Brakes Fail upon Powering On

[GerryAZ]

Have any Leaf owners tried switching to a good quality deep cycle AGM type battery? I went to an Optima Yellowtop on my 2005 Prius, which is also notorious for undercharging 12V batteries, and have had no issues for 5 yrs. Even in Phoenix, which also tends to also be tough on 12V battery life.

It does seem surprising to me that the Leaf uses a flooded type battery, as well as a conservative charging routine. The only advantage of a 12V flooded I can think of is its tolerance to more aggressive charging. I guess the explanation is in the "reduces the electric power consumption from the Li-ion battery" statement, seems like they went a bit too far in the efficiency direction.

The Leaf does also use a 12V backup capacitor bank as someone else mentioned the Prius does. So its a little surprising that it could still get into this sagging voltage failure mode if that is indeed the cause. Unless I guess the 12V voltage is just not sufficient to charge the cap bank sufficiently? But that voltage should come up quickly as soon as the DC/DC converter engages when going ready? There are DTCs in the brake system and VCM for low 12V voltage, but they don't seem to trip until 10V or so.

Still it doesn't seem like a total brake failure should be possible even if the electronic control system fails completely. According to the manuals (and my own experimentation) there is still manual hydraulic braking force available in the event of a complete system failure. In my case this was simulated by disconnecting all control and power connections to both the ABS and IBU/master cylinder. Without the boost pump I will say the braking is very heavy, and the pedal position quite low from what I recall. So if the brake boost motor cuts out it may well feel like you've lost the brakes, but a firm pressure on the pedal should still stop the car.

Additionally its perhaps worth noting that the parking brake can (according to the manuals) be used while the vehicle is in motion to apply mechanical cable driven force to the rear brakes as long as the handle is pulled up. Of course this motor does depends on 12V power, but not sure how sensitive it is to voltage.

Rob

+1

I have used red top Optima batteries in my gasoline engine vehicles in Phoenix for many years and they always last longer than conventional batteries (unless the charging system overcharges them). I purchased a yellow top Optima deep cycle battery for the 2011 Leaf when the original flooded-cell Nissan battery failed even though I could have gotten a replacement from Nissan under warranty. It would be in the 2015 if the insurance company's storage yard would have let me remove it after the 2011 was declared a total loss. I believe the Leaf's charging algorithm is ideal for the yellow top Optima and I will replace the original Nissan battery as soon as it gets weak.

I have also tested the brakes without assist on both the 2011 and 2015 and found that the hydraulic brakes still function, but they require a lot of pedal pressure and the pedal is only about 1/2-inch above the floor. To someone who has not tried this it could seem like the pedal was going to the floor without applying the brakes.

Gerry

[TimLee]

Or Exide Edge AGM.

From the one time I experienced the brake failure while parking when 12V had bad cell, I agree the brakes may have actually finally worked as I did not hit the car behind me.
But even when moving at slow speed and there is only three or four feet, I really thought I was going to hit it and that the brakes totally failed.

Similar to GM ignition switch issue.
Yes the cars would steer.
Have you tried steering a car with the power assist not working
Really difficult.

[RegGuheert]

Or Exide AGM.

Again, note that the Exide AGM has a standing voltage above 13.2V when fully charged:



Member 69800 took that data. Note the voltage at the beginning of April 6 before he drove the LEAF. The point is that the LEAF's charging system DISCHARGED this battery when it was driven by operating at a voltage of 13.1V. Without occasional charging using a high-quality trickle charger, this battery will suffer he same fate as a flooded battery: sulfation. It might even happen more quickly due to the higher battery voltages resulting in a lower average SOC.

[DesertSprings]

Got a call from the dealer (Corona Nissan), they said there's 8 or 9 codes stored, from different components, so their Leaf guy (they have only one) is required to research and troubleshoot each individual code.

I'd asked them specifically to load-test (or whatever the correct term is) the 12v battery, but it wasn't specifically listed on the work order. When I pointed this out, they assured me it would be one of the tests they run, but would make a point to specifically mention it to the Leaf tech.

It's 2pm, so I'm not very hopeful that I'll get the car back before the weekend. Luckily I still have my old ICE as backup and for longer trips.

(This AM it was cold enough for frost to form on the roof of my house (Leaf was in the carport, protected from wind). When I started the Leaf up to take to the dealer, the red brake light was on and the orange ! was lit. Pumping the brakes before putting it into gear caused the lights to turn off, and the car to maintain braking when shifting into gear)

[miscrms]

Not sure I agree with the conclusion from the chart. When the DC:DC is on it looks pretty steady at ~13.1V. That should be beyond 100% SOC even for the AGM, so its not discharging the battery. Anything over 13V or so shown on the battery initially is likely surface charge. The occasional spikes to ~14.4V should be the VCM increasing the output voltage to charge the battery rather than maintain.

Any idea what the temperature was like for this April data? 100% SOC even on AGMs can be as low as 12.6V in the cold. The way its ramping down consistently reminds me of a battery acclimating to temperature and/or shedding surface charge. Its interesting to note that the voltage sags before the DC:DC kicks in, and after it kicks out (but before the loads shut off) seem to remain relatively constant over time, and almost looks like resting voltage is trending toward that same voltage.

Interesting chart:
http://www.exide.com/Media/files/Downlo ... 5_9_13.pdf

While 90% SOC Voltage is a little higher for the AGMs, they are same for 70% and lower. Also trickle / float voltages are similar, but absorption charging voltage and bulk charging termination voltage are actually lower on the AGMs.

AGMs also typically have much better internal resistance, charging efficiency, and much lower (up to 10X) self discharge rate.

In either case, flooded or AGM, putting a charger on it periodically is certainly not a bad idea.

Rob

[miscrms]

Got a call from the dealer (Corona Nissan), they said there's 8 or 9 codes stored, from different components, so their Leaf guy (they have only one) is required to research and troubleshoot each individual code.

I'd asked them specifically to load-test (or whatever the correct term is) the 12v battery, but it wasn't specifically listed on the work order. When I pointed this out, they assured me it would be one of the tests they run, but would make a point to specifically mention it to the Leaf tech.

It's 2pm, so I'm not very hopeful that I'll get the car back before the weekend. Luckily I still have my old ICE as backup and for longer trips.

(This AM it was cold enough for frost to form on the roof of my house (Leaf was in the carport, protected from wind). When I started the Leaf up to take to the dealer, the red brake light was on and the orange ! was lit. Pumping the brakes before putting it into gear caused the lights to turn off, and the car to maintain braking when shifting into gear)

Would be interesting to see what the codes are, if you can get a list.

Rob

[RegGuheert]

Not sure I agree with the conclusion from the chart. When the DC:DC is on it looks pretty steady at ~13.1V. That should be beyond 100% SOC even for the AGM, so its not discharging the battery. Anything over 13V or so shown on the battery initially is likely surface charge.

Nope. Resting voltage is clearly seen to be 13.25V for about six hours. There is a load on the battery during that time, so it is not surface charge.

The occasional spikes to ~14.4V should be the VCM increasing the output voltage to charge the battery rather than maintain.

That's right. And since these spikes are too short, the voltage drops with time.

Any idea what the temperature was like for this April data? 100% SOC even on AGMs can be as low as 12.6V in the cold.

Lead-acid battery voltage goes UP when it is cold, not down. You won't see 12.6V for a full resting battery unless it is quite hot. I've never seen the LEAF OEM battery hot enough to give such a low resting voltage wen full.

The way its ramping down consistently reminds me of a battery acclimating to temperature and/or shedding surface charge.

It's simply discharging due to the load of the LEAF on the battery.

Its interesting to note that the voltage sags before the DC:DC kicks in, and after it kicks out (but before the loads shut off) seem to remain relatively constant over time, and almost looks like resting voltage is trending toward that same voltage.

The loaded voltage is typically around 12.3V. Unfortunately, the LEAF will continue to discharge the battery until the resting voltage is around that level. That is because charging at 13.1V only charges the battery to around 60% SOC.

In either case, flooded or AGM, putting a charger on it periodically is certainly not a bad idea.

Agreed. Too bad the algorithms don't simply keep it charged so we don't have to do it.

[DesertSprings]

Sorry, I wasn't able to get the codes. They didn't call me to pick up until 5pm, and I just barely got there before 6 which is the cut off for picking up. All the techs had gone home.

But per what they told me on the phone, all the codes were likely caused by low 12v voltage. When they originally tested my battery when they first brought it into the shop, it passed. However after looking into the codes, they retested the battery and it failed.

So I was likely right on the edge. One of the consistent factors during my issues was much colder than typical weather, which probably was the tipping point.

[miscrms]

Lead-acid battery voltage goes UP when it is cold, not down. You won't see 12.6V for a full resting battery unless it is quite hot. I've never seen the LEAF OEM battery hot enough to give such a low resting voltage wen full.

I believe this relates to charge voltage. I've always assumed that's due to increased internal resistance when cold. All the data I've seen on open circuit resting voltage is that it goes down with colder Temps.

For example, here's the charts from batteryfaq.org:





Agreed, it would be hard to get cold enough to get resting voltage of 12.6V on an AGM. Maybe less so with the flooded.

Rob

[RegGuheert]

I believe this relates to charge voltage. I've always assumed that's due to increased internal resistance when cold. All the data I've seen on open circuit resting voltage is that it goes down with colder Temps.

Thanks! I stand corrected.

Still, I stand by my conclusions for the graph above. The 12.9V value at 90% charge is the nominal value and I have seen significantly higher voltages on AGMs depending on the unit and SOC, including the 13.25V shown above. Some AGMs I have will sit at 12.9V while others will sit at 13.15.