Ground Path for High Current Accessories

[billygoat162]

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 ground (ie starter ground) comes loose the current will find its way back to the battery through other components and burn them up. I’ve also heard ground loop arguments for/against both.

The chassis is a common ground used for most small accessories, but obviously some accessories (ie winches) are intended to be wired directly to the battery’s ground terminal.

I’m wiring two audio amplifiers (500W total RMS), an air compressor (20amp), and inverter (800/1600W). I might add more stuff later, who knows. My plan is to run a single positive wire from a 100amp breaker at the battery to a distribution block in the passenger compartment for all of these, and either run a shared ground wire back to the battery or ground each accessory to the chassis and beef up the chassis to battery ground wire. I have 6ga single conductor power wire and about 100’ of 2ga 2-conductor wire (gotta love thrift stores). What’s the best way to do this?

 

[arlindsay1992]

Your 1600W inverter theoretically draws 133 amps at full throttle so the 100 amp breaker will trip if you put a decent load on it. Watts/voltage=amps. It may not be a problem if you don't actually approach that much draw.

The only thing I'd run a dedicated ground wire for is a winch. Everything I've ever added is grounded to the body. I have an 800W inverter (66 amps max) and run it through an 80 amp breaker. The breaker also powers a small amplifier and an air compressor. Both of those are individually fused down after the breaker. I don't forsee a situation where this could be a problem. I don't think I'll ever use all three at once, and even so, the inverter is only used to power small draw items so it won't likely draw anywhere near 66 amps. I have a single 4 gauge wire powering these items, and then they are individually grounded to the body.

 

[DaveInDenver]

There's no reason you can't use the frame as a high current common bus. The reason it's done with things like winches is so that the bumper connection doesn't need to be electrically sound. If you do use the frame as a bus then you have to make sure it's reliable and you don't create a situation where undersized connections get utilized should the main connection be broken.

IOW if you tie an inverter and battery to the frame with a short length of 1/0AWG at each end but for some reason the inverter pigtail comes loose then the combination of all the little grounds for your ECU and stereo are going to probably get melted. If you do a full run from the back for the inverter and it comes loose you don't put the rest of the harness at risk.

But from a performance standpoint, at least generating interference, it's actually better to use the frame than a long run. There's going to be trade-offs to balance and periodic inspection might be something you'll have to do.

 

[OllieChristopher]

Anything I ground is directly to the battery via directly off battery or buss bar. A do not do chassis or body grounds for any type of aux accessory. The factory does and it creates problems when chasing down a shorts, voltage drops, and other issues. I have been doing this for years and it is the very best, albeit little harder install. When it comes to electrical I like redundancy and simplicity when it comes to a circuit that needs diagnostics to repair. Not to mention a carbon steel frame or body is a poor conductor when compared to copper wire.

Here is an example of how I did my recent dual battery install:

These aux plugs are all wired into a fused positive/negative buss bar with 4 AWG wires directly to house battery under the hood.



All factory grounds are replaced with 1/0 and a few added. Every single ground is directly to buss bar then to battery.

 

[john61ct]

I only use chassis as the negative return path for DC devices that are

cheap and easily replaced

unimportant functionality, and

low current say under 2-3A

Otherwise round-trip wiring for the win.

 

[DaveInDenver]

I don't see any mention of what type of vehicle. On modern vehicles a continuous run to the negative terminal might circumvent the charge management as the current sense is usually in the return. Therefore if you do decide on a long run be sure to terminate it correctly, which is not at the battery terminal itself but on whatever common side of the high current sense circuit makes sense.

 

[broncobowsher]

Just looking at the factory installed 400W inverter. Mounted by the tail light. Followed the ground. Attaches to the body about 6" from the inverter. 8 or 10 AWG wire. Single 6mm machine screw attaching the copper ground lug to the body.

With as much crap as I have seen internet electrical engineers pull I trust the factory engineers a lot more than the keyboard wonder who probably has read 3 books on the subject and has zero real world engineering.

 

[OllieChristopher]

I don't see any mention of what type of vehicle. On modern vehicles a continuous run to the negative terminal might circumvent the charge management as the current sense is usually in the return. Therefore if you do decide on a long run be sure to terminate it correctly, which is not at the battery terminal itself but on whatever common side of the high current sense circuit makes sense.

Hi Dave, My model of truck is an 05 GMC Sierra with a RVC (Regulated Voltage Control). It measures the negative amps and regulates the voltage as needed. The way I did mine was to replace both of the #2 and 10AWG grounds that run through the RVC with 1/0 wire. The block wire goes from the start battery through the RVC to the buss bar. The front crossmember wire goes from the start battery through the RVC to crossmember.

They barely fit but I managed. It is 100% factory routing so as to not mess up the ECU. After the buss bar it gets interesting. All kinds of 1/0 grounds going to OEM block location next to starter, to alternator body, to top of block, to OEM chassis to block ground strap, and finally to the house battery. The redundancy I have built in is crazy solid and reliable. I have owned many GM vehicles through the years and the alternators/grounding is a weak point on the brand.



The beauty of this system is I'm able to regulate the voltage right from the cab with no special switches. Simply turn on the lights and it creeps up to around 14.7 volts. Turn off the lights and it goes into float charge. The Mechman alternator does the rest automatically regulating the amps as needed for house battery and accessories. I could have gone crazy and purchased a manual adjustable regulator. But no need because of my application. Big sound system then yes it would be needed.

 

[OllieChristopher]

Just looking at the factory installed 400W inverter. Mounted by the tail light. Followed the ground. Attaches to the body about 6" from the inverter. 8 or 10 AWG wire. Single 6mm machine screw attaching the copper ground lug to the body.

With as much crap as I have seen internet electrical engineers pull I trust the factory engineers a lot more than the keyboard wonder who probably has read 3 books on the subject and has zero real world engineering.

You have to take into consideration who your audience is. Some of us have electrical knowledge and experience far beyond the car company engineers. I agree there are poor electrical setups posted on the web. I also see some fantastic electrical builds that will put OEM to shame.

Reason that the manufacturers engineers grounded your inverter to the frame is cost. I am not positive but pretty darn sure that your factory inverter is not a pure sine wave either. Again cost. I am 100% positive that an inverter will be better served and perform better by using a ground to battery connection.

Let me give you an example of poor engineering right from the factory. I have a 2012 Beta 498. 2 things that sucked right off the bat. 1st one was wire routing. That was an easy fix.

2nd issue was hard starting cold or hot. I had a hell of a time tracking down the cause. My dealer who happens to be a master fabricator, racer, and overall engineering whiz had a simple fix. It was a damn ground issue!! The factory starter is bolted to the engine using motor and frame as a ground path. NOT GOOD!! There is one small short ground wire from top of frame to battery from the factory. I ran a 8awg ground wire directly from the battery to the starter bolt. Problem solved.

Another not so big issue is most all European bikes run a dual DC/AC electrical system. It's not bad until you have a short on the trail. I converted my Beta into a DC only system. I installed a high output stator running directly into an adjustable rectifier. IMHO this is the only way to run these bikes for reliability. Some guys go cheap and float the OEM stator ground to the regulator to achieve this. Those are the same guys who are broke down on the trail with dead batteries or failed regulators.

 

[evldave]

I leave factory wiring alone, with very minimal accessories added outside the factory wiring harness. I do this to make sure I don't mess with the core reliability from the factory. I use the factory connections and a dedicated battery.

For any of my bolt-ons (winch, inverters, compressor, trailer charge harness, solar, etc) I use a completely separate circuit including ground and a 2nd battery. This allows me to make sure all my house gear is isolated.

Specific to ground, I use dedicated (direct to battery) for my winch, my inverter (1500w), and my trailer charge harness (which doubles as my compressor connector). For all other accessories (aux lights, camera, laptop power, etc) I use a busbar connected to the battery with a single connection.

Total connections to ground post on my 2nd battery is 4 - inverter, busbar, trailer, main battery (the winch connects to main battery but is powered by both when using it)

This setup has been 100% reliable for 15 years now. I did have a short once on my trailer charge cable but it didn't cause any damage beyond blown fuse because it was an isolated circuit.

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