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 =)