Amperage of Aluminum Rod?

A

Arcygenical

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Does anyone know what the maximum amperage a 1/2" or 1/4" (diameter) aluminum rod can carry? It'd likely be a 2xxx or 3xxx series alloy if that matters.

I'm looking to carry close to 100a on a bar for some HV projects I"m looking at.

I'm assuming that, using the NEC guidelines for aluminum, at around 700a/sqin, a 1/4" bar with a cross-sectional surface area of 0.19sqin, could carry up to 130a or so using NEC standards. Would this be a good assumption?
 
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The 'allowable' carrying capacity of a conductor really depends on how hot the conductor is allowed to get ( and this is determined by what insulation...)

According to my handbook of chemistry and physics , aluminum wire is rated at 84% of the capacity of copper.

Copper 2 awg wire is ~257 mils (1/4 ") and is rated for 125 amps (bare conductor)
Copper 0000 awg wire is 460 mils and is rated for 325 amps (bare conductor)

:D
 
1/4" aluminum has a resistance of about 0.256 Ohms/1000 ft. Household wiring is rated for about 1/2W per foot (14AWG @ 15Amps), so that's probably a decent place to start. P=I^2*r, so 0.5/(100^2) = 50uOhms/foot. That puts you in 00000 gauge (getting closer to an inch!) territory. Using 1/4" aluminum at 100A puts you at about 2.5W/foot.

If you're running this type current intermittently, the smaller gauge should be fine. If you're running this type of power continuously, though, I'd recommend the larger gauge. And I hope the electric bill isn't coming out of your pocket :)

What is this for, anyway?
 
hmmm.......those numbers seem low Mohonri.....my suggestion would be 3/8 " diameter aluminum roundbar.

Tell yah what though guys.Let's put it to the test.

I have a welder on the back of my truck capable of 200+ amps ac/dc CW , a thermometer and a place to get bits of aluminum roundbar for free.

:p


I'm on holidays , it's monday tomorrow , gives me a reason to get outta bed.

:D
 
Cool !

That was fun and educational.

I'll do the bottom line first : Arcygenical , yes , the listed ratings hold up. 1/4 " diameter aluminum roundbar will do 100 amps no problem.

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The test :

Here's the welder :

bar0.jpg


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Test setup for roundbar :

bar1.jpg


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Test material is 6061 aluminum 1/4 inch diameter , 2 feet long . Test time is 30 seconds or so (the time it takes to burn a rod)....
Ambient temp is 4 c , DC voltage.

90 amps : 1 degree C rise in 30 seconds......(Maybe , it was back to 4 c so fast it might be within error.....)

125 amps : 5 degree C rise in 30 seconds.I burned a couple rods , it never got any hotter.

175 amps : 14 degree rise in 30 seconds.This is too much I suspect....

:D
 
Wow, you're a god (between this and the think tank). Thanks so much.

I'm making hard transmission lines for some HV projects like a tesla coil. Basically, I want it to look cool, be safer (lines can't cross) and I have around 400ft of 1/4" and 100ft of 1/2" stock sitting around... I'm going to dip it in plastikote a few times first, then wrap the lines in teflon tape carefully for insulation.

The 100a maximum limit was for a transmission time of about 1ms, but I'd rather be more than less careful with my first few forays into HV stuff. Sustained currents will be far below 10a.

I'm also thinking of incorporating the 1/4" lines in a new sponsored case mod I'm working on, as a way to transfer power without the rats nest of cables (like that mod using copper bus bars awhile back). But we'll see... I'd be looking at a maximum amperage of 33a per bar in this scenario.

Thanks again, it's much appreciated.
 
How high a voltage are you designing this for? Dipping in plasticote and wrapping in electrical tape isn't going to do much if you're in the KV-and-up range. I was on a project a few years back with 33kV supply, and the cables for each phase were about 3" in diameter (90mm2 cross section of the copper)
 
The Black Book - Ampacity - Aluminum wire open air, 86°F room temp @ 0-2kV
140°F - 2 AWG (110A) - Most common for house wiring)
167°F - 4 AWG (100A)
194°F - 4 AWG (110A)
 
Hehe , you are very welcome Arcygenical.

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The whole "allowable" current capacity thing is actually quite irritating.Allowable by who ?
That's the problem.There's a multitude of different 'standards' and therefore , a multitude of 'answers' to this question.Even within the National Electrical Code , the variance for 1/4" aluminum ( 2awg) is about 40 amps....

According to the NEC (handbook of chemistry and physics) , the allowable capacity for aluminum 2 awg wire , insulated with rubber (plastikote) is 75 amps.....but thats a continuous current value , designed for safe operation in residential type situations....it's been seriously derated for safety.

This is'nt that kind of situation though , this is a 'lab' type setting.When you make your own wire , YOU get to determine it's rating.100 amps is within the ballpark , giver !

:D

As far as Insulating into the Kv range I have an Idea or two , let me dig something up.

Edit :

I wanted to double check the insulation specs on the Belden 9867 30 Kv wire I've got.
My advice would be to try and avoid doing your insulation with anything 'paint-on' .Been there, done that , HV always finds the thin spots in your coatings. :p
Get some 1/4" I/D polyethylene or teflon hose and some di-electric grease....voila , nice uniform insulation.
 
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