DC-AC INVERTER FAQ

1. What is a power inverter?

A power inverter is a device that converts DC (Direct Current) power into AC (Alternating Current) power. The AC output is usually 120 VAC, 60 Hz (USA domestic power) or 230 VAC, 50 Hz (International power). Aircraft applications often require 115 VAC, 400 Hz. Nova Electric offers all three of these common output voltages, in both single and three-phase configurations, as well as other special / custom outputs.

2. How can an inverter be used?

With a large enough battery bank, or a large enough alternator output from a vehicle, almost anything within reason can be operated from a power inverter – this assumes that the inverter has the proper power output for the given load. Everyday appliances such as microwaves, power tools, TVs and VCRs, lights, audio/visual equipment, battery chargers, and computers are common loads. An inverter sized for loads with heavy inrush current can be used to power air compressors, water pumps, heaters, ventilation fans, and air conditioners. Nova Electric’s Pure Sine Wave inverters are ideal for running sensitive test equipment such as communications equipment, oscilloscopes, scales, high end stereos & video equipment, communications equipment, etc.

3. What is the difference between Square Wave, Modified Square Wave & Pure Sine Wave Inverters?

Square Wave: Nova Electric neither recommends nor offers any inverters that produce a square wave. Square Wave units could be harmful to some electronic equipment, especially equipment with transformers or motors. The square wave output has a high harmonic content which can lead such equipment components to overheat! Square Wave units were the pioneers of inverter development and, like the horse and buggy, are no longer relevant for modern use.

Modified Square Wave: The most common, general-use inverters available are of the “Modified
Sine Wave” variety, usually available at more moderate pricing compared to pure sine wave models. Modified Square Wave (or “Modified Sine Wave” and “Quasi Sine Wave”) output inverters are designed to have somewhat better characteristics than Square Wave units, while still being relatively inexpensive. Although designed emulate a Pure Sine Wave output, Modified Square Wave inverters do not offer the same perfect electrical output. As such, a negative by-product of Modified output units is electrical noise, which can prevent these inverters from properly powering certain loads. For example, many TVs and stereos use power supplies incapable of eliminating common mode noise. As a result, powering such equipment with a Modified Square Wave may cause a “grain” or small amount of “snow” on your video picture, or “hum” on your sound system. Likewise, most appliances with timing devices, light dimmers, battery chargers, and variable speed devices may not work well, or indeed, may not work at all. For this reason, Nova Electric offers only Pure Sine Wave Inverters!

Pure Sine Wave: Nova Electric offers only Pure Sine Wave output Inverters, which are mandatory for powering any device that requires sensitive calibration. Pure or True Sine Wave inverters provide electrical power similar to the utility power you receive from the outlets in your home or office, which is highly reliable and does not produce electrical noise interference associated with the other types of inverters. With its “perfect” sine wave output, the power produced by the inverter fully assures that your sensitive loads will be correctly powered, with no interference. Some appliances which are likely to require Pure Sine Wave include computers, digital clocks, battery chargers, light dimmers, variable speed motors, and audio/visual equipment. If your application is an important video presentation at work, opera on your expensive sound system, surveillance video, a telecommunications application, any calibrated measuring equipment, or any other sensitive load, you must use a Pure Sine Wave inverter.

4. What size inverter do I need? (Starting Load and Continuous Load)

The power output rating of the inverter you choose (in VA or in watts) is directly dependant on the load you will be powering. It is absolutely critical that you select an inverter which is powerful enough to operate your specific loads.

Step 1: The first step in your inverter selection is to calculate the total (Watts or Amps) of all appliances you plan to power. Virtually all AC powered equipment will bear a label (usually placed near where the power wire enters the unit), indicating how many Amps or Watts of electricity the equipment uses.

Step 2: The second step is to determine the characteristics of your load. AC loads generally fall into two categories: Electronic loads, such as switching power supplies (or SMPS, as found in computers), and motors, such as the compressor in a refrigerator. Both of these types of loads require different levels of the initial surge of power required to start up, often called a Peak Surge for electronic loads, or Locked Rotor Current for motor loads. The Peak Surge or Locked Rotor Current is almost always considerably higher than the Continuous Load (which is the power needed to run the load after initial start up) and must be considered when sizing the inverter, the battery, and the cables that connect the two. The following formulas should therefore be strictly observed:

Electronic Load / Switching Power Supply: Some SMPS type load are extremely reactive, with a poor power factor at the input, due to very high peak current and high harmonics content at the input. Consequently, selecting a high-frequency topology inverter with a power output rating equal to or only slightly greater than the power rating of the load will result in an overloaded inverter, with a distorted wave shape at the output. Therefore, for high-frequency topology inverters (GL and CGL Series), Nova Electric suggests maintaining a ratio of 3:1 between the power output rating of the inverter in VA, and the rating of the load in watts. For example, if a GL or CGL Series Inverter is to be used, we would recommend powering a 300 watt telecom gear load with an inverter which has a minimum power output rating of 900 VA. For units which have a transformer isolated topology (such as our GS or Classic Series), this ratio can be reduced to 2:1 (e.g., a 1,000W SMPS load can be powered by a 2 KVA inverter). In effect, the tradeoff for utilizing a lightweight, compact high frequency topology inverter is the requisite higher ratio between the power rating of the inverter and the power rating of the load.

Motor / Compressor Load: Nova Electric does not recommend the use of high frequency inverters (GL or CGL) for motor or compressor loads in general, though they can be modified for such use in certain applications where weight savings are critical (consult factory for details). Whenever possible, we recommend using the low-frequency transformer isolated GS or Classic Series models for motor loads. The formula to use for all inverters which are to power motor loads is: Inverter’s output AC voltage multiplied by Locked Rotor Current of motor load equals minimum rating of inverter in VA. For example, if you have a pump which runs off of 120 VAC and has a Locked Rotor Current of 10 Amps, you would need an inverter of at least 1200 VA to run the pump (120 VAC x 10A = 1200 VA). It is not recommended to start two motor loads simultaneously unless a very large capacity inverter is being used.

5. What is the difference between Automotive and Deep Cycle batteries?

Automotive batteries are usually adequate for small inverters, (< 500 Watts). When used in a car, we suggest you run the vehicle of your engine occasionally while operating your inverter. If you use the inverter while the engine is off, you should start the engine regularly and let it run to charge the battery. Deep Cycle (marine) batteries are best for larger inverters as they are designed for several hundred charge/discharge cycles. (Automotive batteries wear out much more quickly after heavy discharge).

6. How do I charge the battery for my inverter?

Because inverters operate from a DC (Direct Current) power source, usually a battery bank (one or more batteries), the battery source will have to be recharged at some point. (Remember that a battery discharged more than 50% is probably close to being dead.) Most cars and trucks recharge their batteries from an onboard alternator. Depending on the inverter load and runtime required, most power use applications will be covered by the charged battery, augmented by the operating alternator supplying a continuous charge to the battery. If the load is large (air conditioner, large draw power tools, large microwave, food freezer, ice cream machine, etc.), the user should verify that the installed vehicle alternator is of large enough capacity to operate the vehicle’s power requirement as well as to fulfill the capacity of the inverter load. If it’s not, a motor throttle installation may be required to carry a small load, a larger alternator may be required, or a larger alternator, battery isolator and additional onboard battery bank may be required in order to meet the power requirement of the large load. Remember: it takes 12 DC Amps (at 12 VDC) to run 1 AC Amp (at 120 VAC single-phase) of power because there are voltage and efficiency factors to take into consideration.

7. What are some safety precautions to keep in mind?

Improper use of a power inverter could result in personal injury. The inverter should not be installed in the vehicle’s engine compartment. Keep the inverter free from moisture as liquids conduct electricity, which may lead to serious damage or injury! Do not use the inverter near flammable materials or where fumes or gases may accumulate. The AC Output (neutral) wire should be vonded to ground, except in special applications. See owner’s manual for more details.