Continuity at the Inverter

[tom91]

prevent the driver from being able to take off with too low batteries

this is UDCmin

Param info here: https://openinverter.org/wiki/Parameters

[johu]

Ah, Tom beat me to it. Anyway everything was said just no by everyone

Thought the higher setting was just to prevent the driver from being able to take off with too low batteries.

That may be a side effect but the primary aim is to prevent the main contactor from closing at a voltage that indicates that precharge hasn't happened. With inverse polarity you'd measure 0V at the DC bus. So if udcsw were, say, 300V then after 5s the precharge contactor would open (giving the precharge resistor some chance to survive) and the main contactor would never close and would have prevented your fireball.

Same goes for a short circuit created by crimping into the shielding.

I didn’t change anything from when it worked perfect on 36v Confirmed precharge working with on switch, then main switching on/pchge off was confirmed

Well you did connect it to a different battery. That is a change. Do you just assume it was correct polarity or know for sure? I.e. before giving the start signal did you measure > 300V AT the inverter terminals?

EDIT: one way to prevent such mishaps is to measure on the battery side of the contactors which one is + and which one is -. Then measure in diode mode on the inverter side. You should see slowly rising voltage, then OL. If you see steady 0.6V you know polarity is reversed.

Look here:

[phillipschip]

I did measure > 300v at the inverter terminals. I guess I shouldn't have done this alone, and done much more careful testing. Then could have tested for correct precharge/etc at the inverter terminal immediately after the 12v power switch to on. I did have a green LED wired in to the main contractor and this would only light after hitting the start signal. The 12v on signal would trigger the other/precharge contactor and it wouldn't release until I pressed the on button, which would then cause 2 clicks and the green LED to light up. I never noticed any reverse polarity.

[phillipschip]

I got up a little bit of nerve and went out to do some testing. The negative plug seems to be fused into the inverter, but the positive I can remove. When testing for continuity, I get it when testing the negative plug against the motor housing, but I don't get it when testing the negative inverter cable with the very center prong inside positive (positive unplugged). I do however get continuity at the end of the positive cable with negative cable both plugged in. Not sure if this makes any difference but not sure whey I wouldn't get it with that very center prong on the inverter.

Edit: Now that I understand the below, it makes more sense. Maybe there isn't continuity at the inverter cables after all. More testing tomorrow to confirm.

[phillipschip]

Another possibility is that you accidentally crimped the shield of the high voltage cables. The shield of both cables in the SDU is connected to the chassis ground, so if you crimp them into the HV, things will explode, but I guess you'd have noticed this during the low voltage test.

It's not a setting, it's how you hook it up or crimp it

Ok, pretty sure this was a problem. I didn't realize this was the case at the inverter connections as part of the OEM wiring harness. I guess I just thought the shielding was a physical barrier to protect the cable at whatever polarity the cable was. I'm pretty sure I crimped the shielding :0 Learning new things along the line at every step. I didn't notice in the low voltage test because I was using the factory connections and hadn't done any crimping myself to that harness.

[johu]

Well in that case if you manage to remove the molten cables your inverter could be fine.

[J0hannes]

Just to get an idea on how detailed process crimping a shielded HV cable is, you can check this Aptiv RCS800 assembly instriction just as a reference.

This snip is from the document, you need to be also careful that you don't cut the insulation in a wrong place.

Yes it may seem fine, but with HV you can't really go with gut feeling. A slit in insulation means that the angry pixies can get out there and then it's no fun trying to find out where's a problem after a while (because it may not cause an issue right away and the problems can occur intermittent)

Also check that you have enough creepage distance between the shield and the end of the middle insulator. Usually these are specified in such assembly instructions which not all manufacturers have openly available.

Pages 25-33 have good pictures of steps and pics of defects not allowed on page 32 are something that can be used more generally as rules on what's good and whats not.

[phillipschip]

Luckily it’s just one. Any ideas on how to get that connector off the inverter? Maybe cut off and carefully drill out remaining strands with Dremel? Remove the inverter cover or not? Leave in to test?
Thanks for that above info! That all makes sense now.

[tom91]

Thanks for that above info! That all makes sense now.

Do a detailed teardown of your build something has failed somewhere. Take loads of photos when you do, others may notice issues you have not yet seen.

[muehlpower]

Just for my understanding. When the ignition is switched on, the HV- contactor is closed and the OI board starts precharging. When you press the start button or continue turning the ignition key, the HV+ contactor is closed if the voltage at the inverter is above the value set for UDCSW. This means that if someone regularly leaves some time between ignition and starting, they can be lucky and nothing happens with UDCSW=0. So is UDCSW=0 a ticking time bomb, even if it often went well?

[phillipschip]

Well, I did some testing with just a basic multimeter for continuity at the inverter. Shielding pulled back now :0 And, cables plugged into inverter. (It's super cold in the un-heated garage so the steps will take some time.)

I get continuity as I should between both + and - cable shielding, and the housing/chassis. Reading of 000
I get no continuity when I test the inside copper of the + and -, but only with the correct polarity on the meter +to+, -To-.

When I switch the probes I get a reading of like 780 or something. If I unplug the positive (negative stuck and still plugged in) and test the inside center contact with the probes swapped like this, it will read no continuity unless I dig around in there for a while, then I get the 780.
Any idea why switching the probes makes a difference? I am really new at this, and each time I test something it either give me no continuity, or 000.

[tom91]

Any idea why switching the probes makes a difference?

The capacitors the appear as a dead short when fully discharged. Other way around you read something else.

[phillipschip]

I’ll tackle that diode test soon. It’s just sooo cold in my garage right now!

[johu]

Any idea why switching the probes makes a difference?

one way to prevent such mishaps is to measure on the battery side of the contactors which one is + and which one is -. Then measure in diode mode on the inverter side. You should see slowly rising voltage, then OL. If you see steady 0.6V you know polarity is reversed.

[phillipschip]

I took some brief videos to document some stuff. I'm kind of shy, don't shoot much video like this, but here it is.
If you are kind enough to take a look, make sure to watch the really short ones after the first. I should have just taken one :0





Thanks so much for all the help.

[phillipschip]

Ok, passed the first part of the diode test with just the pos and neg at the inverter.
viewtopic.php?t=3348
I believe it passed the second test with the 3 motor phase holes against the pos/neg. It didn't look exactly like the video, but basically showed rising voltage with each test. It never really got to OL, but I stopped after a little bit while still rising. I was testing through the negative cable due to the fact that it is still welded in there.

[phillipschip]

Got it spinning on 40v today

[johu]

It survived, very good!

Now be extra careful.