forestrider
Posts: 18
Joined: Wed Nov 04, 2015 10:37 am
Delivery Date: 04 Nov 2015

Re: 12 Volt Lead Acid Battery Replacement

Fri Dec 25, 2015 1:48 pm

Quick question, I'm trying to understand how my LEAF works more clearly.

Tim mentions an inverter sending voltage to the 12vdc bus? That makes no sense to me, I would expect a DC-DC converter with charging logic.

Can you please clarify, I'm still trying to sort out the charging system on my vehicle.

Additionally, does anyone know of a schematic or diagram of the electrical on these things?

dhanson865
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Leaf Number: 16156
Location: Tennessee

Re: 12 Volt Lead Acid Battery Replacement

Fri Dec 25, 2015 5:52 pm

forestrider wrote:Quick question, I'm trying to understand how my LEAF works more clearly.

Tim mentions an inverter sending voltage to the 12vdc bus? That makes no sense to me, I would expect a DC-DC converter with charging logic.

Can you please clarify, I'm still trying to sort out the charging system on my vehicle.

Additionally, does anyone know of a schematic or diagram of the electrical on these things?


I was the one that used the phrase 12v bus.

Doesn't matter to me where it sends it directly because the 12v wiring is all interconnected and any loads are shared between all the devices on the loop.

I'm a computer guy not a electrician or electrical engineer so it may be that I'm using terminology loosely and you can fee free to use the correct terminology from your preferred field of experience. We'll find common ground.
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TimLee
Posts: 2810
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Leaf Number: 2026
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Re: 12 Volt Lead Acid Battery Replacement

Sat Jan 02, 2016 10:53 am

forestrider wrote:... I would expect a DC-DC converter with charging logic.

Can you please clarify, I'm still trying to sort out the charging system on my vehicle.
...

Yes, it has a very strong DC to DC power supply that takes high voltage pack power and produces power to charge the 12V battery. Capable of around 100 amps at 14.4V.

But its charging logic appears to mainly be based on current flow that has been measured by the current monitor in the 12V negative cable, although there are some adjustments based on temperature.

But the current sensor does not see the current drain when the LEAF is Off.
Like the high drain from an OBDII adapter.

And it does not appear to do an adjustment based on voltage like a battery maintainer charging logic.

So depending on use and loads while Off, the LEAF can leave the 12V poorly charged.

Unfortunate it does this.
But for many people using a battery maintainer while the LEAF is Off every week or two is a good practice.

Tim Lee
Chattanooga, TN

Man. Date: 03/10/11, VIN # 2026
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Arlington
Posts: 94
Joined: Tue Jun 23, 2015 11:47 am
Delivery Date: 29 Oct 2015
Leaf Number: 414434

Re: 12 Volt Lead Acid Battery Replacement

Mon Jan 04, 2016 9:43 pm

My OBD adapter appears to have drained my 12v down to ~6.9v while I was away last week--enough to kill most functions and get psycho error messages. This is just bad design--if the car needs a 12v computer, the 12v battery should be on the list of critical systems (alongside battery temp an charging timers) that get kept operable.

BrockWI
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Re: 12 Volt Lead Acid Battery Replacement

Tue Jan 05, 2016 11:57 am

This is just my $.02 but if your OBD is what killed your 12v battery you have a bad 12v battery. There are other things in the car that consume power as well and a good 12v battery should last a week easy.

I replaced my 12v with the next larger size up and the car has been great, no more low 12v battery lights or dead batteries. The Leaf's 12v charging system seem to work fine with a healthy battery but falls short when the battery starts to fail causing a cascading 12v battery failure. Honestly I think even replacing the stock battery with a average quality same size battery would help a LOT.

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LeftieBiker
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Re: 12 Volt Lead Acid Battery Replacement

Tue Jan 05, 2016 3:55 pm

This is just my $.02 but if your OBD is what killed your 12v battery you have a bad 12v battery. There are other things in the car that consume power as well and a good 12v battery should last a week easy.


If the battery was chronically undercharged before the trip, this could happen. If the car was plugged in and not charging as well, it would almost certainly happen.
Last edited by LeftieBiker on Tue Jan 05, 2016 9:32 pm, edited 1 time in total.
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QueenBee
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Re: 12 Volt Lead Acid Battery Replacement

Tue Jan 05, 2016 8:55 pm

Arlington wrote:My OBD adapter appears to have drained my 12v down to ~6.9v while I was away last week--enough to kill most functions and get psycho error messages. This is just bad design--if the car needs a 12v computer, the 12v battery should be on the list of critical systems (alongside battery temp an charging timers) that get kept operable.

Unless you were measuring the draw on the battery the entire time and have measured what your ODB adapter uses and then have done the math to determine that the ODB adapter is what resulted in the discharge and not the other systems that stay on when the car is off I'm not sure how you were able to determine it was the cause.

It's common enough problem with people that don't have ODB adapters that I think it's likely it would have happened either way.

rawhog
Posts: 457
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Delivery Date: 11 Apr 2011
Leaf Number: 898
Location: Vacaville, CA

Re: 12 Volt Lead Acid Battery Replacement

Tue May 03, 2016 2:23 pm

So Autozone and O'reilly list the 12v battery as a 51R. Does anyone know if that is correct?
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BrockWI
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Re: 12 Volt Lead Acid Battery Replacement

Tue May 03, 2016 2:46 pm

Yes the 51R is the stock battery size.
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rawhog
Posts: 457
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Re: 12 Volt Lead Acid Battery Replacement

Mon Jun 20, 2016 11:03 pm

To anyone that has replaced the 12V battery. Did you go through all of the steps the manual calls out? Or, just replace the battery like any conventional car. Pull negative cable first , then positive. Reverse for installing new battery.
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