Copper pipe as a conductor

[Captain Goddammit]

I want to put the two Costco 115ah marine batteries under the floor up forward in my mutant vehicle, about 10 or 12 feet from where they need to connect. I'll be drawing 50+ amps from them. Heavy gauge wire is horribly expensive... I was thinking about using 1/2" copper plumbing pipe as conductors. I could hammer the ends flat, drill a hole, and bolt the cables from the batteries at one end and the cables to the load at the other.
Anyone see any electrical issue with this? The logistics will be taken care of, the pipes will be under the floor, and probably run inside PVC as an insulator.

[Canoe]

Are the 12 VDC batteries in parallel at 12 VDC or in series for 24 VDC?
Is the 50A load a momentary load or a continuous load?

The conductor has to be able to handle the current.
It will have a resistance that will cause a voltage drop and generate heat.
The insulator has to be able to handle the resulting heat.

A 12 VDC run of 12 feet with 50A will have a loss of:
~1% using 00 AWG
~2% using 2 AWG
~3% using 3 AWG
~5% using 5 AWG

http://en.wikipedia.org/wiki/American_wire_gauge

You might find some used cable at a good price. The copper inside has less salvage value than "clean" copper, as you have to strip the insulation off before it's "clean" and that work costs $. So clean $ value - the $ cost to strip it.

[Canoe]

Subbing in copper pipe.
It's not the optimum for electrical (corrosion), but you'll be using it in a dry environment and for a short period of time. It's also subject to vibration fractures over time, whereas the cable will flex.
For the type of pipe, get the wall thickness and calculate the area of the copper in a cross-section. Compare that to the area of the AWG cable in the link above.
Or compare the weight of a foot of copper pipe to the weight of a foot of the conductor.
The higher the AWG equivalent, the higher the loss and the higher the heat generated.

Going without a rated insulation for that much current?
Gives me a bad feeling.
Running it in PVC pipes.
Also gives me a bad feeling.

Copper Pipe
Type K http://www.copper.org/applications/plum ... ble2a.html
Type L http://www.copper.org/applications/plum ... ble2b.html
Type M http://www.copper.org/applications/plum ... ble2c.html

[Canoe]

1/2" Copper Tube, type K, L & M
Outer diameter 0.625
Area 0.3067962

Type, Inner Diameter, Area, Net Area, Equivalent Diameter
K, 0.527, 0.2181278, 0.0886683, 0.3360
L, 0.545, 0.2332829, 0.0735133, 0.3059
M, 0.569, 0.2542813, 0.0525149, 0.2586

AWG, Diameter
00, 0.3648
0, 0.3249
1, 0.2893
2, 0.2576

Assuming the type K, L & M alloys will conduct as well as that used for AWG cable:

Type K, ~= a little better than 0 AWG
Type L, ~= better than 1 AWG
Type M, ~= 2 AWG

I really don't like conductor running 50A in what may not be a guaranteed protected space, and then on top of that it's a bare conductor.
I really don't like the idea of PVC providing a protected space for a bare conductor.
And it's out of sight under the floor, where it will contain heat and there would be a delayed detection of a problem.
And you'd better redo the math to make sure I got it right.

Hopefully someone who knows better than I will step in.

[FIGJAM]

I can usually find used welding cable on Craig's list for a buck or two a foot.

[Sham]

Have you considered bundling multiple stranded wire together to get the size you need? You could also use a section of a heavy duty extension cord to make your connections.
Using copper pipe seems like the wrong way to get an electrical connection--although it would probably be heavy enough to work.

[TT120]

I think copper pipe would be too stiff and prone to breaking with all the bouncing and vibration from a moving MV.

You could tie all 3 conductors from a heavy duty extension cord together to make one wire that could handle the current. Do that twice and it could work.

Auto jumper cables are rated for big amps. You could tie both conductors together from a couple sets of jumper cables and that could work too.

[Captain Goddammit]

I use both conductors of an old set of about 8 gauge jumper cables for my ground wire between the starting battery and house batteries (there's a switch to connect both systems so both alternators are charging the house batteries when the engine is running) - that was my first thought but I couldn't find any better than 10-guage jumper cables lying around.

The batteries are in parallel. One is sufficient but I wanted more running time with the boat motor off.

I'm not worried about copper pipe physically breaking, it'd only be a 10-foot piece and it can be mounted with a little wiggle room. The boat doesn't flex that much. There's about 8 inches of height in the space it would occupy, and all the steering, brake, and shifting machinery is on the other side of the boat under the floor. It's a very well protected space.

I could use much larger pipe, there's plenty of room and I think I can get it in there through the front wheel well. I could also use steel pipe.

What do you think about just going heavier on the pipe? I'd use cable if I could find some but I want at least 2 gauge or bigger and I haven't had any luck scrounging up any.

My night time lighting load is down to about 350 - 400 watts with all the new LEDs (120VAC running through an inverter) but there are sometimes other loads from a few hundred watts up to occasional 900-or-so watts for things like the coffeemaker or the toaster (gotta have unfrosted strawberry pop-tarts in the morning!) There could be short-time loads around 100 amps. The boat has an 800 watt inverter and a 1200 watt inverter but I never max out both of them. Two units is mostly for fail-safe redundancy on the playa.

I could keep the batteries behind the couch where they always were, right there close to the electric panel, but (A.) the starboard side is already the heavier side and I'd like to get some weight up forward and to port, and (B.) I want the interior as clean and clear of all visible machinery as possible. It's supposed to be "magic".

[ygmir]

I've bought super heavy wire like 000 at yard sales, and Habitat, super cheap. At one military vehicle show, I bought a 50' set of military jumper cables (00) for 25 bucks, because I let the guy cut off the NATO ends and keep them for sale.
Also, many welding shops have to switch out their cables and you can get a good buy there.
If you send me an exact measurement, I can see if I have a spare piece.
If the pipe is a "one time" gig, well, It'll prolly work. Could you put a short piece of cable in the run, just to allow for movement?
How about a "ground rod" like used in electrical boxes to ground a house into soil? or oversize with aluminum wire, coating connections with "goo" against corrosion?
As stated, you could bundle smaller wire......maybe visit a Habitat store, or other used building material and get a big roll of single strand commercial pull wire cheap and combine enough to equal the size you need?

[Captain Goddammit]

I can look more for heavy cable... I have welding cable in my '55 Chevy for the trunk-mounted battery and it doesn't really start well...

I get the point about vibration and flex but I can't see a 10 foot piece of pipe having such failure if it's not rigidly mounted and just lies on the sub-floor. It ain't gonna break. There's zero physical stress on it.

I'm mostly wanting to know if it's enough conductor for a pretty high amount of current.

Or I can give up and let the starboard side be that much heavier... I beefed up the starboard side springs to compensate but I just don't like it. One rouge wave in a heavy nor'wester and I could capsize... and I'm supposed to go down with the ship!

[ygmir]

yeah but consider starting load. How big a draw is that? and what size is the welding cable?
I think the vibration/breaking concerns come from the pipe being rigidly attached to the battery posts at both ends. if the batteries are mounted solidly, and if not, the leverage of them moving.

[FIGJAM]

Would EMT work as a conductor?

It would be cheaper than copper.

Why would copper break?

Seems it would be soft enough to flex.

[Captain Goddammit]

Oh! I didn't mention it, but I intended to flatten the ends of the pipe, drill a hole, and bolt regular, short, heavy battery cables to them for connection to the batteries. I was just thinking of using pipes as cable extensions. I'd also use a regular battery cable from the load side of the pipe to the electric panel. Now I see why everyone is worried about cracks and breakage... sorry.

[some seeing eye]

#6 is fine for 50A. You need to use the "NEC Copper Wire Ampacity" column. Be sure to select high temperature insulation THHN.

Unfortunately car jumper cables are not often speced on insulation temperature, nor would welding leads necessarily be. A ground rod is steel, just plated copper, not a good idea. I have a hard time believing plumbing pipe for the same cross sectional area is going to be significantly cheaper. I don't think the resistance and cross sectional area of steel pipe is workable.

My guess is that #6 is a $1-$1.50 a foot at a home store, just to get in calibration. #2 maybe $4. Marine stores are going to have new wire with higher spec insulation up to about 2x that price. Larger sizes are what electricians pull out of building entries, industrial sites and telco facilities/data centers. I'm sure they would accept scrap value for it (especially cash), which is easily calculated. If you are buying it from an electrician, have them crimp on some lugs with their professional crimpers. Craigslist. Mr Ygmir has some great suggestions on used wire.

Just remember Tesla was right! (in the sense that AC and transformers save on wire gauge and voltage drop)

Best with the boat!

[unjonharley]

I can usually find used welding cable on Craig's list for a buck or two a foot.

What the Fig said +1

[Captain Goddammit]

Solution, ended up buying a set of 2-gauge 16 foot jumper cables, on sale. Was cheaper than just the wire in bulk or pipe, will work just fine.

[ygmir]

Solution, ended up buying a set of 2-gauge 16 foot jumper cables, on sale. Was cheaper than just the wire in bulk or pipe, will work just fine.

yay!!

[Canoe]

Solution, ended up buying a set of 2-gauge 16 foot jumper cables...

I like this solution a lot better!

Keep in mind that their cable/insulation is expected to be used in open air, not in an enclosed space. And some of the budget stuff out of china isn't rated or isn't what the rating says.
I'd run the cables secured such that they aren't touching each other and, other than the surface they're mounted on, that there's some air space around them.

If you ever do go with using such pipe, consider "terminating" the ends with cable stuck into the ends, soldered, clamped, etc..

[unjonharley]

Solution, ended up buying a set of 2-gauge 16 foot jumper cables, on sale. Was cheaper than just the wire in bulk or pipe, will work just fine.

Damn, He used his head for something besides a hat rack..

put a little grease on the terminals after it;s all hooked up.. It helps keep them clean.. Easy to clean after TTITD run..

[Token]

Wouldn't the economical solution be to move the inverters closer to the new battery location? Order of magnitude less current on 120V.

[ygmir]

Solution, ended up buying a set of 2-gauge 16 foot jumper cables...

I like this solution a lot better!

Keep in mind that their cable/insulation is expected to be used in open air, not in an enclosed space. And some of the budget stuff out of china isn't rated or isn't what the rating says.
I'd run the cables secured such that they aren't touching each other and, other than the surface they're mounted on, that there's some air space around them.
If you ever do go with using such pipe, consider "terminating" the ends with cable stuck into the ends, soldered, clamped, etc..

Oh! I didn't mention it, but I intended to flatten the ends of the pipe, drill a hole, and bolt regular, short, heavy battery cables to them for connection to the batteries. I was just thinking of using pipes as cable extensions. I'd also use a regular battery cable from the load side of the pipe to the electric panel. Now I see why everyone is worried about cracks and breakage... sorry.

[Canoe]

...If you ever do go with using such pipe, consider "terminating" the ends with cable stuck into the ends, soldered, clamped, etc..

...I intended to flatten the ends of the pipe, drill a hole, and bolt regular, short, heavy battery cables to them ...

Exactly.
Even if you clamp with a wood buffer instead of hammer the pipe flat, it's more likely to stress and fracture by that method.
And drilling a hole removes the material that handles the current, unlike bolting terminators that are formed around the bolt-hole so they maintain all their material.
Other than that, my concern about fractures is from vibration.

[Canoe]

Wouldn't the economical solution be to move the inverters closer to the new battery location? Order of magnitude less current on 120V.

Excellent point!
He needs the 50A capability for charging the batteries, but if he powers the inverters from the battery end he'll have less power loss when running off the batteries alone.

[Captain Goddammit]

It occurred to me to move the inverters forward near the batteries... I could but I really didn't want to. They go in a cabinet next to the sofa amidships, where they are reasonably well dust protected and easy to reach to turn on and off. I've been working hard to get everything out of sight, so the interior is totally "living room" with zero wiring, machinery, etc. and there just wasn't as good a place up front for the inverters. Remember, on a Burning Man mutant vehicle, form is as important as function!

And yeah, I'd still need fairly stout wires for the charging system anyway. There's a separate starting battery by the engine with a manual battery switch to connect all together; it's for tying both alternators together for max charging when all the lights are on, but it can also be used to self jump-start should the starting battery go dead for any reason, and the cables have to be robust enough for that.

There is lots of air space around them, and no moving parts anywhere in their vicinity.

There's a continuous-duty-rated solenoid that automatically connects both systems when the engine is running. You can switch it on or off, but when it's on, it activates when the key is on - so the engine is actually starting on the house batteries too unless you have the solenoid switched off. Another reason for stout cables. I might get fancy and activate that solenoid from the engine's oil pressure sensor switch so it doesn't connect until the engine is actually running... but for now screw it, it works fine, I'm up to my ears in shit to do. The only time I see it being a real issue is if I ran the house batteries totally dead and the starting battery was draining into them too much to turn the engine over, but if that ever happened I can just flip a switch and shut off the auto-connect.

[unjonharley]

You better leave enough dance floor.. So I can melt some cougars shorts.

[unjonharley]

You better leave enough dance floor.. So I can melt some cougars shorts.

[maladroit]

I was going to suggest rebar. Rebar solves everything.