# High Voltage Isolation Fault on Tesla Large Drive Unit (LDU)



## ev-swap (Jan 31, 2020)

As a quick follow up, Tesla says in Tech article SB-10052460-6095 :



https://static.nhtsa.gov/odi/tsbs/2013/SB-10052460-6095.pdf



_As part of the Model S high voltage safety philosophy, the high voltage electrical system is isolated from the vehicle. This
means that there is no electrical current carrying path between the vehicle and any high voltage conductor._

So I guess I have an issue inside the drive that is causing this short. Time to take off the cover ...


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## boxmonkeyracing (Mar 9, 2019)

ev-swap said:


> As a quick follow up, Tesla says in Tech article SB-10052460-6095 :
> 
> 
> 
> ...



I just went back over the TSB. Step 15 you're metering the Drive unit to ground. It appears anything over 3.5 Meg Ohms is g2g. I'm going to do some more research on the Orion BMS and see if it's a settings issue. 

Mine however, by the TSB would require replacement. So Time to tear mine down further. I've got some stuff to clean up the connections. But I still need to pull the motor side and look into that.

Tony


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## grayk (Feb 15, 2021)

boxmonkeyracing said:


> I just went back over the TSB. Step 15 you're metering the Drive unit to ground. It appears anything over 3.5 Meg Ohms is g2g. I'm going to do some more research on the Orion BMS and see if it's a settings issue.
> 
> Mine however, by the TSB would require replacement. So Time to tear mine down further. I've got some stuff to clean up the connections. But I still need to pull the motor side and look into that.
> 
> Tony


Hi,

I believe that is your BMS Isolation detection system at work but I'm not 100% sure. That could be something for you to check out.


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## ev-swap (Jan 31, 2020)

In case anyone else runs into this error code (_P0AA6_) in the future, the Orion BMS has four settings for the Isolation Fault detection circuit. By default, it is set to 'Normal Sensitivity'. According to my reseller, that setting is too sensitive for most builds, and he recommends changing it to 'Low Sensitivity'. Changing the setting to Low has kept the BMS from throwing that error, in my case.

So I didn't really solve the issue, but the Orion BMS is not throwing that error now. For what its worth ...


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## ev-swap (Jan 31, 2020)

Also, for more reference, if you get this error, you can see the actual reading it is getting that causes this Isolation error to be thrown. Its under the Live Text Data tab, Advanced parameters pulldown (at the bottom of the screen), the value it is tracking is the Shortest Wave (Isolation) and the Average Wave Isolation. In the screen shot below, you can see a 'normal' reading. This is what my BMS reads when the High Voltage (HV) is not connected to the Tesla drive.

Once I turn on the HV, the Shortest Wave reading drops to about 2.6V. Then, after about 30 seconds, the lower reading will drag down the Average Wave number and the Isolation Fault error code gets thrown. But as I mentioned above, changing the sensitivity to 'low' on the BMS kept it from throwing the code.

I hope this info helps someone down the road.


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## Lowcoe (Jul 3, 2020)

Thank you for your post. I’m experiencing the same issue and this may be the solution. I was looking for a “ best practices for HV isolation” thread on here. Still looking. 
For example should metal battery box be isolated from frame? Or can it sit directly on frame? Should insulated HV cables be prevented from touching one another or is that ok? How much stand off should HV terminals have from box edges? 1/2 inch? 1inch? Doesn’t matter as long as not touching?


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## boxmonkeyracing (Mar 9, 2019)

Lowcoe said:


> Thank you for your post. I’m experiencing the same issue and this may be the solution. I was looking for a “ best practices for HV isolation” thread on here. Still looking.
> For example should metal battery box be isolated from frame? Or can it sit directly on frame? Should insulated HV cables be prevented from touching one another or is that ok? How much stand off should HV terminals have from box edges? 1/2 inch? 1inch? Doesn’t matter as long as not touching?



It's been my observance that most do not isolate the HV battery box from the frame at the mounts. That includes an AMP'd Saturn Sky I am currently working on. The HV cables can be ran next to each other without issue. Especially, if they are shielded exrad xle HVFX. 

I think I'm over thinking your last question. Are we talking about talking about the most negative and positive terminals on the pack? Contactor terminals? Personally I use HV connectors like


https://www.mouser.com/ProductDetail/Amphenol-PCD-Shenzhen/HVSL1200062B195?qs=byeeYqUIh0N3AkvHoe%2FvMA%3D%3D&countrycode=US&currencycode=USD




https://www.mouser.com/ProductDetail/Amphenol-PCD-Shenzhen/HVSL1200022B1H10?qs=byeeYqUIh0PjyytKCHsZmA%3D%3D&countrycode=US&currencycode=USD



to pass through the box.


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## Lowcoe (Jul 3, 2020)

Thanks! 

And do shielded cables need to be attached to ground at one end? Both? Neither?? Even though I’ve spent my fair share of dough on this project I went cheap on the quick disconnect HV terminals. Instead I ran the cables through a plastic gland attaching the ends to a threaded terminal . All good until you have to take the boxes out 6 or 7 times and unsnake all the cables…. Same with all the bms wires…. As of now those connectors are in the mail … delivery is any day now….


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## boxmonkeyracing (Mar 9, 2019)

Lowcoe said:


> Thanks!
> 
> And do shielded cables need to be attached to ground at one end? Both? Neither?? Even though I’ve spent my fair share of dough on this project I went cheap on the quick disconnect HV terminals. Instead I ran the cables through a plastic gland attaching the ends to a threaded terminal . All good until you have to take the boxes out 6 or 7 times and unsnake all the cables…. Same with all the bms wires…. As of now those connectors are in the mail … delivery is any day now….



A shield only works with one end grounded. 

What BMS are you utilizing Orion BMS2? Great example of a low volt shielded cable is the CAN bus on them. The black coating over the low and high CAN lines has that medal shield wrapped around it. If you were to wire up the shield on the CAN bus segments together and multiple parts terminate the shield internally you will induce faults. You effectively make the shield another conductor within the wiring harness.

I totally understand wanting to do the gland, but yeah After working avionics in aircraft for 20 years I prefer connectors. LOL. 

Which reminds me I need to talk to the owner of the Sky about upgrading the connections on the HV system. There was no gland or connector. The boxes have just openings for the HV cables to attach directly to the battery. I can't really say that AMP did that or not because this car has clearly been worked on several times by multiple people.


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## Lowcoe (Jul 3, 2020)

What happens if you don’t ground either end?


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## remy_martian (Feb 4, 2019)

Then it's no longer a shield, but a capacitor


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## Lowcoe (Jul 3, 2020)

Ahhhh


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## boxmonkeyracing (Mar 9, 2019)

Lowcoe said:


> Ahhhh


Those thread has some good info.









Grounding Shielded HV Cable


I have tried a number of searches and can't seem to find a reliable answer to my question. I am looking at using shielded 2/0 cable to connect my motor (Edit for clarification: Tesla Drive unit battery connection not the internal 3 phase) . My assumption is that the shielded would get grounded...




www.diyelectriccar.com


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## remy_martian (Feb 4, 2019)

It has a lot of Googled nonsense and one useful posting. Connect shield to case, not HV.

Edit: and the case is grounded to the chassis


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## boxmonkeyracing (Mar 9, 2019)

remy_martian said:


> It has a lot of Googled nonsense and one useful posting. Connect shield to case, not HV.
> 
> Edit: and the case is grounded to the chassis


This is what happens when you're half awake responding to people. 

Like seriously; I should have realized they recommended attaching the shield to the battery terminals.


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## Lowcoe (Jul 3, 2020)

Deleted see below


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## Lowcoe (Jul 3, 2020)

What is an acceptable number? (Higher is better). Best I have gotten so far is 2.6. By disconnecting the dc/dc converter feed from the hv battery side of the contactor…. It increased the number from 2.2 to 2.6…. ideal is 4.5 shortest wave. 



ev-swap said:


> Also, for more reference, if you get this error, you can see the actual reading it is getting that causes this Isolation error to be thrown. Its under the Live Text Data tab, Advanced parameters pulldown (at the bottom of the screen), the value it is tracking is the Shortest Wave (Isolation) and the Average Wave Isolation. In the screen shot below, you can see a 'normal' reading. This is what my BMS reads when the High Voltage (HV) is not connected to the Tesla drive.
> 
> Once I turn on the HV, the Shortest Wave reading drops to about 2.6V. Then, after about 30 seconds, the lower reading will drag down the Average Wave number and the Isolation Fault error code gets thrown. But as I mentioned above, changing the sensitivity to 'low' on the BMS kept it from throwing the code.
> 
> ...


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## Lowcoe (Jul 3, 2020)

This has continued to trouble me. What I have found is that by putting the EV controls T2C into charge mode which opens contractors (Removing the motor from the HV circuit) the shortest wave reading increased from 2.6 V to a more comfortable 4.3V. ( apparently 4.5 shows comple HV isolation).

This is same as what original poster reported. I’m curious if OP moved on after this or??

When measuring voltage from most positive terminal on contactor to chassis When motor is disconnected via open contractors I get a voltage that starts at 170v and then drains almost to somewhere between 29-25 V over a 30 second period.

When the contactor is closed the Voltage starts at 180 V and drains down to 130V over 30 sec when using meter.
Pack voltage currently at 377 volts. 

Not sure whether to be concerned or if it is something that is just typical with the Tesla motor/inverter. I also ran a ground wire from the tesla motor case to chassis but that didn’t seem to change any readings.. 

Do I just move on or do I have a problem?

w


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## ervinjason (9 mo ago)

ev-swap said:


> As a quick follow up, Tesla says in Tech article SB-10052460-6095 :
> 
> 
> 
> ...


I just went back over the TSB. Step 15 you're metering the Drive unit to ground. It appears anything over 3.5 Meg Ohms is g2g. I'm going to do some more research on the Orion BMS and see if it's a settings issue.

Mine however, by the TSB would require replacement. So Time to tear mine down further. I've got some stuff to clean up the connections. But I still need to pull the motor side and look into that.


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