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On my balcony I have a satellite dish and two coaxial cables attached to it. I don't use that dish, and I want to remove it and reuse those coaxial cables to power some other device on the balcony (a kind of IoT stuff).

Can I send DC power over that coaxial cable? If yes, then can I use a single cable and its centre wire as positive and outer wire mesh and foil as ground?

EDIT: my dish has LNB sign on it if it matters: enter image description here

Marian Paździoch
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  • Would you care to mark one of the answers as accepted? You have several that explain things clearly. – JRE Jun 17 '17 at 17:40

3 Answers3

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Yes, this should work fine. Even in its original application, the coax was probably carrying a DC bias to power the LNB on the satellite dish.

Assuming it's RG-6 cable, it should be good for at least 3 amps.

It's considered conventional to use the shield as ground and the core as +V, though it doesn't particularly matter from a functional point of view.

pericynthion
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  • Typical resistance per foot for rg 6? – Passerby Sep 16 '16 at 16:52
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    Consult the data sheet/specification for the actual thing you have. Don't assume that someone on the internet knows what it is. Also it would probably be nice to confirm keeping the shield as ground. –  Sep 16 '16 at 17:17
  • "Also it would probably be nice to confirm keeping the shield as ground" So do you think using 2nd cable center wire as ground is better? – Marian Paździoch Sep 16 '16 at 17:55
  • @MarianPaździoch Yes. I think it is expected to use the shield as ground unless you have a good reason. –  Sep 16 '16 at 18:24
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    @roses assuming you could find the datasheet for some random run of unmarked coax cable... it's typical to use typical numbers for standard cable. AWG reference guides are used all the time. – Passerby Sep 16 '16 at 21:11
  • @Passerby I might go so far as to take your word for the characteristics of a device (in a low risk project) but I would double check that what I have is likely to be the same thing as what you are talking about. –  Sep 16 '16 at 21:57
  • In an outdoor coax installation, the shield might be grounded, and in general coax connectors have exposed shield metal, so I'd consider it unwise to try to put any nonzero ground-referenced voltage on the shield of reused coax. I'd suggest changing your claim that it doesn't matter. – Kevin Reid Sep 17 '16 at 13:42
  • There is also the matter of noise cancellation. Carrying a signal a few hundred feet may not seem hard but it takes a lot to keep the signal readable. Running a ground through the outer mesh prevents interference from messing up the signal too much, and it also prevents your signals from radiating too much. – Drunken Code Monkey Jul 26 '17 at 01:44
  • @DrunkenCodeMonkey this is in the context of carrying DC power. – pericynthion Jul 26 '17 at 02:02
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RG-6 coax has a 18-gauge center conductor, and exhibits a resistance of 6.385mOhm per foot. Its insulation is suitable for a max of around 10A, but it may get too hot before that. Typical satellite TV operates at voltages between 13v and 18v. At 18v, a 200ft long RG6 will allow up to ~14A. However at 10A, the voltage drop is about 7.8v, so your mileage will vary.

So, yes, it is entirely suitable to carry power. That is after all what it does in a satellite TV setup. The set-top box powers the LNB through the coax.

Drunken Code Monkey
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Yes, you can. In fact, using coaxial cables to deliver power to small-scale electronics is a common engineering practice, with all corresponding approvals (EA, UL, etc). You can combine DC on coax even with AC signal transmission if you need. All TV cable amplifiers (usually located on attic) use this method of delivering DC over a single coax cable.

Using outer shield of coax cable as negative end of supply makes a lot of practical sense since it is frequently exposed at connectors and junction boxes, and it is advisable to maintain it as common ground.

Ale..chenski
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    Please note that anything standing outside with a cable running inside should be earth-grounded. You don't want lightning to follow the cable inside. – Drunken Code Monkey Sep 16 '16 at 18:57
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    @DrunkenCodeMonkey wished I could +1M on that comment. People forget that a conductive wire running outside to inside is a perfect opportunity for lightning to "pay you a visit inside". – cbmeeks Sep 16 '16 at 20:26
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    Practically speaking how does one ensure that something standing outside with a cable running inside is indeed "Earth-grounded"? – Keegan Jay Mar 24 '17 at 04:09
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    @JayKeegan, I believe that in accord with any reasonable building code, coax cables (say RG-59 for cable TV) are connected via F-F couplers that are attached to earth ground, like this one, https://www.computercablestore.com/grounding-block-single-f-type – Ale..chenski Mar 24 '17 at 06:14
  • In addition to the F-F coupler it's a good idea to ensure the antenna frame is also connected to earth. Run a thick copper wire from the coupler and antenna to a metal rod planted at least a few feet in the ground. Or run the wire the shortest route possible to a metal structure that is already grounded. – Drunken Code Monkey May 14 '17 at 04:30