Imagine finally paying your light bill on-time after years of paying late fees and then BOOM lightning flash and mash-up your smart TV and Desktop PC. Or, you finally made some progress in that assignment you’ve been postponing until last-minute and then BOOM the power gone. An unlucky scenario for sure especially since the power company isn’t gonna reimburse your precious electronics.
But fear not! This could have been avoided with a UPS battery backup. For the less informed, UPS stands for uninterruptible power supply. As the name suggests it acts as a power source when power is gone and typically lasts for a few minutes before dying. One might wonder what the difference between a UPS and a standby generator is since they both supply backup power when there is power loss. In fact, the generator typically lasts for much longer, and is cheaper per Kilowatt! The key difference lies in the load it is powering. While it’s no major problem when simple linear loads lose power, eg. lights, speakers, heaters, and motors to name a few; many electronic devices are more sensitive to the power feeding them, and often times require a shutdown process to protect the information from corruption. As such, an active power back up solution is required so there is no noticeable switchover time when there is a power failure.
The UPS operates by taking AC utility power, conditioning it, and switching over to battery backup when there is a loss of the source power. Like most things, there are many different types and size of power supplies, but the taxonomy of UPS systems can be broken down as:
- Line interactive
- Online/ Double Conversion
There are other classifications, but these represent the majority of UPS system topologies. Just think of the classifications as a ranking of their quality and cost, with the Standby variant being the cheapest and Online being for the most mission-critical applications. The most basic UPS (standby UPS) allows utility power to pass through to the connected loads and switches over to battery inverted power when there is power loss. The line interactive UPS is similar to the standby with the difference being that the incoming power is ‘conditioned’ before being supplied to the connected loads. Conditioning power refers to the process of filtering and smoothing an electric signal to bring the signal close as possible to an ideal form. The Online/ Double Conversion variant operates by transforming incoming AC power to DC, and then back to AC to power connected loads. This design makes it so that there is zero switch-over time during a loss of source power since power is constantly being generated from the batteries, while the source power constantly charges back the batteries. The UPS has 3 key components that accomplish this; the batteries (DC power), Rectifier (converts AC to DC power), and the Inverter (converts DC to AC power). For most home appliances, the standby and line interactive variants are more than good enough, while most businesses with server room equipment would use the online variant.
Now that we got the intro and theory out-of-the-way let’s work on a project. The objective is to supply UPS power to a TV, 2 desktops, monitor, speakers, camera system and wireless router, all located in 3 different rooms.
Disclaimer: This project will involve working with mains electrical power and as such safety precaution should be made to follow all relevant electrical standards. Only a certified electrician should perform electrical installations within your home.
Tools needed for this project are from the How to cable your home or office for power, audio, or video post. Other tools include :
The first step in doing this project is evaluating the total power of all the connected loads. This is done by finding each equipment’s power rating or current draw. Note that Electrical Power = Voltage used x Current consumed. Most times these are shown on a label on the device. If that’s not accessible you could also get an estimate from this List of the Power Consumption of Typical Household Appliances. For a more accurate estimate you could measure the current draw from the particular device with a clamp meter then multiply by the utility voltage (typically 110-120Vac).
For the scientists and engineers reading, yes there are two types of AC power with units of W(Watts) and VA (Volt Amps) which represents the real power consumed and apparent power. However for the scope of this project we will assume they are equal for ease of calculation. The mathematics will be discussed in a separate post.
|CRT Colour TV||150|
As we can see the maximum theoretical power usage is about 956W but in actuality only a fraction of this will ever be used at any one time. This fraction will vary but a reasonable estimate would be about 60% of the total load = 573.6W. The Tripp Lite 1500VA 900W UPS was chosen for this project as it can supply my power needs with room for future growth.
The next step is choosing where you will lay the UPS and where to route the electrical cables. The post on How to professionally cable your home or office for power, audio, or video goes in further depth on how to run cabling in your home. The size electrical cable you choose depends on how much current is being transferred, the voltage, and the distance. Since I’m running power to two 15Amp power strips I need a minimum 1.5mm2 cable (cross-section) or 16AWG. See SAE & Metric Wire Size vs. Amps. This simply tells you your minimum size cable you can use safely; larger sizes are of course acceptable.
- 5 lengths 16x16mm PVC Trunking
- 70 ft 3-core flexible 2.5mm2 cable
- 3 x PVC handy box
- 2 x NEMA 5-15 (US) receptacle
- 6 bonding nipples
- Electrical tape
- 5 x Wire Nuts
- 3/4″ concrete/drywall nails
For ideas on any other future projects you’d like to see me cover please comment below.