Power Inverter Fundamentals

Introduction

Inverter 3

If you want to run your AC powered (110-120Volt) equipment off of your wind turbine(s) or solar panel(s) through your battery banks, you will need an Power Inverter. A Power Inverter is a piece electronic equipment designed to convert your Direct Current (DC) power, stored in your batteries to Alternating Current (AC) power.

This article will go into the basics of a Power Inverters. Depending on your setup, your battery banks are typically configured into banks that are in multiples of 12-Volt (12V, 24V, 36V and 48V being the most popular). Batteries are Direct Current (DC) power storage devices. Most home electrical devices such as lights, fans, compressors, air filters, computers, “wall’ chargers, HAM radios, toasters, microwaves etc operates on 110-120Volt and need Alternating Current (AC) to work.

Power Inverters converts Direct Current (DC), the power that comes from your battery banks into Alternating Current (AC), AC power is what the Utility (the electrical Grid) supplies to your home, and that is what most home appliances and equipment need in order to function.

Input Voltage

It’s important to know your Battery Bank‘s voltage (12V, 24V, 36V or 48V being the most popular) because the voltage rating of the power inverter can handle / selected should match the voltage of your bank.

Don’t forget that batteries / battery banks can only provides DC power. This means that the current flows continuously from the negative terminal of the battery, through the completed circuit and back to the positive terminal of the battery. The is a one direction flow (hence the name Direct Current).

DC can be useful, but most batteries and battery banks can generally only provide low-voltage DC power. Most devices need more power to function properly than DC can provide since they are designed to run on 120-volt AC power (supplied to homes in the U.S.).

Alternating current or AC works differently. AC works by constantly changes polarity by first sending current one way through the circuit, then reversing and sending it the other way. Utilities in US and Canada does this around 60 times per second (cycles per second, also known as Hertz or Hz). Our normal voltage is around 110V (Thats where 110VAC @ 60Hz comes from). In other parts of the world (i.e UK and parts of Europe), you will see this oscillation taking place around 50 times per second, but at a higher voltage (UK & parts of Europe uses 220VAC @ 50Hz). AC power generally works well at higher voltages, and can be “stepped up” (going from a lower voltage to a higher voltage) or “stepped down” (from higher to lower voltage) by using a transformer.

How Power Inverters Work

A Power Inverter is designed to do two things: i) increases the DC voltage (from 12/24/36/48V to 110 or 220V), and then it changes the DC to AC current before sending it out to your electrical wiring (to power your device). Many Power Inverters can also work backwards to convert AC (from the grid) into DC (battery banks) and work as a Charger. Modern Power Inverters use electronics (oscillator circuits) to accomplish create AC from DC. Oscillators circuits are made with transistors or semiconductors.

Waveforms

Inverter waveformsDifferent Inverter Output Waveforms

Alternating Current supplied by Utilities are normally in the shape (waveform) of a sine wave. However, the output from a basic Power Inverter is usually square wave that does not have the smooth, round wave of a perfect sine. Because some devices (such as a radio or video receiver, transceivers or instruments) are sensitive to the signal produced by an AC wave and you may see or hear these square waveforms as lines on the screen or a steady buzz or hum (interference or noise).

Cleaning up the sine wave requires a series of filters, inductors and capacitors (waveform shaping). Cheap inverters have little or no filtering and the AC they produce has a very square wave, which is fine if you just want to make coffee or run something with a simple electric motor. If you need a smoother sine wave, you’ll need an inverter with better filtering.

Better waveform shaping will mean the Power Inverter will costs have, and have more parts. Really good, Full Sine Wave Power Inverters can get extremely expensive if you’re looking for an inverter with a smooth sine.

The good news: Given a large enough budget, you can purchase AC Power Inverter that produces virtually perfect AC sines. In fact, some high-end DC to AC inverters can make sine waves that are even smoother than the AC power supplied to your house.

Power Inverter Selection

Step One - Match the inverter to the voltage of the batteries / battery banks you’ll be using for power. In the majority of cases, you’ll be using a 12-volt batteries (connected in series and/or parallel), so you would want to select a 12/24/36 or 48-volt inverter unit.

Step Two - Determine which devices you plan to power with the inverter. Figure out the amount of power (in Watts) that you will need. The wattage rating of your inverter must exceed the total wattage of all the devices you plan to run simultaneously. For instance, if you wanted to run a 800-watt blender and a 1,000-watt microwave oven at the same time, you’d need an inverter capable of a 1,800-watt of output. However, if you knew you would never be making coffee and fruit smoothies at the exact same time, you’d only need a 1,000-watt inverter.

Step Three – Determine the wave output of the inverter. If you’ll be powering any of the equipment that is sensitive to square waves, look for an inverter with “perfect sine” waveform output. Remember that a perfect sine power inverter can cost almost 10 times as much as the same wattage inverter with a “modified sine” output.

A modified sine waveform means that the current is run through some filtering, so it isn’t a square wave, but it isn’t totally smooth sine wave. It is a compromise.

Sizing your Power Inverter

Important: Some devices that have electric motors, and compressors on refrigerators and freezers will draw a higher wattage than their normal operating wattage rating when they first start up. This is known as peak or surge. Most inverters also have a peak rating, so make sure the inverter’s peak rating is higher than the peak wattage of the device you intend to power.

Inverter Installation

Inverters are very easy to install. Inverted wattages above 500W typically will require direct connection to the batteries / battery bank or to the Charge Controller. The inverter cables should be bolted onto the appropriate battery or charge controller terminals.

The inverter itself can be mounted anywhere, although it should be in a place with good air flow. Power Inverters generate a fair amount of heat, and they use cooling fans and heat-sinks (heat dissipation fins) to prevent overheating. The larger, heavier Power Inverters have mounting holes in their chassis so they can be bolted to any surface.

Obviously, with a permanent installation, you’ll probably want to bolt your converter in place, but this isn’t absolutely necessary. It’s possible to simply place the inverter in a secure, stable position, bolt the leads to the battery or the Charge Controller and plug it into your electric system. Also remember the higher the wattage, the larger and heavier the inverter. At the top of the inverter wattage scale, some inverters can be more than two feet long and weigh over 30 pounds so make sure your mounting is secure.

Bells and Whistles

Power Inverters have some built in safety features that make them even easier to use. Some models sound an alarm when the battery’s voltage gets too low. This is more of a convenience, but depending on what sort of equipment you’re powering, it could also be a valuable safety feature.

Most Power Inverters today have automatic shut-off capabilities and if the Inverter detects a current overload or an overheating situation, most will shut down to lessen or prevent the chance of a fire. Inverters can also shut off in the event of a short circuit, such as a piece of metal falling into the chassis or the inverter getting wet. Short circuit shut-off is an effective way to prevent electrocution.

Pricing

So how much will all of this going to cost? It really does vary. You can buy a modified sine wave inverter rated for continuous power of 200 watts between $20 and $40, a 6,000-watt (6KW) modified sine wave inverter are around ($900-$1200). Pure sine wave inverters cost much more, from about $200 for a 300 watt unit to about $10,000 for a 8,000-watt (8KW) inverter.

Here are a Power Inverter Introductory Video from Youtube:

Posted in Articles, Battery, Energy, Generators, Inverters, Lead Acid Batteries, Skills, Supplies, Technology, Videos, YouTube Videos Tagged with: , , , , ,

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