nlspace
Posts: 60
Joined: Mon Jun 05, 2017 10:21 pm
Delivery Date: 06 Jun 2017

Re: Leaf range after battery module replacement

Thu Oct 10, 2019 6:26 pm

Excuse me, but you still haven't provided any information of how more energy is added to the lower cells than the higher cells during charging?

If you made a mistake or don't know, then at least be man enough to admit it. Don't imply that i have an attitude problem when i ask about the rationale for statements about charging and cell energy. Nobody wants to read or repeat bad information on the forum.

The same current flows thru each cell of a series string, so if the car is charging at 10 Amps for 3 hrs, then 30 A-hrs has been added to each cell. The only way to correct the OPs issue is for the balancer circuits to activate for a long time to bleed down the higher cells, or to open the pack and put charging current thru only the low cells to bring them up, or replace the low cells with some that are closer in capacity to the rest.

People come here looking for help to solve problems; let's give them solid answers based on facts and data, and not wild-axed guesses.

Lothsahn
Posts: 512
Joined: Thu Apr 05, 2018 4:35 pm
Delivery Date: 04 Jan 2018
Leaf Number: 007797

Re: Leaf range after battery module replacement

Thu Oct 10, 2019 7:00 pm

nlspace wrote:
Thu Oct 10, 2019 6:26 pm
Excuse me, but you still haven't provided any information of how more energy is added to the lower cells than the higher cells during charging?

If you made a mistake or don't know, then at least be man enough to admit it. Don't imply that i have an attitude problem when i ask about the rationale for statements about charging and cell energy. Nobody wants to read or repeat bad information on the forum.

The same current flows thru each cell of a series string, so if the car is charging at 10 Amps for 3 hrs, then 30 A-hrs has been added to each cell. The only way to correct the OPs issue is for the balancer circuits to activate for a long time to bleed down the higher cells, or to open the pack and put charging current thru only the low cells to bring them up, or replace the low cells with some that are closer in capacity to the rest.

People come here looking for help to solve problems; let's give them solid answers based on facts and data, and not wild-axed guesses.

The BMS has shunt resistors. These are controlled by the BMS and they open to allow a small amount of current to flow between the cells. The greater the voltage difference between the cells, the more current is able to flow. Greater voltage differential, as you stated, exists at lower %SOC.

It definitely makes sense that at low pack voltages, the greater voltage differential would result in a higher current flow across the shunts. Practically speaking, I don't know how much that will accelerate the balancing, but there will be an effect.

Personally, I'd take the car back and say that the new cells are either bad or the pack has not been properly balanced. The repair was simply not done correctly. It's possible that over a few months the problem may work itself out, but that's an awfully long time to wait.

If gary doesn't want to do that, it might make sense to leave the car running with no AC/Heat, etc from 50-5% SOC for hours in the garage, following it with an immediate L1 charge. This would allow for a prolonged period of low-amperage discharge with a prolonged period of charge--maximum balancing time.
Last edited by Lothsahn on Thu Oct 10, 2019 7:06 pm, edited 2 times in total.
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)

LeftieBiker
Moderator
Posts: 13283
Joined: Wed May 22, 2013 3:17 am
Delivery Date: 30 Apr 2018
Location: Upstate New York, US

Re: Leaf range after battery module replacement

Thu Oct 10, 2019 7:01 pm

Let's not get into a fight over cell balancing please. ;) Sagebrush means that charging from a low SOC adds more energy to all of the cells, and that the charging time is extended. This doesn't directly balance the lower cells, but it helps the process indirectly. How much more energy is added? How about "5"? I don't know of a specific number, especially as it will vary from car to car and probably from BMS version to BMS version.

Lothsahn slipped. I think he knows what is happening, but is frustrated by not seeing it quantified.
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.

Lothsahn
Posts: 512
Joined: Thu Apr 05, 2018 4:35 pm
Delivery Date: 04 Jan 2018
Leaf Number: 007797

Re: Leaf range after battery module replacement

Thu Oct 10, 2019 7:05 pm

LeftieBiker wrote:
Thu Oct 10, 2019 7:01 pm
Let's not get into a fight over cell balancing please. ;)
Agreed.
LeftieBiker wrote:
Thu Oct 10, 2019 7:01 pm
Lothsahn slipped. I think he knows what is happening, but is frustrated by not seeing it quantified.
What do you mean Leftie? I hope I didn't sound frustrated--I'm not frustrated at all.. I was trying to provide some clarity on why it would cause faster balancing at lower SOC with higher voltage differentials. As you said, I have no idea how to quantify how fast the balancing will occur--the only out of balance pack I've seen or read about is Dala's, and he fixed it by opening it up and manually balancing the affected cells. :)


This is all so much easier on RC airplanes. The charger has a wire to each cell and can just directly apply a charge for each cell. :)
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)

Lothsahn
Posts: 512
Joined: Thu Apr 05, 2018 4:35 pm
Delivery Date: 04 Jan 2018
Leaf Number: 007797

Re: Leaf range after battery module replacement

Thu Oct 10, 2019 7:16 pm

One other thing--I bet this car will now fail a CVLI test--because the new cells are so much lower than the rest of the pack, I bet the voltage difference at low SOC will be enough to trigger consult into flagging those cells as failed. Gary may be able to use that as additional ammunition to get his car fixed properly.
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)

LeftieBiker
Moderator
Posts: 13283
Joined: Wed May 22, 2013 3:17 am
Delivery Date: 30 Apr 2018
Location: Upstate New York, US

Re: Leaf range after battery module replacement

Thu Oct 10, 2019 7:51 pm

I wasn't clear, Lothsahn: I was referring to nlspace being frustrated, not you.
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.

goldbrick
Posts: 618
Joined: Tue Aug 01, 2017 3:33 pm
Delivery Date: 01 Aug 2017
Leaf Number: 311806
Location: Boulder, CO

Re: Leaf range after battery module replacement

Thu Oct 10, 2019 9:22 pm

Can someone school me on how the BMS switches the shunt resistors on/off to balance the cells? With a cell difference of xx mV what type of device could be used to switch the resistors since the drop across the switch junction would be more the cell voltage difference? Mechanical switches seem like a non-starter so how does the BMS connect 2 cells with a 10mV cell voltage difference so they can be balanced? And why use resistors? Is the balancing current that high when 2 cells are just xx mV apart, given the internal resistance of the cells, etc?

Lothsahn
Posts: 512
Joined: Thu Apr 05, 2018 4:35 pm
Delivery Date: 04 Jan 2018
Leaf Number: 007797

Re: Leaf range after battery module replacement

Thu Oct 10, 2019 9:36 pm

goldbrick wrote:
Thu Oct 10, 2019 9:22 pm
Can someone school me on how the BMS switches the shunt resistors on/off to balance the cells? With a cell difference of xx mV what type of device could be used to switch the resistors since the drop across the switch junction would be more the cell voltage difference? Mechanical switches seem like a non-starter so how does the BMS connect 2 cells with a 10mV cell voltage difference so they can be balanced? And why use resistors? Is the balancing current that high when 2 cells are just xx mV apart, given the internal resistance of the cells, etc?
Can't say I fully understand the Leaf BMS behavior, but here's the electrical diagram that explains it:
viewtopic.php?t=17470

If you have specific questions and I have some time, I could study the diagram and try to figure out the details of how it all works.

If you connected a shunt with no resistor, I'm pretty sure that'd be bad. I'm quite tired and not thinking straight right now, but you've got a bunch of cells in series. If the shunt had no resistance, you'd be basically placing a wire between two of the cells in series, which would affect the output voltage of the pack and possibly create a lot of current on the shunt.
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: 618
Joined: Tue Aug 01, 2017 3:33 pm
Delivery Date: 01 Aug 2017
Leaf Number: 311806
Location: Boulder, CO

Re: Leaf range after battery module replacement

Fri Oct 11, 2019 9:17 am

Thanks for the link. Apparently the balancing isn't as simple as I imagined which makes a lot of sense now that I think about it. I was envisioning some simple electronic switch to connect a higher voltage cell (group) to a lower voltage cell (group). I guessed the groups would be a pair of cells but from the schematics, a group appears to be 4 cells. Even then, as you mentioned, the cell groups are also in series so that complicates matters more. But the BMS does have plenty of voltage and current available to charge any cell group, the trick is just to determine where to pull the power from and where to send it. On closer thought, that's not a trivial problem so it makes a lot of sense that the BMS doesn't supply a trivial solution. Thanks again for the link.

nlspace
Posts: 60
Joined: Mon Jun 05, 2017 10:21 pm
Delivery Date: 06 Jun 2017

Re: Leaf range after battery module replacement

Fri Oct 11, 2019 9:36 am

You have an incorrect assumption--that the BMS balancer pulls current from one cell to charge another.

The bleed resistors (430 ohms) on the LBC board can only burn off excess energy of a higher cell to bring it down to the level of the lower cells. The ASIC chips have internal transistors that provide the switch path for the balancing control of each individual cell in the 4-cell groups that each chip monitors and controls.

There is no shuttling of charge around the board from high cells to low cells.

Image
Last edited by nlspace on Sat Oct 12, 2019 8:43 am, edited 1 time in total.

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