The 12V battery charging algorithms

By now most Leaf owners are aware of, and too many of us have experienced, the problems with the algorithms used to control the charging of the 12V accessory battery. I am referring of course to the fact that if you leave your car plugged in to an EVSE for a week or more you will often return to find an unresponsive vehicle that cannot be started due to a dead 12V battery, unless you have gone through some complicated work-arounds involving charge timer settings.

Does anyone else find it odd that such complicated tinkering as this is needed simply to enable us to start our Leafs after leaving them plugged in for week or more? Why can't Nissan program this logic into its sophisticated computer so the owner doesn't have to worry about such details? Why should the the 5-day timer get reset each time the charging timer activates, even if no actual charging is done? Should we just accept that, or ask why is this necessary? Fix it Nissan!

Better yet, why can't the Leaf just charge the 12V battery whenever it senses that it NEEDS charging, regardless of whether it is plugged in or not, or the state of the charging timer?

When I first heard a about these goofy limitations that have led many a Leaf owner to need to jump start their EVs (I have had to do this 3 times now), I thought surely it is a bug in the software that Nissan will fix soon. But no such fix has come and the problem persists. If anyone knows of any good reason why a simple software change cannot overcome these serious problems, please explain. And if there is such a reason, then I would urge Nissan to install the feature that someone on this board mentioned the EV-1 had: a button to manually initiate a jump-start off the main battery.

You can also get a dead accessory battery by using a "lot" of 12 volt accessories at once, over time. I did this by running the steering wheel heater (but not constantly), one seat heater, on Low, and a 12 volt heated throw that draws 4.5 amps. I also - gasp! - used the stereo and blower (but never on High). I did this many times, and because Nissan doesn't seem to have realized that Winter can last more than a few days, it drained the accessory battery.

LeftieBiker said:

You can also get a dead accessory battery by using a "lot" of 12 volt accessories at once, over time. I did this by running the steering wheel heater (but not constantly), one seat heater, on Low, and a 12 volt heated throw that draws 4.5 amps. I also - gasp! - used the stereo and blower (but never on High). I did this many times, and because Nissan doesn't seem to have realized that Winter can last more than a few days, it drained the accessory battery.

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This should not be a problem while driving. The DC/DC converter puts out more than enough amps to handle these loads. Did you determine this was the cause of the failed battery, or did some Nissan service dept. tell you this ?

Yep, over 1,000 watts.

Nubo said:

This should not be a problem while driving. The DC/DC converter puts out more than enough amps to handle these loads. Did you determine this was the cause of the failed battery, or did some Nissan service dept. tell you this ?

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jstoos said:

By now most Leaf owners are aware of, and too many of us have experienced, the problems with the algorithms used to control the charging of the 12V accessory battery. I am referring of course to the fact that if you leave your car plugged in to an EVSE for a week or more you will often return to find an unresponsive vehicle that cannot be started due to a dead 12V battery, unless you have gone through some complicated work-arounds involving charge timer settings
....
Better yet, why can't the Leaf just charge the 12V battery whenever it senses that it NEEDS charging, regardless of whether it is plugged in or not, or the state of the charging timer?

When I first heard a about these goofy limitations that have led many a Leaf owner to need to jump start their EVs (I have had to do this 3 times now),

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It's odd this was your first post since you joined in September 2011.

As for the bolded part, why are you doing that? Why do you need to leave it plugged in a for week? It's already well known here that for some reason, the Leaf has a goofy behavior of not being able to charge the 12 volt while plugged in and that leaving it plugged in for extended periods will lead to a dead 12 volt. Just leave it unplugged.

As for the 2nd paragraph, I believe it does, as long as it's not plugged in.

I've never had to jump start my Leaf, but I've only had it since late July 2013 and it's not ever been plugged in for even 24 hours at a time. I suspect the 12 volt was never the same after you ran it flat the 1st time. AFAIK, deep discharging lead acid batteries is bad for them.

I don't know anything about goofy charge timer workarounds that you mention. I already pointed to the simplest solution for the time being.

Nubo said:

LeftieBiker said:

You can also get a dead accessory battery by using a "lot" of 12 volt accessories at once, over time. I did this by running the steering wheel heater (but not constantly), one seat heater, on Low, and a 12 volt heated throw that draws 4.5 amps. I also - gasp! - used the stereo and blower (but never on High). I did this many times, and because Nissan doesn't seem to have realized that Winter can last more than a few days, it drained the accessory battery.

Click to expand...

This should not be a problem while driving. The DC/DC converter puts out more than enough amps to handle these loads. Did you determine this was the cause of the failed battery, or did some Nissan service dept. tell you this ?

Click to expand...

The battery didn't fail. It just lost so much charge it wouldn't start the car. I charged it and the car was fine again. I don't use all three devices at once now, and it's been ok since. I also top it off once a week, now. The dealer isn't going to replace a battery that is working fine when they look at it. Yes, we know the converter can handle those loads, but it apparently isn't, in all circumstances...

cwerdna said:

AFAIK, deep discharging lead acid batteries is bad for them.

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More accurately, it's bad for automotive "starting batteries". Since the LEAF never needs anything remotely near "450 cold cranking amps", for example, a deep-cycle battery seems to make more sense to me for this application.

Exactly!

Nubo said:

a deep-cycle battery seems to make more sense to me for this application.

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cwerdna,

I can think of several reasons, but my main point is that such a constraint should not exist -- the owner should not have to think about it in order to avoid such a serious consequence. A common scenario that has been discussed on this board is driving to the airport and parking the car in one of the increasingly common EV spots where you can plug in and charge while you're out of town so you can come home to a charged-up vehicle with enough juice to get home. But if it's a bit too long a trip, you won't be able to start your car!

Is there any engineering-based reason why the computer can't allow the DC-DC converter to charge the 12V battery while it is plugged in? If not, it should be a simple software change that would avoid a lot of aggravation!

Thanks for noticing it is my first post; I've been a long time lurker but don't believe in posting unless I have something interesting to say. This issue has bugged me enough I needed to get it out!

One place I saw the timer setting work-around is this post from the topic "Leaf is dead after vacation...":

"So, if you want to remain plugged in for extended periods, set your charging
Timer to allow at least 5 consecutive days of no-charging during the week.
Then, the car's 12v battery should remain charged, unless there is some
excessive drain on the 12v battery.
Due to this "feature" that an ATTEMPT to charge resets the 5-day top-up
timer for the 12v battery, too-frequent futile charging attempts will inhibit
the 12v top-ups and allow the 12v battery to severely discharge."

jstoos said:

I can think of several reasons, but my main point is that such a constraint should not exist -- the owner should not have to think about it in order to avoid such a serious consequence. A common scenario that has been discussed on this board is driving to the airport and parking the car in one of the increasingly common EV spots where you can plug in and charge while you're out of town so you can come home to a charged-up vehicle with enough juice to get home. But if it's a bit too long a trip, you won't be able to start your car!

Is there any engineering-based reason why the computer can't allow the DC-DC converter to charge the 12V battery while it is plugged in? If not, it should be a simple software change that would avoid a lot of aggravation!

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I agree it's a lame design. It's unclear if a software change can fix this.

As for the airport scenario, I haven't taken many trips lately while I've had my Leaf. The airport I had to use has some charging spots but the parking at the lots w/them was too much $ and there was no guarantee that the charging stations would even be open. I ended up taking my Prius and parking at a much cheaper lot.

As for doing that, personally, I'd rather not hog a charging spot for a week or even more than 2 days. Even at L1, the car will be done charging to 100% within 24 hours from 0%. And, I sure wouldn't like to leave my car at 100% charge for days on end.

If the spots were arranged in a way that plug sharing was possible, I'd leave a sign saying, please unplug me/take my plug after _____ date. I think it's bad etiquette to tie up an EV charging spot/equipment for a week, or whatever duration it takes for the Leaf's 12 volt to run flat while plugged in.

Yes, I do find it odd, no I don't expect a fix, and I suspect my battery still works only because my local weather is so kind to it. Here's another goofy workaround for cwerdna. Set the timer to charge one hour (or less) each night, so that the LEAF reaches full charge shortly before you return. The 12 volt battery is brought back up each night during this charging time.

The LEAF, like the Prius, is designed so that the traction battery is completely disconnected when the car is off. The only way to connect it is for the computer (on 12 volts) to initiate the start up sequence. This is what it does if the 5-day battery recharge come up. It's also why we need a 12v jump-start if the 12v goes dead. And it is the reason that a solution like the EV-1 had can't be done, at least not easily.

Now for my own mini-rant. I have had this LEAF almost 3 years, and Nissan hasn't even acknowledged that there is a problem like this. I think after three years, if they've done nothing about it, they have no intention of ever doing anything about it. Here is where the lie about electronic-brain based cars comes in. A problem could be addressed, upgraded, or fixed, but there's no incentive to create new firmware releases for "old" products. That's why my Prius still tells me to change the oil every 5000 miles (the factory changed it to 10000 after the change to synthetic oil). And this is where Tesla is going to turn the industry on its head, because they apparently believe in making your car better if they come up with a way to do so. That's competition the competition doesn't even realize it has yet.

So anyway, my battery sits around 12.5 volts or less and that's with the car on (it's about 12.0 when off). I've wondered if I couldn't fake out some sensor and have it be maintained at a little higher voltage. Those on other threads say this would be better for it.

If an EV is plugged in and any battery goes dead it is just poor engineering.
Easy program fix to charge the 12v 30 minutes every day when plugged in.

smkettner said:

If an EV is plugged in and any battery goes dead it is just poor engineering.
Easy program fix to charge the 12v 30 minutes every day when plugged in.

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No one disagrees with your first point. The second one may be open to debate, since the EVSE is "dead" when the car is not charging.

LEAF knows it is plugged in. Does not even need to draw wall power to charge the 12v for a few minutes every day.
Could probably float the 12v at 13.2 continuous and the big battery would never know.

Has anyone tried setting the climate control timer for 30 minutes a day to keep the 12 volt battery charged?

pchilds said:

Has anyone tried setting the climate control timer for 30 minutes a day to keep the 12 volt battery charged?

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I suspect that the fact that it runs the fan on High would make it hard to keep the battery charged that way.

True, the car can supply the power without the EVSE. It looks like you need a full powerup to use the DC/DC converter, though.

I'm beginning to find the multiple 12v starter battery threads amusing. On the one hand, there was (apparently) a "bad batch" of 12v batteries installed in a bunch of (2013?) Leafs; on the other hand, lead acid batteries of all sizes in all kinds of cars go dead EVERY DAY.

If you want a permanent solution, replace the 12v lead acid battery with a (good) LiFePO4 battery and your problem will be solved for years; this battery and this car (really any EV that doesn't need "cranking amps") are a very good fit for each other. Read my blog post to see what I did...

http://stanton.myevblog.com/2012/01/16/getting-the-lead-out/" onclick="window.open(this.href);return false;

smkettner said:

LEAF knows it is plugged in. Does not even need to draw wall power to charge the 12v for a few minutes every day.
Could probably float the 12v at 13.2 continuous and the big battery would never know.

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The DC to DC and other loads would be far to significant to float the battery even for 30 minutes. My battery was still fine after three years, I never use any position other than "on" or "run".

How many watts does the DC/DC converter idle at? The 12v only needs <200 mA to stay charged.
The "other loads" are already on causing the dead battery. Keeping the 12v battery charged adds very little.
Worst case the car can pull some power from the wall once a day or once a week.

cwerdna said:

As for the airport scenario,
...
I'd rather not hog a charging spot for a week or even more than 2 days. Even at L1, the car will be done charging to 100% within 24 hours from 0%. And, I sure wouldn't like to leave my car at 100% charge for days on end.

If the spots were arranged in a way that plug sharing was possible, I'd leave a sign saying, please unplug me/take my plug after _____ date. I think it's bad etiquette to tie up an EV charging spot/equipment for a week, or whatever duration it takes for the Leaf's 12 volt to run flat while plugged in.

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Indeed, long term parking at charging spots is problematic for efficient sharing of the resource. Although a bit off-topic, I have 2 suggestions for ways this can be handled without requiring consumer cooperation like leaving a note:
(1) an airport employee could visit the charging spots once a day and unplug any cars that are not actively charging (under the assumption that they are finished charging -- may not always be valid??? (don't want to have to require the employee to know how to read the charging lights on different make cars to know if they are actually fully charged.)
(2) This one requires a specially designed public EVSE station type: build one that has many cables/plugs per EVSE and a "multiplexer" system that only provides juice to one cable at a time (first come first serve) and then switches to the next one when the first one completes its charge. Then you could have as many cables/plugs as you have parking spaces they reach. (Are you listening AeroVironment, GE, Siemens etc.?)