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Old 14-07-2009, 10:09   #1
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Suggestions for Battery Terminal Tie Rods?

I am changing my battery bank to use the tall 6 volt 8L16 flooded batteries, four of them in series/parallel to provide a large amp hour capacity at 12 volts. Because the terminals are assymetrical, the lug leads provide a challenge to routing the battery cable connectors for a series/parallel cable configuration inside the limits of the battery box. The mass of curving 2/0 cables makes access to the fill caps a challenge.

I am considering using solid flat stock, insulated with some material, and bent at sharp angles to allow conduction between all the positive and negative lugs, with exception for the final exit cables to the battery selector switch. This will only be for the house bank, the engine battery is a separate group 31.

In the past, when tying ground busses together, I have used copper pipe, flattened, with lug holes drilled, to connect the busses. I am envisioning something similar. The issue is cross-sectional area. In order to achieve equivalency with that of 2/0 battery cable, I am unsure of the appropriate size of copper pipe to use. My other option, more difficult to obtain, is copper flat stock to produce the tie rods between positive and negative posts, as well as to tie the two positives and negatives of the parallel sides.

Anyone have some suggestions for non-cable, insulated, intra-battery case tie conductors?

Here are some data servings:
2/0 cable cross sectional area = 0.1045 sq. in (133,100 mils)
4/0 = 0.1662 sq. in (
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Old 14-07-2009, 10:42   #2
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Missing data: 4/0 cable cross sectional area = 0.1662 sq. in ( 211,600 mils)
Ampacity:
2/0: 225amps at 60 degrees C
4/0: 300 amps
amp-hour capacity of battery bank = >700 Ah

Can I assume the equivalency of a 1" X 1/4" bar of copper to 2/0 cable? For the very short runs inside the case, would this material also suffice for equivalency with the 4/0 cable?
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Old 14-07-2009, 10:57   #3
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How would you ensure adequate insulation of the copper stock and maybe more importantly, how would you prevent fatigue at the sharp bends?
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Old 14-07-2009, 11:02   #4
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I would worry about rigid flat stock between batteries putting too much stress on the posts with the movement of the boat. Even a minor amount like 1/16" could damage the posts over time. Get some Welding Cable, it uses much finer strands in the copper and a more flexible cover making it much more flexible than standard battery cable.
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Old 14-07-2009, 11:15   #5
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Goto "DC Copper Busbar Ampacities"
Copper.org: Electrical: Busbar - DC Copper Busbar Ampacities

Then more info' at
Copper.org: Electrical: Busbar
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Old 14-07-2009, 13:16   #6
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Roy, I'm sure you can dig up copper bus bar stock and have it bent to fit by any competent machine shop. You might want to actually make up a set of dummy bars from corrugated cardboard or foamcore, cut to fit, before they start playing with the expensive stuff though.

Rod stock or bar stock would be a better bet than crushed pipe, simply because there's so much more carrying capacity, and once you find a supplier, you're probably going to pay less for the solid stock, by the pound. (So to speak.)

As noted though, you'd better make sure those batteries can't move or flex any, or else the solid busbars are going to be pushing the plates apart internally.
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Old 14-07-2009, 13:56   #7
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For Copper cables with 105 deg. C insulation:

2/0 Cable (Min. 125,100 cm2) rated 280 Inside Eng. Space - 330A Outside

4/0 Cable (Min. 205,400 cm2) rated 378 Inside - 445A Outside

From the table ➥ Copper.org: Electrical: Busbar - DC Copper Busbar Ampacities

330 Amp Copper Bus Bar equivalents (2/0):
1/8" thick x 1.5" wide Cu. Bus Bar is suitable for 390 A
1/4" x 1" Bar = 409A

445 Amp Cu. Bus Bar equivalents (4/0):
1/8" x 2" Bar = 503 A
1/4" x 1.5" Bar = 572 A

I 1/8" thick copper bar is quite easy to manually (w/ hammer) bend in a vice, and 1/4" is not too difficult.

Notwithstanding, Battery (cell) Interconnection Bus Bars, are not usually bent - just flat bar.

Two, half-laps of electrical tape will provide more-than adequate insulation. I'd use a colour-code phasing tape, and sleeve with heat-shrink, just because I can, cheaply*.

* Purchased in bulk, as a tradesman would, heat shrink can be purchased for $1 - $3 per foot, depending upon size.
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Old 14-07-2009, 20:37   #8
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I have 6 L16's, 3 strings of 2 batteries. The jumpers for connecting each pair in series is very small and doesn't cross any fill caps.

Each pair is connected to a set of bus bars in the battery compartment; this technique allows you to use regular cables without limiting access to fill caps.

cheers,
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Old 14-07-2009, 21:43   #9
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I used copper flat bar what had a cross sectional area of at least 2/0 cable for doing something quite similar when I was trying to save space. I found it at a place that sells recycled non-ferrous metals. In the San Francisco Bay Area it was called Alco. I would bet there is a similar place in San Diego.
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Old 15-07-2009, 09:18   #10
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Thanks folks, especially GordMay. It's illuminating how much talent and experience exists out there. For those who worry about this rigid bar system, fear not. All batteries are individually secured in a manner that eliminates such potential concerns. The terminal lugs of my L16 batteries are located awkwardly, requiring an alternative to bulky cable to make the connections in a tight fitting battery box. The box, itself, has separators to secure the bases of the batteries, ventilation is sufficient around each battery, a sealed cover, capable of supporting the full load if inverted, and forced air venting to remove fumes and keep the batteries cooler. Each cell uses Hydro-Caps to reduce water loss. 2/0 cables carry the positive and negative to respective shunt and class-T fuse units, then onward to the distribution system. I'll send pics when all is installed and more cosmetic. This won't, hopefully, be too much longer as I have to get back to the projects I was working on before the battery issue emerged. Again, thanks for the specific information I was looking for. CF is truly a resource, as well as a source of entertaining alternative views and critiques.
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Old 15-07-2009, 10:26   #11
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... I'll send pics when all is installed and more cosmetic. This won't, hopefully, be too much longer ...
Sounds premium. I look forward to the photos.
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Old 15-07-2009, 15:47   #12
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Okay, photo's, here's our current setup. What you see is the positive busbar where the three pairs of L16's are connected in parallel plus the link to the fuseholder.

As you can see none of the cables blocks access to the fill caps.

There's another busbar for the negative side.

The second photo is to please Gord because he loves to see the protective covers ;-)

ciao!
Nick.
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Old 16-07-2009, 04:07   #13
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Nick:

That’s a beautiful installation!
(I knew you had those covers hidden away, somewhere)


I used to install a short piece (4-6"?) of clear vinyl hose on the battery cables, just large enough to fit snugly over the terminal lugs. When removing cables for servicing (whatever) the hose is slipped up the cable to cover the lug, thereby preventing accidental shorting from a restless cable.
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Old 16-07-2009, 04:57   #14
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Looks good Nick. What is the bus bar on the left side for?

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Originally Posted by s/v Jedi View Post
Okay, photo's, here's our current setup. What you see is the positive busbar where the three pairs of L16's are connected in parallel plus the link to the fuseholder.

As you can see none of the cables blocks access to the fill caps.

There's another busbar for the negative side.

The second photo is to please Gord because he loves to see the protective covers ;-)

ciao!
Nick.
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Old 16-07-2009, 09:43   #15
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Looks good Nick. What is the bus bar on the left side for?
That's not a bus bar; it's the holder for the class-T fuse.

cheers,
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