Conductors

Tom-D

Tom-D

Taxi to Parking
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Tom-D
I need an electrical engineer to tell me which has the better conductivity
a 4/0 multi strand cable, or a solid 1/4" X 1/4 " copper bar? at less than a foot long.

They are to connect the battery pack in my coach.
 
A 4/0 cable has a cross-section of 211.6000 kcmil or about .17 sq inches.
A quarter inch square bar has a cross section of .0625 sq inches.
If the cable is also copper the 4/0 wins hands down.
Even 4/0 aluminum is better by a bit than quarter inch copper.
 
1/4" X 1/2" copper bar has an Ampacity of 234-238, from the following link: https://www.copper.org/applications/electrical/busbar/busbar_ampacities.html

So, 1/4" X 1/4" will be much less (a little less than half of 234-238, based on the 1/4" X 1" numbers)

4/0 Copper has an Ampacity of 260, from the following link.
https://www.altestore.com/howto/wire-sizing-tool-for-12-24-and-48-volt-dc-systems-a106/
The following link shows 230 - 260 depending on copper wire/cable selected:
http://encorewire.com/wp-content/uploads/amp voltage.pdf
 
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I should have explained the answer. Conductivity is all about crosssectional area and the material used. Assuming copper in both cases, it's easy to see which one is better. The 4/0 much larger than 1/4" (which is only about 1/3" along the diagonal). Hold them up together, you can easily see it.
 
Resistance goes up .4 % per degree C, so you pretty much have to get it up 45degreesF hotter to make a 10% change.
Absent knowing how much current he intends to pull through it, we really can't indicate what the issues are. The 260 ampacity Glenn posted was the NEC rule for continuous draw in building wiring. The question is how much are you drawing over how long a distance and what is the voltage drop you're willing to tolerate. For a non-continuous load like cranking an engine, you don't really have to worry about heat issues so much, just how much you're going to lose in the run of the conductor.

(Oh and yes, I am an electrical engineer).
 
flyingron said:
Absent knowing how much current he intends to pull through it, we really can't indicate what the issues are.

(Oh and yes, I am an electrical engineer).
Click to expand...
I have 4 T-125 (Trogan)6 volt batteries wired two in series then parallel to the coach DC buss.
The 4/0 cable is very stiff and to go from one battery minus to the next battery plus, this is a 6-8" distance and not a straight shot. it's more like a "S" curve. I was going to fabricate a connector. using material I have.
I do not know what the maximum current would be from one battery to the next.
Problem being I have very little clearance over the battery pack, I can't simply jump over the stuff in the way.
 
flyingron said:
I should have explained the answer. Conductivity is all about crosssectional area and the material used. Assuming copper in both cases, it's easy to see which one is better. The 4/0 much larger than 1/4" (which is only about 1/3" along the diagonal). Hold them up together, you can easily see it.
Click to expand...
When you examine the 4/0 cable it has a terminal end swaged to it. that terminal end has a cross section of about 1/8" X 3/8" between the eye portion and the swage. that part never heats or shows any signs of being the high resistance section. I'm thinking that the 4/0 cable is way over kill.
The battery pack has a fuse between the pack and the buss, (300 amp).
 
OK, just for convenience, the quarter inch bar is roughly the same as 1 gauge wire. 300A will drop 0.01V over a foot. Sounds like the bars will do fine.
 
flyingron said:
OK, just for convenience, the quarter inch bar is roughly the same as 1 gauge wire. 300A will drop 0.01V over a foot. Sounds like the bars will do fine.
Click to expand...
Thanks a bunch.. now I've to to go see what a 1 gauge wire looks like :) Wire sounds easier than the bars just solder on the terminals.
 
I wouldn't just solder, [not because you've shown us your soldering ability ;( ]. You already had a failure due to heat. I'd crimp, that's a better mechanical connection, and solder, for a better electrical connection.
 
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GlennAB1 said:
I wouldn't just solder, [not because you've shown us your soldering ability ;( ]. You already had a failure due to heat. I'd crimp, that's a better mechanical connection, and solder, for a better electrical connection.
Click to expand...
Proving you don't know a fuse (that was not soldered) from a battery connection.
The fuse failed from a loose connection. Had it been soldered it would not have had a loose electrical connection.
The next time you wish to present a solution to a problem, understand the problem, and be less condescending.
 
Why don't you put a loop in, a rigid connection to the battery sounds like you are asking for trouble down the line from vibration damage.
 
PaulS said:
Why don't you put a loop in, a rigid connection to the battery sounds like you are asking for trouble down the line from vibration damage.
Click to expand...
This is exactly what started this adventure. the Bolted connection to the 300 amp fuse came loose, which caused a high resistant connection, and burns up the fuse and holder.
In order to get to this fuse and holder I was required to remove the battery pack, While out I cleaned the batteries, serviced the water in each then recharged them.
Now that the battery tray was empty I pulled it and had it sand blasted and powder coated, and all rollers replaced due to rusted bearings.
Now that every thing is cleaned and ready for service these huge 4/0 cables are starting to turn green and are very difficult to install.
these are the short cables that attach one battery to the other. I simply want a method to make these connections a whole lot easier. I'm now thinking of a solid strap shaped to clear the items in the way.
A way to do this is to form a flat strap of copper by flatting a piece of 1/2 inch copper tube, this will be a larger cross section than is there now, because the 4/0 cable is restricted by the shape of the Eye type end swaged there now, it is less than 1/8th inch thick by 1/2 inch wide.

Any suggestions?
 
A picture is worth a thousand words, I think you have a good plan except I worry about a rigid connection (mechanical) between large masses (the batteries) basically connecting them by the terminals. I think cable will have more give than a rigid bar which will allow some flex preventing damage to the battery terminals over the long term. They sell flexible 4/0 cable for welding and probably for applications like yours. Also if the cable you have now is corroded that makes it inflexible versus new cable. If it was a stationary setup the bars would be fine, but in a vehicle you might have an issue down the road when you least want it to happen. YMMV
 
PaulS said:
A picture is worth a thousand words, I think you have a good plan except I worry about a rigid connection (mechanical) between large masses (the batteries) basically connecting them by the terminals. I think cable will have more give than a rigid bar which will allow some flex preventing damage to the battery terminals over the long term. They sell flexible 4/0 cable for welding and probably for applications like yours. Also if the cable you have now is corroded that makes it inflexible versus new cable. If it was a stationary setup the bars would be fine, but in a vehicle you might have an issue down the road when you least want it to happen. YMMV
Click to expand...
You have a point on rigidity and thus cracking. I wonder how much rigidity a copper strap that is bent to fit would have?
just so you know, these house batteries are 75 pounds each, fit tightly in the tray. and are bound down. buy they will move some.
 
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If rigidity and cracking of the solid bar is a concern, make it a "U" bend with flanges....think of the shape of the ohm symbol.
 
I think the bar would be fine, but the terminals really are only secured in plastic and lead. If you have the room I'd use some new cable with the crimp connectors, if you have enough room, put a loop in the cables to make it a little easier to install, then be done with it. Otherwise the bar should work with the caveat that you have a lot of vibration and road sock going on under way, it may not last.
 
PaulS said:
I think the bar would be fine, but the terminals really are only secured in plastic and lead. If you have the room I'd use some new cable with the crimp connectors, if you have enough room, put a loop in the cables to make it a little easier to install, then be done with it. Otherwise the bar should work with the caveat that you have a lot of vibration and road sock going on under way, it may not last.
Click to expand...
I wish I had the room to put a loop in the cable, remember this is 4/0 cable, and the battery terminals are 8-10 inches apart.
I have about 2" above the battery tray to allow it to slide in and out.
the real question I still can't answer is, how much amperage do I really need to conduct between the two batteries?
to add, the most amps I'v seen on the charger is 130 amps for less than 5 minutes then it lowers the charge rate.
 
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Instead of connecting 4 batteries, why not just get one 24 volt battery?
 
Not easy to come by 24V deep cycle batteries. I suspect he's using 6V vs 12V because it fits better in the compartment he's trying to stuff it in.
 
How about running each battery's cables out to a more convenient spot and tie them together there?
 
JAWS said:
How about running each battery's cables out to a more convenient spot and tie them together there?
Click to expand...
no room when the tray is closed.
how the batteries are arranged
the short ties
with the tray closed.
 

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A Z-configuration. 1/2" copper pipe with L fittings on each end. Short copper pipe into one end of the ell at both ends, beat until flat, drill for stud. Cover with shrink. Make it any length you want to fit odd configurations. Get crazy with 45° fittings if that fits the installation better.

Jim
 
weirdjim said:
A Z-configuration. 1/2" copper pipe with L fittings on each end. Short copper pipe into one end of the ell at both ends, beat until flat, drill for stud. Cover with shrink. Make it any length you want to fit odd configurations. Get crazy with 45° fittings if that fits the installation better.

Jim
Click to expand...
It's all in and working, tray is closed, maybe next time we do our battery maintenance.
 
I would have suggested replacing each 4/0 with two 1/0 cables. Bending would have been much easier
 
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