Power to the rear - do I need to run negative of can I ground to frame? | OVERLAND BOUND COMMUNITY

Power to the rear - do I need to run negative of can I ground to frame?

  • Hi Guest, you may choose a LIGHT or DARK theme that works best for you with the "Style Chooser" button at the bottom left on this page!
  • HTML tutorial

PoorlyTiedFly

Rank I
Member
Adventure

Member I

233
Columbus, IN, USA
First Name
Ryan
Last Name
Doughty
Member #

29141

Hello, I am prepping to run a 4g wire from battery to the rear primarily to power a Dometic drawer frig. I will also have a few accessory ports in back. I plan to run... from the battery - 4g wire to low voltage disconnect to circuit breaker to distribution block. Am I OK to just ground frame everything back here or should I run a designated ground off the battery? Also, if a designated ground is preferred do I need to match the 4g off the battery or can it be a smaller gauge wire?

Thanks in advance for the help!
 

waexplorer

Rank 0

Contributor I

You can ground to frame as long as the battery has a ground to the frame. You can also run the ground back to the battery. The ground does need to be at least as big as the power wire.
 

PoorlyTiedFly

Rank I
Member
Adventure

Member I

233
Columbus, IN, USA
First Name
Ryan
Last Name
Doughty
Member #

29141

How do I tell if the frame is grounded? Is it just a yes or no or can there be 'degrees' of how well it is grounded? I am guessing that a dedicated ground wire is preferred - right?
 

waexplorer

Rank 0

Contributor I

I meant if you want to ground at the frame in the rear, then I would make a dedicated ground from the battery to the frame. I wouldn't want to assume the battery is grounded to the frame. Still, the ground wires need to be at least as big as the power wire.
 
  • Like
Reactions: PoorlyTiedFly

M Rose

US Northwest Region Director
Expedition
Benefactor
Member

Explorer I

5,171
La Grande, Oregon, USA
First Name
Michael
Last Name
Rose
Member #

20990

Ham Callsign
KJ7MFV
Service Branch
US ARMY Retired
I meant if you want to ground at the frame in the rear, then I would make a dedicated ground from the battery to the frame. I wouldn't want to assume the battery is grounded to the frame. Still, the ground wires need to be at least as big as the power wire.
All manufacturers ground the battery to the frame, body, and engine… usually a large gauge cable runs to the engine and splices to the frame with a 1/ gauge wire leading from the battery terminal to the body.

Secondly… ALWAYS run a dedicated ground wire for your power distribution needs to the rear of the vehicle isolated from the frame and body. The reason being… there are a lot of devices that cause RFI (Radio Frequency Interference) which effects the vehicle computers. By isolating the ground, the RFI diminish as it travels back the length of cable to the battery where the battery acts as a filter and filters the RFI before it can reach the computer systems and sensors.
 

rtexpeditions

Rank IV
Member

Enthusiast I

960
Hobart, Tasmania, Australia
First Name
Randall
Last Name
Treloyn
Member #

5615

Ham Callsign
VK7VWK
If your vehicle is newer and has a smart alternator or engine start-stop, you should NOT connect the earth cable to the negative terminal of the battery.
There is a sensing circuit between the negative terminal and the vehicle body/chassis. And a direct connection will provide a bypass circuit disabling that functionality.

If you run a separate negative cable it should be run from where the negative circuit connects to the chassis.

Personally, in a vehicle like you have (metal-bodied SUV), I would run the earth to the chassis close to the fridge/ports. My thinking is similar to Mike's (no hard feelings), but I do think he is wrong in this case as connecting it to the chassis will actually lessen the potential for interference.

If you run a distribution block, with a negative bar, +/- feeds should be the same gauge cable. However, if the fridge and port negative are connected directly to the chassis, then they only need to be big enough for the things you are running, each with a separate cable. Use appropriate independent fuses for the wiring to your ports/fridge etc.
 

M Rose

US Northwest Region Director
Expedition
Benefactor
Member

Explorer I

5,171
La Grande, Oregon, USA
First Name
Michael
Last Name
Rose
Member #

20990

Ham Callsign
KJ7MFV
Service Branch
US ARMY Retired
If your vehicle is newer and has a smart alternator or engine start-stop, you should NOT connect the earth cable to the negative terminal of the battery.
There is a sensing circuit between the negative terminal and the vehicle body/chassis. And a direct connection will provide a bypass circuit disabling that functionality.

If you run a separate negative cable it should be run from where the negative circuit connects to the chassis.

Personally, in a vehicle like you have (metal-bodied SUV), I would run the earth to the chassis close to the fridge/ports. My thinking is similar to Mike's (no hard feelings), but I do think he is wrong in this case as connecting it to the chassis will actually lessen the potential for interference.
if I plug my fridge (largest RFI generator I have) into my cig lighter my noise floor raises from 2dBi @3.955 MHz to +10 dBi. If I plug my fridge into its own dedicated ground still using the same auxiliary power source my noise floor remains at 2 dBi.
My IC-7100 is on its own dedicated battery and circuit that is not tied into the vehicle’s wiring harness at all.. it’s only bonded to the body and chassis.
 
  • Like
Reactions: El-Dracho

rtexpeditions

Rank IV
Member

Enthusiast I

960
Hobart, Tasmania, Australia
First Name
Randall
Last Name
Treloyn
Member #

5615

Ham Callsign
VK7VWK
if I plug my fridge (largest RFI generator I have) into my cig lighter my noise floor raises from 2dBi @3.955 MHz to +10 dBi. If I plug my fridge into its own dedicated ground still using the same auxiliary power source my noise floor remains at 2 dBi.
My IC-7100 is on its own dedicated battery and circuit that is not tied into the vehicle’s wiring harness at all.. it’s only bonded to the body and chassis.
I'd be questioning the +ve side wiring, to the cig lighter socket, for that one.
 

M Rose

US Northwest Region Director
Expedition
Benefactor
Member

Explorer I

5,171
La Grande, Oregon, USA
First Name
Michael
Last Name
Rose
Member #

20990

Ham Callsign
KJ7MFV
Service Branch
US ARMY Retired
I'd be questioning the +ve side wiring, to the cig lighter socket, for that one.
Does it also on my aux positive wire from battery to distributor box and common chassis ground… goes away when on a dedicated ground back to the battery
 

M Rose

US Northwest Region Director
Expedition
Benefactor
Member

Explorer I

5,171
La Grande, Oregon, USA
First Name
Michael
Last Name
Rose
Member #

20990

Ham Callsign
KJ7MFV
Service Branch
US ARMY Retired
I'd be questioning the +ve side wiring, to the cig lighter socket, for that one.
Ohh and I should mention that the Bronco has brand new wiring. So no chance of a cross feed or short.
 

rtexpeditions

Rank IV
Member

Enthusiast I

960
Hobart, Tasmania, Australia
First Name
Randall
Last Name
Treloyn
Member #

5615

Ham Callsign
VK7VWK
Let's not hijack Ryan's post any further.
Both ways have their own advantages and disadvantages depending on use and vehicle.

The only things that I would mention are making good electrical connections and correct fuse ratings for the minimum wire gauge used.
Keep it safe.
 

M Rose

US Northwest Region Director
Expedition
Benefactor
Member

Explorer I

5,171
La Grande, Oregon, USA
First Name
Michael
Last Name
Rose
Member #

20990

Ham Callsign
KJ7MFV
Service Branch
US ARMY Retired
So back on track, I was showing how I was checking RFI… what RFI does to the engine management systems is horrific. RFI can in some cases be strong enough to disable your vehicle. I’m currently working an RFI issue on another Bronco for a customer who’s ECU was shutting down due to RFI from accessories. The solution was adding a negative ground cable, and a faraday cage around the ecu.