Guide written by:
Jeremy, construction site supervisor, Cardiff
Need to use 230V tools when you only have a 12- or 24-volt power source? There's one simple solution: a voltage converter! But what power rating? What efficiency? Mono- or bi-voltage? Just follow our high-voltage guide to find out!
- Square signal
- Pseudo-sine wave
- Pure sine wave
- Network coupling
- Input voltage
What's a voltage converter used for?
As the name suggests, a voltage converter is a device that converts the electrical signal (or waveform) from DC to AC voltage. It can also be referred to as an inverter.
Although power generation has been understood for a long time now, there's been no real improvement on the battery principle when it comes to storing it. Once charged, whatever its size or capacity, a battery delivers DC voltage (12, 24, 48V etc).
The mains electricity supply delivers an AC voltage at 230 or 400V.
Essentially, a voltage converter lets you supplyan AC voltage to a device or tool normally running on mains power with a DC power source.
It's a question of electronics how the voltage signal is transformed. Depending on the quality of the components in a given converter, the reproduced signal will be more or less faithful to that of the network it's imitating, i.e. with more or less imperfections in waveform and frequency. The better the components, the closer the delivered voltage resembles a perfect sine wave of constant frequency.
In terms of power, it all depends on the model and type of converter. Just bear in mind that no converter will operate at 100% efficiency. This means that overall moreelectrical power is consumed than is delivered in a usable form. To work out the effective power delivered by a converter, you multiply the efficiency factor by the rated (supplied) power; for instance, if you have a "1000W" inverter with an efficiency of 85%, the useful power output will be 850W.
Voltage converters are widely used in sailing, caravanning, and increasingly in the home when equipped with a wind turbine or solar panels. On the one hand, they allow you to watch TV in your camper; on the other, they can run domestic appliances from battery power.
What different types of converters are there?
There are several different types! Big, small, heavy, light, ventilated, passive... However they all work on the same principle: by means of electronicfilters, they transform a DC voltage into alternating voltage. Converters are primarily differentiated by the quality of AC voltage they produce.
- Squared signal converters: less and less widely used because the quality of theoutput signalis poor, both in terms of waveform and consistency of frequency. They are low power (lightweight and compact). With this type of converter, you can't power and operate any device equipped with a motor or winding (such as drills, refrigerators, etc.).
- Pseudo-sinusoidalconverters: the most common type, these are suitable for almost any appliance. The shape of the generated signal is close to a sinusoidal wave and its frequency is relativelyconstant. They are available at a whole range of power ratings, from 50 to 2500W. They are suitable for all common uses and give good value for money.
- Sine-wave converters:high-end kit, these guys! Packed with sophisticated filters and electronic components, they recreate a near-perfect sinusoidal wave (very similar to that of a mains electricity signal). Thanks to the good quality signal, they can power sensitive devices such as computers, audio-visual gear etc. Like pseudo-sinusoidal converters, they offer a range of powers ranging from 200 to 2500W. However, they are generally more expensive.
- Converters for network coupling: a somewhat specialized type, distinguished by their ability to synchronize with a grid supply rather than to provide a good quality voltage signal. It's actually quite common for inverters to be equipped with an additional electronic chip which allows them to detect the voltage oscillations of the network and synchronize to them. If you have or plan to install solar panels, these are what you need to feed your excess generated power back into the grid. In this case, the voltage you supply back to the grid must exactly match the voltage delivered through the mains. Thanks to this type of converter, this is now easy to achieve.
How do I make my choice?
First of all, assess your needs as accurately as possible. To help you choose the ideal converter, consider the following points:
- Input voltage: this is the starting point! What kind of DC voltage are you starting off with? Are you a sailing fanatic, caravan enthusiast, truck driver, etc, or do you want to convert power from your solar panels?... It's essential to choose a converter in line with your source of DC voltage.
- Output voltage: as a rule, the output voltage you want to aim for is 230V AC with a frequency of 50Hz (Hertz). This converted signal will allow you to use any device you would normally plug into a mains power outlet.
- Power: this is also an essential parameter, and may require a little work on your part! Make an inventory of all the devices you want to connect to your converter. For each of them, you'll want to assume a higher value than the rated power. For any device with a motor, look for peak power (or multiply the rated power by 2). When you add up, add a 10% safety margin by multiplying your result by 1.1. This will give you the maximum power to deliver your converter. Be careful not to get confused between the different 'powers' (useful, rated, peak...) Some converters clearly indicate their range of use: for instance, you'll find 12/230V, 500/1000W sine-wave converters (this means that the converter's rated output power is 500W, but when starting up a power tool for example it can produce a peak power of 1000W for a short period). If you still do not know what you're planning to hook up to your converter, try to leave a comfortable margin of error (think peak power if you plan to use power tools).
- Efficiency: not the same thing as power, remember! To narrow down your choice, consider the efficiency factor (%). This expresses the loss of power caused by converting the signal. For example, the majority of pseudo-sinusoidal converters have an efficiency factor around 85%. This means that a "1000W" converter actually delivers 850W.
- Signal type: as we've already seen, it all depends on what you're going to plug into your converter. In most cases, a pseudo-sinusoidal signal is sufficient (you can ignore the square signal, now in decline). If you plan to use your laptop or another electronic device, you'll need a perfect sine-wave.
Final advice on choosing my voltage converter?
If you want a converter to use as a primary power source via a battery, you need to take into account one last important factor: time. In other words, you've got to start off with a power source that will last you!
For example, consider a 12/230V, 100W converter connected to a 12V, 75Ah (ampere per hour) battery. This will last for about 7 hours. On the other hand, if you plug it into a 400Ah battery, you'll get a full 40 hours of battery life.
Think about your entire electrical network when choosing your converter. Power and duration of use are closely linked.
Learn more about home electrical installations...
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Guide written by:
Jeremy, construction site supervisor, Cardiff, 128 guides
Electrician by trade, I first worked in industrial estates where I installed, wired and fixed a large number of electrical installations. After this, I managed a team of electricians for this type of work. 10 years or so ago, I turned to building and construction. From the modest family home, to gyms and theatres; I have been able to coordinate, audit and organise all sorts of construction sites. for 4 years now, I am restaoring and bulding an extrension to a bungalow in the heart of the welsh countyside. My experience in manual work and my knowledge means I am proud to be of service. Terraces, interior design, roofing, plumbing, electricty, anything goes! We have, my wife, daughter and I, built almost everything we have from scratch! So to answer all of your questions, and to orientate and advise you on coosing your tools? Easy!