Question about battery wiring (with diagram)

[JoshInReno]

You guys have been great! A little background:

I have two group 27 batteries I am installing on my trailer. My trailer did not have an existing electrical system. I know to connect the batteries + to + and - to - for parrallel. I am using 4AWG cables to connect the batteries. I am then running a 10AWG (red) wire to my fused switch panel, and running a 10AWG (black) wire to my ground block.

So my question:

1. Do I need to ground the battery bank to the frame of the trailer? If so, should I run an additional 4AWG cable, or is the 10-12AWG lead coming off the battery cable sufficent? And does it matter which negative post I run it off of?

2. Does this all look right:

[dh]

The diagram looks good.

Are you using the trailer as a ground? I personally wouldn't, but would ground everything to a grounding strip and run a single wire from the strip to the battery bank.

The ground wire guage will need to be the same size as the + wire going to the fuse block/distribution pannle. You have X amps going out, and X amps comming back. The heavier stuff tying the batteries together is to reduce resistance between them which hleps them act as one better as far as charging and discharging evenly goes.

[Shadow Catcher]

I will second dh and add there is no good reason to ground to the frame. I will add however that the two batteries need to be identical including age and condition otherwise they settle to the condition of the "weaker" of the two batteries.

[JoshInReno]

The diagram looks good.

Are you using the trailer as a ground? I personally wouldn't, but would ground everything to a grounding strip and run a single wire from the strip to the battery bank.

That really is the basis of my question - which I probably didn't ask the right way. Let me see if I can explain it better:

The body of my trailer is fiberglass - so none of my electrical is self-grounding. I have a 10AWG wire running from one of the negative terminals to a ground buss. The negative side of my lights are connected to this ground buss, which runs back to a negative terminal. The question is, do I ALSO need to ground the battery bank to the frame? In the diagram, this question is listed as FRAME?

I really hope I am asking this question in the right way - thanks for your patience.

[JoshInReno]

double post

[JoshInReno]

I will second dh and add there is no good reason to ground to the frame. I will add however that the two batteries need to be identical including age and condition otherwise they settle to the condition of the "weaker" of the two batteries.

They are basically identical.

[eamarquardt]

I will second dh and add there is no good reason to ground to the frame. I will add however that the two batteries need to be identical including age and condition otherwise they settle to the condition of the "weaker" of the two batteries.

They are basically identical.

Unless they are identical identical you would be wise to keep them only connected together while charging. If always connected together and they are not identical you will not get the maximum life out of them. Better, IMHO. to have a 1/2/Both switch.

Hope this helps.

Cheers,

Gus

[JoshInReno]

I will second dh and add there is no good reason to ground to the frame. I will add however that the two batteries need to be identical including age and condition otherwise they settle to the condition of the "weaker" of the two batteries.

They are basically identical.

Unless they are identical identical you would be wise to keep them only connected together while charging. If always connected together and they are not identical you will not get the maximum life out of them. Better, IMHO. to have a 1/2/Both switch.

Hope this helps.

Cheers,

Gus

Thanks for the response. They are the same brand, manufactured a month apart, bought new and have been on a Battery Tender since I bought them. I HOPE they will be ok.

[dh]

Those sound identical enough, assuming same modle/AH rating...

[dh]

There are many arguments for and against grounding the frame. It is not required, but I personally chose to.


If you choose to ground the frame, use the same - battery terminal as is connected to the - terminal strip, as depicted in your diagram and run a 10g wire to match, no smaller. The reason being that if you have a short somewhere, your + terminal will be fused for a 10g wire, and may not blow, while the 12g ground wire overheats.

[JoshInReno]

There are many arguments for and against grounding the frame. It is not required, but I personally chose to.


If you choose to ground the frame, use the same - battery terminal as is connected to the - terminal strip, as depicted in your diagram and run a 10g wire to match, no smaller. The reason being that if you have a short somewhere, your + terminal will be fused for a 10g wire, and may not blow, while the 12g ground wire overheats.

Thanks - got it.

Now one more question and I THINK my system will be complete. Can I wire my solar charge controller to the "empty" terminals in my bank, or is there a better place to attach them?

[bdosborn]

There are many arguments for and against grounding the frame. It is not required, but I personally chose to.

There are a lot of good reasons to ground to the trailer frame that have been discussed to great length. AND, its required by the national electrical code and every commercial trailer has it.

You didn't say whether your batteries are 12V or 6 volt. In parallel is correct for 12V batteries.

Don't forget the fuses!
Bruce

[JoshInReno]

There are many arguments for and against grounding the frame. It is not required, but I personally chose to.

There are a lot of good reasons to ground to the trailer frame that have been discussed to great length. AND, its required by the national electrical code and every commercial trailer has it.

You didn't say whether your batteries are 12V or 6 volt. In parallel is correct for 12V batteries.

Don't forget the fuses!
Bruce

Will be grounded to the frame for sure. Already drilled the holes.

Yes, 12 volt batteries. 2 group 27's were installed in their boxes on the tounge yesterday.

And no worries about the fuses - I followed the diagrams on this site closely.

But it really is ok to use the same 10AWG wire I've been using to ground the bank??

[bdosborn]

Will be grounded to the frame for sure. Already drilled the holes.

Yes, 12 volt batteries. 2 group 27's were installed in their boxes on the tounge yesterday.

And no worries about the fuses - I followed the diagrams on this site closely.

But it really is ok to use the same 10AWG wire I've been using to ground the bank??

The #4 requirement comes into play if you're running an inverter and pulling a lot of amps from the batteries. A #10 should be fine if that's the size of your main feed from the battery to your fuseblock. I can look up the code tomorrow at work if you want the size required there.

Bruce

[Breytie]

Can I wire my solar charge controller to the "empty" terminals in my bank, or is there a better place to attach them?

I would not. If the battery gets disconnected for any reason while the panel is charging, you may get a very high and damaging voltage from the panel fed to the loads - not good!

Rather feed it straight to the battery via it's own fuse.