessing a 2nd "charging complete" event.

Since I only do this once a month or so, I'm not too worried about a few hours at 100% SOC. My default timer is to 80% but with Leaf Link I can fairly easily set a one-time start-charging timer that will override that and get me to 100% with the desired lead time, so the car is ready to go the next day when I am, having included the 4 hour window.

 

[Rauv]

Here is my typical charging load profile that clearly shows tapering and bumps, presumably when balancing is occuring.

http://www.tc.umn.edu/~rauvo001/2013 Leaf Charging.pdf

 

[RegGuheert]

I don't know whether this tapering behavior contributes to better balancing.

I'm quite sure it does. I think Nissan improved the tapering in the 2013s to ensure that a single charge to 100% would result in a well-balanced pack.

 

[linkim]

Here is my typical charging load profile that clearly shows tapering and bumps, presumably when balancing is occuring.

http://www.tc.umn.edu/~rauvo001/2013 Leaf Charging.pdf

Do you have results for 80% charge? I mainly charge to 80% so wonder what the level of balancing is. Thanks.

 

[DaveEV]

So, it has to stay plugged in after 100% is reached to optimally balance, and for at least four hours?

Why is that? Does it draw small amounts of power occasionally during this process? I've never noticed it draw anything after 100%, but then, haven't ever looked for it.

Keep in mind that the behavior of '11-12 LEAFs is different than '13 LEAFs.

I don't think it's been determined that it needs to stay plugged in, but it does appear that on occasion if you leave a '11-12 plugged in on a 100% charge (no timers), it will top off the battery after 4-5 hours, presumably after some balancing has been done.

The '11-12 will cut off charging quickly on a 10% charge. Once power starts to taper from 3.3 kW, it will only charge for 15-30 more minutes - you won't see much time spent with the car pulling less than 1kW if at all.

The '13 LEAFs will sip electricity for a while after the pack is 100% - up to an hour has been reported. This appears to be much more effective at topping off/balancing the pack.

RegGuheert's trick of starting up climate control for an hour or more after a 100% charge simulates the behavior of the '13 on the '11-12 LEAFs, since the car will attempt to charge the battery as long as there is left over power after powering the HVAC.

This may be more effective than letting the car sit for a couple reasons:
1. Someone has said that the BMS doesn't actually remain active for all that long after the car shuts off (perhaps 30 minutes). Whether or not this is true is up for debate, but I haven't seen hard proof either way.
2. You can be certain that the BMS will be trying very hard during that hour the HVAC is running to keep the highest voltage cells from overcharging.
3. Less time spent at 100% charge is always better!

It would be very interesting to compare before/after LEAF Spy cell-pair plots after both techniques to see what kind of difference there is if any. I would give it a shot, but I'm still waiting for my pack to get down into the mid-60F temps to minimize the effects of high SOC/temp capacity loss - saw 6 TBs the other day!

Here is my typical charging load profile that clearly shows tapering and bumps, presumably when balancing is occuring.

http://www.tc.umn.edu/~rauvo001/2013 Leaf Charging.pdf

Do you have results for 80% charge? I mainly charge to 80% so wonder what the level of balancing is. Thanks.

There won't be much to see, you will simply see it go from ~7 kW to 0 kW in a minute. Balancing will still be done if necessary - don't equate the tapering of the charge to balancing as they they are two separate functions.

The charge is tapered off to prevent cell-pairs from exceeding a maximum voltage. Cell-pairs are balanced by bleeding off the CPs with the highest voltage. The shunts can not bleed off voltage/energy from cells very quickly, so the car tapers off the charge and even pauses for a bit before topping off the pack a few times.

It would be great to get a chart as detailed as Rauv's (VERY nice plot!) for a '11-12, but the lower resolution charts I've seen taper off from ~3.8 kW to ~1 kW before shutting off. If the car comes back on to top off the pack (and I don't think this has been documented very well), it will happen hours later.

 

[Rauv]

It would be great to get a chart as detailed as Rauv's (VERY nice plot!) for a '11-12, but the lower resolution charts I've seen taper off from ~3.8 kW to ~1 kW before shutting off. If the car comes back on to top off the pack (and I don't think this has been documented very well), it will happen hours later.

I had a 2012 SL and the tapering off during the final hours of 100% charge was not nearly so dramatic as my 2013. It tapers, as seen in the graph link below, but not as gradual. Also, I do not have any data to support any balancing ocurring later (several hours) but that does not mean it doesn't happen, just not for me because I never left it at a high state of charge for very long.

2012 charging graph:

http://www.tc.umn.edu/~rauvo001/2012 Leaf Charging.pdf

 

[DaveEV]

I had a 2012 SL and the tapering off during the final hours of 100% charge was not nearly so dramatic as my 2013. It tapers, as seen in the graph link below, but not as gradual. Also, I do not have any data to support any balancing ocurring later (several hours) but that does not mean it doesn't happen, just not for me because I never left it at a high state of charge for very long.

2012 charging graph:

http://www.tc.umn.edu/~rauvo001/2012 Leaf Charging.pdf

Great chart! Matches up with the others I've seen, but with better resolution.

 

[cwerdna]

Here is my typical charging load profile that clearly shows tapering and bumps, presumably when balancing is occuring.

http://www.tc.umn.edu/~rauvo001/2013 Leaf Charging.pdf

Thank you! This saved me the trouble posting my tiny Chargepoint EVSE graph that only is in 5 minute increments.

Yep. This looks basically like what I see when charging to 100% at work.

For me, on my charge to 100% on Friday, I received a charging complete email from Carwings at 5:22 pm. Chargepoint graph showed a 0.55 kW draw at 17:23:24, but again, they only show 5 minute increments. I noticed no more bumps in their graph after that. At 5:38 pm (they probably have a built in delay before sending this), I received a

ChargePoint Notification: Charging Complete

Dear (my name),

We wanted to let you know that your vehicle, which is charging at (work location), is drawing very little power. Typically, this means it's fully charged, however, it may also indicate that your vehicle is configured for delayed charging. Your vehicle has accepted 7.72 kWh of electricity and has been plugged in for 02:35:10 (hh:mm:ss)....

I pulled the plug at 7:19 pm and was monitoring the graph until a few minutes before that (received ChargePoint Notification: Plugout Detected mail at 7:19 pm).

For me, on my '13 SV, if I charge only to 80%, the draw abruptly drops from ~5.8 or 5.9 kW to 0 and I'm pretty sure there are no bumps after that. EVSEs at work run at 208 volts, per the Chargepoint tech who came to my work a few weeks ago.

 

[arnis]

I also confirm this on European 2014 Leaf.
3-10 bounces (depending on temperature) are expected if charging to 100%.
It stops when consumption drops to 500W or less and highest cell at maximum
voltage (4,136V or smth, depends on temperature a little bit) and resumes after
after small pause. Does make sense. Why keep charging if more than half of
the juice is wasted on pumps and other parasitic devices :lol:

If battery is below freezing charging might take 2-4 hours from 90% to 100%.

 

[cwerdna]

2012 charging graph:

http://www.tc.umn.edu/~rauvo001/2012 Leaf Charging.pdf

Here is my typical charging load profile that clearly shows tapering and bumps, presumably when balancing is occuring.

http://www.tc.umn.edu/~rauvo001/2013 Leaf Charging.pdf

Rauv,

If you're still active here, can you repost these somewhere? The URLs are dead and I guess nobody submitted them to http://archive.org/web/.

 

[Rauv]

Oops. been gone a while. Here is the '13 Leaf charging graph:

https://www.dropbox.com/s/ip156e47rqztw1p/2013%20Leaf%20Charging.pdf?dl=0

 

[cwerdna]

Oops. been gone a while. Here is the '13 Leaf charging graph:

https://www.dropbox.com/s/ip156e47rqztw1p/2013%20Leaf%20Charging.pdf?dl=0

Thanks!

Do you still have the '12 charging graph?