Electrically challenged....Help me design a house battery system

[gtbensley]

Well lets hope that doesn't happen.

 

[gtbensley]

Started running wires last night and installing the switch (I bought one rated for much more amperage as I dont want to worry). Question about grounding the house battery, should I go to the body itself which would be very easy to do or should I figure out how to run the cable through the floor and ground to the frame? The frame run would require 3 feet or so while the body would only require 8-12" run.

 

[patoz]

Technically, it should go to the frame. Look at the OEM battery and see how it's done.

Also, don't forget to install a fuse as near as possible to the positive terminal of the new battery. I use battery fuses like this...
https://www.bluesea.com/products/5190/MRBF_Terminal_Fuse_-_300A

You will need a terminal block like this to mount it...
https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A


Gotta run, later...

 

[gtbensley]

Why not the body though? That should be grounded to the frame as well? Ill poke around tonight and see how hard that will be to run it outside to the frame.

Already have a fuse set up that will go close to the battery.

 

[patoz]

Why not the body though? That should be grounded to the frame as well? Ill poke around tonight and see how hard that will be to run it outside to the frame.

Basically, it has to do with resistance. Think of the frame as a full length, one piece, bus bar, whereas the body is made up of many individual pieces joined together by nuts, bolts, screws, and welds. Each one of these joints is subject to a certain amount of resistance.

When I said frame, I forgot you will be using the second battery as a start battery also in an emergency. So as I said, look at the ground for the OEM battery. I'm betting it goes to the engine block or the starter housing. The engine block is then grounded to the frame, and the frame is then grounded to the body. If you look under the vehicle, you should see several different points of grounding between the frame ans each different sections of the body. The body is the last link in the process. So with that being said, the engine block would be my recommendation.

BTW, where are you mounting the second battery?

Check out this short article which explaines it in more detail...
http://www.hotrodwires.com/how-to-ground-automotive-electrical-system.html

And if you really want to get into the details, check out this article...
https://www.w8ji.com/negative_lead_to_battery.htm

 

[gtbensley]

I will brows those articles, thanks.

Going to mount the second battery inside the bulkhead directly behind the drivers seat. Sealed compartment with a breather to the outside.

That second link you posted is pretty deep. I never realized it was a bad idea to ground right to the negative battery post. As the author states, "some people thing ground is a ground". Thats always what I thought but I realize thats not the case. After reading that, I am under the impression either the body or frame rail will be okay to ground to....but that the body would be better?

From his math, running a ground up the the engine block would have more resistance then grounding to the body. Or did I understand that incorrectly?

 

[patoz]

I will brows those articles, thanks.

Going to mount the second battery inside the bulkhead directly behind the drivers seat. Sealed compartment with a breather to the outside.

That second link you posted is pretty deep. I never realized it was a bad idea to ground right to the negative battery post. As the author states, "some people thing ground is a ground". Thats always what I thought but I realize thats not the case. After reading that, I am under the impression either the body or frame rail will be okay to ground to....but that the body would be better?

From his math, running a ground up the the engine block would have more resistance then grounding to the body. Or did I understand that incorrectly?

I'm not sure about his math because he contradicts himself in several places, but I do know I have never seen a battery grounded strictly to the body of a vehicle. You can do what you want, but considering the distance you are from the engine, I would ground it to the frame and the body also.

Basically, what you are doing is the same as a trunk mounted installation. No matter what you do, you're still going to have to use a section(s) of cable and it should be fairly large diameter, and as short as possible.

My trunk mounted battery:

Trunk mounted batteries in metal chassis vehicles are a very special wiring situation. With a rear-mounted battery, we have to get the high starting and charging currents to the engine block with minimum resistance and high current capacity. Do not run a ground wire to the battery unless the vehicle chassis is an insulating material, like fiberglass. The vehicle chassis should be the ground lead. The battery should be high-current grounded to the vehicle chassis with short direct leads. The engine block should be high-current grounded to the vehicle chassis.

https://www.w8ji.com/battery_wiring.htm#My_trunk_mounted_battery:

 

[gtbensley]

As the title states, I am electronically challenged. I just dont have much experience with it.

I will ground to both the frame and body I think. Cover both bases and not worry about it.

 

[patoz]

That is my thinking also! :coffeedrink:

 

[gtbensley]

Hopefully get it finished up this evening.

 

[Mwilliamshs]

...Question about grounding the house battery...

...That second link you posted is pretty deep. I never realized it was a bad idea to ground right to the negative battery post...

Not always a bad idea..."The only connection to a battery post negative should be to another battery negative, the vehicle chassis, and/or the engine block."

IMO, All batteries which share any circuits should be grounded to one another as directly as possible, post-to-post being ideal. Battery to engine block, battery to body, block to frame, and frame to body grounds should be the minimum. Add a second battery and it should be either completely isolated or share all the same connections. My auxiliary battery will have junction posts for both positive and grounds due to the high number of high-amp circuits connected to them and these posts will be connected to the ground post of the starting battery directly (and the body and frame) and the positive post of the starting battery via a constant-duty relay/ACR/VSR/etc cable sized for <1% voltage drop based on ampacity charts. I use a second frame to body ground at the rear of the van as well just because the body is so long.

 

[gtbensley]

Up and running, now I just need to make everything neat and clean up and put the seat back on.

I ended up grounding to the frame as well as the body. While it might not be ideal, reading how sportsmobile just ground to a stud in the body by the rear wheel well I figured I would be just fine.

Thank you for the help everyone, it has been a learning experience.

 

[patoz]

Glad to hear that, and good luck with it!

I learned a few things myself while doing the research, so if any problems surface later on, please let us know.

 

[gtbensley]

Will do.

All and all its a pretty simple idea so hopefully nothing will go wrong. I need to play around about with charging them and also convincing myself there is no drain while the house battery is in use on the starting batteries. Also need to do some research on house battery types. I would like to use 6v golf cart batteries I think.

 

[patoz]

Will do.

All and all its a pretty simple idea so hopefully nothing will go wrong. I need to play around about with charging them and also convincing myself there is no drain while the house battery is in use on the starting batteries. Also need to do some research on house battery types. I would like to use 6v golf cart batteries I think.

Using two 6V golf cart batteries will give you 225AH, so that pretty good for your needs.

Are you going to install a volt meter(s) so you can monitor the batteries?