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Old 04-07-2016, 04:30 PM   #1
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Critique my battery box and plans

This is where I am right now...



My plan is to install my disconnect/transfer switch inside the box between the batteries. I am also planning on installing my shunt on the inside/backside of the box.

Couple questions.... My interconnect cables are 2/0. I have some 4awg that should be here tomorrow. Should I use the 2/0 to run my positives to the switch or can I use the 4awg? I know they need to be the same length.

Same for the negative... My plan is to run it to a common post inside the tool box and then have a single ground exiting the box and tying into the frame where the existing ground is. Can I/should I use the 2/0 or will the 4awg be sufficient? Do the negatives off the batteries to a common post need to also be the same length?

Right now I do not have a ground coming from the converter/charger to the batteries. When I open up the belly to replace the 8awg with 4awg, should I also run a ground up to the box and tie it into the common ground inside the box?
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Old 04-07-2016, 06:56 PM   #2
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The size cable depends on the load. How much current (in amps ) do you plan to take out of the batteries at once? Are you running an inverter for example? If the load is close to what comes from the factory then 4awg is plenty. That alone would be a big step up from the 8awg used by FR. I really like your set up. When I figure out how I will post pics of what I am working on for our camper a 2504S. Running 3 group 31 combination deep cycle and starting batteries with 180 rc minunites each. Not as good as those golf cart batts that you have but at $72 each from work and they fit how could I not pass them up. I am going to run 4awg cable in place of the FR supplied 8awg. Jay
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Old 04-07-2016, 07:01 PM   #3
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TT power is 30 amp so total amperage at once should never exceed that. I doubt we will ever come close to that, anyway. My desire to replace the wire from the converter to the batteries is for proper charging from the power center. Which is also getting the WFCO 8955 unit upgraded to a 60 amp boondocker.

I am not currently planning on installing an inverter.
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Old 04-08-2016, 05:22 AM   #4
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If those batteries are not tied down somehow, I'd insulate the cover with ridged foam. Nice looking set up. Sound X like your upgrade plans are sound!
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Old 04-08-2016, 06:03 AM   #5
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If those batteries are not tied down somehow, I'd insulate the cover with ridged foam. Nice looking set up. Sound X like your upgrade plans are sound!
I would worry about packing the batteries down with a large foam bat. Better to put a piece of pressure treated 2x4 on top of each battery (perhaps with double stick) to keep them in place but let them breathe.
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Old 04-08-2016, 06:08 AM   #6
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... should I also run a ground up to the box and tie it into the common ground inside the box?
You are going to have maybe 20 feet of #4 in the run from the converter, another foot or two to the switch is not going to make any difference. #4 or 2/0 either way. Whatever you have and whatever makes you feel better. Performance wise it makes no difference.

Equal length is only necessary if you are going to charge both in parallel.
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Old 04-08-2016, 06:21 AM   #7
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I'm not going to tie them down, per say. I'm going to take up free space with blocking. There isn't enough room above the batteries for anything and in fact, I need to do a little trimming on the brace that runs length wise on the lid. It just clears now but it's to close for comfort to the battery posts.

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Old 04-08-2016, 06:27 AM   #8
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You are going to have maybe 20 feet of #4 in the run from the converter, another foot or two to the switch is not going to make any difference. #4 or 2/0 either way. Whatever you have and whatever makes you feel better. Performance wise it makes no difference.

Equal length is only necessary if you are going to charge both in parallel.
Thanks.

All my positive leads will be equal length inside the battery box. Do the negatives coming off each bank also need to be equal length to the common connection inside the box? I do want to maintain the ability to charge them in parallel since that will help maintain equality between the banks. My only reason for using the switch I am using is if one bank goes afoul. You're reasoning for charging both banks at once makes more sense than separating them.

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Old 04-08-2016, 06:52 AM   #9
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I didn't see any mention on venting.
That many batteries in that small of area will need plenty of venting for off gassing. 🏻️
Looks good!


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Old 04-08-2016, 07:25 AM   #10
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Acid absorbent material under the battery?
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Old 04-08-2016, 07:52 AM   #11
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Not to rain on anyones parade.......but if that is aluminum.......any spilled Sulfuric acid will eat it up and create more Hydrogen Gas......more so than what the batteries are themselves are throwing out if they are wet batteries.
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Old 04-08-2016, 08:26 AM   #12
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Thanks....I do want to maintain the ability to charge them in parallel...
if you want to charge them in parallel then both banks need to have exactly the same wire lengths up to the point that they come together. In your case that is the selection switch. There is only one wire from that point on. I assume that you are using a 1-2-Both-off marine switch. That means identical length and gauge from the batteries to the switch and to the common ground. Any reasonable gauge will do.
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Old 04-08-2016, 08:27 AM   #13
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Perfect, thanks.

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Old 04-08-2016, 08:31 AM   #14
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Opie, I wonder why you have this many batteries. I don't know what kind of camping you do, and / or how you plan to recharge them. If you go camping for a couple of days and then use shore power to recharge via the factory converter / charger? I can tell you the low charging voltage as well as the inability to program to match the needs of the batteries is problematic for these cheap units. Both, in performance and providing long life to your batteries.

The first thing I would add is a good monitor and Trimetric (such as the TM-2030); without one, you will be guessing how many AH you are using or when you need to conserve or charge. This typically requires either a 100A or 500A shunt in series with the negative side to frame ground.

I would also add a 300A catastrophic fuse on the positive side.

I would also suggest getting a marine type switch that allows battery string 1, 2, both or none to be switched and connected to the negative side. I reasoned the switch or a cable if contacting the box will be less harmful that if a + was to contact. It is handy to cut all power or to only one string for maintenance.

The shunt size depends on the total amp load, whether charging or using. At around 800 A and below get a 100A shunt; over that use a 500A shunt.

You question about the wire gauge size to the WFCO, I would go with a #4. Again, in my case I have 75 Amp charger in an Inverter and don't charge across this small cable. But, I have the factory Converter / charger in place but switched off "just in case" I ever need it.

BTW, charging can be accomplished with a good charger in several hours via shore power or generator, but the time frame drove me towards solar to do this. The factory converter charger could take, actually, days to get to maybe 90% full, while PV is doing this silently and for very little dollars, over the long run.

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Old 04-08-2016, 08:36 AM   #15
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I didn't see any mention on venting.
That many batteries in that small of area will need plenty of venting for off gassing. 🏻️
Looks good!


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Once I get everything where it's going to sit I will cut in some vents.

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Old 04-08-2016, 08:37 AM   #16
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Acid absorbent material under the battery?
I will look into it, thanks for the suggestion.

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Old 04-08-2016, 09:17 AM   #17
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Not to rain on anyones parade.......but if that is aluminum.......any spilled Sulfuric acid will eat it up and create more Hydrogen Gas......more so than what the batteries are themselves are throwing out if they are wet batteries.
I didn't know that and will be cautious. Thank you.

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Old 04-08-2016, 09:18 AM   #18
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Wolf,

I will address all your points this evening when I have a computer.

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Old 04-08-2016, 09:53 AM   #19
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WW, thanks for all the good info! Would you please elaborate on the purpose and importance of a "catastrophic fuse"? Perhaps a picture or two of where you placed yours and why? I've heard of this fuse on this forum before but it was a long time ago. I would really appreciate it! Thanks!! PT1655
P.S. Opie, great write up and battery box setup!
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Old 04-08-2016, 02:33 PM   #20
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Speaking of battery boxes, can you just mount battery's in the rack on the tongue of a TT?? Only have one battery and want to add another. 400watt solar, 200w portable & 200w on roof. 18 days camping 2016, 7 more the 14th on Grand lake, OK
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