dhanson865
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Location: Tennessee

Re: Car moves while I am pressing on the brake.

Mon Sep 29, 2014 3:14 pm

RegGuheert wrote:
daryler wrote:Apparently the 12v battery was bad.
As predicted.

I'm convinced that the 12V battery is the first thing to check on the LEAF when there are braking issues, particularly if codes are being thrown. In this case, it was likely just a bad battery, but the poor 12V charging algorithm in the LEAF conspires with the extreme sensitivity of the braking system to 12V-system voltage to make this a potentially severe issue as these batteries age. I suppose things are O.K. as long as a cell does not fail shorted...
Please tell that to Nubo in thread http://www.mynissanleaf.com/viewtopic.php?f=9&t=17890" onclick="window.open(this.href);return false;

I tried to let the thread know that and he poo pooed the idea with his "onboard DC-DC converter can supply 90 amps or more" dismissal.

I'm in the camp that believes that Nissan Leaf or Toyota Prius either way they don't charge the 12v battery aggressively enough.
Blue 2012 Leaf 195/65/15 tires, 15" Rims
Silver 2012 Leaf 16" stock wheels
http://www.mynissanleaf.com/wiki/index. ... acity_Loss
(efficiency 3.x KW vs 6.x KW)
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Bob
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Re: Car moves while I am pressing on the brake.

Mon Sep 29, 2014 6:45 pm

There have been lots of people posting on this forum with battery problems. Fortunately, 12V lead-acid battery technology is very well understood and mature.

There are two possible reasons for battery problems: either the system is not charging the battery correctly or the Leaf is leaking current out of the battery while parked. Either one will cause the battery to fail prematurely.

It is very easy to test for Leaf leaking current out of the battery. In the Leaf service manual, they call this "Dark Current". Just put an ammeter in series with the 12V battery and turn off everything in the car. According to the service manual, it should consume less than 50mA. The battery is rated for 45 amp-hours, so it should last for roughly 900 hours (5 weeks) with 50mA of leakage. On top of that, the Leaf tops off the battery for 5 minutes every 120 hours from the traction battery, so even if you park the car for a month, the battery should not go dead.

It is very easy to test for improper charging. Just put a voltmeter on the battery while the car is on. It should be approximately 14.5V, indicating that it is being charged correctly. If it is below 13.5V, then the charging system isn't working correctly.

If charging is good and dark current is low, then it was just a bad battery. But if either of the other things is bad, changing the battery won't solve the problem.

If you are not comfortable doing these tests yourself, find a friend who is good with electronics or ask the dealer to do it in front of you. The procedures are right in the service manual.

Bob

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RegGuheert
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Re: Car moves while I am pressing on the brake.

Tue Sep 30, 2014 6:41 am

Bob wrote:There are two possible reasons for battery problems: either the system is not charging the battery correctly or the Leaf is leaking current out of the battery while parked. Either one will cause the battery to fail prematurely.
In fact, it appears both are likely involved here.
Bob wrote:It is very easy to test for Leaf leaking current out of the battery. In the Leaf service manual, they call this "Dark Current". Just put an ammeter in series with the 12V battery and turn off everything in the car. According to the service manual, it should consume less than 50mA. The battery is rated for 45 amp-hours, so it should last for roughly 900 hours (5 weeks) with 50mA of leakage. On top of that, the Leaf tops off the battery for 5 minutes every 120 hours from the traction battery, so even if you park the car for a month, the battery should not go dead.
I've already made this measurement in my MY2011 LEAF.

But this measurement was done under only one scenario and with only one set of firmware. It is entirely possible that there are conditions which can occur which cause some larger loads to be improperly left on. In fact, it appears from some of the reports with MY2013s and later that this is the case.
Bob wrote:It is very easy to test for improper charging. Just put a voltmeter on the battery while the car is on. It should be approximately 14.5V, indicating that it is being charged correctly. If it is below 13.5V, then the charging system isn't working correctly.
I think your approach here is a bit old-fashioned. The charging system in the LEAF (and apparently other recent cars) does not keep the charger at 14.4V for the duration of the time the vehicle is on. It attempts to replace only the charge which has been lost and then quickly drops down to a float voltage of 13.1V. Herein lies the real problem. It seems to not properly account for HOW LONG the LEAF was off, and generally does NOT restore the battery to a full charge level. The issue is premature sulfation of the battery and early failure.
Bob wrote:If charging is good and dark current is low, then it was just a bad battery. But if either of the other things is bad, changing the battery won't solve the problem.
It's not so simple as you imply. It seems the charging algorithms coded into the LEAF's 12V system work fine for some users and not as well for others, depending on driving regimes. In any case, the system works the way it does and, to my knowledge, no one has reported an actual "failure" of the 12V charging system. Rather, I feel it is simply poor software design (the hardware seems extremely robust to date).

There have been more than a few batteries which have failed with a shorted cell, both from Japan and from the U.S. That is likely just due to poor quality control.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

Wufnu
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Re: Car moves while I am pressing on the brake.

Wed Oct 01, 2014 9:18 am

dhanson865 wrote: Please tell that to Nubo in thread http://www.mynissanleaf.com/viewtopic.php?f=9&t=17890" onclick="window.open(this.href);return false;

I tried to let the thread know that and he poo pooed the idea with his "onboard DC-DC converter can supply 90 amps or more" dismissal.

I'm in the camp that believes that Nissan Leaf or Toyota Prius either way they don't charge the 12v battery aggressively enough.

I went and read what he said. He was 100% correct. He gave reasons why a battery might not have accepted much charge after being completely discharged then followed that up with a possible way to nurse your battery back to usefulness.

I think you misread what he said.

dhanson865
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Re: Car moves while I am pressing on the brake.

Wed Oct 01, 2014 10:49 am

Wufnu wrote:
dhanson865 wrote: Please tell that to Nubo in thread http://www.mynissanleaf.com/viewtopic.php?f=9&t=17890" onclick="window.open(this.href);return false;

I tried to let the thread know that and he poo pooed the idea with his "onboard DC-DC converter can supply 90 amps or more" dismissal.

I'm in the camp that believes that Nissan Leaf or Toyota Prius either way they don't charge the 12v battery aggressively enough.

I went and read what he said. He was 100% correct. He gave reasons why a battery might not have accepted much charge after being completely discharged then followed that up with a possible way to nurse your battery back to usefulness.

I think you misread what he said.
do you honestly think that a 12v battery charging process that should be feeding something near 14v will do so anywhere near 90 amps?

the smart charger I use is rated for 7a and is rated for charging batteries as large as 120Ah capacity.

I think any line of thinking about a Leaf charging a 12v battery at 90a is flawed.

I also think he is probably of the mindset discussed above by RegGuheert that people assume if a charging system starts out at 14.x volts that it will stay there but the controller will lower the charging rate well before the battery is truly charged sufficiently.

If you want to keep a Leaf or Prius 12V battery charged and you take frequent short trips, or use radio/fans/etc while in accessory mode, or have a always on device that drains the 12v while the car is off the car will do a piss poor job of maintaining the battery and you'll need something like a CTEK 3300 to do a better job.
Blue 2012 Leaf 195/65/15 tires, 15" Rims
Silver 2012 Leaf 16" stock wheels
http://www.mynissanleaf.com/wiki/index. ... acity_Loss
(efficiency 3.x KW vs 6.x KW)
please join Truedelta.com and input your repairs.

Wufnu
Posts: 41
Joined: Mon Sep 08, 2014 7:10 pm
Delivery Date: 08 Sep 2014

Re: Car moves while I am pressing on the brake.

Wed Oct 01, 2014 5:53 pm

dhanson865 wrote: do you honestly think that a 12v battery charging process that should be feeding something near 14v will do so anywhere near 90 amps?

the smart charger I use is rated for 7a and is rated for charging batteries as large as 120Ah capacity.

I think any line of thinking about a Leaf charging a 12v battery at 90a is flawed.

I also think he is probably of the mindset discussed above by RegGuheert that people assume if a charging system starts out at 14.x volts that it will stay there but the controller will lower the charging rate well before the battery is truly charged sufficiently.

If you want to keep a Leaf or Prius 12V battery charged and you take frequent short trips, or use radio/fans/etc while in accessory mode, or have a always on device that drains the 12v while the car is off the car will do a piss poor job of maintaining the battery and you'll need something like a CTEK 3300 to do a better job.
Based on my past experience with batteries, yes I believe the charger is capable of 90A and no I don't think it would hurt the battery to be charged at that amperage for a short time (even though it's the max).

I believe your understanding of the relationships involved between a charger and a battery are flawed, e.g. oddly proclaiming that your 7A charger can charge a 120AH battery. Of course it can. That's ok, it's no big deal. Just believe me when I say he wasn't "poo pooing" your statement. He was explaining something.

Even so, I would suggest everyone gets a battery maintainer and use it every so often. Until they program the Leaf to correctly maintain the battery under all conditions, it will be on the user to make sure it's being treated well. It doesn't have to be a smart charger, a simple wall wart will do. Their charge rate is self adjusting due to physics alone.

neva6
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Delivery Date: 11 May 2017

Re: Car moves while I am pressing on the brake.

Mon Nov 13, 2017 12:08 pm

Not meaning to raise this from the dead but wanted to say that I had this exact issue on my new '17 SV. Weird intermittent issues backing up with the brake on. Finally, a TM failure and the car wouldn't start. Towed to dealer and replaced 12V battery. It was a dangerous safety issue because I had to pump the brake once for it to stop reversing. Strange to me that it is still a problem on the '17 models.

GerryAZ
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Re: Car moves while I am pressing on the brake.

Mon Nov 13, 2017 7:01 pm

It takes really hard foot pressure on the brake pedal, but you can apply the friction brakes without power assist (without any 12-volt auxiliary power) much like a conventional car with no vacuum boost. It feels like the pedal is on the floor, but it is actually not. I tested it for myself with my 2011 after this issue was raised and I tested the 2015 when I first started driving it.
Gerry
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
Silver LEAF 2015 SL purchased 2/7/2015; traded 8/10/2019 at 82,436 miles
White LEAF 2019 SL Plus purchased 8/10/2019

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