Possbile to Damage DC-DC Converter?

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rhumbliner

Member
Joined
May 29, 2014
Messages
13
Location
Las Vegas
i've been searching thru the forum trying to answer these questions and wanted to let the group weigh in on this topic. i know the question of leaving the leaf in storage mode has been discussed extensively but i'm not sure the DC-DC Converter has.

in this thread http://www.mynissanleaf.com/viewtopic.php?f=31&t=12442&hilit=storage&start=20 Ingineer suggests the safety of connecting a trickle charger to the 12v battery while the battery is still connected to the DC-DC Converter. but in my readings i vaguely recall someone (don't remember who) claiming that the DC-DC Converter could be damaged by being exposed to a trickle charger and that the 12v battery should always be disconnected at the negative post before being connected to a trickle charger.

this also leads to the idea that if it's safe to connect a trickle charger connected to the 12v battery while its connected, then perhaps, for ultra-cold weather storage it would be possible to leave the EVSE plugged in to warm the Li-on battery without discharging the 12v battery.

any thoughts?
 
The answer is - Totally easy to damage the DC to DC converter

You put more current than the forward bias on the DC to DC converter and toast!

Magic smoke and good luck on the getting a warranty repair.
 
Hopefully someone with more technical knowledge will come along and set us straight. What I can say is I have a Deltran Battery Tender 1.25 charger lead connected directly to my 12v battery, with the lead snuck up and out under the EVSE connector door. So when I pop that to charge I can connect the battery tender and all is good. I haven't noticed any ill effects and a few times I unintentionally had the battery tender and the EVSE on at the same time.

Personally I would have no issue with leaving the battery tender connected and do just that when we are not using the Leaf for a few days when we are out of town.
 
Battery tender. Scares the crap out of me! Recipe for disaster in my book.

Let the car manage the battery and stop screwing with it. For f*cks sake!

Leave it at 50% and store it. I had a 2011 and never had a problem with storing it for a month.
 
bluedream42 said:
The answer is - Totally easy to damage the DC to DC converter

You put more current than the forward bias on the DC to DC converter and toast!

Magic smoke and good luck on the getting a warranty repair.
Many people (including myself) use battery tenders on the 12v battery. There is a protection diode inside the DC/DC to prevent backfeeding the converter. That's standard practice on such a device. Further, the converter is disconnected when the car is completely off.

bluedream42 said:
Let the car manage the battery and stop screwing with it.
The car does not take good care of the 12v battery and an occasional top up is a good idea. There are many posts on this forum documenting failing and replacement of the 12v battery.

I would not recommend trickle charging the 12v when the car is on or charging, however.
 
I would not recommend trickle charging the 12v when the car is on or charging, however.

Damn, I've been doing that: I plug in both the EVSE and the 2 amp Diehard battery maintainer, so the 12 volt battery isn't drained when charging finishes and I'm not there to unplug it. The maintainer usually shows a charged battery while the car is charging. So far no problems, but I'll rethink doing it that way.
 
A battery tender just seems redundant to me and probably best for ICE vehicles.

After looking in the Leaf service manual unless the traction battery is depleted let the VCM do the automatic charging when left for a long period of time. Here's the what it says:

Code:
Control Description:

Power ON
VCM monitors 12V battery voltage during POWER ON cycle and immediately starts charging when VCM judges that the voltage is lower.

When Vehicle is Left for a Long Period of Time
VCM measures the time of no operation using its internal timer.  If the time of no operation reaches 120 hours, VCM performs automatic charge for 5 minutes.
VCM resets the no operation status continuous time when the vehicle satisfies one of the following conditions.
• The READY has continued for more than 5 minutes.
• Normal charge has continued for more than 5 minutes.
• Quick charge has continued for more than 5 minutes.
• Timer air conditioning or remote air conditioning has continued for more than 5 minutes.
NOTE:
• During automatic 12V battery charging, the charging status indicator blinks.
• The automatic 12V battery charging control does not start within approximately one hour when the power switch is turned ON/OFF.

Seems like the Leaf can handle topping off the 12V battery just fine.

Just my .02
 
bluedream42 said:
Seems like the Leaf can handle topping off the 12V battery just fine.

Just my .02
You need to go back and read the multiple threads that explain the weaknesses of the LEAF 12 volt charging approach.
If you drive the car regularly and never use 12 volts other than in Ready mode it is barely adequate for some people.
But a large % of people have had trouble.

Your .02 is a bit tarnished :shock:
 
TimLee said:
bluedream42 said:
Seems like the Leaf can handle topping off the 12V battery just fine.

Just my .02
You need to go back and read the multiple threads that explain the weaknesses of the LEAF 12 volt charging approach.
If you drive the car regularly and never use 12 volts other than in Ready mode it is barely adequate for some people.
But a large % of people have had trouble.

Your .02 is a bit tarnished :shock:

Just relating what the technical manual says and had a 2011 up until December of this year without issue. Are you asserting that the Leaf has a design flaw and nissan should recall it?

So 150,000 Leafs sold - What percent of those are reporting this issue? Just trying to cut through the misinformation.
 
http://www.mynissanleaf.com/viewtopic.php?p=394495#p394495" onclick="window.open(this.href);return false; has a link to one such finding of the 12 volt charging algorithm. I don't have time right now to dig up all the others.

I've had no trouble w/my 12 volt (got my car end of July '13). I'd wager the majority of Leaf owners even going back to the '11 haven't had issues w/their 12 volt yet, but some of the older Leafs will likely need a new 12 volt in the next year or two.

There does seem to be a set of folks who have 12 volt dead/drainage problems. To me, it could be a one or a combination of these and the algorithm may not help:
- bad 12 volt (Nissan did give us a % long ago, but I can't find the post, it was a very low %, IMHO)
- 12 volt that got killed in shipment or by the dealer or somewhere before the customer bought the car
- bad/underperforming DC to DC converter
- bad sensors it uses to determine when the 12 volt should be charged and at what voltage
- software bug, even a possibly bug where there's a way around the automatic power cut to the interior and map lights
- abnormal parasitic load caused by some defective part
- abnormal parasitic load caused by an accessory (e.g. OBD2 dongle, stereo, alarm, etc.)
- certain usage/plug in habits (e.g. leaving car always plugged in for extended periods of time, way beyond what's needed to charge the car)

The problem is, since the Leaf has no starter motor (just like Toyota Hybrid Synergy Drive cars like the Prius don't either), you don't get the slow starter cranking or insufficient power to turn over the engine symptoms. So, you can't easily tell (w/o measuring voltages) that the 12 volt is low. On the Prius, all sorts of weird stuff happens (e.g. not being able to reliably go to READY, I think the alarm going off, etc.) I'd imagine radio presets are intermittently lost too.

Back to case 2, http://priuschat.com/threads/closed-minds.100011/" onclick="window.open(this.href);return false; was a case of a dealer killing 12 volt batts on Priuses. Toyota has TSBs telling dealers what to do to maintain the HV and 12 volt battery on Priuses: http://priuschat.com/threads/tsb-pg007-03-maintenance-for-hv-and-auxiliary-batteries.121078" onclick="window.open(this.href);return false; and http://priuschat.com/attachments/maintenance-for-hv-and-aux-batteries-pdf.19412/" onclick="window.open(this.href);return false;. Not sure if there's a Leaf equivalent.
 
bluedream42 said:
So 150,000 Leafs sold - What percent of those are reporting this issue? Just trying to cut through the misinformation.

I'm sure that I am one of VERY MANY who have found their Leaf battery dead after a weeks vacation and never reported it. I just popped the hood myself, gave it a brief charge, and off I went.
The solar panel on my SL is worthless, as my Leaf is garage-kept. So, YES, this is a well known design flaw that a Leaf can't do a simple thing like keep the 12 volt battery properly charged while you are away. A very small percentage of Leaf owners are on this site, so how else would you hear about it?
 
LeftieBiker said:
Isn't it great to have a Newbie come in and tell us that this is all our imaginations, and "misinformation"...?

LeftieBiker - It's incorrect to call me a 'newbie'. Look at my join date. Compare it with your join date. I'm a bit autistic so don't know if you meant to really do that.

Now back to the question at hand. After looking over a number of posts I can see that people's 12v batteries have died. And as cwerdna has pointed out there are number of issues that cause this. If you trickle charge the battery then it might be covering up issues like a bad DC to DC converter or a bad 12v battery delivered in the car. I'd rather have warranty issues fixed.

I'm also trying to find out what the 'right' way to store a Leaf as well. I was on vacation for over a month last year and the car seemed to be ok. Maybe I was dangerously close to killing my 2011's battery too?
 
I am one of those folks with a problem with my 12v aux battery. I can tell you it's not the battery itself (that is not to say some don't have a bad 12v battery) and the problem is very inconsistent. There is no harm in leaving the 12v aux battery on a smart 12v charger, it won't damage the the cars electronics in any way and will protect the 12v battery from a potential complete discharge or from deficit charging from the on-board dc-to dc converter or it's charging system.

So while for most people there is no need to put the 12v battery on a charger, it won't hurt to do so. Thinks of it as insurance, you may never need it, but when you do, you do.

If we don't use our Leaf for 3 days or more, I put it on the charger, better safe than sorry in our case.
 
Never used a battery tender (not a fan), never had a dead battery, and I've left my Leaf UNPLUGGED for days/week at a time--and that was before I swapped out the lead-acid 12v for a Lithium (and I used my Aux periodically).
 
Stanton said:
Never used a battery tender (not a fan), never had a dead battery, and I've left my Leaf UNPLUGGED for days/week at a time--and that was before I swapped out the lead-acid 12v for a Lithium (and I used my Aux periodically).

Leaving it UNPLUGGED is exactly what you are supposed to do. It's leaving the charging cable connected that can cause problems. So why not just disconnect it as soon as charging stops? In my case I usually charge to 80%, rarely use all the charge I have, and the car usually finishes charging in the middle of the night, with me sleeping well into the next day. So I've been leaning it on the maintainer when it will be finishing hours before I disconnect it. I also find that in Winter, using the seat warmer, wheel warmer and heat a lot, the accessory battery tends to 'lose ground', especially when I'm doing mainly short trips. Clearly Nissan didn't look at all of the normal driving patterns the Leaf would be subjected to, and so it only keeps the battery charged for some of them. Not all.

Sorry about the Newbie crack, Bluedream, but your post gave that impression. Quoting a service manual as biblical truth while dismissing real world experiences as 'misinformation' isn't going to encourage folks to believe you.
 
If the DC/DC converter was broken, the 12v system (and battery) would probably die within a half hour. There are coolant pumps that draw quite a bit of current. You would also see the red battery light come on.
 
BTW, here's one (of several threads) of people complaining about dead 12-volt batteries:
http://www.mynissanleaf.com/viewtopic.php?f=30&t=12448" onclick="window.open(this.href);return false;
http://www.mynissanleaf.com/viewtopic.php?p=402584#p402584" onclick="window.open(this.href);return false; (another poster in there)

I don't have time to go through that entire thread finding any others w/the same issue.

http://www.mynissanleaf.com/viewtopic.php?p=402127#p402127" onclick="window.open(this.href);return false; was someone talking about the poor charging algorithm.

I'm sure one can find more by Googling for stuff along these lines: site:mynissanleaf.com 12 volt drain.
 
Finally, a bad 12 volt battery would not virtually die (I lost power unlocking and had dim lights but was still able to start the car) and then go another 12+ months with no problems just because a maintainer was used a couple of times a week. It would have died completely many months ago.
 
I've had my car since June of 2013, and have had no trouble at all with the 12 v battery. I even left the car sit for 2 weeks once. I say if it's not broke, don't fix it. If your 12v battery ever dies, worry about the battery tender then. Most likely it won't.
 
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