Making wires longer

April 13, 2009 7:44 AM

I have several situations where the electrical power is a long way from the electronic device. Is it best/right to run the house power the extended distance and then plug in the device's transformer? Or best/right to plug into the 'mains power' and then run an extended run of the low voltage wire to the device?

Image a network router that has a plug in 'power brick' transformer thingy. Outputting 9v and 1A. The router wants to be about 200feet from the closest house power outlet.

Do I have to run 200' of the 110v wire with proper electrical boxes and 'to code' wiring, terminating with a proper outlet where the router is. And then plug in the router's transformer?

OR Do I cut and splice in an extra 200' of low voltage stranded wire (of same gauge) on the 12v side of the transformer and run that to the router ?

I'm thinking about heating of wires, voltage drop, electrical code issues (in the USA) ...

Any thoughts please.

I mentioned "several situations" - in 3 different locations, the devices involved so far are the above mention router, a electronic photo frame and the laptop-like computer that runs off a big 12v power brick (and the computer itself will be an a weather proof enclosure outside).

Thanks

posted by Xhris to technology (7 comments total)

R = V/I
The loss at higher voltages is lower than at lower voltages. That's why main power lines run at higher voltages.
posted by Brennus at 7:52 AM on April 13

The low voltage wire will cost a lot less than 12 or 14 gauge copper to those locations.
posted by orme at 7:58 AM on April 13

Do what Brennus says and the what powercompany does. High voltage to the target. Running 12V for that distance will lower the voltage significantly at the target.
posted by Ferrari328 at 8:04 AM on April 13

Is a simple extension cord an option? It would save holes in walls, splicing, and wiring new outlet boxes.
posted by attercoppe at 8:32 AM on April 13

What you need for the router and photo frame is a Power Over Ethernet mid-span and endpoint adapter. This will allow you to use the same cat-5 cable already running to the device. These can deliver about 12w.

Here is an example:

http://www.dlink.com/products/?sec=0&pid=332

The laptop will probably draw too much to use a 12v run. By the way, are you sure it is 12v? My Dell adaptor is 19v. Higher voltages will work better (less current). You can use this to calculate the voltage drop over a run. I'd suggest you allow no more that 5% to be safe.
posted by cosmac at 9:08 AM on April 13

The laptop will probably draw too much to use a 12v run. By the way, are you sure it is 12v? My Dell adaptor is 19v.

Just as a data point, my Eee PC's charger provides 12v at 3A.
posted by Mike1024 at 1:19 PM on April 13

There are two issues here that you need to think about.

1) Power loss over a fixed resistance will increase as the square of the current [double the current, quadruple the power loss]. This is why utilities use high voltage to move power over any distance, so from an engineering perspective, running 110v is the better choice.

2) Wiring code issues. I'm no expert on US wiring code, but especially if you're running wiring outdoors, you'll have some hoops to jump through with 110v wiring that might not be an issue at lower voltages.

An alternative approach, if you have less-stringent code requirements for low voltage wiring, but you're unhappy about running 12v is to use 2 [suitably rated] 110/24v or 110/32v transformers. Use 1 transformer to drop down to the lower voltage, which you run over your cables, and the second transformer to step up to 110v at the other end. 24v will mean 1/2 the current over the cable run [compared to 12v], 32v will be 1/3.
posted by HiroProtagonist at 9:58 PM on April 13