BSM: V_ess too low during precharge

[scotty2541]

It's been a while since I've been in the PEM so I'm just going to throw out ideas for discussion based on my experience (and fuzzy memory)...

1) We definitely had problems with the precharge circuit and traced it back to the IGBT on the CIC I/O board (the one with it's own heatsink) which had shorted. Without that circuit functioning the car would not charge.

2) We also had blown at least one of the capacitors

Sorry I don't have any more info, it's been a while and we replaced a LOT of components.

I would start with the IGBT on the CIC I/O board - it probably took the brunt of the spike and shorted.

Thanks. Easier Questions: Where is that board?

(All fuses I could find, under just that the power connection panel, or with the entire PEM opened, were fine)

I don't know what the CIC I/O board is, nothing is labeled. The only heat sink I see is mounted on the vertical board, off to the left of the big white molex connector hidden (marked on the image below)

Here is a picture looking in the PEM. Under that is another picture of my measurement of a power resistor.
I think it's the one that is supposed to be 39 ohms, but it's 100 ohms. 2 /12 times the resistance would make the precharge circuit too low after the defined interval (about 4 seconds).

Is the board in question where this resistor is plugged in? Mounted vertically above the bottom PEM connectors?
I'd like to be more confident before unscrewing everything, taking it apart.

And advice is appreciated.

 

[thefortunes]

Thanks. Easier Questions: Where is that board?

(All fuses I could find, under just that the power connection panel, or with the entire PEM opened, were fine)

I don't know what the CIC I/O board is, nothing is labeled. The only heat sink I see is mounted on the vertical board, off to the left of the big white molex connector hidden (marked on the image below)

Here is a picture looking in the PEM. Under that is another picture of my measurement of a power resistor.
I think it's the one that is supposed to be 39 ohms, but it's 100 ohms. 2 /12 times the resistance would make the precharge circuit too low after the defined interval (about 4 seconds).

Is the board in question where this resistor is plugged in? Mounted vertically above the bottom PEM connectors?
I'd like to be more confident before unscrewing everything, taking it apart.

View attachment 524077

View attachment 524069

And advice is appreciated.

Yep that is the CIC I/O board. There is a label on it somewhere, and it is a pain to get out.

 

[scotty2541]

Yep that is the CIC I/O board. There is a label on it somewhere, and it is a pain to get out.

Next question:
(The actual precharge circuit is inside the battery , and beyond my ability to get to...)

Tesla service just told me that since the car won't even charge on a 110V plug, then it is in the PWM, and is NOT the precharge circuit inside the battery.

Does this sound correct?

(If it is, I could try to fine a replacement board, or even remove it and test the components individually.)

 

[thefortunes]

Next question:
(The actual precharge circuit is inside the battery , and beyond my ability to get to...)

Tesla service just told me that since the car won't even charge on a 110V plug, then it is in the PWM, and is NOT the precharge circuit inside the battery.

Does this sound correct?

(If it is, I could try to fine a replacement board, or even remove it and test the components individually.)

Not sure why lack of 110v charging would limit the problem to the PEM, maybe someone else can chime in.

Your service center (if they service Roadsters) has a machine that can take the PEM out of circuit and mimic it to validate that the charge or drive problem is inside the PEM or battery.

Here is a mine going through that procedure when I thought we had fixed everything in the PEM. Unfortunately it won't tell you WHAT is wrong, just that there is still a problem in the PEM. I believe it cost me $150 for that test which was worth it vs dropping the battery.

That's when we dug further and found the blown IGBT on the CIC I/O board.

 

[GeorgeK]

Hi all,

Wondering if anyone has more info on how the precharge system of the Roadster works.

Long story short - I popped an ESS sheet fuse while accelerating a few months back, replaced it, and am now working through precharge errors (BSM: precharge too fast at t1 ID:275, and BSM: V_ess too low during precharge, t2 ID:288), similar to others on this thread.

I've checked the CIC board in the PEM (FET), along with the 400v controller (FET, resistor) under the hood, and haven't found any damage to components on those boards.

I did find some evidence of what looks like arcing in my PEM between the B+ and B- busbars that feed the three phase boards, potentially from the back EMF of the motor at high RPM when the ESS fuse popped (top-right in photo). It looks like a capacitor on the filter board that bridges those busbars exploded, but after cleaning with alcohol those components look fine, and there looks to have been some blackening on the bottom of that board where there are no components. So pretty confident that there was an arc large enough to jump between the two busbars and vaporize a plating on them, or some of the bar itself.

I've checked my IGBT FETs, and they all tested good (no shorts or visual damage). I replaced thermal pad while I was at it.

Anyone have recommendations on what to check out next?

 

[thefortunes]

You mention that you checked the CIC board.

When I had this error the IGBT on that board (with the heat sink) was shorted.

 

[GeorgeK]

@thefortunes - thanks for the reply. I did check that FET with continuity and didn't find any pins shorted to any other pins in doing so.

 

[slcasner]

What about failing open?

 

[GeorgeK]

What about failing open?

I believe (with limited knowledge of the precharge circuit) if it were to fail open, then the system should never reach precharge voltage (opposite of it reaching precharge too fast).

 

[GeorgeK]

I created my own precharge problem in this case. While servicing the pack, I capped and stowed a lug that goes to the B- terminal and forgot to reconnect this after sheet reinstallation. Ideal fix!