12 volt light wiring size?

This is a 12 volt 4 watt 320 lumen RV fixture I want to use in my BOL. I want 12 mounted in various rooms powered from a wiring block off my solar batteries. I would like to limit the circuits to 3 or less. The longest run would be 60 feet with 4 fixtures. What would be the correct wire size? Each fixture only draws 1/3 amp. Would I use an inline fuse and what size if so? I plan to replace the toggle switch with a pull chain.

 

Do you have any code to comply to ?
Is this a " Shack " hidden ?
No code wire like a house
Use a combiner box as breakers & use Pyle converter from 48Vdc down to 24 & 12 Vdc (2 pyles ) 24vDC fridge , 12 V lighting & 48V solar harvest .

 

No code. Rural Texas.

 

It isn easy to calculate the losses in an electrical wire. Ohm's law states that volts equals amps times ohms, E=IR, and 3 lights would have about 1 am of current draw. If that load were 50 feet from the battery, you would have 100 feet of wire, 50 out and 50 back. One source gives the resistance of 100 feet of solid copper wire as 18 ga .64 ohms, 16 ga .40 ohms. 14 ga .25 ohms, 12 ga .16 ohms. Thus you would drop .64 volts across the 18 ga, .40 volts across the 16 ga, .25 volts across the 14 ga, and .16 volts across the 12 ga. While the 12 ga would have 1/4 the loss, in your numbers it would make no real difference and nearly all the power will be delivered to the load. If we take the same system and increase the amp draw to 10 amps, disregarding the load, the 18 ga would drop 6.4 volts while the 12 ga would drop 1.6 volts. Thus the lights or other 12 volt loads drawing 10 amps would probably work with 12 ga but would not work with 18 ga. As a kid, all the old dc lighting systems were 28 or so volts, a long string of batteries, to minimize the current draw and keep the wiring size down. Today many of the more efficient solar and wind systems are using higher voltages to the charge controller and converting it there to the lower battery voltage. Losses due to wire resistance are often called I squared R losses and as the current goes up with the same resistance, for example 1 ohm, the power loss across that 1 ohm will be, 1 amp = 1 watt, 2 amps = 4 watts, 3 amps = 9 watts and by 20 amps we are up to 400 watts. When you start designing systems it gets very complicated as it takes more voltage to push the current thru the line and then you have to figure out the effect of the load as well. If your source happens to be a wind generator, located 50 feet in the air and 100 feet from your battery bank in your house, the choice of the connecting wire and its operating voltage will determine if it works or doesn't. Please talk to someone who has done it, as the math is well beyond me. Repairing power tools, I would estimate that close to half of all those I have seen destroyed have been due to low voltage caused either by a faulty supply or an inadequate extension power cord and such damage is called abuse and not covered by the warranty..

 

^^^^^^^^^^^^Like

faulty supply or an inadequate power cord size , causing a bad voltage drop & over amperage .
Wind turbines systems use 3 phase ac wires to a rectifier , If you need to move 200' from blade to building , use High voltage AC 3 phase .
Ours is 180Vac to a 200V rectifier times 3 in grabbing all 3 legs(diode trio system ) . Very clean DC then into a Midnite CC .

I stand on my earlier post . Harvest 48Vdc battery bank use Pyle converters for 12 Vdc @ 720 Watt (lights & 12 v water pump ) & 24 Vdc pyle for a fridge danfoss fridge freezer.. The higher the battery bank voltage the more the harvest . ..
My panel string Voltage is 130Vdc to my Classics .
Its all the same bits required , but built better . If AC is needed for a drill / (hot tub ) buy a 48Vdc inverter charger , grid tie & then a generator can help when you have snow & charge the bank .
Your choice of bits will all cost about the same , BUT YOUR not limited.

Sloth

 

While this is very true, I am getting lazy in my old age. I use charts more often now, for such voltage calculations.

First, wire or cable size and run length:


Second, fuse size to protect the circuit:


Last, fuse holder or block type:

Charts stolen from Blue Sea Systems.

I hear ya, BTPost, as loudly as my electronics cluster (two class periods, rather than one) instructor. Lord knows, he stopped just short of beating that into our heads back then.

 

Asia off grid, while I totally agree with you about using charts and do so myself, they do not teach you the importance of the chart, A neat color code saying you need x gauge wire for y distance and z amps is a visual tool, but for me when you calculate it yourself for a few values, and burn up a couple air compressors, it makes the chart meaningful. A chart just doesn't get across the fact that with the same cord, going from 1 amp to 20 amps gives you 400 times more loss. Once I got that beat into my head I use the charts, but what about rewiring a 110 volt motor to 220 volts. If it draws 10 amps at 110, they will usually draw 5 amps at 220. With a given resistance, now usually in series rather than parallel, 1 will have 100 units of loss and the other 25, so that would seem to indicate the 220 would be less likely to have problems with an extension cord. In the real world, your well, air compressor, etc, it is even more important. If your cord has a 2 ohm resistance, at 10 amps it would nominally drop 20 volts, leaving the motor to run at 90 volts or close to 20 % under voltage, now if you rewire the motor to 220, with the same 2 ohm resistance cord, it will drop10 volts, leaving the motor 210 volts to run or about 5 % under voltage. One will destroy the motor and due to both the lower loss and higher voltage, the other is operating at near its peak. Once you understand the concept, you can use the tools, but if you don't understand the basics, and they are no longer taught, you can not safely extrapolate the information to other areas in the field, motors, wiring, optimal power transfer in a starter, current limits on switches and relays, etc.

An ac motor draws more current when it starts and until the back emf builds up from the rotating magnetic fields. That is one of the magic things listed in the motor codes, A, B. etc. As a general rule, it is 5 to 8 times the full load amps and determined by the actual resistance of the motor winding's rather than the inductive resistance. Thus a motor drawing 10 amps will for a brief moment when starting, or if it is locked and unable to rotate, will draw 50 to 70 or so amps. With a 2 ohm resistance in the cord etc, and 50 amps, it would be about 100 volts drop and it will have no voltage left to start the motor, as almost all will be dropped across the extension and power cord. The 220 volt motor will have a so called inrush current of 25 to 40 amps and at 25 amps, the line would drop 50 volts, leaving 170 volts to start the motor and it will probably start. Not completely true as you hopefully don't have 2 ohms of resistance in your power cord and as the voltage drops, less current will be forced thru that resistance and some more of the power will be used by the motor. End result, minus all the math, is often with a remote site, barn 200 feet from house and 275 feet from transformer, will often work fine on 220 and die a quick death on 110. Likewise a generator rated at 7,000 watts usually will only have 3500 available on the 110 leg and the full 7000 available on the 220 leg and will easily start and run a larger compressor, table saw, etc, at 220 that would burn out either the motor or the generator at 110 volts. If you do have an off grid system and hope to use it for ac water pumps, air compressors, larger table saws, etc and it will be a good distance to your out buildings, please consider a 220 volt system

Not very scientific, but over the last 70 years I have seen several hundred motors and generators that have had the magic smoke escape while running at a low voltage on 110 volts. Now dc brushed motors are a whole different kettle of fish and that would take another and even longer post.

5

 

@duane, no doubt. I agree with you.

As an aside, while I am far from being a formally educated engineer, I've always enjoyed working on various electrical projects, low voltage and high, for both AC and DC. When I was young, oh, 10 or so, I was the cause of many a fuse blowing in my childhood home.

 

I run #12 wire stem to stern for all my LED lighting 6 and 12 volt . and it all works .roughly 120 ' from the batteries.

 

Been using 12/2 for 10 years now with no problems on the battery direct 12V system, it works and nothing has melted or burned down and more important my 12V fan and the Lights work. Beyond that I will leave the OHMs, AMPS and VOLTs to folks smarter than me about that stuff.

 

One final question. My solar is designed to run thru an inverter and into to my house breakers. I can, at present, feed all the 110 circuits and selectively uses outlets and lights in each room. In my bedroom, for example, I can remove 3 bulbs and the overhead fixture will draw 4 watts and can be controlled by the existing switch. 12 volt wiring run to this location would be about 40 feet and using the fixture shown above would still draw the same 4 watts.

So the options are: 120v using regular home wiring and the inverter or 12 volt with 40 feet of wiring and bypass the inverter.

Is the 12 volt option's voltage drop going to offset over 40 feet of 12/3 going to offset any gain I realize not running the power through the inverter.

This is the inverter I am using. I don't know how to calculate how efficient it is. It uses .8 amps at idle.

https://www.amazon.com/dp/B002LGEMOQ/?tag=survivalmonke-20

I did find this in the FAQ about the inverter: Using a 100W GE Soft White Inc Light Bulb as a load the Xantrex PROwatt 2000 SW Inverter gave an efficiency of 86%. This is about the same as other inverters that I have tested. The Xantrex literature states that the Optimum efficiency is 90% and probably was taken at a different power level than I used.

 

THE MOST important is to FUSE all lines .
That way if something go's off or draws are to high.. the fuse if picked correctly for the size it limits , no fire , but blown fuse's .
On 12Vdc with 12 AWG tinned stranded I fuse max at 20 Amps, wire is rated higher , but 20amps is large for lights on LED , then we know were safe and if say a fan motor seizes up (happen here ) ,fuse blew , I was on it for tooooooo long why it was blowing .

I added a fan on the lighting circuit after the fact !! I repaired the wiring with a new fan motor and fused it at 7.5 amps after the 20 amp fused 12 AWG wire.

This is a cold storage under ground .

Sloth

 

Nope , KISS and fix the inverter draw , Real inverters sleep and search .

Spend the time to pull wall wort's out and that includes the doorbell ,builtin vac system , anything that uses power to sense or signal . 110Vac fire detectors , back lit switches .
then my inverters SS300 to a Conext ,outback,Trace Xantrex
all sleep and search . draw for the 9600 watt unit is .3 to.4 watt every 5 seconds .

Once it sees a load , awake it comes . it searches in one line leg , if the load is 220Vac the the second inverter searches , finds and then it also wakes up to 220Vac hot .
This can take up to 8 seconds .

HTH's
Sloth