Dual Battery System Grounding Question

[Smoky]

I've read conflicting comments here about how to properly ground a dual battery system. One line of thinking holds that connecting the negative poles of both batteries and relying on the primary/starting battery ground to the engine is the proper approach. Another holds that grounding each battery separately - the starting battery to the engine bock and the house battery to the frame - is the proper approach. To confuse the issue further for me as a Silverado owner, connecting the two batteries and relying on the primary battery's ground seems to be recommended for new body style vehicles, which apparently have some charging system refinements that can pose risks if both batteries are grounded separately, but that old body style Silverados (like my 2007 Silverado 1500 Classic) can have their batteries grounded separately due to a less complicated charging system.

Can anyone provide some definitive guidance on this issue?

Thanks in advance...Smoky

 

[Smoky]

From said document

"Connecting and Grounding
~ Use only General Motors OEM-approved connecting devices whenever making connections to the auxiliary battery.
~ Always connect auxiliary batteries in parallel with the OEM battery.
~ Under the following conditions, the auxiliary battery should be connected to include within its circuit a device (such as an isolator, relay or switch) that will electrically separate it from the OEM battery:
~ When the auxiliary battery is used strictly as a back-up source of electrical power for engine cranking.
~ When the auxiliary battery is used exclusively to power electrical devices added by the Upfitter. To minimize electrical resistance and maintain full output voltage at electrical devices, auxiliary batteries should be securely grounded to the vehicle engine block."

So my question surrounds what I read as a contradiction between the second and last bullets. That first bullet says to connect OEM and auxiliary batteries in parallel but the last bullet say to ground the auxiliary battery to the engine block. My understanding of "parallel" means that the positive terminals of both batteries are connected, as are the negative terminals. Grounding the auxiliary battery to the engine block would mean both batteries would NOT be connected in parallel. What am I missing? Am I misreading something? Can someone give me some guidance here?

 

[e60ral]

why can you not be both in parallel and both grounded? wire the batteries in parallel and ground the auxiliary battery

 

[dwh]

The engine block thing basically means that since the alternator is grounded to the engine block, make sure that whatever add-on stuff you add has a good ground path back to there so you don't end up with voltage dropping to your loads.

In other words, devices/loads ground to aux battery (of course), and from there straight to engine/alternator ground - in order to get full alternator voltage to the loads when the alternator is running.

Or, in other, other words...don't trust frame/body grounds for battery grounding. (Which is always good advice IMHO.)


If your cranking battery has a ground to the engine, then running your aux battery ground to the cranking battery does connect your aux battery ground to the engine.


(And parallel in this context just means, "don't connect 12v batteries in series, cause that's bad m'kay?")

 

[Smoky]

All I really want to know is why some folks say connecting the negative terminal of the house battery to the negative terminal of the starting battery is correct grounding procedure while others say grounding the negative terminal of the house battery to the frame or engine block is correct grounding procedure.

 

[dwh]

All I really want to know is why some folks say connecting the negative terminal of the house battery to the negative terminal of the starting battery is correct grounding procedure while others say grounding the negative terminal of the house battery to the frame or engine block is correct grounding procedure.

Opinions. Everyone has one.

Battery to frame can make a decent ground, but for high-amp applications, it has to done right or there can be problems of high resistance where the wires bolt to the frame (problems like voltage drop and/or melted connections).

Battery to battery is simpler and has less chance of problems developing. Also easier to do correctly, and doesn't have the same tendency to generate inductive noise in radios. But can cost more in copper and be more of a pain running the wires if the batteries are far apart.

And no matter what you do, you've got to have a decent connection to wherever the alternator is grounded - probably the engine, but not always. But the cranking battery already has that, so again it's simpler to just ground the aux battery at the cranking battery.

 

[Smoky]

dwh..Thank you...THIS is what I was looking for!

 

[doug720]

You can't have too many grounds!

 

[dwh]

You can't have too many grounds!

Uh...well actually...you can...

https://en.m.wikipedia.org/wiki/Ground_loop_(electricity)

 

[doug720]

The link applies more to AC and other systems, not so much to vehicles.

Having good, solid grounds from a vehicles battery to it's engine, frame, body, starter, HF radios, etc are important, and you can not have too many!

Many critical 12 volt systems use dedicated grounds of equal length to the positive conductor, and specify the ground connects to the battery, ie charging systems, HF radios, etc.

 

[Shpook]

Ground loops absolutely can occur in 12V systems and vehicles. You should always try to ground as much as possible to the same locations.

 

[OnWalkabout]

The cable that goes to my aux battery back is grounded to the block. In the engine compartment, I have a 150 amp circuit breaker. The 4 gauge cable for a 300ah battery bank goes to the rear of the vehicle. It's grounded to the chassis in the rear with a 4 gauge cable. I have a couple if other grounding points for my six 12v outlets, the fantastic vent fan, 8 USB outlets and assorted other hardwired electronic items-fridge, lights etc. Works fine. I've a CTEK d250s and an currently adding an additional 30 amp appt charge controller.

I'm not having any problems with ground loops, but if I do, I'll add isolators to the items needing them.


Yeah, a lot of stuff, but I want outlets anywhere I may use them.

 

[Hillbilly Heaven]

My factory ground goes to both the frame and engine block. There is a Tee crimped along the cable for frame attachment then end is attached to block. For my auxiliary battery I did the same at the same locations.

Also due to the age of the vehicle and the riveted crossmembers, I ran a cable from ground point of the frame rail to the other frame rail.

 

[brentdavenport]

You can't have too many grounds!

Actually you can but that's another topic entirely.

 

[OIIIIO]

I grounded mine the frame. There were two grounds at the rear, on the frame. The grounds appeared to come from multiple electronics at the rear of the truck. I checked continuity and it was good. On assumed these were acceptable ground points as other electrical connections were grounded to these points.