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FalconFour
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LEAF's 12V battery behaviors - and why they go bad

Sun Oct 16, 2016 11:49 pm

I was a little stuck between posting this in "technical discussion" forum or the heavier-traffic General forums. This seems to be a topic very relevant to troubleshooting, less about benign technical details. Here, I'll explain how the Leaf's 12V system behaves, and why those of us without 12V solar panels on the back are screwed so bad.
https://www.youtube.com/watch?v=9VuTDCjMzRw

The problem here is that the 12V battery is maintained at a 13.0V trickle charge with a very brief 14.4V boost charge. First of all: 14.4V is the typical charging voltage for lead-acid batteries. Lower than that, they either charge very slowly, or they don't charge at all. There's a threshold voltage that has to be exceeded in order to actively charge the battery. It's possible that the 14.4V charge is continued until the battery is only absorbing a low number of amps, before it drops down to 13.0V.

The Leaf's DC-DC system (which acts as an "alternator" for converting high-voltage ~380v DC into low-voltage 12v DC) is entirely controlled by the computers in the Leaf - with very precise control. The computer uses a single PWM signal to tell the DC-DC unit exactly what voltage to provide to the 12V system - I think between 10V and 15V DC. See here: https://www.youtube.com/watch?v=BMhcHkOg-Mk

The problem is that, while 13.0V will make all the systems run off the DC-DC power (instead of discharging the 12V battery constantly), it will not actively charge the 12V battery. It'll just maintain the charge level it was last left at after the 14.4V charging phase ramps down.

This is also contrary to what the Nissan EV techs (at the hotline) have told people in the past, as well as what the manual seems to indicate - that charging the 12V battery is only done while in "Ready" mode, and that regular L2 charging, quick charging, and remote climate control won't engage charging. That's a complete load of nonsense. It appears to execute the same charging behavior any time the HV battery is involved for any reason - charging, climate control, and driving alike. It may also perform a maintenance charge every couple weeks, as I've heard, but I don't feel like waiting around a couple weeks with a camera and multimeter to find out ;)

So, while the Leaf does this quick little burst to 14.4V, it seems like it maintains only 60-70% SOC in the lead 12V battery, which subjects it to sulfation and an early need for replacement. Additionally, little bugs in the Leaf's software tend to make it occasionally, and randomly, not go completely to "sleep" after 2 minutes - as seen in the video here. With such a limited 12V capacity available, that lack of deep-sleep makes the 12V battery completely die, and you're then left with a car that won't start (or you may think you need a new 12V battery at that point), when really all you need is a full, proper 12V battery charge.

Leaving the 12V battery at ~60-70% SOC is great for those Leaf owners with a solar panel in the rear, but it's a recipe for disaster for those without. Nissan should've provided a different algorithm (13.5V at least, 14~14.4V optimally) for models without a solar panel, so that the 12V battery is properly maintained and continuously left at a full charge as lead-acid batteries prefer. At voltages like those seen in my video, sulfation is occurring constantly in the battery.

Thoughts?

(edit: OH MY GOD this forum has GOT to stop chopping-up partial words and turning them into links... now I look like a Volt advert - aargh!)
100% gas-free since September 2012
2011 LEAF SL - Sep 2012~Sep 2014 - 35,737 miles
2013 LEAF S+Charge - Jan 2014-Feb 2017 - 68,065 miles
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LeftieBiker
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Re: LEAF's 12V battery behaviors - and why they go bad

Mon Oct 17, 2016 2:16 am

That certainly seems to be what's going on. After my 12 volt battery dropped so low, after about a year, that it wouldn't operate the door locks one day, I installed a battery Tender JR lead on the battery, ran it into the charging port compartment, and now I just plug that in as well whenever I have any reason to believe the car will sit plugged in but not charging. Heck, I often plug in just the maintainer, and it always tells me, via its LED, that the battery needed some charge - usually an amp hour or two. Or three. The car's charging behavior seems to have some other quirks, like sometimes (but not always) charging the battery more if the seat heaters are on, but overall it's a case of too little, too briefly. I'm still on that original 2013 battery, but I carry a lithium jumpstart pack just in case...
2013 "Brilliant Silver" SV with Premium Package and no QC, and 2009 Vectrix VX-1 with 18 Leaf cells.

The most offensive, tasteless phrase in use here is "Pulled the trigger." I no longer respond to posts that use it.

RockyNv
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Re: LEAF's 12V battery behaviors - and why they go bad

Mon Oct 17, 2016 2:50 am

Would one of these for $12.99 (and less if you have a coupon) then help for those without the solar panel?
Image
http://www.harborfreight.com/15-watt-solar-battery-charger-68692.html

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RegGuheert
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Re: LEAF's 12V battery behaviors - and why they go bad

Mon Oct 17, 2016 2:55 am

Dead-on, FalconFour! Thanks!
FalconFour wrote:Here, I'll explain how the Leaf's 12V system behaves, and why those of us without 12V solar panels on the back are screwed so bad.
The 12V solar panel makes very little difference. The HIGHEST voltage I have ever seen on the LEAF's battery when parked in the sun is 13.25V. That is only slightly better than the 13.1V that the car normally operates. The problem is that this voltage occurred in the cool of the morning. Once the sun got higher in the sky, the PV panel heated up and the voltage dropped back down to 12.8V. That thing truly is just an ornament. The BEST it can do is to reduce the amount of charge lost during the daytime.
FalconFour wrote:Thoughts?
Note that you get 14.4V whenever the wipers are on, so those in rainy or misty climates may do a bit better with their 12V batteries. Also note that sometimes during charging of the Li-ion battery you will get 14.4V continuously (or at least for a long time). I'm not sure how it decides when to do this.
RegGuheert
2011 Leaf SL Demo vehicle
2011 miles at purchase. 10K miles on Apr 14, 2013. 20K miles (55.7Ah) on Aug 7, 2014, 30K miles (52.0Ah) on Dec 30, 2015, 40K miles (49.8Ah) on Feb 8, 2017.
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arnis
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Re: LEAF's 12V battery behaviors - and why they go bad

Mon Oct 17, 2016 5:43 am

LeftieBiker wrote:that the battery needed some charge - usually an amp hour or two. Or three.


That means battery is nearly full if 55Ah battery can take FEW Ah after raising charging voltage above 14V.

According to Exide "charging & storage guidelines" they recommend to recharge battery if SOC is at or below 60%, or 12.5V OCV.
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QueenBee
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Re: LEAF's 12V battery behaviors - and why they go bad

Mon Oct 17, 2016 9:08 am

FalconFour wrote:It's possible that the 14.4V charge is continued until the battery is only absorbing a low number of amps, before it drops down to 13.0V.

The problem is that, while 13.0V will make all the systems run off the DC-DC power (instead of discharging the 12V battery constantly), it will not actively charge the 12V battery. It'll just maintain the charge level it was last left at after the 14.4V charging phase ramps down.


This is exactly what it does. Use LEAFSpy to watch the amperage going into the battery. It'll start dumping power into the battery at an alarming rate if you've used the battery a lot, then the battery slowly stops taking the power and eventually the LEAF is happy with how slow the battery is charging and switches back to 13 volts. Except sometimes, it seems when it's cold out there are times when it'll sit at 14.4V "forever". Or if you use your windshield wipers, that brings it up to 14.4 volts as well.

I seem to recall that the 13 volts it normally runs at after charging is enough for around 3/4 of amp to be measured going into the battery so presumably some of the power is actively charging the battery, slowly.

FWIW I'm on 5.5 years with my original battery though a couple years back I did somewhat regularly start putting it on a desulphating charger.

arnis
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Re: LEAF's 12V battery behaviors - and why they go bad

Mon Oct 17, 2016 9:47 am

So I got tired of you guys thinking that Leaf is not charging battery correctly.
So I did something.

Facts.
My battery is OEM Nissan-Renault 12V 50Ah battery, manufactured in the first half of 2014.
While it was at 13V float charge I disconnected EVSE.
Switched on full-beams , front fogs, rear fog, standing lights. Got a draw of 19.8A (should be 2x60W, 2x35W, 1x21W, 4x6W). Discharged my
50Ah battery SOC by 20% just be keeping that load for 30 minutes.
Average voltage during 30 minute draw was 11.5V. That means around 10Ah discharge, 115Wh.
Stopped the discharge. Car started to fall asleep. Draw was getting down below 1A.
After waiting for only 2 minutes voltage got up to 12.1V. It would most likely get to 12.2V easily.
That means battery was above 50% SOC, more likely 60% after 20% (10Ah out of 50Ah theoretical) discharge.
Old battery is very likely below rated 50Ah and temperature was 7C - so definitely below 50Ah.

And now comes exactly what I expected.
I connected EVSE back.
Voltage spiked to 14.43-14.47V. Ammeter measured charge above 70Amps for few seconds.
Dropping down to 50Amps. Average charge was around 45Amps during the first minute.
Then 40Amps during the second. 37, 35, 32, 29, 26, 24, 23, 21 during 10th minute, 10.4Amps 20th, 4,9Amps 30th, 1,5-2,0Amps 40th.
During the whole charging process voltage was absolutely steady at 14.42-14.45V. I did measure every minute.
While charging rate was between 1-2A it switched to 13V mode.
Using Excel and video I took I got down to this:
During 40 minute charge cycle 9.27Ah of juice went in. At 14.4V it is 133Wh. Process is 85-90% efficient.


Leaf WILL charge the battery if BATTERY takes the charge. I will test something else soon. I will trick the current sensor with halogen
bulb. I want to verify that switching to 13V mode happens as soon as charge rate at 14.4V drops below 1,3-1,8A, something like that.

I did notice that right after switching back to 13V mode and longer charge time there was a draw from the battery even after Leaf fell asleep (-0,4A)
This is expected as voltage after charging is always above resting voltage for a period of time.
Resting voltage should drop below 13V after like 10 minutes maybe.
Also I noticed that electrolyte was bubbling at very slow rate when battery was charging at 14.4V. This is normal but not recommended on daily basis due to loss of water.

Also we can conclude that SOC definitely stays above 70% during Leafs everyday use. Most likely it is at 80%. Which is not FULL state of charge but not low enough for sulfation to happen within few years.
Like I already mentioned, BMW-s keep their AGM battery charged specifically at 80% to have regen available on demand (3,5kW regen only).
Those batteries last for 5-7 years of heavy use. There is nothing wrong with keeping Lead acid batteries slightly discharged. Like I mentioned in another topic APC UPS's keep their battery at constant 13.5V. This kills the battery (99% guarantee) during 1-2 years of use. I've replaced them multiple times, always the same - ran out of electrolyte.

Therefore there is NOTHING wrong with Leaf charging the battery. It is designed not to charge it to 100%. And there is nothing wrong with that. Charging it to so-called 100% is stressing electrolyte and is not efficient (most likely there are additional losses). If there is a failure it is either because of battery internal defect or unplanned parasitic load. Leaf will charge the battery if it has been drained but will NOT set off an error code like 2005+ BMW-s do.
Therefore if there is a problem it will definitely kill the battery and then the user might do something (if vehicle is out of warranty, otherwise "don't care" policy)

Also Leaf keeps 12V battery at 13V voltage for hours and hours every day during vehicle lifetime! This is like keeping it trickle charging for years. Most Leafs are used daily. Older type Leafs that are used rarely might have problems as recharging happens only after 5 days while draw is more than on average ICE vehicle due to telematics.

Now we need to measure draw during sleep with 0.01A precision (clamp will not do it) 5 minutes after falling asleep and 12 hours after that to be sure (without any disconnections or touching any buttons). Please. Anybody besides me :lol:
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LeftieBiker
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Re: LEAF's 12V battery behaviors - and why they go bad

Mon Oct 17, 2016 11:28 am

arnis wrote:
LeftieBiker wrote:that the battery needed some charge - usually an amp hour or two. Or three.


That means battery is nearly full if 55Ah battery can take FEW Ah after raising charging voltage above 14V.

According to Exide "charging & storage guidelines" they recommend to recharge battery if SOC is at or below 60%, or 12.5V OCV.


I don't think that the US spec batteries are 55AH. Does anyone have the actual number? The fact that these batteries tend to get drained if never externally charged would argue against your position. Some drivers do manage to accidentally use the car in a way that keeps the battery charged enough to stay out of trouble, but it's largely a crap shoot. BTW, most of these batteries seem to measure about 12.5 volts when checked, so that also argues against the battery being almost full. More like 55-70%.
2013 "Brilliant Silver" SV with Premium Package and no QC, and 2009 Vectrix VX-1 with 18 Leaf cells.

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FalconFour
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Re: LEAF's 12V battery behaviors - and why they go bad

Mon Oct 17, 2016 11:40 am

arnis wrote:Facts.


Okay, I think you believe lead-acid batteries have the same characteristics as a capacitor or a lithium battery.

Head to Battery University and do some skimming. In fact, maybe the Nissan techs could use some experience on this site as well.

First of all, it's worth noting, my 12V battery has gone dead at least 8 times in its life so far, because of how sh!t the Leaf maintains it. Usually, they come in bursts - it goes dead once, I jump start it, it's happy for a day or two, then it goes dead again, rinse and repeat. Once I took the battery out and fully charged it overnight, it holds up for months. This highly indicates a problem with the charging system. In fact, when I capacity-tested my 12V battery on an actual metered tester that speaks mAh, not rough calculations, it came out to around 25 Ah and could only deliver about 18 of that before it could no longer sustain a 20A load (so the load decreased until it could only sustain around 4A) -- in other words, it was fuq't.

Lithium batteries don't like staying fully charged all their life. Lead batteries do. Battery University also has a handy table to explain proper habits - and the Leaf breaks several of these rules.

Image

It takes 12 hours to fully absorb a lead battery, so you can't just shove 14.4V into it and wait for it to slow its absorption, then say "aha, it's done" and kill the charge. Also, there's practically no scenario by which running the battery at 13.5V for a charging period (even an L1) would harm the battery (as your APC UPS case). That's why my 12V is being abused as in this video - the battery is not "dead" and it doesn't need to be replaced; it merely has high internal resistance. It has plenty of load capability to operate the car, and it'd be even better-off if the Leaf actually charged the battery properly.
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arnis
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Re: LEAF's 12V battery behaviors - and why they go bad

Mon Oct 17, 2016 11:49 am

I verified by reading studies about lead-acid charging efficiency. Charging lead-acid battery below 80% SOC is something like 90% efficient. Above 90% is less than 50% efficient (due to oxygen production (quiet bubbling) that will recombine, having 0% efficiency). I'm absolutely satisfied with my finding that Leaf does NOT charge 12V battery to 100%. Also I understand WHY float voltage during the rest of charge cycle (either driving or charging the vehicle) is around 13V. This is to make sure battery is not being charged (or almost not being charged) further than was already set by the 14.4V CV charging current threshold which on its own sets SOC pretty accurately without counting Ah (like BMW current sensor does: reads voltage/temperature/current few times per minute and calculates SOC/SOH, something like Leaf Li-ion pack BMS does).

This picture is illustrational but still represents what other studies have mentioned:
Image

Also found out that most lead acid battery manufacturers do not require topping charge above 80% SOC.
This means shelf life is not expected to be any longer above that threshold.
This also explains why BMW batteries that are only 80% charged do not degrade any faster.

This all explains Leaf charging behavior in every possible way. The only mistake they made was with the 2011/12 Leaf top-up charge while long-time stationary. They most likely fixed that too now with 24h limit.


IF leaf would hold 14.4V for longer it would result in parasitic drain not only while EVSE charging but also while driving. 12V battery might be 20% discharged when starting a journey. If Leaf tries to charge the battery it will consume some additional power. As 50Ah battery has about 0.6kWh of energy (main pack contains 24kWh) imagine charging 12V battery from 80% to 95% would take additional 0,1-0,15Wh of electricity EVERY SINGLE DAY. Not to charge the 12V but to heat it up. This results in 3kWh loss each month for nothing.
All that has to be done is NOT charge lead acid battery above 75-80%. Leaf is unable NOT TO CHARGE after 14.4V charge because it is unable to disconnect 12V battery. Therefore simplified version of float voltage 13.0V has been utilized which still unfortunately charges 12V battery way above 80% if kept long enough. Also this inefficiency happens during wipers being used but that is necessary for wiper motor voltage most likely. Also would randomly top the recommended 80% limit.
Short range EVs <30kWh -- Medium range: 30-60kWh -- Long range: >60kWh
Charging: Trickle <3kW -- Normal 3-22kW -- Fast 50-100kW -- Supercharging >100kW

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