I'm planning an installation of twelve 12VDC deck post cap lights, each drawing 1.6 watts. The manufacturer says the lights must be driven by a DC supply. They offer a system that uses a 50 watt supply with proprietary patch cords and splitters to connect the lights. I prefer to use less expensive standard 12/2 wire and a standard low voltage landscape transformer. What I'm finding is that most "standard low voltage transformers" output AC, not DC. Those that do output 12VDC have no built-in timers, dimmers or photocell functions. They're just power transformers that are on 24/7. What I want to do is install the power supply in the basement and turn on the lights at dust and turn them off 6 or 8 hours later. Dusk-to-dawn would be a reasonable alternative. My question is, what would a professional lighting installer use? I suppose one could use an external timer and photocell or convert 12VAC to 12VDC after the transformer but surely there's a proper power supply for 12V DC landscape lights.
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Have you considered looking at low voltage lighting control equipment? There's plenty of it out there, mostly built for commercial work (so several good quality options available)– ThreePhaseEelCommented Dec 9, 2020 at 0:35
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Is this 12/2 cable specifically for landscape lighting, or are you intending to use NM-B (commonly called Romex)?– Harper - Reinstate MonicaCommented Dec 9, 2020 at 18:19
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No, it looks like lamp cord, but bigger. It's labeled Low Voltage Lighting Cable.– RayWCommented Dec 9, 2020 at 23:03
2 Answers
I'm not sure why you're going with DC. I've put in many systems with 12 volt AC transformers with built in timers and or photo cells. The lights I've used are all LED or incandescent and they run on AC. I've got 15 fixtures in my backyard using LED bulbs hooked up to a 12 volt AC transformer. The bulbs will take AC or DC so I went with the AC. Check with some different manufacturers or do some checking at your home stores or lighting stores. They have plenty of fixtures, bulbs, etc that run on AC.
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Hi. These lights will sit atop 2.5" square aluminum posts so my options are limited. I've found only eight lights that will fit. Five of them are 12VDC and another is only listed as 12V. Of course, the ones we like are among the 12VDC options.– RayWCommented Dec 9, 2020 at 4:03
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@RayW consider making adapters that will transition from your post to whatever kind of fixture you purchase - it will open your options.– FreeManCommented Dec 9, 2020 at 13:11
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@RayW Also check with some light bulb companies because they probably have AC bulbs that will fit in your preferred DC fixtures. what's the model number for your fixture?– JACKCommented Dec 9, 2020 at 13:17
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@JACK I don't think there are light bulbs in these small lights. Here's an example. I think these consist of a circuit board with LEDs attached. I asked the manufacturer of these lights about using an AC supply. Their response: "Our lights must run on a DC transformer. Using an AC transformer will end up burning out the LED boards and cause failure."– RayWCommented Dec 9, 2020 at 15:04
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In principle, DC makes more sense because that makes the LED driver circuitry as simple as possible. Rectifying AC->DC at one point for all lights instead of at/in each light should be more efficient and reliable (one to fail instead of 'n', the LEDs themselves being super long lasting). That being said, the prices of drivers (even 120V -> low voltage DC for LEDs, as is the case inside individual Edison-base LED bulbs) is so low now as to be absurd. Commented Dec 9, 2020 at 15:06
Get the ac model and wattage you want then put a simple full wave bridge rectifier on it. A full wave bridge is 4 diodes that’s it ac goes in on the 2 terminals with squiggly lines and DC comes out on the + and - working with low voltage (the output of the transformer is simple it’s only 12-17v depending on how large a transformer and how heavily loaded. Full wave bridges in the 35 amp range can be found on E-bay for around 10$ 20 amp around 4$ all the ones I looked at had well over 60 v PIV and most 300-1000 watts so they will do just fine (I think 35 amps is the code max but if you are LED’s the space station would be able to see you at 35 amps...
Most of the electronic dusk to dawn type controls will be fine turning the transformer on and off but there are low voltage ones also.
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Great answer Ed Beal. I was thinking along the same lines, but thought it would too much into electronics on this group. BTW. The OP might want to throw a capacitor after the bridge rectifier to even out the DC, otherwise he might get a bit of flicker. Commented Dec 9, 2020 at 11:51
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A cap would flatten the ripple but I can’t see it on my work bench. I have about a dozen 4’ led retrofit lamps that the drivers all failed 60v 2 in series with a small FWB just to see how long they would last like that going on 3 years no visible flicker and the 1 amp bridges were less than 1 dollar.– Ed BealCommented Dec 9, 2020 at 14:07
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I am NOT electronics savvy, unfortunately. I can assemble specified components, but selecting components would be over my head. I do like the idea of converting the AC output to DC because it's the most straightforward. In the interest of simplicity, I found this converter on Amazon. Does that accomplish the objective?– RayWCommented Dec 9, 2020 at 15:15
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Check out Taiss / 4Pcs KBPC2504 400V 25A AC to DC Full Wave. 4 for 1/2 the price these are rated for 8x the current. the one you are looking is a ripoff in my opinion. I have no connection to them just picked the first one that would meet just about anything you could use. The terminals are standard sized and a female “spade” or disconnect crimp connector will attach them but the wires could also be soldered.– Ed BealCommented Dec 9, 2020 at 15:35
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Thanks, Ed. As you can tell, I can't be trusted selecting electronic components. I was fixated on the 12V. I take it that the actual voltage isn't relevant. What about a capacitor as George Anderson suggests? Necessary? Can you point me in the direction of one? I assume I can solder it across two terminals before connecting the wires. This has been very helpful.– RayWCommented Dec 9, 2020 at 18:10