The 12V battery charging algorithms

[jstoos]

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.

[LeftieBiker]

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.

[Nubo]

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.

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 ?

[TomT]

Yep, over 1,000 watts.

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 ?

[cwerdna]

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),

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.

[LeftieBiker]

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.

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 ?

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...

[Nubo]

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

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.

[TomT]

Exactly!

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

[jstoos]

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."

[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!

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.