VitaminJ
Posts: 304
Joined: Tue Jan 03, 2017 11:46 am
Delivery Date: 07 Jan 2017
Leaf Number: 415775
Location: Morrison, CO
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Re: LEAF's 12V battery behaviors - and why they go bad

Wed Jan 25, 2017 10:27 am

Well I am having second thoughts about the LifePO battery after watching Leaf Spy's voltmeter more. I watched it this morning and for a good part of my commute it was holding at 14.6v. I definitely don't want a fire so I will need to inspect the battery when it gets here, I don't even know if it has a BMS, I just recognized my favorite brand and clicked buy now. It is designed for motorcycles so I assume (hope) it has a way to deal with higher than normal LifePO4 voltage.

Also this is an interesting data point that suggests Nissan changed a few things. I don't know what model year this is but mine is a later 2013 that never had any recalls issued.
viewtopic.php?f=30&t=12448&start=190#p482871

VitaminJ wrote:
Durandal wrote:That's a very good point. I certainly intend on swapping my Pb battery for a LifePO battery once the Pb battery fails. I do charge it every couple of months on a 2a charger when I think about it to desulfate the battery a bit.

Mine died over the weekend, brought it back to life, but I just ordered this as a replacement:
https://www.amazon.com/gp/product/B01J9 ... UTF8&psc=1

Gens-Ace Tattu is about the best brand of lithium battery I've ever used. I have sold hundreds of them all over the world and haven't had a single failure.
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Durandal
Posts: 200
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Leaf Number: 025018
Location: Central Arkansas

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

Wed Jan 25, 2017 10:32 am

VitaminJ wrote:Well I am having second thoughts about the LifePO battery after watching Leaf Spy's voltmeter more. I watched it this morning and for a good part of my commute it was holding at 14.6v. I definitely don't want a fire so I will need to inspect the battery when it gets here, I don't even know if it has a BMS, I just recognized my favorite brand and clicked buy now. It is designed for motorcycles so I assume (hope) it has a way to deal with higher than normal LifePO4 voltage.

Also this is an interesting data point that suggests Nissan changed a few things. I don't know what model year this is but mine is a later 2013 that never had any recalls issued.
viewtopic.php?f=30&t=12448&start=190#p482871

VitaminJ wrote:
Durandal wrote:That's a very good point. I certainly intend on swapping my Pb battery for a LifePO battery once the Pb battery fails. I do charge it every couple of months on a 2a charger when I think about it to desulfate the battery a bit.

Mine died over the weekend, brought it back to life, but I just ordered this as a replacement:
https://www.amazon.com/gp/product/B01J9 ... UTF8&psc=1

Gens-Ace Tattu is about the best brand of lithium battery I've ever used. I have sold hundreds of them all over the world and haven't had a single failure.


The features listed on Amazon include:
5. Accurate LED battery indicator and built-in charge and equalizing protection board with over-charging&over-discharging, over-current, short-circuit protection.
Pulled the trigger on going EV on 10/2016

VitaminJ
Posts: 304
Joined: Tue Jan 03, 2017 11:46 am
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Location: Morrison, CO
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Re: LEAF's 12V battery behaviors - and why they go bad

Wed Jan 25, 2017 10:43 am

That's why I like Gens-Ace! :mrgreen:
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VitaminJ
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Re: LEAF's 12V battery behaviors - and why they go bad

Sat Jan 28, 2017 3:31 pm

Well I got the 5Ah LifePO4 that I posted. So far everything is as described. It came at 13.3v and the instructions said if it was above 13v it can be used right away. Leaf Spy showing 12v system voltages about the same as before and I will keep monitoring, especially while sitting on a CHAdeMO with all the accessories going (I believe CHAdeMO doesn't charge 12v at the same time).

The battery is much smaller and required some spacers. I used an old aluminum arduino case and a cut down block of wood. The new battery is 2lbs which represents about 18lbs savings over the lead acid battery right over the front end (and driver's side!). I also had to buy some aftermarket screw-on battery posts as it only came with a couple 10mm bolts.

Image

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e: I should note that I charged the original battery full on the bench and then put it in the back of the car along with a 10mm wrench in case I need it!
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FalconFour
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Re: LEAF's 12V battery behaviors - and why they go bad

Sun Jan 29, 2017 11:16 pm

VitaminJ wrote:Well I got the 5Ah LifePO4 that I posted. So far everything is as described. It came at 13.3v and the instructions said if it was above 13v it can be used right away.

Oh that is fantastic! Looks awesome, and I'm thinking of replacing mine with that now, too. When it comes time, that's probably exactly what I'll do ;)

Leaf Spy showing 12v system voltages about the same as before and I will keep monitoring, especially while sitting on a CHAdeMO with all the accessories going (I believe CHAdeMO doesn't charge 12v at the same time).

Aha... but not. ;) Literally any time the HV battery is engaged, it's running the standard charge cycle, same as driving, L2 charging, L1 charging, preheating/cooling, quick charging... um, did I miss any? But yeah, it does the same charge cycle (14.4v down to 10 amps -> 13.0v) any time.

What I'd be concerned about is that the Leaf's DC-DC actually selects a voltage, so if it goes to 14.4v, pumps charge in until it draws under 10 amps, then decreases to 13.0v, the lithium battery could begin supplying power to the car's systems (as the Leaf's DC-DC is only trying to run 13.0v, the now-higher 12v battery will begin discharging) until its standing voltage goes below 13.0v. Lead batteries just *pff* stop cold at 13.0v; their standing voltage is never over that but for a couple seconds after stopping a charge, thus that wouldn't be a problem with lead... but lithium is very linear. It could be doing a 80~100~80% sweep every time you start/drive/stop the car...

It'd be interesting to put a clamp meter on it and watch which way the power flows, and what the Leaf starts holding its voltage at...
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
2014 LEAF SV+Premium+QC - Feb 2017-present

VitaminJ
Posts: 304
Joined: Tue Jan 03, 2017 11:46 am
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Contact: YouTube

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

Mon Jan 30, 2017 12:30 pm

I have noticed when the DC converter changes voltages to a lower voltage, it will "hang" for a bit. Before it would go from 14.4v to ~13v almost instantly, now it will slowly count down from 14.4 and will linger in the mid 13 range. I'm almost positive that this is what you're describing. Is this harmful to the battery? I don't think so. Also I have been paranoid and constantly popping my hood and feeling the battery, but it's always ambient, never warm.
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FalconFour
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Re: LEAF's 12V battery behaviors - and why they go bad

Tue Jan 31, 2017 12:12 am

Really it's hard to tell if it'll be bad... it's quite an unusual charge/discharge pattern for a lithium battery. It'll sit most of its life at around 80% charge, but with a heavy hammer to 100%* then immediately getting sucked down to 80% (as it briefly powers all the car's 12v systems during that ramp-down). It might not really be harmful at all, especially given that low depth of discharge and that it spends most of its life at a comfortable below-100% level. Even while charging for a long time or driving for a long time, the car will bump it to 100% then level off at 80% for the rest of the time.
* - unlike lead batteries, which slowly absorb the charge while sitting at 14.4v, a lithium battery just eats energy as its voltage increases. So if the battery ever goes totally dead, the Leaf will really ram a charge into that thing FAST! Limited only by the resistance on the lines. It'd be interesting to see how it responds...

80% may not be quite right, either, just a guesstimate from voltage levels -- round-about 3.275v/cell in a 4-cell LiFePO4 pack at 13.0v. 14.4v puts it at 3.6v/cell which is ideal full-charge voltage, and there's a bit of a top-off curve to those cells (between 3.3v and 3.6v is a steep spike based on SOC%). I think 2.0v is fully discharged, and between about 2.9v and 2.0v is another steep curve.

Er, guess I could just Google a graph...
Image

^^ yea yea, that. ;)

So it's probably not doing any damage... hell, in some regards, it might be doing some good ;)
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
2014 LEAF SV+Premium+QC - Feb 2017-present

VitaminJ
Posts: 304
Joined: Tue Jan 03, 2017 11:46 am
Delivery Date: 07 Jan 2017
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Location: Morrison, CO
Contact: YouTube

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

Thu Feb 16, 2017 10:37 am

Well I'm about 3 weeks in with my 5Ah LifePO4 battery and I've had no issues whatsoever with it. In fact I've noticed a big improvement in brake feel at low speeds, the brake booster is electrically actuated, not hydraulically by your foot pressure like most other cars so any change in voltage will cause a change in braking pressure. I had noticed jerky brakes, especially at slow speeds where I would keep constant pressure on the pedal but the braking force would increase and decrease suddenly. This is different from the braking/regen mixing. Since I've changed to the Life the braking has been super consistent. I'm chalking that up to the lithium battery's ability to delivery high current and have very low voltage sag under load compared to the lead acid, especially a weak lead acid.

I have been regularly checking the voltage while driving and after parking the car without driving over the weekend and the lowest I've seen it when it was sitting outside for over 24 hours at about 10F and it was 13.2v. Most of the time at rest it is 13.4v or higher, especially if I have been driving it. Heat, A/C, accessories, etc all function normally. My Carwings has worked 100% for the last 3 weeks as well.
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drees
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Re: LEAF's 12V battery behaviors - and why they go bad

Fri Feb 17, 2017 9:11 am

Disconnecting and reconnecting the 12V battery usually improves low speed braking feel for a while if they've gotten grabby. It has nothing to do with the actual battery, the DC-DC converter can supply plenty of power for all 12V systems.
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2 months too late.
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VitaminJ
Posts: 304
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Re: LEAF's 12V battery behaviors - and why they go bad

Fri Feb 17, 2017 9:47 am

drees wrote:It has nothing to do with the actual battery, the DC-DC converter can supply plenty of power for all 12V systems.

Then why does the 12v battery exist in the first place? Why does the 12v system voltage drop momentarily when load is applied like AC or heater? That's where the jerkyness comes from; press on the brakes, 12v system voltage dips for a moment until DC converter increases power, voltage climbs back up, and the brakes grab harder than they originally did.
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