# Grounding. A wonderful day at a Service Center in Chicagoland.



## Garlan Garner (May 24, 2016)

I frequent a Service Center in the Chicagoland area because I am great friends with one of their techs.

Today was a wonderful day there because a TOP tech from Omaha was there. He is regarded as one of the best Tesla Techs in the country. Anywhoo....I had the opportunity to just overwhelm him with questions all day. He didn't mind as he flew in to work on a Model S that technically wouldn't go into reverse - and it was a first.

I started off with questions about grounding. I started with that because I install 3rd party applications here in Chicago. I install things like the automatic Hansshow and Teslaoffer trunk and frunk openers. Strangely enough - he didn't discourage it.

He indicated that the main problem that Tesla is finding with these is in the installation directions/videos. This is what is happening.....

Both of these vendors have changed their instructions to no longer tap the 12V battery as a power source, but instead - Tap the PCS under the rear seat. Guess what....things will probably work. So what is the problem? They have not changed anything concerning the ground. They still say tap the negative of the installation to a bolt on the body that is closest to their controller.

The service tech indicated that the installation will probably continue to work so long as the 3rd party controllers remain functional HOWEVER both Hansshow and Teslaoffer controllers are known to "go bad" if they get wet. This is where the problem happens.

He indicated that Frame Ground is 12V battery ground, but PCS ground is NOT 12V battery ground - those are 2 different grounds. When these controllers go bad and short out - they are creating a short between PCS 12v+ and Frame/Battery ground.

This is what he did today. There was a penthouse there that was opened and he tapped PCS CAN to a cool digital tiny scope in his bag and grounded the negative of the scope to Penthouse ground and the signal was perfect. He then moved the ground to Battery 12v negative and the scope showed nothing but noise. He indicated that these grounds will actually show a false continuity on a cheap ohm meter, however they are isolated as far as signaling/etc. is concerned. He has actually been surprised as to how much current is being allowed through the PCS positive terminal to Body ground, however its causing tremendous noise and data errors in the PCS atmosphere and erratic errors within the vehicle itself that don't show up as critical for months to years after the installation of these products.

Basically - if I tap the CAN bus behind the center console on the floor or anywhere else close to there- USE the 12V battery as a power source. If I tap the CAN bus under the front dash - read the wiring diagram to find where the CAN is coming from and use the matching power source and its ground.

So...he indicated that there is no telling what will happen in the PCS when a 3rd party application shorts PCS 12V+ to battery negative. He says that it all depends on how much current is being called for / etc. This was his suggestion - if you use PCS positive - then use PCS negative. Then he laughed and said - stay away from PCS as the terminals were designed for another purpose. If you use Battery positive then use Battery negative. He indicated that for my applications that I should ALWAYS use the 12V battery as my source and stay as far away from the Penthouse as I can. He indicated that shorting the 12V battery is vastly safer and cheaper than shorting out the PCS. He indicated that this isolation between 12v ground and Penthouse ( PCS ) ground is vital and needs to stay in place in the case of an accident or various other safety applications.

Short out the 12V battery - replace the 12V battery. Short out the PCS and damage it - warranty over and pay for another battery pack because Tesla no longer fixes PCS stuff - unless its the PYRO fuse or something simple/quick. 

Needless to say - I had to call 2 of my clients back and get them back to my house ASAP. I also reached out to both of my guys at Hansshow and Teslaoffer and 2 other vendors for other 3rd party applications....to let them know to change their install. I'll just say......only 1 of them has looked at this so far.

That's the short story ( pun intended). I'm going back tomorrow.


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## JasonF (Oct 26, 2018)

Garlan Garner said:


> Short out the 12V battery - replace the 12V battery. Short out the PCS and damage it - warranty over and pay for another battery pack because Tesla no longer fixes PCS stuff - unless its the PYRO fuse or something simple/quick.


This is why I kept making myself annoying and reminding people to fuse connections to the PCS! But after reading your post, it definitely sounds like you can destroy the DC-DC converter by shorting somewhere else and pushing +12V/+14V back in through the ground, so I should probably start steering people away from the PCS.

Where I always thought that connection point was kind of risky anyway is that if you're not extra careful, you can create a short right there at the connection point, which would very quickly kill the DC-DC converter. And if it's shorting to the battery casing, maybe damage other components like chargers. The 12 volt battery, on the other hand, behaves like a ballast with 12 volt shorts, sacrificing itself and keeping the shorts from destroying things.


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## TrevP (Oct 20, 2015)

I've had my Hansshow power trunk kit installed in my car for over 1 year and half without any issues. I tapped directly to the 12V battery because I didn't want to pull power from any other electronic sources in the car. Easier to have the fuse blow inline on the 12V battery than risk shorting out something else in the car. That battery is way cheaper than....


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## Needsdecaf (Dec 27, 2018)

TrevP said:


> I've had my Hansshow power trunk kit installed in my car for over 1 year and half without any issues. I tapped directly to the 12V battery because I didn't want to pull power from any other electronic sources in the car. Easier to have the fuse blow inline on the 12V battery than risk shorting out something else in the car. That battery is way cheaper than....


Is the only downside to that having to run to the front of the car?


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## iChris93 (Feb 3, 2017)

Can the tech explain how there is +12V across the PCS and battery ground if the grounds are isolated? You need a loop to create a circuit; can't get around Kirchhoff's laws.


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## Garlan Garner (May 24, 2016)

iChris93 said:


> Can the tech explain how there is +12V across the PCS and battery ground if the grounds are isolated? You need a loop to create a circuit; can't get around Kirchhoff's laws.


I really don't have to. There are hundreds of ways to do that ( google ).

Yes, the same way a transformer ( air gap ) works with diodes that rectify AC to DC - except in this case - its DC to DC using similar methods. I built isolation circuits 40 years ago in college here in Chicago ( DeVry ).

We might have to have a PM chat @iChris93 and @JWardell.


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## iChris93 (Feb 3, 2017)

Garlan Garner said:


> I really don't have to. There are hundreds of ways to do that.
> 
> Yes, the same way a transformer works with diodes that rectify AC to DC - except in this case - its DC to DC using similar methods. I built isolation circuits 40 years ago in college here in Chicago ( DeVry ).
> 
> We might have to have a PM chat @iChris93 and @JWardell.


I'm not questioning the ability to isolate a DC-DC converter, I built those in college more recently than 40 years ago. I'm questioning being able to have 12 V across the PCS 12V and the battery ground if the grounds are isolated.


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## Garlan Garner (May 24, 2016)

iChris93 said:


> I'm not questioning the ability to isolate a DC-DC converter, I built those in college more recently than 40 years ago. I'm questioning being able to have 12 V across the PCS 12V and the battery ground if the grounds are isolated.


Sure...absolutely. You can isolate anything. Positive - Negative - Signal.

Lets do it this way......imagine the input side of an isolator and the output side of an isolator - you could tap the output side positive and the input side negative and pull current. - But then you have partially lost your isolation in most cases.

I know for sure you can do it with this DC to DC isolator.....I do it all of the time with this one. This is what I use to isolate the positive of a self made USB port accessory that is extremely noisy and badly built.


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## JWardell (May 9, 2016)

Remember that we have repeated examples that information coming from Tesla Sales and Service Center employees is very often not accurate.
This one even defies physics.

Here is the bus bar that connects the PCS to the chassis ground, same as the battery:









What is likely happening is the tech is confusing the fact that the high voltage side of the HV battery and CPS has isolated power and ground from the rest of the vehicle. That is certainly true. 
But the 12v side is the 12v side. That is its function. The system is in reference to the car chassis. If the PCS and 12v battery were isolated, there would be no solid voltage or current between them.

When the car is on, the PCS is the source of the 12v system. It is the highest potential. It's charging the 12v battery. And therefore it is absolutely the best place to put your large 12v loads.

Unlike every other car, Tesla monitors every bit of power in and out of the 12v battery, as it first connects to VCFront before connecting to the rest of the large 12v modules. And we see one example after another of the car producing errors when large loads are connected to the 12v battery, insisting on its replacement, because power that should have only gone into the battery went elsewhere.


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## Garlan Garner (May 24, 2016)

JWardell said:


> Remember that we have repeated examples that information coming from Tesla Sales and Service Center employees is very often not accurate.
> This one even defies physics.
> 
> Here is the bus bar that connects the PCS to the chassis ground, same as the battery:
> ...


What we did was simply watch CAN messages and followed the ground.

Take either the Hi or Lo CAN lead and connect the negative to Penthouse ground / negative. The signal on the scope is perfect. Then ground the negative of the scope to Frame Ground - you can't even see the signal on the scope because of the noise.

THEN

We did the opposite. We took the Hi and Lo CAN and read it from behind the console and the Penthouse ground had noise on the screen and the Frame Ground showed a perfect signal.

I can draw current around an isolated circuit. I'm certainly not supposed to ( defeats the purpose of isolation ), but I can.

----------------------------------

I tap both the positive and negative of the 12V for my Hansshow installations and there is no way for Tesla to see that current draw. If I draw too much current...all tesla will know is that the battery voltage would sag an look like a bad battery.

In the winter time during a heavy snow - my FSD cuts out because the Forward Facing Radar can't see through the caked up snow on the bumper. I installed a heater/blower ( with temp sensor ) behind the bumper that heats up the plastic and melts the snow. Well, I tapped the 12V do to this and it works just fine. My bumper was free of snow this winter....but I caused a message on the screen to appear that my battery needs to be replaced. It only said that when the heater was cycling. I still have it connected, but I don't turn it on anymore because FSD during a snow storm is just not that important to me.


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## Garlan Garner (May 24, 2016)

Guys....get this: 

This is what happened today: 

There was a Model S that the technician was flown in to look at because NO ONE could figure out why it wouldn't go into reverse. After looking and looking he found the issue. 

There is a 3rd party guy out there that is making color changing / animated headlights and tail lights for Teslas. They really look cool. What this guy is doing is taking OEM lights and opening them up and modifying them and its actually working. So from the outside of the car....everything looks normal. 

The problem came in when putting the Model S in reverse. 

1. The screen showed he was in gear R
2. The rear camera came on on the screen.
3. The white lights on the rear tail light came on, 

But there was no attempt by the car to make the motors reverse. There was no error or anything. It just wouldn't go into reverse. Well, he started looking at CAN messages going to to motors and this is what he saw. 

1. move the stalk to reverse.....beautiful CAN.
2. milliseconds later - NOISE and spikes on the CAN bus. 
3. move the stalk to forward or park....beautiful CAN again. 

He found that the Model S owner had gotten these new Modded Tail lights and that this 3rd party vendor was pulsing LED's to get the super powerful white lights to light because he couldn't get enough power draw to light them up all at once at the same time. Tesla disconnected the rear lights and put the car in reverse and the car moved. 

Long story short - I knew the guy and told Tesla that he lives on facebook and that I could message him. We got him on the phone to which he indicated that he thought he had resolved this issue. I covered the cost of Tesla's work and the new headlights. Needless to say.....the Model S owner was super angry, but eventually calmed down and went on his way. 

Going back tomorrow as the tech will be there all week.


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## JWardell (May 9, 2016)

Garlan Garner said:


> What we did was simply watch CAN messages and followed the ground.
> 
> Take either the Hi or Lo CAN lead and connect the negative to Penthouse ground / negative. The signal on the scope is perfect. Then ground the negative of the scope to Frame Ground - you can't even see the signal on the scope because of the noise.
> 
> ...


Shorting the CAN to ground is a no-no. It is at least above ground level, and more likely has various isolation techniques to keep it further from 12v and ground. So I'm not surprised by shorting it you saw wierd things.
You are confusing the two independent sides of an isolated circuit, and stating that the output is isolated from itself....that doesn't make sense.
Wiring to your 12v battery may or may not see current on VCfront, depending on how the car is powered and if the PCS is supplying it. But it is keeping track. And watching voltage very accurately. Your extra voltage sag is exactly what will trigger those errors and convince the car that the battery health has deteriorated.
Step back and think about it a little bit.


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## Garlan Garner (May 24, 2016)

JWardell said:


> Shorting the CAN to ground is a no-no. It is at least above ground level, and more likely has various isolation techniques to keep it further from 12v and ground. So I'm not surprised by shorting it you saw wierd things.
> You are confusing the two independent sides of an isolated circuit, and stating that the output is isolated from itself....that doesn't make sense.
> Wiring to your 12v battery may or may not see current on VCfront, depending on how the car is powered and if the PCS is supplying it. But it is keeping track. And watching voltage very accurately. Your extra voltage sag is exactly what will trigger those errors and convince the car that the battery health has deteriorated.
> Step back and think about it a little bit.


Yes....you are correct.

Indeed shorting CAN is a NO NO. We didn't short CAN.....we simply moved the ground of the scope lead back and forth between Penthouse ground and Chassis Ground and got different readings. These negatives are NOT the same although an Ohm meter would disagree. I'm 100% confident we all know why the Ohm meter shows continuity.

I agree with you 100% about the 12V and voltage sag. My point was - a Tesla can't track the current draw of a circuit that taps the positive and negative of the 12V. A Tesla can only see voltage sag.


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## JasonF (Oct 26, 2018)

I'm not at all surprised that connecting one end of an oscilliscope to a filtered and regulated DC+ source (which CAN is) and the other to raw body ground is noisy. There are a lot of devices in cars that induce alternating current, create electromagnetic pulses, or add RF noise, and not all of them are filtered on the ground side. That's probably what the Tesla tech was pointing out.

As for those colored lights that stopped the Model S from going into reverse, that person probably could have avoided a lot of problems if he would have filtered the ground connection and added some capacitance on the input so the light pulsing wouldn't leak to the car's DC system or ground.


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## Long Ranger (Jun 1, 2018)

Garlan Garner said:


> My point was - a Tesla can't track the current draw of a circuit that taps the positive and negative of the 12V. A Tesla can only see voltage sag.


Tesla can certainly track that current draw whenever the PCS is charging the battery. Telsa's current measurement at VCfront will measure the total current going to the battery circuit (the current going to the battery PLUS the current drawn by your device).



Garlan Garner said:


> Indeed shorting CAN is a NO NO. We didn't short CAN.....we simply moved the ground of the scope lead back and forth between Penthouse ground and Chassis Ground and got different readings. These negatives are NOT the same although an Ohm meter would disagree. I'm 100% confident we all know why the Ohm meter shows continuity.


But measuring CAN signals relative to ground is also a no-no. You won't hurt anything by doing so, but the results aren't really meaningful. CAN uses differential, isolated signaling, and you have to measure between CAN-L and CAN-H to get meaningful data. Sure, I'm not surprised that you see more noise relative to different ground points, but that doesn't mean that the grounds are isolated from one another.

I think you're confusing DC isolation with high frequency AC impedance. The ohmmeter shows continuity because the grounds really are connected via a DC path. However, when you get into the realm of high speed digital signals, then connected ground points can start to look like there are inductors between them just due to the size and path of the grounding connections. That can result in signal integrity and ground bounce issues like you saw on the scope, but that would only matter for noise-sensitive applications such as trying to run some single-ended high speed digital signal around the car. For supplying 12VDC to any given accessory, ground is common (chassis ground) for both the PCS and the battery.


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## Garlan Garner (May 24, 2016)

Long Ranger said:


> Tesla can certainly track that current draw whenever the PCS is charging the battery. Telsa's current measurement at VCfront will measure the total current going to the battery circuit (the current going to the battery PLUS the current drawn by your device).
> 
> But measuring CAN signals relative to ground is also a no-no. You won't hurt anything by doing so, but the results aren't really meaningful. CAN uses differential, isolated signaling, and you have to measure between CAN-L and CAN-H to get meaningful data. Sure, I'm not surprised that you see more noise relative to different ground points, but that doesn't mean that the grounds are isolated from one another.
> 
> I think you're confusing DC isolation with high frequency AC impedance. The ohmmeter shows continuity because the grounds really are connected via a DC path. However, when you get into the realm of high speed digital signals, then connected ground points can start to look like there are inductors between them just due to the size and path of the grounding connections. That can result in signal integrity and ground bounce issues like you saw on the scope, but that would only matter for noise-sensitive applications such as trying to run some single-ended high speed digital signal around the car. For supplying 12VDC to any given accessory, ground is common (chassis ground) for both the PCS and the battery.


Those testing measures are what the Tech used to determine the faults and isolation. They seemed to prove themselves correct.


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## JasonF (Oct 26, 2018)

You will get the same result as the tech got at the main battery if you ground directly to the negative terminal on the 12 volt battery. It has to do with signal to noise ratio - the closer you are to a "quiet" ground (negative terminal at either the 12V or main battery) the less interference there will be.


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## Long Ranger (Jun 1, 2018)

Garlan Garner said:


> Those testing measures are what the Tech used to determine the faults and isolation. They seemed to prove themselves correct.


I don't mean to discount the ability of a good tech to use measurements like that to track down faults. I know a few techs that are really good at tracking down problems with techniques like that. However, they don't always get it right when trying to explain the actual circuit. In this case, claiming that the two 12V grounds must therefore be isolated from one another is not the correct conclusion.


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## Garlan Garner (May 24, 2016)

Long Ranger said:


> I don't mean to discount the ability of a good tech to use measurements like that to track down faults. I know a few techs that are really good at tracking down problems with techniques like that. However, they don't always get it right when trying to explain the actual circuit. In this case, claiming that the two 12V grounds must therefore be isolated from one another is not the correct conclusion.


It certainly is the correct conclusion.

We proved it over and over at the service center today. Criticize him all you want.....this guy is great.

I wish you could come out and see what is going on.

This other guy has proved it on many occasions during his videos. They are long and I can't remember which ones are specific to him not isolating ground to the BMS, but you can search for it yourself. I will look for it and report back if I find it.

(59) Tesla Model 3 BMS Hacking Update - YouTube


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## iChris93 (Feb 3, 2017)

Garlan Garner said:


> Criticize him all you want.....this guy is great.


No one is doing that.


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