Low Voltage Lighting Control with Raspberry pi

Loxone Mon, 03/25/2013 - 01:20


Here you will learn how to control and dim low voltage LED lighting with your Raspberry pi. Emphasis is placed on energy efficient lighting sources which can be run on 12 VDC. The benefit oof 12VDC of the standard 16 VAC typically used by electricians is the ability to back up the lighting power with a battery source. In addition, low voltage lighting can also be more easily powered by alternative energy sources such as solar panels, wind generators, and small scale water driven turbines. I guess you can call it Green lighting, or the ever growing "Eco" lighting. Unlike CFL's and 110 VAC LED bulbs, the impact on the environment as well as copper usage and energy efficiency is more favorable when using 12 VDC lighting sources.

Number of Transformers / Power Supplies

- Unlike the ever popular screw in 110 VAC or 220 VAC screw in light bulb replacements for standard incandescent light bulbs, 12 VDC lighting sources are far more efficient. First of all, LED's typically run on approximately 3 VDC. Simple math combined with Ohms law will tell you there is far more waste heat when you rectify and drop 110 VAC down to 3VDC vs dropping 12 VDC to 3VDC. Yes, we are always starting out at line voltage when running a typical 12VDC power supply, however, with the screw in 110/220 VAC LED replacement bulb option, we are dealing with a transformer, rectifier and voltage regulator in EVERY bulb. Aside from being a waste of resources, this is a massive waste of energy. One simply needs to look at the size of the heat sink on every bulb to see the waste preparation as well as the obvious waste of natural resources (Aluminum). This, in itself, is the reason for the over inflated price of line voltage LED replacement bulbs.

In the 12VDC model, there is a reduced number of power supplies required and each power supply can be backed up by a battery source, in the case of a power failure. Really, there should be no reason for me to go into the how and why this is more efficient. However, for the critical out there

1 - less copper required for transformers
2 - less components required for voltage regulators
3 - less aluminum required for heat sinks
4 - less energy to heat waste as the voltage is dropped from line voltage at the transformer, not the light source.
5 - Transformers do not last forever, there is more cost to replacement in the Line voltage option. Yes, the LED's can last 20 plus years, however a transformer and voltage regulator responsible for dropping and rectifying line voltage to 3VDC produces a substantial amount of waste energy in the way of heat. This heat WILL burn out the components in less time than LED's typically last. In fact, there is no reason a low voltage LED should ever burn out, aside from over powering or reverse voltage. In the case of the low voltage option, the transformer, power supply and light source are three separate entities. The transformer typically drops line voltage to 16 or 24 VAC. This then powers the power supply / regulator which rectifies the AC to DC and then drops it down to the desired voltage. In most cases, the output voltage is 12VDC which is then dropped down to 3 VDC via a simple resistor.

Battery Backup and power supervision

- Most modern security alarm control panels have the ability to monitor the line voltage. Typically when the power goes out, the security alarm panels' back up battery takes over and the communicator notifies the central station. With some alarm panels, the system can also trigger a PGM or relay output upon failure of power. This output can be used to activate alternative 12 VDC light sources, also backed up by either the control panels' back up battery, or the battery of a secondary power supply. Personally, I would opt for the secondary power supply as the current draw from the LED's will not drain the main control panels' backup battery. This is particularly important during long power outages. Paradox, a Canadian security alarm panel manufacturer, has supervised power supplies available. This means the status of the power supply's back up battery is always monitored. That way, when the battery becomes too weak to power the lighting for any substantial amount of time, the security alarm panel will notify you so you can replace the battery before the next power failure. Paradox Security Alarm control panels are available to both Installers and end users at http://www.AlarmParts.ca