Learned an important lesson regarding wire gauge for DC power

[MarkEHansen]

Looking back, I realize I didn't plan this very well. In my trailer, I have a couple shelves behind the flat-screen TV. I wanted to install some components to make watching TV/Movies easier without any network connection. The specific components don't matter for this story, just that the combined set was going to draw a little under 15 Amps of 12vdc power.

I decided that the single 12v cigarette lighter-style power outlet in the area was not going to provide enough current to run the whole set, so I decided to make a dedicated 12v power run from the power panel - utilizing a spare fuse location in the panel.

For the wire run, I thought I would be just fine with 14awg, 2-conductor wire. Why did I think this? For the life of me I can't remember.

After running the new power line and setting up all the equipment, including a dedicated fuse block, everything seemed to work - I thought I was done.

Later, it was having problems, like the TV turning off when I tried to change inputs, or just turning off once the screen tried to light up. I checked the voltage at the dedicated fuse block (in the entertainment area) and found that when the TV was on (and the screen was lit), the voltage dropped to about 10 volts. Also, the power wires were getting pretty hot.

I checked a wire gauge chart like this one:

https://www.bluesea.com/resources/1437

and found two mistakes I had made:

1. When considering the length of my wire run (from the trailers power panel to the entertainment closet's fuse block), I didn't consider the return trip. When my run was 15 feet, that's actually a 30 feet circuit.

2. The 14 gauge wire was totally inadequate for the 15amp load - by a lot.

I installed a new 8 gauge power cable with a 15 foot run. Based on the chart (above) this provides enough capacity for a 15amp load. Everything is working fine. The voltage at the entertainment center is a lot better (12.3 volts while the voltage at the battery is 12.6 volts) and the wires are no longer getting hot.

I really found that it takes a lot heavier wire than I thought to provide the necessary current over a given length from the power source.

Lesson learned: Use the published chart and size the wire as needed for the load.

[wiredgeorge]

Why did you decide to hook up your variouis electronics via DC as opposed to AC? I have pretty much a similar set up and have a power strip plugged into the AC behind my television and no issues. Of course, I don't dry camp so that might be an answer; always plugged into shore power.

[MarkEHansen]

Oh, dry camping. I would like to be able to run everything off of the 12v system.

[Frank G]

Mark, don't feel bad about getting cought up in the large conductor sizing of DC power distribution. It plagued Thomas Edison and his plans for electrifying the world with DC allowing George Westinghouse with the help of Nicola Tesla to forge ahead with AC power and distribution systems. The rest is history.

[skids]

Originally Posted by Frank G

Mark, don't feel bad about getting cought up in the large conductor sizing of DC power distribution. It plagued Thomas Edison and his plans for electrifying the world with DC allowing George Westinghouse with the help of Nicola Tesla to forge ahead with AC power and distribution systems. The rest is history.

True, true!

[LHaven]

Originally Posted by Frank G

Mark, don't feel bad about getting cought up in the large conductor sizing of DC power distribution. It plagued Thomas Edison and his plans for electrifying the world with DC allowing George Westinghouse with the help of Nicola Tesla to forge ahead with AC power and distribution systems. The rest is history.

I had a professor for History of Technology who was a wealth of fascinating anecdotes. Edison was quite the street-brawler when it came to business practices. During this particular platform battle, he bid on and won the contract for NYC's first electric chair. He publicized the fact that, unlike his own residential electric system, the chair would be powered by the new and terrifying principle of "alternating current electricity."

He also tried to get the NYC officials to announce upcoming executions by saying that such-and-such a criminal was scheduled to be "Westinghoused," but he never did get any traction on that.

Naturally, the first executions were travesties. The condemned twitched and jumped interminably, and smoked wonderfully, but never actually died. He ended up losing the contract, and his equipment was replaced by a DC unit, as they all eventually were.

[sourdough]

Mark please forgive me but I just wanted to expound a little on the AC vs DC conversation. I worked with both and they were both fascinating but had their own uses. Here is just a little excerpt about the evolution of the electric chair...AC vs DC.

The introduction of the electric chair was accompanied by a secret, and very high-level, war between the proponents of Direct Current (DC) electricity (Edison) and Alternating Current (AC) electricity (Westinghouse). The electric chairs used a thousand-or-so volts of AC to electrocute the prisoner. Edison (the DC man) secretly funded the research into AC electric chairs, so that the citizens would refuse to have Westinghouse's AC electricity in their houses. On hoarding read, "Do you want electrocutioner's current in the your children's bedroom wall?". In retaliation, Westinghouse secretly paid out hundreds of thousands of dollars in lawyer's fees to try to stop the electric chair execution of the axe murderer, William Kemmler. He was unsuccessful, and Kemmler became the first person to be executed in the electric chair in Auburn Prison, NY, on August 6, 1890. Edison had won the war but he lost the battle. AC became the accepted form of electricity sold in the USA, because of its technical advantages.

There is a lot more on the evolution, and distribution, of AC vs DC but is is pretty interesting if you are into that sort of thing. As you found in your attempts "thar's stuff in them weeds". Back to regular programming....and thanks for the heads up to all.

[flybouy]

Mark, just a guess, but perhaps your “brain flatulence” was thinking that an A.C. circuit of 15 amps requires #14 AWG min size. Maybe that just jumped a few synapses over to the dc thoughts?

It happens.

[MarkEHansen]

Yeah, brain damage... Now that's something I can get behind!