Electrical – Powering LED strip lights at two different brightness

electricalled

The Plan

I am working on finishing my basement and planning on installing LED strip lights inside a lowered crown facing up.

Now where it gets complicated. I'd like the lights to have a dim setting to be controlled by a timer, on at sundown and off at midnight (easy too), but I would like the lights to come on at full brightness when the overhead lights are flipped on for the specific room. 5 zones in total, bathroom, kitchen, family room, hall and gym.

No Software

I don't want any software solutions with smart switches / dimmers, etc. (Aside from the timer switch) and no wireless anything.

Idea #1

I was originally thinking the easy way would be to have two strips, one at dim on the timer and the other controlled by the power for the light switch, but I don't like this idea because of the additional cost and I'd need 6 power supplies.

Better Idea (so I think)

I was thinking last night and thought about having two power supplies, one set to dim and one to full brightness. Then have 5 double throw relays, that are switched to low when it's not energized and then switch to full power when it gets a 120v signal from the overhead switch for the specific room. What I'm not sure about this idea is if the power supply will keep the LEDs in the different zones at constant brightness when the load increases/decreases. I'm thinking I just need a constant output voltage power supply, but I've never tried this myself.
(Not thrilled with having to run 14/2 for each overhead back to the utility room, but I can live with it. Easier than dropping the voltage and sending a 12v signal back)

Will this idea work or is there a better way to achieve my goal.

Additional info

  • No drywall in the basement yet (done with framing, plumbing and
    running electrical now), I can run anything anywhere.
  • Total is about 200' of LEDs
  • Planning on having all LED controls in one spot, utility room
  • Power for LEDs will distributed with thermostat wire.
  • White LEDs, no color.
  • Each room will have additional lights, mainly 6" recessed
  • Locale, US
  • Mostly dealing with low voltage issue here, but I need to pass inspection NEC 2020 rules.

Best Answer

Be warned that your understanding of this tech is limited and you'll need to skill up more to pull off a successful project.

The power section

OK, the way I'd do that is by having an always-on 12V (or 24V, better for the voltage drop) power supply in the basement.

I will remain silent on the question of that having a battery back-up, but, if you do have a battery back-up, that favors 12V since TVs, Internet modems and routers are readily available for 12V, not so much for 24V. 12V USB chargers are sold in more places than eggs.

The next step out of the 24V supply will be a timer with PWM dimmer, set to do that "sundown-midnight" thing that you want.

So now we have 2 power sources: Negative always-24V, and "negative sometimes" PWM 24V. LED systems use positive common.

I'd watch voltage drop like a hawk. If I found it advantageous to carry it some distance to remote distribution hubs, I'd use fat aluminum feeder for that, because it's cheap, using MAC Block Connectors for the Al-Cu splices.

The switching section

I would use 3-wire cable (e.g. 12/3*) to carry both of those, with positive common, in 3-wire cable to the switch for each LED segment. I would use these colors:

  • Black = always-negative
  • White with black marking = sometimes-negative PWM
  • Red = positive common

The switch is a 3-way switch. The "negative sometimes PWM" goes to one traveler screw, "negative always" goes to the other. The "3-way common" goes onward to the LED negative. Positive common passes through to the LED without going to the switch.

The 3-way switch either connects the LED power to "sometime PWM" or "always".

Now if you actually want "3-way" i.e. multiple switches controlling the light, that is simplicity itself: the first control position (the one power comes into) gets a "4-way" switch instead of the normal 3-way.

Complying with Code

You need to comply with Code's low-voltage wiring rules. The safest way to do that is use wiring methods legal for 120V. 90% of Code is about physical execution of work - correct wiring methods, correct terminations, etc. You are not allowed to rinky-dink this thing together in a barf of wires all over the place, like a typical workbench electronics project. You need to comply with NEC 110.12, "neat and workmanlike".

Power supplies and controllers will need to be physically installed correctly and may need to be UL approved. You may get in trouble with the AHJ for using non-approved luminaires, NEC 110.2.

The #1 area of concern is complying with the building codes regarding required lighting in any given room. There must be a light switch in the normal/expected location(s). The light switch must operate a light (a switched 120V receptacle is an acceptable substitute). You will need to satisfy the AHJ that this is good enough.

There's another reason to use 120V rated cables and wiring methods: Resale value. Later when you are selling this house, you don't want the home inspector going "WTH" and warning the buyer that the lighting circuits are bizarre and unsupportable. Also, if this experiment fails, absolutely no one will be surprised. If you make it easy to "fall back" to 120V arrangements and wiring methods, these problems become trivial, and you can proceed with confidence that you always have a plan-B.

The additional cost of wire and proper boxes is trivial compared to the advantage of avoiding difficulties with the mortgage lender and future home buyer.

* Romex for easy fallback to AC mains if stuff doesn't work. #12 not #14 for voltage drop...

...and because everywhere Code requires a 15A circuit, it accepts a 20A circuit. At the scale I do wiring, the cost diff per foot in #14 vs #12 is not large enough to justify tying up capital in a completely redundant set of wire reels, as well as having to drag those around.

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