Lothsahn
Posts: 511
Joined: Thu Apr 05, 2018 4:35 pm
Delivery Date: 04 Jan 2018
Leaf Number: 007797

Re: Start Problem--2012 SL with 45k miles

Fri Sep 20, 2019 6:23 am

SageBrush wrote:
Fri Sep 20, 2019 3:50 am
LeftieBiker wrote:
Wed Sep 18, 2019 5:23 pm
You are a braver person than I, shorting the battery cables together.
.
Truly.

This sounds like a case of 'if the person is alive after pulling that stunt, the 12v is defective.'
Not sure if you understood that he meant: "shorting the terminal leads together NOT connected to the battery." It's a common trick on some ICE cars and often fixes diagnostic codes and other weird electrical gremlins.

It should NOT be done on a Leaf for two reasons:
1) The Leaf uses electronics in the battery terminals and it might damage them for the same reason that you should never attach a charger to the negative terminal on the battery while it's connected to the Leaf.

2) The Leaf has a DC-DC converter from the main battery pack. If the converter was on when you did this, you could blow the fuse in the DC-DC converter, or worse, as you said: 'if the person is alive after pulling this stunt'
2011 Silver SV, purchased 2018, lives in Missouri (previously in CA)
LeafSpy Pro + BAFX Products OBDII dongle
Battery swap 2019/04/24 (87% SOH, 12 bar)

SageBrush
Posts: 4907
Joined: Sun Mar 06, 2011 2:28 am
Delivery Date: 13 Feb 2017
Location: NM

Re: [Solved] Start Problem--2012 SL with 45k miles

Fri Sep 20, 2019 6:31 am

^^ Very informative, thanks
2013 LEAF 'S' Model with QC & rear-view camera
Bought off-lease Jan 2017 from N. California
Two years in Colorado, now in NM
03/2018: 58 Ahr, 28k miles
11/2018: 56.16 Ahr, 30k miles
-----
2018 Tesla Model 3 LR, Delivered 6/2018

LeftieBiker
Moderator
Posts: 13265
Joined: Wed May 22, 2013 3:17 am
Delivery Date: 30 Apr 2018
Location: Upstate New York, US

Re: [Solved] Start Problem--2012 SL with 45k miles

Fri Sep 20, 2019 12:00 pm

Not sure if you understood that he meant: "shorting the terminal leads together NOT connected to the battery." It's a common trick on some ICE cars and often fixes diagnostic codes and other weird electrical gremlins.

I understood the procedure, but thought it was a bad idea. Apparently it is.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
BAFX OBDII Dongle
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

nlspace
Posts: 57
Joined: Mon Jun 05, 2017 10:21 pm
Delivery Date: 06 Jun 2017

Re: Start Problem--2012 SL with 45k miles

Fri Sep 20, 2019 1:18 pm

Lothsahn wrote:
Fri Sep 20, 2019 6:23 am

Not sure if you understood that he meant: "shorting the terminal leads together NOT connected to the battery." It's a common trick on some ICE cars and often fixes diagnostic codes and other weird electrical gremlins.

It should NOT be done on a Leaf for two reasons:
1) The Leaf uses electronics in the battery terminals and it might damage them for the same reason that you should never attach a charger to the negative terminal on the battery while it's connected to the Leaf.

2) The Leaf has a DC-DC converter from the main battery pack. If the converter was on when you did this, you could blow the fuse in the DC-DC converter, or worse, as you said: 'if the person is alive after pulling this stunt'
i fail to see how your two reasons indicate any problems with this procedure:

1) The only electronics is a current sensor that surrounds the wire just before it reaches the negative terminal. Currents normally flow in both directions thru this wire/sensor, sometimes very high currents, and it is designed to handle these. Attaching a chargger to the negative terminal actually by-passes this sensor altogether, so how could it be damaged with no current flowing thru it? The positive terminal has large in-line fuses but no electronics.

The admonition against connecting a chargger lead to the negative terminal is due to the potential of sparking and possible ignition if there is excessive hydrogen gas venting nearby.


2) How is it that you think the DC-DC converter could turn ON when the 12-volt battery is disconnected? What current source would drive the relays and main contactors necessary to connect the main pack to the converter?

Lothsahn
Posts: 511
Joined: Thu Apr 05, 2018 4:35 pm
Delivery Date: 04 Jan 2018
Leaf Number: 007797

Re: Start Problem--2012 SL with 45k miles

Fri Sep 20, 2019 2:36 pm

nlspace wrote:
Fri Sep 20, 2019 1:18 pm
i fail to see how your two reasons indicate any problems with this procedure:

1) The only electronics is a current sensor that surrounds the wire just before it reaches the negative terminal. Currents normally flow in both directions thru this wire/sensor, sometimes very high currents, and it is designed to handle these. Attaching a chargger to the negative terminal actually by-passes this sensor altogether, so how could it be damaged with no current flowing thru it? The positive terminal has large in-line fuses but no electronics.

The admonition against connecting a chargger lead to the negative terminal is due to the potential of sparking and possible ignition if there is excessive hydrogen gas venting nearby.
This explains why from the person who made the rule "Phil's Law". See his two posts in the same thread:
viewtopic.php?f=30&t=8588&p=191318&hili ... or#p191318
viewtopic.php?f=30&t=8588&p=191318&hili ... or#p191304

In addition to draining the battery and sulfating it, or possibly sending reverse current through the 12v current sensor, there's one other issue. It's also been found that in certain cases leakage to ground can cause the car to throw diagnostic codes thinking that there is an HV battery fault to ground, which can only be cleared by a Nissan Dealer (not LeafSpy).

nlspace wrote:
Fri Sep 20, 2019 1:18 pm
2) How is it that you think the DC-DC converter could turn ON when the 12-volt battery is disconnected? What current source would drive the relays and main contactors necessary to connect the main pack to the converter?
I don't think it could turn on while it was disconnected. But if it was on prior to disconnecting the battery, and it was still supplying power when you pressed the two leads together, it would get exciting, to say the least.

While I assume the DC-DC converter would recognize the open circuit and shut off, I don't know how quickly the DC-DC converter does so. It's probably pretty fast. But I don't know anywhere that it's documented as such, and I sure don't want to prove that hypothesis wrong.

An ICE, while off, has no electrical power to the 12V system other than the battery and some capacitors. That is not true of an EV.
2011 Silver SV, purchased 2018, lives in Missouri (previously in CA)
LeafSpy Pro + BAFX Products OBDII dongle
Battery swap 2019/04/24 (87% SOH, 12 bar)

goldbrick
Posts: 617
Joined: Tue Aug 01, 2017 3:33 pm
Delivery Date: 01 Aug 2017
Leaf Number: 311806
Location: Boulder, CO

Re: Start Problem--2012 SL with 45k miles

Fri Sep 20, 2019 6:56 pm

Lothsahn wrote:
Fri Sep 20, 2019 2:36 pm
An ICE, while off, has no electrical power to the 12V system other than the battery and some capacitors. That is not true of an EV.
I was a bit skeptical at first too until I realized this point.

It is probably a safe thing to and something I have often done on ICE cars before working around airbags, etc but I don't think I'll do this to my Leaf.

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