CMU reporting battery cell temp of 57 deg [solved]

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MickeyS70

Well-known member
Joined
Feb 23, 2022
Messages
495
Location
West of Ireland
Hi there
My 2012 I-Miev doesn’t charge more than 3 bars (no 10 year battery warranty where I live). I have possibly 2 faulty cells #85 @ 4.095V and #86 @ 3.695V while the remaining are all around 3.89V.

So far everything points to faulty cells and I was planning to replace them tomorrow, however I only discovered today that temperature sensors 64,65 &66 report 57 deg Celsius, compared to 7deg on the rest.

I gather both issues seem to originate in one of the 4 cell packs, most likely caused by a faulty CMU?

Anyone come across this, if yes, how did ye fix it?
 
Howdy Mickey,

i would guess that the CMU board has a defect, such as power supply, loose connection or some other issue that is causing false readings. The car thinks that one cell is nearly full so it won't allow charging; the 3 errant temp readings are 3 different sensors on the CMU board--not likely for all 3 to fail at the same time.

when you open the pack be sure to check the voltages with a voltmeter to compare with the CMU values. i'm puzzled by how a cell could be higher than all the rest.
 
kiev said:
Howdy Mickey,

i would guess that the CMU board has a defect, such as power supply, loose connection or some other issue that is causing false readings. The car thinks that one cell is nearly full so it won't allow charging; the 3 errant temp readings are 3 different sensors on the CMU board--not likely for all 3 to fail at the same time.

when you open the pack be sure to check the voltages with a voltmeter to compare with the CMU values. i'm puzzled by how a cell could be higher than all the rest.

You were spot on, opened up the pack this morning all cells (bright yellow) measure 3.88V in both 4 packs, and after messing about with CMU 12 ODBZero now reports an amazing RR of 410km (250 miles) with a battery voltage of 6.5kV and hot (205 deg Celsius) 4 pack…

Swapped the position with CMU6; no change in reporting so problem seems on CMU 12 PCB. Can’t remember exactly where I read about a similar problem, but the solution was to replace LTC6802G-2.

Will order a new one tomorrow and look out for a phone repair shop that might swap it for me, anything else I should consider (was thinking about ordering spare CMUs but they seem hard to come by at the moment) as there was another chip mentioned?
 
There is a thread about the circuits on the CMU boards, take a look here for a photo of the board with the parts identified;
http://myimiev.com/forum/viewtopic.php?p=42633#p42633

The LTC chip is a battery management chip, read cell voltages and turns on the balancer bleed-off transistors, etc.
 
Looking at the link and other discussions I seem to have a couple of options:

A. Replace CMU12 with another CMU12
B. Replace CMU12 with a CMU6 and re-ID
C. Replace CMU12 with any other CMU, re-ID and disconnect slave board
D. Replace LTC6802 on faulty CMU12

In reality currently only C & D are viable (don’t seem to be any 4 cell CMUs available presently). Option C is what I plan to do next, unless someone can confirm D is viable (ID chip is easier to swap/ reprogram than LTC):

The PCB itself is 8-cell (G8D-795M-8), however some components are missing (e.g only 4 balance resistors). The sticker on the board (where the connector would be on an 8 cell) defines it as G8D-795M-4. Is there is a way to tell the CMU only to look for 4 cells or (crazy idea alert) could I use the slave board in parallel e.g measure the same cells again?

I have ordered one to do some testing…
 
Thanks for the info, I recon that the EEPROM data identifies if a CMU monitors 4 or 8 cells. It should therefore be possibly to take any 8 cell CMU and either swap the EEPROM or clone the data from a 4 cell to make it work. Should have all the necessary materials to test my theory next week…
 
Received my programmer ahead of schedule, was able to read data of both CMU12 and CMU8 and proceeded to re-ID CMU8

Replaced the board and started ODBZero: temperature values are now reported correctly, however cell voltages were still off (same 329.78V as with original CMU12?)

DTCs P1A5D & P1A81 both relating to CMU12 low cell voltage which was confirmed 2.1V for IDs 85-88 (all measured a healthy 3.88V though).

Looks like cloning the eeprom isn't enough, some sort of HW mod is also required. Slight differences have already been documented, see link http://myimiev.com/forum/viewtopic.php?t=4302.

Connecting the slave board and running 'sense' wires back to the cells did not change any reported voltage. But during the course of swapping boards and messing about I lost CAN communication with CMU12 again (U11AB)?! Looks more and more like a CAN/BMU problem at this stage:

1. car only charging to 3 bars, CMU12: 2 cells reporting high/low voltage, battery temp 57deg
2. after dropping battery pack and troubleshooting actions: CAN communication lost with CMU12 (329.78V 205deg C)
3. new 8 cell CMU with cloned 4 cell EEprom reports correct battery temp (13 deg C) but low cell values (P1A5D & P1A81)
4. after troubleshooting actions: CAN communication lost with CMU12 (U11AB, 329.78V 205deg C)

Planning do main battery CAN termination resistance check next and swap position with CMU6 but if that doesn't reveal anything new then I'd say I'm dealing with a BMU issue??
 
Finally managed to solve this problem by replacing all the SMD fuses and LTC chip on the original CMU12.

Be warned:
Do not connect the 12V aux battery & CAN connector if the CMU is not connected to all the battery cells: it can blow the on-board CMU fuse(s) and permanently damage the LTC chip!

If it wasn’t for that mishap I’m pretty certain that an 8 cell CMU could work in a 4 pack after changing/programming the ID chip and some simple HW changes on the PCB. Unfortunately I only had one new LTC chip at my disposal
 
приветствую всех. купил машину с похожей проблемой. пока смог прочитать только на стоянке состояние ячеек. фото приложу. завтра попробую почитать в ходу под нагрузкой. симптомы:ставлю на зарядку, авто какое то время заряжается, потом перестает. панель приборов при этом показывает полностью разряженную батарею. проезжаю несколько километров, снимаю клемму с 12в аккумулятора, панель приборов начинает показывать заряд без последних трех делений. но ка-кто очень быстро разряжается. при подключении зарядного постоянно есть ошибка(машинка с знаком восклицания) и почти постоянно горит черепаха........куда копать?
 

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greetings to all. I bought a car with a similar problem. So far I have only been able to read the status of the cells in the parking lot. I'll attach a photo. Tomorrow I'll try to read it while running under load. Symptoms: I put it on charge, the car charges for a while, then stops. The instrument panel shows a completely discharged battery. I drive a few kilometers, remove the terminal from the 12V battery, the instrument panel begins to show the charge without the last three bars. but some are discharged very quickly. when connecting the charger there is always an error (a machine with an exclamation mark) and the turtle is almost constantly on fire........where to dig?

Hello

Yes, that looks familiar,

The car won’t charge for long as most cells reach 4.1V very quickly and your range is low because the weakest cell is used to determine range/capacity.

Disconnecting the 12V battery will fool the BMU into recalculating the capacity based on pack voltage, but as soon as individual cell voltage info is available your range drops again.

Initially I thought this was due to a faulty cell but when I opened the pack and measured, its voltage it was no different, I.e it was reported wrongly to the BMU.

The CMU 4 board mounted on top of the battery pack is most likely causing this problem as it also reports wrong cell temperatures.

Either way I suggest to remove the battery next (easiest and safest to be done with a car lift) and verify cell voltages with a multimeter.

Mickey
 
Поздравления всем. Купил машину с похожей проблемой. Пока мне удалось прочитать только статус ячеек на стоянке. Фото приложу. Завтра попробую прочитать во время работы под нагрузкой. Симптомы: Ставлю на зарядку, машина какое-то время заряжается, потом останавливается. На панели приборов видно полностью разряженный аккумулятор. Проезжаю несколько километров, снимаю клемму с аккумулятора 12В, панель приборов начинает показывать заряд без последних трёх полосок. но некоторые разряжаются очень быстро. при подключении зарядного постоянно ошибка (автомат с восклицательным знаком) и черепаха почти постоянно горит.......куда копать?

Привет

Да, это выглядит знакомо,

Автомобиль не будет заряжаться долго, так как большинство ячеек очень быстро достигают напряжения 4,1 В, а ваш запас хода низкий, поскольку для определения диапазона/емкости используется самый слабый элемент.

Отключение аккумулятора 12 В обманет BMU, заставив его пересчитать емкость на основе напряжения аккумулятора, но как только станет доступна информация о напряжении отдельных ячеек, ваш диапазон снова упадет.

Сначала я думал, что это произошло из-за неисправного элемента, но когда я открыл упаковку и измерил, его напряжение не изменилось, т. е. в BMU было ошибочно сообщено.

Плата CMU 4, установленная на верхней части аккумуляторной батареи, скорее всего, является причиной этой проблемы, поскольку она также сообщает неверную температуру элементов.

В любом случае я предлагаю затем снять аккумулятор (проще и безопаснее всего это сделать с помощью автомобильного подъемника) и проверить напряжение элементов с помощью мультиметра.

Микки
Думаю, вы правы. Эта плата cmu просто меняется или необходимо кодирование? Спасибо.
 

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Думаю, вы правы. Эта плата cmu просто меняется или необходимо кодирование? Спасибо.
Могу ли я использовать эту схему для поиска нужной ячейки и нужной платы?
 

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Еще вопрос. Какое напряжение должно быть на полностью разряженной ячейке? Около 2.7-2.8v?
 
I think you're right. Is this cmu board just replaceable or is coding necessary? Thank you.
Can I use this diagram to find the right cell and the right board?
Another question. What voltage should a fully discharged cell have? About 2.7-2.8v?
Translation using google for 3 previous posts.

P1A35 is a BMU Balancer Error

P1A2F is a BMU Cell Error

Not shown is P1A4B, which is a BMU error related to a difference in cell voltage between the highest and lowest cell of greater than 200mV. This condition may be the underlying issue that is causing the 2 DTCs above, so if you can read out all of your cell voltages that would give some clues.
 
Last edited:
Перевод с помощью Google 3 предыдущих постов.

P1A35 — ошибка балансира BMU.

P1A2F — ошибка ячейки BMU.

Не показан P1A4B, который представляет собой ошибку BMU, связанную с разницей в напряжении ячейки между самой высокой и самой низкой ячейкой более 200 мВ. Это состояние может быть основной проблемой, вызывающей два вышеуказанных кода неисправности, поэтому, если вы сможете считать напряжения всех ячеек, это даст некоторые подсказки.
Итак, я купил целую хорошую сборку из 8 элементов с платой. Заменил целиком. Правда ничего не программировал, надеюсь и так заработает. Достал и разобрал «дефектную» батарею из 8 элементов и измерил вольтаж каждой банки. Все ровно, просадки нет( ранее obdzero показывал просадку 1 из 8 на 0.3v). Надеюсь проблема в плате, и все будет хорошо. По крепл несколько фото.
 

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Итак, я купил целую хорошую сборку из 8 элементов с платой. Заменил целиком. Правда ничего не программировал, надеюсь и так заработает. Достал и разобрал «дефектную» батарею из 8 элементов и измерил вольтаж каждой банки. Все ровно, просадки нет( ранее obdzero показывал просадку 1 из 8 на 0.3v). Надеюсь проблема в плате, и все будет хорошо. По крепл несколько фото.
 

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So, I bought a whole nice assembly of 8 elements with a board. Replaced it entirely. True, I haven’t programmed anything, I hope it will work. I took out and disassembled the “defective” battery of 8 cells and measured the voltage of each cell. Everything is smooth, there is no drawdown (previously obdzero showed a drawdown of 1 out of 8 by 0.3v). I hope the problem is with the board and everything will be fine. Attached are a few photos.

That's interesting that the cell showing low voltage was actually okay and not unbalanced with the others.

Thanks for sharing the pictures.
 
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