12V thru house 110V wiring

[Mark Fisher]

I have a cabin in my backyard that has been wired to the 110V grid. I
want to remove the feed cable and install solar panels.

Rather than re-wire for 12V, is there amy technical problem with using
the existing in-wall 110V wiring?

Of course, for safety, sockets and lighti fistures will need to be
replaced with 12V versions, or at least relabelled.

Mark Fisher

 

[Martin Brown]

I have a cabin in my backyard that has been wired to the 110V grid. I
want to remove the feed cable and install solar panels.

Rather than re-wire for 12V, is there amy technical problem with using
the existing in-wall 110V wiring?

Depends whether or not you mind if your shed burns down.

The current flow in the wires for a fixed power load will be roughly 10x
larger when running at low voltage 12v compared to 110v. The resistive
heat dissipation in the wires I^2R will be 100x more.

A 100W lamp at 110v draws less than an amp, at 12v it draws 8A.

I would do the sums again *very* carefully for solar power if I were
you. It generally is not at all economic if you are already on grid. How
many Ah of batteries needed and what panels & charge controller.

Most times it is a lot cheaper to hump a heavy battery around and charge
it at home than to charge it in situ by solar (or wind) power.

Of course, for safety, sockets and lighti fistures will need to be
replaced with 12V versions, or at least relabelled.

Provided you don't exceed the total current rating it might be OK. But
remember to use a low voltage automotive fuse in the circuit to protect
against accidental short circuits causing red hot cables.

I saw a very nasty fan heater failure at the weekend - one of those
oscillating ones and the power cable failed by stress fracture on the
wrong side of the thermal cutout protection. It was a filled plastic
chassis construction and well alight when the owner found it.

Regards,
Martin Brown

 

[Mark Fisher]

The current flow in the wires for a fixed power load will be roughly 10x
larger when running at low voltage 12v compared to 110v. The resistive
heat dissipation in the wires I^2R will be 100x more.

A 100W lamp at 110v draws less than an amp, at 12v it draws 8A.

I would do the sums again *very* carefully for solar power if I were
you. It generally is not at all economic if you are already on grid. How
many Ah of batteries needed and what panels & charge controller.

Hmm... maybe I should consider gas lamps and a Sterling engine.

Mark Fisher

 

[hamilton]

Hmm... maybe I should consider gas lamps and a Sterling engine.

Mark Fisher

Wouldn't running Natural Gas through the Romex be just as problematic ??

Just asking.

;-)

 

[PeterD]

I have a cabin in my backyard that has been wired to the 110V grid. I
want to remove the feed cable and install solar panels.

Rather than re-wire for 12V, is there amy technical problem with using
the existing in-wall 110V wiring?

Of course, for safety, sockets and lighti fistures will need to be
replaced with 12V versions, or at least relabelled.

Mark Fisher

I can't imagine you'll be producing much more than 20 amps per circuit
so it should work OK. I'd use a breaker panel (or fuses) to limit the
current to an acceptable level. I'm assuming you will 'buffer' with a
deep cycle LA battery, right?

Personally I'd replace the connectors/fixtures with 12V ones, for no
other reason other than you'd be able to control polarity and anything
plugged in won't accidentally be plugged into a 120 V circuit.

 

[nospam]

Hmm... maybe I should consider gas lamps and a Sterling engine.

If you are not technically competent to judge the suitability of a bit of
wire you are not technically competent to judge the suitability and cost vs
benefit of grid vs any other form of power generation.

My advice would be to leave the grid connection and wiring intact because
he will almost certainly want to use them in the future.

Batteries alone cost more than the amount of electricity at grid prices
they can charge and discharge in their lifetime.

 

[mike]

I have a cabin in my backyard that has been wired to the 110V grid. I
want to remove the feed cable and install solar panels.

Rather than re-wire for 12V, is there amy technical problem with using
the existing in-wall 110V wiring?

Of course, for safety, sockets and lighti fistures will need to be
replaced with 12V versions, or at least relabelled.

Mark Fisher

There aren't many reasons to be off grid.
1) there is no grid available.
2) you derive some personal non-economic benefit, well being,
"hey look what I can do", from being off grid.

You can live in a tent...but unless you are willing to dramatically
decrease your needs for energy, there is no economically feasible
solar system, today. No, the schemes whereby you transfer the cost
to ME thru government subsidy or force the utility to buy electricity
at inflated rates raising MY bill don't count. I don't want to pay for
your system!

The current you can get thru the wiring is the rating on the breaker.
So you get 1/10th the power. Unless your peak load on the circuit
was less than 1/10th the rating, you're gonna have a problem.
See "living in a tent" above.

You don't want to put 12VDC on 110VAC wiring. Plug in a device
with a transformer and sparks will fly. Polarity is important.
Lotsa devices have non-polarized plugs. Call up the local electrical
inspector. If he's on his toes, he won't let you do it.

I can hear the villagers lighting torches to come after me.
"No that can never happen", "I won't tell the inspector", "he
has no jurisdiction", "I'll never have any visitors who might
compromise the system"...Use common sense. Stuff happens.

Put separate 12V wiring in the place, or use an inverter and
the existing AC wiring.

Go visit newsgroups that address these issues for details, but...
Use more than 12V for your DC storage system into the inverter.

Here's how you talk yourself out of the project.
These are round numbers, but the message is the same.

Turn on everything you want to power simultaneously and spend
some quality time with the utility meter. You need at least that
much peak power plus any additional for motor starting peaks etc.

Measure consumption over an average day in the season when you
use the most energy. Multiply that by
how many consecutive cloudy days you want to survive. Times some
efficiency factor. That's how big your batteries need
to be.

Google for insolation charts for where you live. That'll tell you
how much solar energy you can expect to get from a typical winter day.
Divide that by 10 for the efficiencies of the solar system and charging
system and and and...
Divide that number into the average daily energy requirement to see
how many square meters of panel you need.

A popular number is 1KW/square meter. Depending on the efficiency of the
panels and other system components you can afford, you're looking
at 10% of that on a sunny summer day with no buildings or trees
to block any of it. But averaged over the day, it's
a lot less. And in winter it can be near zero depending on where you live.

Add up the installed cost of all that stuff.

Bottom line is that solar power is a fool's errand.
There's no way it can pencil out on an individual basis with current
technology. Unless you can get someone else to pay for it...that would be
me...and I object to my tax dollars fueling your errand.

Wiring is the least of your worries.
Find a different hobby...like convincing the tree-huggers that we
need to get some nukes on line BEFORE we kill off all the trees.

 

[Sjouke Burry]

Hmm... maybe I should consider gas lamps and a Sterling engine.

Mark Fisher

Or buy a 12v->120v ac invertor, they have about 70-80% efficiency,
and your wiring gets not loaded with unreasonable currents.
Then put in high efficiency lamps, etc.
But you will need about an acre of sun panels, and 10 or twenty
deep discharge lead battery's.
If you go for an ac invertor, higher battery voltage will be better,
use 24 or 48 volts, and choose an invertor accordingly.
That will provide better battery efficiency and less losses.

 

[Sylvia Else]

Sounds fine to me. If someone plugged a 120v appliance into the 12v
outlet, nothing dramatic would happen.

What happens when you put 12v DC across a transformer winding designed
for 110V AC?

Sylvia.

 

[Kevin McMurtrie]

I have a cabin in my backyard that has been wired to the 110V grid. I
want to remove the feed cable and install solar panels.

Rather than re-wire for 12V, is there amy technical problem with using
the existing in-wall 110V wiring?

Of course, for safety, sockets and lighti fistures will need to be
replaced with 12V versions, or at least relabelled.

Mark Fisher

I thought large solar panels were 16 to 48 volts. I think it would be
easiest to get a mini inverter that produces 120VAC rather than 12VDC.
Some will hook up to storage batteries.

12V is difficult to move any distance because the wire losses are so
high. It wouldn't be practical for more than a few feet.

 

[Jasen Betts]

I have a cabin in my backyard that has been wired to the 110V grid. I
want to remove the feed cable and install solar panels.

Rather than re-wire for 12V, is there amy technical problem with using
the existing in-wall 110V wiring?

Of course, for safety, sockets and lighti fistures will need to be
replaced with 12V versions, or at least relabelled.

Mark Fisher

As long as the wiring can handle the current you should be alright.

if you don't replace the outlets label the appliances too. plugging a
110AC appliance into 12DC could burn out motors etc, but plugging a 12V
appliance into 110 is almost certain to be spectacular.