Grounding a Battery

[RFB]

Im mounting a battery in the rear of the truck and want to know the best place to ground it, Do I need to run it all the way back to main battery or can I ground it to frame under rear cargo. Im really asking.

 

[thatcabledude]

I'd ground to frame and body back there.

 

[bhsdriller]

Frame

 

[LC4LIFE]

Pretty much straight over from the rubber plug where the cable would exit the lower quarter panel there is a perfect spot to ground to the frame rail.

 

[ATXLX]

Where are you planning on mounting it? You shouldn't have any issues grounding to the frame, but I'd double check with someone who has a dual batt setup.

 

[RFB]

Where are you planning on mounting it? You shouldn't have any issues grounding to the frame, but I'd double check with someone who has a dual batt setup.

I have dual batteries up front this is lithium going in rear, I want a short solid ground for this thing. SO Ill go straight down and to the frame. thanks Guys

 

[Irish Reiver]

For what it is worth Richie, I ran a ground cable all the way back to the engine bay and the second battery. Overkill for sure but peace of mind..

 

[-Spike-]

For what it is worth Richie, I ran a ground cable all the way back to the engine bay and the second battery. Overkill for sure but peace of mind..

Probably underkill. The cable likely has more resistance than the frame, and especially depending on where the draw is. Overkill would be doing it both ways.

Sorry for contributing to your therapist bill...

 

[fz1boxer]

main frame and body(heavy cable),what will you be using this battery for?

 

[leonard_nemoy]

I permanently removed the third row seats in my rig and grounded my rear quarter panel amp (1000w) to the floor where the third row seat belt bolted down. This has worked great for my amp and let me use a very short ground cable... I don't know if it's any different for a battery. I was worried it wasn't a good enough ground but my buddy the electrical engineer checked it with his fluke and said it was more than adequate.

 

[Irish Reiver]

Probably underkill. The cable likely has more resistance than the frame, and especially depending on where the draw is. Overkill would be doing it both ways.

Sorry for contributing to your therapist bill...

Actually I did do it at both ends so therapy bill is back to normal.

 

[ZackR]

I permanently removed the third row seats in my rig and grounded my rear quarter panel amp (1000w) to the floor where the third row seat belt bolted down. This has worked great for my amp and let me use a very short ground cable... I don't know if it's any different for a battery. I was worried it wasn't a good enough ground but my buddy the electrical engineer checked it with his fluke and said it was more than adequate.

View attachment 1962529

Looks like a great option since its inside where the connection will stay clean and dry, plus you verified the resistance was minimal.

 

[Shoredreamer]

Make sure you ground you engine batteries to the frame too if you go that route. All need a common ground. Body, block and frame are all isolated I believe.

 

[RFB]

For what it is worth Richie, I ran a ground cable all the way back to the engine bay and the second battery. Overkill for sure but peace of mind..

yea I have that now actually pos and neg running 1 guage from auxbattery to ARB amd iverter. Im not going to need those big azz wires anymore only an 8 guage or so for redarc which will mount right next to new battery in question which is lithium. and that will now serve the ARB twin, 700watt PSW inverter and dometic, plus a couple USB plugs. so red arc feeds the lithium ground straight to a 3rd row seat mount. Im on it. thanks gents

 

[cruiserdan]

Belt and suspenders would be both to the frame and to the body. Charging current would be satisfied by the frame ground and powered accessories by the body ground.

this is lithium going in rear

Be sure to upgrade your fire suppression as well........

 

[Bambusiero]

Some things to consider -

The ground current path resistance is low, but not zero (cable / body / frame, regardless of which you choose).
So - whenever current flows, there will be voltage drop from one end of that ground return path to the other.
V = I * R
Ground resistance is usually (better be!) so low that it's very difficult to actually measure, but the effects of voltage drop from transient current events can be troublesome.

Concept to grasp:
Ground loops - if there is more than one possible ground return path, then the current will split up and take all possible paths.
How will it split? Depends on both DC resistance, and AC inductance - gets very difficult to predict.
Chassis grounding (or ground plane) is like an infinite number of parallel loops, which is much better than a few.

The issue is that there are other bits of circuitry scattered around the vehicle that rely on the chassis for 2 things.
1) Ground current return of their own smaller load currents.
2) Zero volt reference - this is the important one.

Vulnerable to I*R drop & noise trouble:
- Audio equipment - you'll hear it.
- Vehicle computers, like the ECU - measurement & control circuitry acting unpredictably.
- Added in computers - acting glitchy.

These are probably the troublemakers:
- Starter motor current - very high DC for a few seconds.
- Ignition / spark - high short transients, constantly varying with engine speed.
- Fuel injectors - medium short transients, constantly varying with engine speed.
- Inverters - 60Hz or DC, chopped & modulated at high frequency.

Dedicated isolated cable ground return:
Pro :
- Most "pure" and idealized.
- Copper cable - lowest resistance, size selectable.
- Most predictable.
- Resistance here can be thought of as internal battery resistance, with no cable.
- Least likely to cause interference with other circuitry.
- Any interference can be addressed by filtering components, if needed.
Con :
- Expense of heavy cable.
- Routing of cable.
- Body passthrough of cable.

Chassis distributed ground return:
Pro :
- Free for the taking.
- Massively parallel.
- Lowest possible AC inductance / impedance to AC loads.
- Resistance may be low enough.
Con :
- Other sensitive loads attached mid-way, sensing ground current I*R drop as noise.
- Steel - medium high resistance.
- Resistance may not be low enough.
- Difficult to predict.

Blended / hybrid approach - chassis / cable parallel ground return:
It's definitely got ground looping going on, but impossible to really control it.
Plus, what did it actually gain over the other 2 approaches? You still invested in long cables.
I would suggest staying away from this, as a basic strategy.
But, this could be added in later, as a band-aid "fix" to remedy trouble with the chassis ground approach.
Notice that modern vehicles have ground straps sprinkled all over - frame, sub-frames, several around engine.

p.s. I realized that I sort of unconsciously use the word "loops" in connection with ground current paths, by long habit, and the meaning of this might not be clear to the casual observer.
- If you can draw a schematic circuit diagram, somewhat representing the physical arrangement of connections, both to and from source and load, and returning current has a single physical pathway back to the source, then no ground loop. Situation is stable and repeatable. You always know how the current is getting back home.
- But, if there are multiple possible current return paths, then you have "loops" in the ground path - ground loops. Then, when various loads located on the various pathways turn on and off, you have return current voltage drops adding together in strange ways, causing changes in behavior. Not stable. And possibly "shocking".

 

[RFB]

Some things to consider -

The ground current path resistance is low, but not zero (cable / body / frame, regardless of which you choose).
So - whenever current flows, there will be voltage drop from one end of that ground return path to the other.
V = I * R
Ground resistance is usually (better be!) so low that it's very difficult to actually measure, but the effects of voltage drop from transient current events can be troublesome.

Concept to grasp:
Ground loops - if there is more than one possible ground return path, then the current will split up and take all possible paths.
How will it split? Depends on both DC resistance, and AC inductance - gets very difficult to predict.
Chassis grounding (or ground plane) is like an infinite number of parallel loops, which is much better than a few.

The issue is that there are other bits of circuitry scattered around the vehicle that rely on the chassis for 2 things.
1) Ground current return of their own smaller load currents.
2) Zero volt reference - this is the important one.

Vulnerable to I*R drop & noise trouble:
- Audio equipment - you'll hear it.
- Vehicle computers, like the ECU - measurement & control circuitry acting unpredictably.
- Added in computers - acting glitchy.

These are probably the troublemakers:
- Starter motor current - very high DC for a few seconds.
- Ignition / spark - high short transients, constantly varying with engine speed.
- Fuel injectors - medium short transients, constantly varying with engine speed.
- Inverters - 60Hz or DC, chopped & modulated at high frequency.

Dedicated isolated cable ground return:
Pro :
- Most "pure" and idealized.
- Copper cable - lowest resistance, size selectable.
- Most predictable.
- Resistance here can be thought of as internal battery resistance, with no cable.
- Least likely to cause interference with other circuitry.
- Any interference can be addressed by filtering components, if needed.
Con :
- Expense of heavy cable.
- Routing of cable.
- Body passthrough of cable.

Chassis distributed ground return:
Pro :
- Free for the taking.
- Massively parallel.
- Lowest possible AC inductance / impedance to AC loads.
- Resistance may be low enough.
Con :
- Other sensitive loads attached mid-way, sensing ground current I*R drop as noise.
- Steel - medium high resistance.
- Resistance may not be low enough.
- Difficult to predict.

Blended / hybrid approach - chassis / cable parallel ground return:
It's definitely got ground looping going on, but impossible to really control it.
Plus, what did it actually gain over the other 2 approaches? You still invested in long cables.
I would suggest staying away from this, as a basic strategy.
But, this could be added in later, as a band-aid "fix" to remedy trouble with the chassis ground approach.
Notice that modern vehicles have ground straps sprinkled all over - frame, sub-frames, several around engine.

yea......................

 

[Azca]

Some things to consider -

The ground current path resistance is low, but not zero (cable / body / frame, regardless of which you choose).
So - whenever current flows, there will be voltage drop from one end of that ground return path to the other.
V = I * R
Ground resistance is usually (better be!) so low that it's very difficult to actually measure, but the effects of voltage drop from transient current events can be troublesome.

Concept to grasp:
Ground loops - if there is more than one possible ground return path, then the current will split up and take all possible paths.
How will it split? Depends on both DC resistance, and AC inductance - gets very difficult to predict.
Chassis grounding (or ground plane) is like an infinite number of parallel loops, which is much better than a few.

The issue is that there are other bits of circuitry scattered around the vehicle that rely on the chassis for 2 things.
1) Ground current return of their own smaller load currents.
2) Zero volt reference - this is the important one.

Vulnerable to I*R drop & noise trouble:
- Audio equipment - you'll hear it.
- Vehicle computers, like the ECU - measurement & control circuitry acting unpredictably.
- Added in computers - acting glitchy.

These are probably the troublemakers:
- Starter motor current - very high DC for a few seconds.
- Ignition / spark - high short transients, constantly varying with engine speed.
- Fuel injectors - medium short transients, constantly varying with engine speed.
- Inverters - 60Hz or DC, chopped & modulated at high frequency.

Dedicated isolated cable ground return:
Pro :
- Most "pure" and idealized.
- Copper cable - lowest resistance, size selectable.
- Most predictable.
- Resistance here can be thought of as internal battery resistance, with no cable.
- Least likely to cause interference with other circuitry.
- Any interference can be addressed by filtering components, if needed.
Con :
- Expense of heavy cable.
- Routing of cable.
- Body passthrough of cable.

Chassis distributed ground return:
Pro :
- Free for the taking.
- Massively parallel.
- Lowest possible AC inductance / impedance to AC loads.
- Resistance may be low enough.
Con :
- Other sensitive loads attached mid-way, sensing ground current I*R drop as noise.
- Steel - medium high resistance.
- Resistance may not be low enough.
- Difficult to predict.

Blended / hybrid approach - chassis / cable parallel ground return:
It's definitely got ground looping going on, but impossible to really control it.
Plus, what did it actually gain over the other 2 approaches? You still invested in long cables.
I would suggest staying away from this, as a basic strategy.
But, this could be added in later, as a band-aid "fix" to remedy trouble with the chassis ground approach.
Notice that modern vehicles have ground straps sprinkled all over - frame, sub-frames, several around engine.

Forgive my automotive electrical ignorance. What systems/equipment on our vehicles uses AC? The alternator converts AC to DC within the enclosure, not sure what else may be AC on the vehicle?

 

[leonard_nemoy]

Forgive my automotive electrical ignorance. What systems/equipment on our vehicles uses AC? The alternator converts AC to DC within the enclosure, not sure what else may be AC on the vehicle?

A lot of times you can get AC current ripple in the DC coming from the alternator. This can cause lots of sensors to act up on newer vehicles. I have seen a few crank sensors replaced that we're good, this was caused by a bad alternator that seemed fine until an AC ripple test was ran. I don't think this happens on our old rigs but new cars with can bus systems can get weird real fast if electronics get out of whack at all.

 

[Qball]

So where and what size battery do you put in the back? I’m thinking about doing the same thing