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FAQ
DC-AC Inverter FAQ
1) What is power inverter?
A power inverter is a device that converts DC (Direct Current) power into AC (Alternating Current) power. The AC output is usually 110 VAC, 60 Hz (USA domestic power) or 220 VAC, 50 Hz (International power). Wenzhou New Focus offers all of these common output voltages, in single 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. Wenzhou New Focus’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: Wenzhou New Focus 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, Wenzhou New Focus offers only Pure Sine Wave Inverters!

Pure Sine Wave: Wenzhou New Focus 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 assures that your sensitive loads will be correctly powered, with the lowest 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.
An inverter needs to supply two needs - Peak or surge power, and the Continuous or typical power.    Surge is the maximum power that the inverter can supply, usually for only a short time (usually no longer than a second unless specified in the inverter’s specifications). Some appliances, particularly those with electric motors, need a much higher start up surge than they do when running. Pumps, compressors, air conditioners are the most common example-another common one is freezers and refrigerators (compressors). You want to select an inverter with a continuous rating that will handle the surge rating of your appliance so you don’t prematurely burn out the inverter. Don’t rely on the inverters surge to start your equipment because inverters don’t like to operate in their surge mode unless the manufacturer claims to have a longer surge time than normal.                                                                                    Typical is what the inverter has to supply on a steady basis. This is the continuous rating. This is usually much lower than the surge. For example, this would be what a refrigerator pulls after the first few seconds it takes for the motor to start up, or what it takes to run the microwave - or what all loads combined will total up to. (see our note about appliance power and/or name tag ratings at the end of this section)
Here is an example:
First, you need to determine what items you need to power during a power failure and for how long. Here is a brief example (watt requirements vary):
Lights - About 200 watts
Fridge - About 1000 watts
Radio - About 50 watts
Heater - About 1000 watts
Total wattage needed is 2250 watts. The fridge and heater have a start up power requirement so let’s allow 2x the continuous wattage for start up requirements. 2250 * 2 = 4500 watts
Second, select an inverter. For this example, you will need a power inverter capable of handling 4500 watts. The continuous power requirement is actually 2250 but when sizing an inverter you have to plan for the start up so the inverter can handle it.
Third, you need to decide how long you want to run 2250 watts. Let’s say you would like to power these items for an 8 hour period. Well this can be tricky because heaters and fridges run intermittently. Let’s assume all of the appliances will run 40% of the 8 hr period which is 3.2 hours of actual run time. We need to convert the ac watts to dc amp hours because that’s how batteries are rated.

To convert ac watts to dc amps per hour you divide the watts by the DC voltage (usually 12v or 24volts). Let’s use 12volts since it is the most common.
2250 watts / 12 vdc = 187.50 dc amps per hour
187.50 is now your power requirement per hour
You have now determined that 187.50 is your power requirement per hour and now you need to multiply that by total hours of run time which is 3.2 in our example.
187.50 dc amps per hour 3.2 hours = 600 dc amps
Because you are using an inverter, you want to calculate the loss for converting the power which is usually around 20%.
(600 dc amps * 20%)+ 600 dc amps =720 dc amps per hour (this is how much power you need in an 8 hour period running your appliances 40% of the time)                                                      
Fourth, now that you know your total power requirement is 720 dc amps we can select a battery source.     So if battery is 12V 100AH, then 720 amps / 100 amp= 7.2 batteries;
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 bonded to ground, except in special applications. See owner’s manual for more details.
 
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