How to choose Power inverter?


How to choose Power inverter?

To answer this question, let’s explain a few terms: Resistive Load appliance and Inductive Load appliances. Modified Sine Wave Inverters and pure sine wave inverter.

What is the resistive load appliance?

Normally, resistive Load is a kind of electrical load which is characteristic of not having any significant inrush current. When a resistive load is energized, the current rises instantly to its steady state value, without first rising to a higher value.An electrical load in which voltage and current are converted to energy in the form of heat. The voltage and current peaks coincide.For example, an electrical heater, candescent bulb. mobile,laptop, TV, LED light, toaster, oven, hot plates, curling irons, coffer makers, video player, small printer, water dispenser, electric cooker, etc.

What is inductive load appliance?

Inductive Load is an electrical load which pulls a large amount of current ( an inrush current) when first energized. After a few cycles or seconds the current settles down to the full-load running current. And the time required for the current to settle down depends on the frequency or/and the inductance value. Inductive loads generally are those in which electricity flows through the coils. Normally are motors, transformers. This application of the principle of electromagnetic induction produced by high-power electrical products, such as electric motors, compressors, relays, and so on. Such products requires a start than to maintain the normal operation of the desired current is much larger (about 3-7 times) starting current. For example, a normal operation of the power consumption of about 150 watts Refrigerator, the start power will up to 1000 watts.

What is the difference between a modified sine wave inverter and pure sine wave inverter?

Alternating current (AC) has a continuously varying voltage that swings from positive to negative. PSW, like shore power, alternates smoothly with a sinusoidal curve that has a rounded peak and a clean ‘zero cross’ to a rounded valley. MSW produces instantaneous peak voltage for a few milliseconds, down to zero for a few milliseconds. PSW great advantages in power transmission over long distances. Power from your power company is carefully regulated to be a perfect sine wave, because that is what naturally comes out of a generator, and also because sine waves radiate the least amount of radio power during long distance transmission.

On the other hand, a sine wave is expensive to make in an inverter, and many sine wave techniques use heavy, inefficient transformers. The most inexpensive way to make AC is to switch the DC on and off–a square wave. A modified sine wave is scientifically designed to simulate a sine wave in the most important respects so that it will work for most appliances. Modified sine wave products are initially more economical than true sine wave products. It consists of a flat plateau of positive voltage, dropping abruptly to zero for a while, then dropping again to a flat plateau of negative voltage, back to zero for a while, then returning to the positive voltage. This pause at zero volts puts more power into the 60HZ fundamental than a simple square wave does, so it is called “modified sine wave” instead of “square wave.” Because the MOSFETs only have to turn completely on and completely off the dissipate he least amount of heat for the power generated, and so smaller semiconductors and heat sinks are needed than if you were trying to generate a real sine wave.

How do I determine which power inverter is right for me?

The following gadgets work well with a modified sine wave: electric blankets, computers, motor-driven appliances, toasters, coffee makers, and most stereos, ink jet printers, TVs, VCRs, many microwave ovens, etc.

Devices such as laser printers, digital clocks, most light dimmers and most medical equipment require a pure sine wave inverter to run correctly. As noted above, as a precaution, please contact the manufacturer of your device to determine if pure sine wave power is required. For Medical equipment, oxygen generators, etc. talk to the manufacturer of the equipment. Longjann inverters are never tested or rated with medical equipment, and we don’t guarantee that they will work to save your life. For such applications please find inverters that are rated and tested for such applications. As a precaution, please contact the manufacturer of your device to determine if it is compatible.

What size inverter should I buy?

Different devices require specific wattages to run correctly and efficiently. First add up the power ratings of all the appliances, then buy the next larger inverter! For resistive load appliance, You can also look at the VA and Watts consumed on Grid Power and inverter and if either goes up a lot on inverter (say +20% or higher vs grid power). We recommend you buy a larger model than you think you’ll need (at least 20% more than your largest load). For Note, however, that some appliances, such as table saws, refrigerators, and microwaves have a surge requirement. Longjann inverters are designed to supply such surges, but since every appliance has its own requirements sometimes you will need to get a bigger inverter than you would otherwise think. Note that the inverter isn’t the only consideration when you are pondering the mysteries of start-up surges. The battery must also be able to supply the surge power, and the cables must be able to supply the increased current without dropping the voltage too much.

Helpful formulas:
To Convert AMPS to WATTS:
Multiply: AMPS X 120 (AC voltage) = WATTS
This formula yields a close approximation of the continuous load of the appliance
To calculate approximate Startup Load:
Multiply: WATTS X 2 = Starting Load This formula yields a close approximation of the starting load of the appliance, though some may require an even greater starting load. NOTE: Induction motors such as air conditioners, refrigerators, freezers and pumps may have a startup surge of 3 to 7 times the continuous rating. Most often the startup load of the appliance or power tool determines whether an inverter has the capability to power it. For example, you have a freezer with a continuous load of 4 amps, and a startup load of 12 amps: 4 amps x 120 volts = 480 watts continuous 12 amps x 120 volts = 1440 watts starting load You would need an inverter with peak-surge rating greater than 1440 watts. FORMULA to convert AC Watts to DC Amps: AC Watts divided by 12 x 1.1 = DC Amps (this is the size vehicle alternator you would need to keep up with a specific load; for example, to keep up with a continuous draw of 1000 watts, you would need a 91 amp alternator) Click for a Chart of Estimated Watts Used by Common Appliances and Tools

What is a microwave rated for wattage?

When you buy a microwave oven you want to know how intense the microwave field is, not how much the oven draws from the wall. The power rating used with microwave ovens is the “cooking power” which refers to the power being “delivered” to the food being cooked. The actual operating power requirement rating is higher than the cooking power rating. A microwave oven that boasts 600 watts on the box will have an input requirement of 1200 watts on the boilerplate in the back.

How far can I keep my inverter from my batteries?

Keep the cables between your inverter and batteries as short as possible. This will help your batteries perform their best and keep the inverter’s signal clean. Power is volts times amps (Watts = V x A). So if you have a lot of voltage you don’t need many amps to get a watt. Roughly you need 12 times as much current from the 12 volt battery as you need from the 110 volt AC outlet. Current is what causes cables to heat up, not voltage. That is why they use thousands of volts in long distance power transmission grids. The thing to do when you have lots of current is to lower the resistance of the cable. The larger the wire the lower the resistance. Think of the cable as a water pipe. A big pipe (wire) can carry more water (current or amperage) with less pressure (voltage), and will present less pressure (voltage) drop from one end of the pipe to the other. The cables that come with the inverter are “rated” or good for up to six ft. If you plan on going over six ft., drop down to a larger gauge cable. Please contact your manufacturer if you are still unsure. This is pretty important that should NOT be overlooked. If the cables between your battery and inverter get hot while under heavy load, then you should use larger gauge cables.
Many small inverters (450 watts and under) come with a cigarette lighter adapter, and may be plugged into your vehicle’s lighter socket. Although you will not be able to draw more than 200 watts from the cigarette lighter socket, because it may damage the fuse of your vehicle’s lighter socket.

How long can I expect my devices to run if the power inverter was powered by batteries?

Working time= U (Voltage)* I(battery capacity)*0.8*0.9/load
Take a 12V 60AH batteries and a 220v 60w bulb for example.
Working time=12V*60AH*0.8*0.9/60W=8.64(H)
Note: 0.8 is the battery discharge rate, 0.9 is the efficiency of the power inverter, The working time also relate with the performance of the battery. This formula is only for reference.

What types of batteries are recommended for power inverter?

Small Inverters: Most automobile and marine batteries will provide an ample power supply for 30 to 60 minutes even when the engine is off. Actual time may vary depending on the age and condition of the battery, and the power demand being placed on it by the equipment being operated by the inverter. If you use the inverter while the engine is off, you should start the engine every hour and let it run for 10 minutes to recharge the battery.

500 Watt and larger Inverters: We recommend you use deep cycle (marine or RV) batteries which will give you several hundred complete charge/discharge cycles. If you use the normal vehicle starting batteries they will wear out after about a dozen charge/discharge cycles. If you do not have a deep cycle battery, we recommend that you run the engine of your vehicle when operating the power inverter. When operating the inverter with a deep cycle battery, start the engine every 30 to 60 minutes and let it run for 10 minutes to recharge the battery. When the inverter will be operating appliances with high continuous load ratings for extended periods, it is not advisable to power the inverter with the same battery used to power your car or truck. If the car or truck battery is utilized for an extended period, it is possible that the battery voltage may be drained to the point where the battery has insufficient reserve power to start the vehicle. In these cases, it’s a good idea to have an extra deep cycle battery for the inverter (installed close to the inverter), cabled to the starting battery. It is recommended to install a battery isolator between the batteries.

The advantages of deep cycle marine batteries are:
Delivers higher peak amps faster than conventional batteries
Provides up to twice the life of conventional batteries
More consistent voltage across the discharge curve
Superior cold and hot weather performance vs. conventional batteries

How to connect two or more batteries?

If your battery application requires more starting power or reserve capacity you can install multiple batteries (12V) together in parallel by connecting the like terminals together (positive to positive / negative to negative). Two such batteries will generate twice the amp/hours of a single battery; three batteries will generate three times the amp/hours, and so on. This will lengthen the time before your batteries will need to be recharged, giving you a longer time that you can run your appliances. You can also connect 6 Volt batteries together in “series” configuration to double the voltage to 12 volts. Note that 6 Volt batteries must be connected in pairs.

connect 12v battery for power inverter

connect 6v battery for power inverter

Suggestions for connecting two or more batteries:
Use batteries of identical model, and age.
Make sure cable gauge is sufficient to handle the current flow.
Prevent cables from shorting (do not allow them to rub against the vehicle body).
Use high quality connectors; clean all contacts prior to installation.
Periodically check all connections for snugness.

General Safety Precautions and Installation Tips:

Place the inverter on a reasonably flat surface, either horizontally or vertically.
The inverter should not be installed in the engine compartment, due to possible water/oil/acid contamination, and excessive heat under the hood, as well as potential danger from gasoline fumes and the spark that an inverter can occasionally produce. It’s best to run battery cables to a dry, cool inverter mounting location.
Keep the inverter dry. Do not expose it to rain or moisture. DO NOT operate the inverter if you, the inverter, the device being operated or any other surfaces that may come in contact with any power source are wet. Water and many other liquids can conduct electricity which may lead to serious injury or death.
Avoid placing the inverter on or near heating vents, radiators or other sources of heat. Do not place the inverter in direct sunlight. Ideal air temperature is between 50° and 80° F.
In order to properly disperse heat generated while the inverter is in operation, keep it well ventilated. While in use, maintain several inches of clearance around the top and sides of the inverter.
Do not use the inverter near flammable materials. Do not place the inverter in areas such as battery compartments where fumes or gases may accumulate.

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