Using RF coax cable as DC Solar PV cable

[Xringer]

Originally Posted by Christ

For testing purposes, would it be sufficient to use, maybe, some prepared RG-6? I think that's what it is.

I understand that the wire is thin and the shielding is more like aluminum foil, but how well do you think it would fare for short term beta testing type stuff?

RG-6 is cable TV cable. Mostly it uses the center conductor as it's center pin.
They call them 'F' connectors. Most are crimp type.
Aluminum shielding foil isn't the best conductor. Copper mesh is way better.
The wire gauge is small..The cable itself isn't real bad. It could handle a few amps..

But the female connectors have a very smallish contact area.
I don't think they can handle much power.

[Christ]

Awesome. I have a couple friends who work for cable and satellite TV companies and have to build direct burial line all the time. I might be able to snag some bits from them to use for panel interconnects, etc of the higher quality stuff.

Teh last time a sat installer came out here, they used double-line coax [DirecTV] and it had a mesh copper ground sleeve on it.... come to think of it, there's over 200ft of it coiled in the root cellar... I may have to look into that. I'll have to change the ends on it, I think... no center pin, just has the wire poking through.

[Mikesolar]

I will only use proper solar cable because I might use strings of 13 panels which will be 500+vdc. It needs to be rated for 1000Vdc and UV rated. What is the co-ax rated for or is it even rated at all?

[Xringer]

This is RF cable. It's not designed for DC use, therefore, there is no DC voltage or current spec.
But, people have used it at high DC & AC voltages. I've used RG8 at 2,000 volts DC @ 300 to 400 watts, with no problems.
Because of the center conductor's size, there is going to be a limitation on current.
(See the loss info above). It's current squared x R.

If you had a real long run of small size wire with 2 ohms of resistance,
the loss at 10A would be 100 x 2= 200 watts of wasted power..
But, if it was 20A, 400 x 2 = 800 watts of loss.
40A would be 3.2 kW of loss.. Those wires would be kinda warm!

Here's some RG8 info on higher voltages.

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RG8 is water proof and UV resistant. It's been used outdoors for decades (radio antenna connections).

BUT, I'm pretty sure that using any kind of coax for PV won't meet code around here..
www.senecass.com/NEC2000.pdf

I don't think any city electrical inspector would allow you to use anything
that didn't meet NEC and/or local codes.


One might use Coax for low current / high voltage for PV, during an emergency when no other cable is available.
Or, you might use it strictly for experimental research or testing to see if it
is really a safe temporary replacement for NEC approved cable.

[beecrofter]

So, how large was the fire, and did you get the coax disconnected fast ?

[berniebenz]

Originally Posted by Xringer

Is that labeled as a 220v~ 3,000 amps??
That's not really going to work with a 0.66 megawatt load is it?

What uses that much power??

~~~

An AC~ breaker that had large self-wiping contacts and
a good air-gap when open might to the job on DC.
You could try it.

On any kind of switch for DC power switching,
one thing you want is speed. It's going to arc anyways,
but if you minimize the time it's arcing, the contacts will last longer.

Circuit breakers designed for breaking AC currents use the fact that AC current goes thru zero every half AC cycle. Thus arcing is short and less destructive allowing relatively small contact seperation.

Not so for DC contacters and circuit breakers. They normally use larger and faster contact seperation and often employ magnetic arc blow out devices and power factor correction.

[NeilBlanchard]

Isn't DC capacity just based on resistance and gauge?

[Xringer]

Originally Posted by NeilBlanchard

Isn't DC capacity just based on resistance and gauge?

It's all about the resistance of the wire. More resistance = more power loss.



But, if you only have small gauge wire, using higher voltage allows it to
conduct more power.

My Coax has performed pretty well at 100V at 8A..
The heat dissipation is minimal. But if I were using really small wire,
with a lot of resistance, it could get hot and even melt in half.

[Xringer]

Getting 800+ watts today. (from the 800w array) But, I noticed the sun is being reflected back into the house.



(Reflected sunlight should be pointed right back at the sun)..
That means I have to get on my snow shoes and go lower the angle of the array!
Wow, it's almost springtime!

[Christ]

For maximum /panel/ efficiency, it should reflect back at the sun... BUT, seems that if you're not using all the power you can generate, it doesn't hurt to point some solar heat gain into the walls. :P