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Old 12-31-2008, 07:14 AM   #1
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On the topic of 12V lighting.. DIY


I was thinking of running some 12V lighting directly from a deep cycle battery that is charged via solar panels.

Can I use regular old Decora switches to trigger the relays and can I use regular old auto relays?

What is the proper way to protect the wire pair - as in do I need to put something around the wire to protect it (such as slit loom)?

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Old 12-31-2008, 08:47 AM   #2
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On the topic of 12V lighting.. DIY


The wires need to be protected in the same manner as 120/240 volt lines although in most cities, low voltage circuits do not need junction boxes. Now splices may still not be buried in the wall without an access opening.

Relays need to be sized for the amperes being drawn in the circuit being controlled.

Most 12 volt circuits need at least 12 gauge wiring. The same number of amperes are accommodated safely by a given size wire for 12 volts as for 120 volts. Actually you will notice dimming due to voltage drop with 12 volt circuits with fewer amperes. The voltage drop within the same set of wires for the same number of amperes is the same number of volts, not the same percentage of the voltage.

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Old 12-31-2008, 09:00 AM   #3
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On the topic of 12V lighting.. DIY


Hmmm, so can I simply use 12/2 NM for 12v? I am looking at maybe 200 watts on the whole circuit so not getting anywhere near 20 amps.

Last edited by pcampbell; 12-31-2008 at 09:03 AM.
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Old 12-31-2008, 09:25 AM   #4
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On the topic of 12V lighting.. DIY


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Hmmm, so can I simply use 12/2 NM for 12v? I am looking at maybe 200 watts on the whole circuit so not getting anywhere near 20 amps.
That is getting very near to 20 A. It's almost 17 A. You could use 12-2, but you'd be better off with 10-2. You could use decora switches to control the relays, I don't think it would hurt anything, but it would be better if they were AC-DC rated, because a DC arc is hotter than an AC arc of the same amperage. But like I said, relay current is so small I don't think it matters.

Just remember, there are still codes that apply to this, even if it "just low voltage". A 12 V house fire costs as much as a 120 V house fire. I would treat these as any other high voltage circuit, and not like the "power limited" circuits. Because these are not power limited!

Last edited by InPhase277; 12-31-2008 at 09:27 AM.
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Old 12-31-2008, 10:24 AM   #5
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On the topic of 12V lighting.. DIY


Don't forget the FUSES!!!

12V dc will make the wire smoking hot in a matter of seconds.



Look into LED lights.

I wired some cabin lights in Mexico using romex. I installed automobile lampholders/lamps in standard ceiling fixtures. When we pulled up we hooked the feed to a car battery and we had lights!
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Old 01-01-2009, 03:40 PM   #6
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On the topic of 12V lighting.. DIY


Certainly an interesting project. I've toyed around with this idea in my head myself.

Just to reiterate, even at 12 volts, a deep cycle marine/RV/car battery is not "power limited" for this purpose. Such a battery supplies enough amperage to burn up any wiring should there be a short circuit. I've seen a nice set of 4 ga. jumper cables burn up in seconds from unfused current from a car battery.

So definitely use fuses. The battery power should be routed through a fuse box of some sort before it supplies anything else. I'd use the standard rules as a guideline to sizing the wires and fuses, ie, 20 amp for 12 ga, 30 amp for 10 ga, etc. (I might use an old-time home fuse box, or perhaps do some junkyard pilfering for some robust-looking automotive parts that I could adapt (I'd mount them securely inside a metal box, perhaps inside the shell of an old service panel.)

As for the switches, if it was me, I'd try find a way to eliminate the relays, because they'll be a parasitic drain on the system. When we're talking solar power, every milliamp adds up. I'd try to switch the loads directly wherever possible.

Good luck--let us know how it goes.
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Old 01-01-2009, 04:08 PM   #7
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On the topic of 12V lighting.. DIY


Amps are amps right?? I might be doing a solar install at our other property. I want to fuse everything I would be ideal for me to use a standard home breaker panel and breakers( I know lower voltage breakers or fuses should not be used with higher due to the arc possibilities but I would think higher would work fine (ac or dc). Does anyone know why or why not this may not work on 12 volts?
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Old 01-01-2009, 07:44 PM   #8
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On the topic of 12V lighting.. DIY


If you use skinny wires the extra wiring voltage drop will prolong the life of 12v incandescent bulbs, and LEDs don't much care about voltage drop since they are current driven.

The distances between the charger, battery and load can affect what how much of what wire size you need and how tolerant the system is to the wiring voltage drop.

Will you be running a 24 hr charge/discharge cycle or something different?

You might get 6w per sq. ft. of solar panels at varying voltage so you'll need some kind of switching supply to have this kind of output reliably charge batteries.

AmpĚhrs charge out of a battery ≈ 2/3rds of the charge put into it.

100 AĚhrs of lead-acid battery capacity weighs about 70#.

Last edited by Yoyizit; 01-01-2009 at 08:03 PM.
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Old 01-01-2009, 10:04 PM   #9
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On the topic of 12V lighting.. DIY


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Amps are amps right?? I might be doing a solar install at our other property. I want to fuse everything I would be ideal for me to use a standard home breaker panel and breakers( I know lower voltage breakers or fuses should not be used with higher due to the arc possibilities but I would think higher would work fine (ac or dc). Does anyone know why or why not this may not work on 12 volts?

You really want fuses/breakers rated for DC (or AC/DC). As in InPhase said earlier, a DC arc is hotter than an AC one. This means it is easier for a breaker to interrupt a short in an AC system than a DC one.
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Old 01-01-2009, 10:32 PM   #10
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On the topic of 12V lighting.. DIY


Thanks LanterDan I would most likely just make up my own panel then. I have some DC 40 amp breakers from a surplus house I could use for supplys and I could put a automotive fuse box in a cabinet for most other load circuits. The older style push in auto fused can be replace with a resetable breaker or fuses are cheap. I just liked the idea of a full pre made panel that would give a lot of room to work with.
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Old 01-02-2009, 12:16 AM   #11
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On the topic of 12V lighting.. DIY


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You really want fuses/breakers rated for DC (or AC/DC). As in InPhase said earlier, a DC arc is hotter than an AC one. This means it is easier for a breaker to interrupt a short in an AC system than a DC one.
That's why I wouldn't consider using unaltered 120 volt AC breakers--I figure, yeah, amps are amps, but I just wouldn't trust the AC breaker to break DC reliably, or vise-versa. On the other hand, a fuse is such a simple device that it couldn't possibly care whether it's AC or DC. I just figure on keeping it simple, guaranteed-reliable, and cheap. (Of course, if you have a bunch of surplus DC breakers, that's awesome! More power to you. )
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Old 01-02-2009, 08:28 AM   #12
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On the topic of 12V lighting.. DIY


My thought would have been inline automotive style blade fuses, mounted right off the battery. There are only going to be 1-3 circuits on this. I had not realized that relays have a constant draw? I'll have to do the math. Thicker wires and running through the switch might be OK. The plan was that the panels, batteries and lighting were all going to be right below each other so wiring would be minimal.

Last edited by pcampbell; 01-02-2009 at 08:32 AM.
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Old 01-02-2009, 09:53 AM   #13
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On the topic of 12V lighting.. DIY


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I had not realized that relays have a constant draw?
It takes some small amount of power to energize the relay coil.
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Old 02-16-2009, 09:26 AM   #14
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On the topic of 12V lighting.. DIY


an informative though confusing thread guys....
i've been toying with these same ideas, since i'll have access as i build new walls. so.. if/when i can afford a 100 or 200w panel for the roof, (we's po' folks) i need 12-2 to run any lights i decide to install? no problem as i'm doing all my new AC in 12-2 i got cheap at auction. Po)
i have some trailer tail-lights i've been playing with as a small light for maybe a table lamp. using a 'mower' 12v battery, my collector fully charges it within a few days, but output is only a few hours. so, i'm thinking i need deep cycle? and the wiring for car lights isn't 12g is it? i fully understand the need for fuses in the lines if i go this route, but can someone please elaborate on the need/not needing of relays? tnkx for this thread.

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Old 02-16-2009, 10:21 AM   #15
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On the topic of 12V lighting.. DIY


It has been my experience that automotive electrical parts have no specifications printed on the box or on the part. And when I search for the specifications on the internet I can't find a thing. And this information is not listed in factory service manuals for cars which use these parts.

Also the multimeters sold in automotive stores only go up to 10 amps. No wonder people frequently have fuse blowing problems with cars!

So I would use anything other than automotive electrical parts, then you will know what the parts are rated at.

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