Another Grounding questions regarding avoidance grounding loop

geolboy

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Feb 24, 2021
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Just finished reading paper by @FilterGuy: Grounding Made simpler - Part4. Good thing I did as I was planning to run three of 2GA multiple ground connections to a negative bus bar from three different chassis 5/16 bolts, instead of a single 4/0 connection from the neg bus bar to chassis which had to be further away. So I will be changing that to a single 4/0 to van chassis. But I am still not entirely clear on couple points, would appreciate a clarification, please:
1. Is it acceptable to run additionally separate grounding wires from MPPTs/Invertor metal chassis to the closest direct grounding points, instead converging them on the single grounding bar? To me its simply matter of convenience/cost running shorter smaller size wires due to a location placement.

2. I got confused with a picture and wording as on this screenshot:
1654288538372.png

The way I read this - the chassis ground should not be there, yet the picture diag shows it connected with a current flow. Am I misreading this? Sorry, I am new at this, so want to get it right with understanding.
Thanks in advance.

 

FilterGuy

What, me worry?
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Los Gatos CA
2. I got confused with a picture and wording as on this screenshot:
View attachment 97104

The way I read this - the chassis ground should not be there, yet the picture diag shows it connected with a current flow. Am I misreading this? Sorry, I am new at this, so want to get it right with understanding.
Thanks in advance.
The negative DC ground should NOT be between the cells and the BMS. The diagram is trying to show why it should not be there. Sory for the confusion.
1. Is it acceptable to run additionally separate grounding wires from MPPTs/Invertor metal chassis to the closest direct grounding points, instead converging them on the single grounding bar? To me its simply matter of convenience/cost running shorter smaller size wires due to a location placement.
Acceptable: Yes
Good Idea: NO.

There are no safety issues that I am aware of with the additional ties into the chassis. However, it creates loops that can create or amplify issues with broadcast RFI. Inverters are designed to rapidly switch very high currents on and off.... and that is a great way to create broadband RFI noise. If that noise gets onto a ground loop that resonates at one of the noise frequencies, it will act as an antenna and broadcast that noise.

The broadcast noise has the possibility of impacting any type of radio. AM, FM, CB, short wave, Wifi, Bluetooth, Cellular, etc. For the non-digital radio signals, it will present as noise or a weak signal. For the digital signals (WiFi, Bluetooth, cellular) there is error-correcting that may allow the system to work, but at a degraded performance. This will present as low download speeds or shortened range of the signal.

The joke I have repeated too many times is that it might prevent you from tunning in your favorite 70's disco station...... but that is a good thing!

In mobile installs, it is sometimes difficult to prevent loops, but I always try.
 

Zil

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It is good to tie the chassis of the van to the negative BusBar. The troubles come from having a connection that is not quality. My practice is to sand the metal at the connection points to shiny steel and then tin plate the chassis steel. With modern vehicle construction, welded unibody, I am confident of electrical continuance of the steel body shell and chassis.
I would never return high current devices through the chassis. Inverters and such will always have a cable to the negative BusBar. And that with a cable to the shunt and then the battery.
The use of the BMS is a different story, but that diagram is a good start.
 

geolboy

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Feb 24, 2021
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The negative DC ground should NOT be between the cells and the BMS. The diagram is trying to show why it should not be there. Sory for the confusion.

Acceptable: Yes
Good Idea: NO.

There are no safety issues that I am aware of with the additional ties into the chassis. However, it creates loops that can create or amplify issues with broadcast RFI. Inverters are designed to rapidly switch very high currents on and off.... and that is a great way to create broadband RFI noise. If that noise gets onto a ground loop that resonates at one of the noise frequencies, it will act as an antenna and broadcast that noise.

The broadcast noise has the possibility of impacting any type of radio. AM, FM, CB, short wave, Wifi, Bluetooth, Cellular, etc. For the non-digital radio signals, it will present as noise or a weak signal. For the digital signals (WiFi, Bluetooth, cellular) there is error-correcting that may allow the system to work, but at a degraded performance. This will present as low download speeds or shortened range of the signal.

The joke I have repeated too many times is that it might prevent you from tunning in your favorite 70's disco station...... but that is a good thing!

In mobile installs, it is sometimes difficult to prevent loops, but I always try.
Yes, I got that point from your doc, its a great help for people like me, thank you so much for putting time and effort. What I am trying to get through my thick head, is whereas ground loop will be present continuously (which is of course unwelcome outcome), IF a neg bar has a single connection to Van chassis while the invertor/mppt chasses grounded to different ground points, OR the ground loop would happened only in case if surge occurs on the device? Basically is it a continued or a periodic event? I can live with a periodic risk of interference comparing to the wire nest otherwise I have to create, which for my build I would want to avoid. But if those chasses constantly send electricity flow, besides their negative connections, this would be a problem, as you said. Thanks.
 

FilterGuy

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IF a neg bar has a single connection to Van chassis while the invertor/mppt chasses grounded to different ground points, OR the ground loop would happened only in case if surge occurs on the device? Basically is it a continued or a periodic event? I can live with a periodic risk of interference comparing to the wire nest otherwise I have to create, which for my build I would want to avoid. But if those chasses constantly send electricity flow, besides their negative connections, this would be a problem, as you said. Thanks.
Yes.... it gets very confusing and the equipment documentation is never adequate enough to figure this out.

Here are a few points. that might help
  • On all inverters I have ever checked, the AC-input ground, AC-output ground, and the inverter case are tied together.
  • I do not know of any inverters that tie DC negative to the case.
  • I am less familiar with the Solar charge controllers, but I don't think any of them tie DC negative to their case.
So.... if you tie the DC negative to chassis at one point and the inverter case to the chassis at a different point you should be OK. I like to try to make them the same point just in case there is any capacitive linkage in the inverter that forms a virtual loop..... but that is just me being anal. At some point, the realities of wiring a cramped RV override the theoretical possibilities of a problem.
 

geolboy

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Feb 24, 2021
Messages
29
Yes.... it gets very confusing and the equipment documentation is never adequate enough to figure this out.

Here are a few points. that might help
  • On all inverters I have ever checked, the AC-input ground, AC-output ground, and the inverter case are tied together.
  • I do not know of any inverters that tie DC negative to the case.
  • I am less familiar with the Solar charge controllers, but I don't think any of them tie DC negative to their case.
So.... if you tie the DC negative to chassis at one point and the inverter case to the chassis at a different point you should be OK. I like to try to make them the same point just in case there is any capacitive linkage in the inverter that forms a virtual loop..... but that is just me being anal. At some point, the realities of wiring a cramped RV override the theoretical possibilities of a problem.
Thank you! :) that is very helpful and completely make sense now...as I was typing it, a silly thought run through my puny brain: you could have ring that with a multimeter to get your answer duh...lol :)
 

Sinjins

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Jun 22, 2022
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Hello All. I have a question about having multiple chassis grounding points.

The situation background:
I have converted an ambulance (Ford F-350 Super Duty chassis) into a camper. The rear box is entirely (and robustly) built with aluminum. The ambulance came with a complex 12V DC distribution circuit board/panel in the rear box with each DC circuit separately fused and relayed (fuses and relays mounted on a circuit board). Next to that existing rear DC distribution panel/circuit board is a beefy grounding block where all of the existing rear box DC circuits are connected to for their individual grounds. That grounding block is then connected with a beefy cable to the steel truck chassis underneath the rear box. The rear distribution panel is connected to the two 12V starter batteries under the hood of the vehicle via beefy DC wire as well (with a master battery disconnect switch/solenoid in between to turn off the whole system).
FYI, Ambulances out-of-the-box are meant to have their engines running (or connected to shore power) in order to run the rear box and related emergency equipment. As I am planning on boondocking/remote camping, relying on an engine running or shore power to run equipment is a definite no-can-do. So I invested heavily and have installed (more like mounted at this point) a separate power system on the opposite side of the rear box compared to the existing DC distribution panel in order to provide power to the rear box in a more autonomous fashion (no requirement to have engine running or shore power). I have installed a 700W rooftop solar array, an appropriately sized MPPT charge controller, an-in-one Inverter/Charger/Transfer Switch (i.e. a 3000W Victron MultiPlus II 2x120V) along with a Victron Lynx Distributor (a fancy efficiently-designed fused positive and negative bus bar device), and a Sterling 60A DC-DC charger, all powered by a 300Ah LiFEPO4 battery bank, and am now currently wiring it all up.

The grounding question:
I have a question about grounding to make sure I haven't done (or plan to do) anything incorrectly in that regard. As the new Victron-based system is physically located on the opposite side of the rear box compared to the pre-existing 12V DC distribution panel (and its associated grounding block mentioned in the first paragraph), I have installed its own 2/0 chassis ground wire from the negative bus bar of the Victron Lynx Distributor to that side of the truck chassis, rather than run a big ground wire from that aforementioned bus bar through/across the interior of the rear box to the drivers side in order to somehow connect to the pre-existing grounding block in the existing cabinet (but there not really any room to connect to that grounding block given number of ground wires already connected to it either). So now as a result there are 2 separate chassis ground wires and separate grounding points associated to the systems in the rear box, one on the drivers side chassis frame rail and the other on the passenger side chassis frame rail. First, is that ok? Second part of the question is: If I now run the necessary DC power wire(s) across to the pre-existing DC distribution panel from the Victron Lynx distributor, effectively replacing the wire running from the truck's starter batteries so that the pre-existing rear DC circuits are powered from the LiFEPO4 battery bank instead of the starter batteries, but leave the two existing separate chassis grounds in place, is that a problem? Is my plan problematic or incorrect?
 
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