Weird electric question about solid bare wire

[wwhitney]

Again, do the math to figure out the resistive loss and then decide if that's acceptable; all else follows from that.

Well, one constraint that will determine whether it's acceptable is the resulting temperature rise in the conductor. But I guess you're suggesting that the application will itself determine another likely lower constraint, so that the temperature rise won't be the controlling constraint?

That can still only be determined by checking the temperature rise. But I guess if the conductor size from this other application constraint is sufficiently large, it will be easy to give an upper bound on the temperature rise by comparing to one of the NEC tables that is clearly conservative for this application.

Cheers, Wayne

 

[zbang]

My point is that all the discussion of what a conductor is rated for by the NEC is irrelevant in this application, what's going to matter is acceptable loss and heat generated, and whether those affect the end result (sound), the conductor supports, or the overall setup (is 5kw of waste heat acceptable?).

Turning that around- if the supports are to be clear plexi, how much heat can they stand without melting? That itself might drive the conductor size (e.g 14g copper wire might stand the current for a while, but it'll also might start fires).

Going back to #1,
50 amp * 150 volts = 7500 watts
24' of 10g copper is about 0.024 ohm
50 amps @ 0.024 0hm = 1.2 volt drop (not much at 150 volts)
50^2 amps * 0.024 ohm = about 700 watts lost in heat (or a about 2.4 watts/foot)

However, when you reverse the numbers and have 150 amps at 50 volts.... the loss probably becomes unacceptable.

 

[wwhitney]

My point is that all the discussion of what a conductor is rated for by the NEC is irrelevant in this application, what's going to matter is acceptable loss and heat generated

Agreed that most of the NEC tables are not relevant to this application. But we can draw some inferences as to the conductor temperature as a function of current from some of the NEC tables, as per my first post in this thread (#51).

Cheers, Wayne

 

[winnie]

I think that we all are aware that NEC tables don't directly apply, and have been using them to inform the issue of conductor size to avoid overheating.

With that said, I think we weren't giving enough consideration to voltage drop issues. Pumping 150A at 50V will mean resistance is a critical issue. If this were a lab 50V 150A dc supply, I'd be looking at remote feedback of voltage at the end of the conductors.

 

[RASanders]

For the "use copper tubing!" suggestions;
- 1/4" copper tubing has roughly the same amount of copper as #8 solid conductor
- This is the largest size tubing that fits within your 0.4" hole, with a small grommet. (3/8" tubing has an outer diameter of 0.5")
- This handles the expected voltage and resistance, but at unfortunate heat rise potentially approaching the 200F softening of acrylic, but unlikely to cause a problem if you used clear polycarbonate sheet instead, as polycarbonate does not soften until above 290F.
- Are you perhaps prepared for connecting and circulating the car's coolant system "through" the copper tubing used for these connections?
- No, I have no idea whether anyone, anywhere, ever, has attempted such a thing.
- Yes, we now use liquid cooling systems in the middle of the most sensitive electronics you can imagine, right in the middle of the most expensive computers on the planet, or your neighbor's gaming PC...but nobody that I know of is also using that tubing as a carrier for the sonic boom signal of amplified sub-woofers to enhance the gaming experience.

Liquid heat-removal for solid bar conductor on display;
- Alternatively, would it be desired to circulate a clear or translucent fluid (such as one including your usual fluorescent anti-freeze) within the clear channel, water-tight acrylic assembly, until a solid conductor bar exits that portion of the system?
- Rigid water-tight sheet stock glue-joints may or may not withstand 167db vibrations over time.

but hey - we're brain-storming options here, right?