The next few posts will outline some of the ideas I have for how the show will be run. From hardware to software and even specifics about what type of lights to use and how to string them together.
To get things started, I want to talk about the electrical side of things.
To reduce the length of the extension cords, I want to have a modular control setup where I can have ‘nodes’ around the house to connect things to. These nodes will each be connected to one of probably four 20A branch circuits that will be hard wired outside and control circuitry inside will control the group of lights connected to it. I expect the house will have a variety of string lights, lit figures, maybe one of those tacky Happy Holidays signs, etc. We have a detached garage that is bound to have some lights on it as well, but it has a 20A circuit for the outside outlets which should be enough. I also expect to have a variety of things in the front yard as well as lights on bushes that are a fair distance from the house. I will probably put a number of those short heavily lit trees throughout the yard. This means whatever ‘nodes’ there are in the system will need to be ‘networked’ together.
I don’t expect any inductive loads (i.e. motors), but it’s a possibility, especially if I do a display for Halloween. I want to be able to dim the light strings as well as turn them on and off. I want to have the ability to flash the lights and possibly even have them twinkle. This requires a fairly fast switching method - a solid state switching method.
In order to switch the lights that quickly, you need a triac based control board. Triacs allow for very fast switching and dimming. The popular boards from places like Light-O-Rama and X-10 Lamp Modules use triacs. However these devices can only be used on resistive (incandescent lighting) loads. They are not designed to handle inductive loads. You can, however, get dimming systems that are designed to handle inductive loads utilizing zero-crossing circuitry (the triac is fired in sync with the zero cross and is fired long enough to handle the current lag of inductive loads) Many dimming modules used for stage lighting are designed to handle inductive loads.
To handle any type of inductive load (low voltage lighting, fixtures with motors), people often use relays. Relays are most often mechanical devices. A low voltage energizes a magnet coil which pulls a mechanical switch closed, completing the circuit. There are also solid state relays which use high current semiconductors to switch the loads on an off. Given their nature, relays can switch very high currents for their size and also can switch inductive loads as well as resistive loads. However, they are on/off. You can’t dim with a relay. X-10 Appliance Modules use a heavy duty relay, thus the loud ‘click’ when you turn them on and off.
One key difference between the two types of setups is boards with relays tend to be cheaper than dimmable boards with triacs, but not always.
Given the type of show I have in mind, I’ll have a number of loads that I want dimmed as well as loads that just turn on and off. Instead of using just one type of control method, I expect I’ll use both triac dimmers and relays.
I’ve have a healthy respect for electricity which can be the riskiest part of putting together a big holiday display. GFCI outlets and proper overcurrent protection are important. However, when putting together a DIY show, there are a lot of wires carrying 120V running around inside and outside the enclosures increasing the possibility of getting shocked. Point to point wiring is a common practice in DIY projects, but can be dicey when dealing with AC current. Another risk is a short causing 120VAC to feed back into the low voltage control side - a very dangerous situation. So one of my design requirements is to ensure that all AC switching is done via circuit board triac/relay based systems or opto-isolated module packs (see photo right). This also makes construction easier.
So what requirements are there so far?
- Try to use off-the-shelf, optoisolated modules or triac/relay based circuit board for 120VAC switching.
- Ability to handle resistive and inductive loads.
- Ability to dim some circuits (triac based). Relay control acceptable for some things.
- Fast response and switching time. Ability to switch in sub second cycles (twinkle effects, etc).
- Modular control system with networked ‘nodes’.
- GFCI protected circuits. 4-6 dedicated 20A branch circuits.
Further Reading:
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