Question: Auxiliary Battery Grounding

[CharlieS]

All,

I've got my dual battery setup wired, and am happy with it, but after Googling around I see that there is a debate about where to ground the auxiliary battery.

I have wired the auxiliary ground post to the nearby body ground along the inside of the engine bay. The ground point has good continuity to the battery ground and seems to work fine.

That being said, I see that some recommend running the ground direct to the starting battery ground post, others recommend grounding to the engine block, others recommend grounding to both the body and the primary battery. There doesn't seem to be a predominant opinion, or strong argument one way or the other.

I will be using this for self jump starting through a Redarc SBI, so it will see starting loads occasionally. This makes me think I need a more direct ground to the block, starter or primary battery.

I have plenty of cable, lugs, shrink wrap and a crimper, so it is easy to change if one way makes more sense than another.

I'm happy to do whatever makes sense, but would value your opinions to help me make an informed choice.

Thanks!

 

[RobW0]

Will be curious to hear what others have to say. I have mine grounded to the chassis by the aux battery, which has seemed to work fine so far.

 

[OregonLC]

If you ground to the starting battery then you're relying on that battery's ground to chassis. So you could present a situation where you're putting both battery's high amp loads on a single cable. Better to run a discrete ground from the house battery. Any chassis bolt of proper size will work. Keep the lead short, no reason to run to block.

This is not to be confused with the best practice of running separate grounds for other circuits. A Ham Radio, for example, definitely wants to have it's own dedicated ground (as well as dedicated 12V+) for both noise reduction and voltage purity. I run all of my circuits in pairs, even aux lights. It's not that much extra work and eliminates chasing bad grounds later. If you were to run a winch, I absolutely would run a SWITCHED 2ga pair. Do not allow your winch to be connected to your battery full time. I have a friend who happens to work in the industry who had contactor engage spontaneously in his garage in the middle of the night. He's lucky the house didn't burn down. It took out the battery, winch motor, and even melted the synthetic line to the drum. Massive amount of energy was released under the hood in the form of heat. Imagine dumping the full power from your battery out in a short period of time.

 

[prharper]

Will be curious to hear what others have to say. I have mine grounded to the chassis by the aux battery, which has seemed to work fine so far.

Same here.

 

[TeCKis300]

I use to build grounding kits for several vehicle models. You're current ground setup is just fine.

Nothing will ground more effectively than the steel vehicle chassis. The shortest solid wiring connection from the component to chassis is what's desired and you've done that. Dealing with ground loops and ground noise for audio systems is a different concern that doesn't really effect this topic.

Unless there's deficiencies with stock grounding straps that connect major components including engine block/body/frame which shouldn't be an issue in your case.

 

[cboyd]

If you ground to the starting battery then you're relying on that battery's ground to chassis. So you could present a situation where you're putting both battery's high amp loads on a single cable. Better to run a discrete ground from the house battery. Any chassis bolt of proper size will work. Keep the lead short, no reason to run to block.

This is not to be confused with the best practice of running separate grounds for other circuits. A Ham Radio, for example, definitely wants to have it's own dedicated ground (as well as dedicated 12V+) for both noise reduction and voltage purity. I run all of my circuits in pairs, even aux lights. It's not that much extra work and eliminates chasing bad grounds later. If you were to run a winch, I absolutely would run a SWITCHED 2ga pair. Do not allow your winch to be connected to your battery full time. I have a friend who happens to work in the industry who had contactor engage spontaneously in his garage in the middle of the night. He's lucky the house didn't burn down. It took out the battery, winch motor, and even melted the synthetic line to the drum. Massive amount of energy was released under the hood in the form of heat. Imagine dumping the full power from your battery out in a short period of time.

There was another post on Mud in the 200s section this morning talking about just such a thing.... OP on that thread was wondering why he had high parasitic load from the winch. On my 100 I dont have the winch switched, and have never had any trouble, but this is a cautionary tale.

 

[OregonLC]

There’s more reasons to have a positive means of disconnect than just fire too. Runaway winches happen. We view the contactor and remote as being absolute. In reality they fail like everything else. Being able to turn it off quickly in an emergency without needing to get out a wrench is highly valuable.