Teardown - Tesla LDU - Inverter [SOLVED]

[nubster]

I just picked up another LDU, which I knew had a mechanical failure. Upon opening it up, I can see some signs of IGBT failure. Where/what do I need to measure to confirm a blown power stage? I know it's been discussed before but I could not find it.

I asked about this for the SDU recently. I would assume the LDU can be tested similarly. Maybe someone can confirm.

viewtopic.php?p=53781#p53781

[P.S.Mangelsdorf]

I did measure in diode mode, the data sheet say that forward bias should be around 0,5v the ones that was in worst condition was totally shorted, the other around 0,1-0,2v.
Then the low ohm(1ohm) power resistors for "gate" control was in Mohm range. probably therefor the igbts blown, not had the possibility to open/close correctly...
Both +/- side engaged at the same time... My final verdict is that the problem started with bad resistors...

At risk of sounding like an idiot - where do I need to measure? At the input/output? At the IGBT under the goo? Some other point?

I gather from nubster's thread that essentially I'm looking for whether there is continuity between the DC inputs and any of the AC output phases?

[muehlpower]

As I understand, it means that you have to unscrew the small cover in the middle at the bottom of the LDU and then measure the individual phases to the battery inputs.

[P.S.Mangelsdorf]

As I understand, it means that you have to unscrew the small cover in the middle at the bottom of the LDU and then measure the individual phases to the battery inputs.

Ok, thanks. That's where I was headed.

[Haapala]

Hi,
Having problem with one LDU inverter. Infact this one is from Mercedes B250e.
Had HV insulation problem. Had water in rotor area, thought that was the cause.
While open no insulation problem in any component, inverter or stator.

I did assemble it but in first test drive insulation problem came back. Car was drivable, but fault codes on dash.

Did measure from motor HV connections that 200kOhm was the resistance to frame on 500V. That was the same that diagnostics showed from OBD.
Did take motor out again and inverter side open. Did take the end piece from inverter that connects 3 "phase cards" together. Also disconnected stator windings from inverter. Did manage to measure 200kOhms on one "phase card", two other was OK.

I took the one third out and measured on table, the same 200kOhms was result. But after 30 min the insulation problem was gone. Again megaOhms.
Let it sit on table for night and in the morning it was 30kOhms. Again later in day megaOhms.

What component could cause this?

Could there be any way to measure what is the cause?

Pretty hard to find inverter parts for Mercedes.
I do have one Tesla S85 LDU, but it had different part number on PCB and also different components on it.

[hmejl]

Hi,
Having problem with one LDU inverter. Infact this one is from Mercedes B250e.
Had HV insulation problem. Had water in rotor area, thought that was the cause.
While open no insulation problem in any component, inverter or stator.

I did assemble it but in first test drive insulation problem came back. Car was drivable, but fault codes on dash.

Did measure from motor HV connections that 200kOhm was the resistance to frame on 500V. That was the same that diagnostics showed from OBD.
Did take motor out again and inverter side open. Did take the end piece from inverter that connects 3 "phase cards" together. Also disconnected stator windings from inverter. Did manage to measure 200kOhms on one "phase card", two other was OK.

I took the one third out and measured on table, the same 200kOhms was result. But after 30 min the insulation problem was gone. Again megaOhms.
Let it sit on table for night and in the morning it was 30kOhms. Again later in day megaOhms.

What component could cause this?

Could there be any way to measure what is the cause?

Pretty hard to find inverter parts for Mercedes.
I do have one Tesla S85 LDU, but it had different part number on PCB and also different components on it.

weird i just had a mercedes drive unit in the shop as well with the same fault. Found out when i connected the connector for the top board with the powerbridge on it whent from 15mOhm to 4 mOhm. But did not find the fault

[johu]

And it can not be repeated enough, this is an example of fantastic engineering and problem solving

Is there a chance you could restore the pictures in your first post?

[fredd90]

Is there a chance you could restore the pictures in your first post?

Now the pictures are restored =)

[P.S.Mangelsdorf]

Hey fredd90, after removing the goo and the outer rows of sprung metal holding the IGBTs, is the next step in disassembly de-soldering the IGBTs, or is there a way to lift the whole center section up without doing so?

[P.S.Mangelsdorf]

is the next step in disassembly de-soldering the IGBTs

To answer my own question, it appears to be yes.

New question:

First preheat to 150-200 degree, then the desolderring begin, ecuipped with 150w soldergun in combination with Vaccum solder station.

What did you use to pre heat? An oven? a heat gun? Will the other parts (including the gate driver board) be OK at that temp?

Total time from blown inverter piece to this, aprox 4 hours.

Are you sure it wasn't 40 hours? Mine has been an absolute pain, some pins are totally normal solder that I mad quick work of, but others it's clearly something different and worse than pulling teeth.

[Isle]

Then it was time to spread some light over all the broken Large drive units, i have against all odds managed to bring life to my P85 drive unit.
After replacing all the igbt in one of the bridges.
As well as all semiconductors in all three drive cards, everything had a short circuit. Not unexpectedly i constantly had overcurrent alarms.

Everything solder together, just the cap left.
IMG_20210517_234647.jpg
All semiconductor on the "isolated" side replaced.
Everything from igbt driver to diodes and n/p transtors.
IMG_20210603_224627.jpg
After final test i decided to add some re-entering silicone.
Couldn't find any transparent unfortunately.
IMG_20210611_140202.jpg

Not a project for everyone but it has been quite educational, spare parts have cost about 4-500eur. Also had to buy a new soldering iron of 200w to cope with the thick laminated copper. The worst part was all the lacquered circuit boards in combination with the extreme lack of semiconductors...

Are you using this with the openinverter or some other logic board, not the stock one?

Reason I am asking is I went through the same thing, but just elected to replace the entire phase, and the motor still doesn't work. I really, really don't think anything is wrong with any of the hardware at all, just the (OEM) logic board having a stuck fault.

I think if you have this issue using the OEM controller, you must replace the controller as well unless you know how to reflash it. And finding a known good used controller board is not easy. Especially since the sport and non-sport use the same board but are not compatible with each other without a reflash.