Ground to Frame? Seriously Confused -- Need Advice

[dstefan]

Here's what I've got and am building: House battery in truck bed camper with National Luna DcDc portable power pack with BattleBorn 100 AH battery). Powers 50qt ARB fridge, lights, small inverter, occasional heating pad for my bad back.

Currently have the house battery/PPP in the bed with about 25' run of 6awg cable (both positive and negative) to the starter battery with 40 amp fuse (as NL specs). Using NLs supplied 6awg cable. NL only specifies returning the negative to the battery, not additional grounding. The PPP has a 63 amp circuit breaker on/off switch. It's all good, works fine in testing and with the camper vent fan temporarily running of one of the PPP 12v outputs, but have not used in the wild yet.

Plan to run the fridge line directly through the PPP box wall to the battery terminals using ARB's 10 awg wiring loom with fuse. Will run an 6" 8 awg positive and negative cable from the PPP's 50amp Anderson connector output to a Blue Sea 4321 circuit breaker switch panel with 4 protected switches (15amp each) , a 12v outlet (probably wont use this) and a USB outlet. Will have a couple very low amp LEDs lights run into the switch panel as well as the installed MaxFan. Will also add a 500 to 800 watt inverter to the PPP which will be plugged into the PPP's second 50amp Anderson output with a short 6awg cable.

I get that a frame ground isn't really necessary with the main PPP to battery connection in general (right?). Do I need to run a ground from the small Blue Sea panel (it has a negative bus) to the frame even though it returns the negative to the Battle born/PPP? Is there any reason the long run of cable to the starter battery requires a ground from the truck bed near the PPP/battery? If I run a ground from the Blue Sea panel negative bus, does that provide some help for the whole system? I do understand the issues of a good connection to the frame, if I run an additional ground in the truck bed.

For extra credit, what the hell is a ground loop?? I kept finding that in my researching and still don't get it.

Thanks!

 

[curtis73]

Running a full cable for ground back to the battery is not the best way to do it, but it's fine. Your electrical circuit needs a certain gauge of wire for the amperage it carries. Running a cable back to the battery means you're doubling the length of the circuit in the 6ga format. Nothing wrong with that, but the reason they suggest using the chassis is for two reasons. 1) you're using all of the steel in the entire vehicle as your return path with less resistance than another 25' of 6ga wire, and 2) it's just bloody easier that way. If you want to add a redundant ground to the frame, it certainly won't hurt.

Ground loop is a somewhat nebulous term. When you have a load (like an appliance) on a circuit that generates electrical noise, a ground loop can eliminate the noise. Remember back in the day when your TV would get fuzzy when you turned on the blender or an electric shaver? The appliance is putting "noise" into the house's wiring. The noise is worsened by the fact that the two conductors that go from the outlet to the panel are equal length. It makes a resonance. If you change one of the pathways, it helps eliminate the noise. For instance, you may be generating noise in your system that is being made worse by the two equal-length conductors. If you were to add a frame ground, you're making a ground loop and reducing the ability for noise to exist in the system.

Think of it like an exhaust/muffler. If you use straight pipes, they're loud because the sound waves have no change. If you throw a muffler in the system and force the sound waves to change, you eliminate some of the noise. We audio guys do this all the time. When you plug in 4 different amps, 8 speakers, a mixing console, and an EQ on the same circuit, you have a high potential for noise. Most audio equipment has a button that does a "ground lift." It basically turns off the ground wire. By changing the pathway of electricity on some of the components, you can reduce the noise in the system.

 

[dstefan]

Thanks Curtis73 I think I sort of understand the ground loop now!

I can see on a re-read I didn‘t describe the set up unambiguously. National Luna specifies NO ground and specs the negative from the aux battery to return to the starter battery and provides the cable spec’d for that. I hear you on the doubled resistance, but since its DC to DC charging and only pulling a 25 amp load max through 6awg (actually ~5awg since its metric 16 cable) the ~50ft roundtrip run to the battery isn‘t an issue.

I think Im gonna frame ground from my added switch panel since its another 12 to 15ft of round trip wiring and its pretty easy to do, unless someone here warns me off for a good reason.

 

[dstefan]

Any other feedback on this issue so I don't cause a real problem?

 

[OllieChristopher]

I recommend simply adding a negative buss bar to the ground wire you have to your house battery. Then you can run all your aux power directly to the buss. Frames and body make very poor "common grounds" and can have you chasing strange electrical issues that make diagnosing a nightmare.

Here is a better explanation:

Ground Path for High Current Accessories

At what point do you wire an accessory’s ground directly to the battery? I’ve heard that high current ground wires should go directly to the battery to avoid issues with other more sensitive systems, and I’ve heard to never wire an accessory ground wire directly to the battery because if another...

expeditionportal.com

 

[Deleted member 9101]

I've always upgraded my battery to frame ground wire then grounded everything to the frame.

I also upgraded the body to frame ground wire and the motor to frame ground wires.

 

[old_CWO]

A ground loop is when there are multiple paths to ground and they are not all at the same potential. Another term for difference of potential is voltage. Ground loops cause noise on radio circuits and sometimes mess with sensitive electronics. AC circuits by nature tend to have more issues with this than DC.

Generally for automotive 12VDC systems, good clean connections from the battery, chassis and engine are sufficient and the chassis should be fine for use as your ground buss. That has been my method for many years and have never experienced a problem. I do go overkill on wire gauge to help dramatically lower resistance in the conductors. Make sure all your connections are bare clean metal to metal and use electrical grease whenever you can. Install your fasteners with toothed washers that "bite" into the substrate for better conductivity.

Forgot to add: tie the body to the chassis with good ground cables too. Pickups need the cab and bed both done as obviously they are two pieces.