Common household appliances classification: capacitive, inductive, resistive load

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Common household appliances classification: capacitive, inductive, resistive load

Rough classification

Electrical appliances, in terms of technical performance, are roughly divided into three categories: capacitive load, inductive load, and resistive load. The following classification can only be used as a rough classification, because electrical appliances often contain two or more technical performance components, so it is very likely that while having obvious capacitive load characteristics, it also has a certain degree of inductive load characteristics, and vice versa. The same is true. When we talk about a certain electrical appliance as an inductive load, it means that its work performance is obviously inclined to an inductive load, not that it is a purely inductive load.




Capacitive Load

The capacitive load is relative to the power supply. For example, what is common in the home: TVs, computers, mobile phones or camera chargers, etc., powered by switching power supplies can be called capacitive loads, because the first stage of such electrical inputs has a large filter capacitor. The capacitor is connected to the AC resistance and the capacitor current is 90 degrees ahead of the voltage, so it is a short-circuited wire relative to the power supply in an instant. Therefore, there is an instantaneous peak value for such appliances.


Inductive and Resistive Load

Inductive loads, such as fans, speakers (usually powered by low-frequency transformers), pumps, electric drills, air conditioners, and refrigerators are common. Their main working module is an inductance coil, and the coil is an inductance. The voltage of the inductance is 90 degrees ahead of the current. Compared to the power supply, it is also short-circuited when it is turned on instantly. Only after the start-up, the impedance rises, will it run stably. When we use a high-power motor, we can obviously feel that the lights and electrical appliances in the whole house flicker at the moment of starting. This is the peak power, and the instantaneous peak power is many times larger than the power marked on the motor. For example, the standard: 500W motor, 3 times the instantaneous starting power, which is equivalent to the starting power of 1500W.

Resistive load is a common light bulb. Compared with the power supply, it is a pure resistance, and there is no power-on shock problem.

Photo by Naomi Hebert on Unsplash

Inverter for Inductive Loads

The most difficult choice is the motor category, here is a detailed description:

Through the above description, to choose an inverter, you must understand the peak value of the impact of the appliance at the moment of starting! The impact is only manifested in perceptual or capacitive negative electrical appliances. Such as motors, because they are inductive, the instantaneous power is generally 3 to 7 times. For a 500W motor, the power impact is between 1500W and 3500W. Inverters generally have 2 times the peak value, that is, a 500W inverter has an instantaneous power output of 1000W, a 1000W output of 2000W, 1500W, a 3000W output, 2000W, and an instantaneous output of 4000W. Therefore, according to the 500W motor, it is necessary to choose an inverter above 2000W, but on the other hand, it is not that the motor has 7 times the peak value.

Just understand: the inverter can output 2 times the nominal power instantly, and the capacitive or inductive load needs 3 to 7 times the peak power to start instantly.

How to determine whether it is 3 times or 7 times the peak value? It's actually not that difficult. No-load operation is 3 times, full-load operation is 7 times, so the peak number is, we can judge according to the degree of motor driving load. For example, hand electric drills, we only drill holes under normal operation under no load, so we can count as 4 times the peak value (actually 3 times, more than 1 is the amount of She), 500W hand electric drill, 4 times, peak 2000W, use A 1000W inverter is fine, and other motors follow this example.
For example, the air conditioner is purely perceptual and has a large starting peak, because every time the compressor is started, the motor is working at full load. It can be considered that its start is 7 times the peak value. 1000W requires an air conditioner, the peak value is 7000W, and the inverter doubles the peak value. 7000 divided by 2 is equal to 3500W, which means that the air conditioner with 1000W power must be equipped with an inverter with power above 3500W to start.

Nowadays, air conditioners are equipped with frequency converters. We can calculate by 4 times the peak value, 1000W inverter air conditioner, 4000W peak value, and 2000W inverter for safe operation. So with 1000W air conditioner, we can buy inverters between 1500W and 2000W.

If it is a solar lamp or a light bulb, all of them are purely resistive, so the size of the bulb can be matched with the inverter. For example: a 500W inverter must be able to drive a 500W bulb. If it cannot be driven, it proves that your inverter is rated for high power. Now on the market, especially on Taobao, 300W, 500W standard, 1000W standard, 1000 standard 2000. According to the inverter standard, the actual output power reaches 90% of the nominal power as a qualified product. For example, a 500W inverter can drive a 450W bulb at least. If it doesn't work, what you buy is a parallel product.

Battery bank calculation

The correct battery for your power inverter

Let's take a Lead Acid battery example. To be able to imagine how long your inverter can be operated with your battery, there is also a simple way.

t:  operating time

V: battery voltage

Ah: battery  capacity

80%: usable battery capacity percentage)

90%: Inverter convert efficiency

W: the rated wattage of the converter
t  = V x  Ah  x 80% x 90% /  W
In one case it would look like this, for example:

t = (12 V x 220 Ah x 80% x 90% ) / 1000 W / 90% = 1.9 h

It means that you can only run a 1000 watt inverter with a 12v/220Ah battery for just under two hours within the battery recommendation range.

Photo by james kovin on Unsplash
Photo by daffa z on Unsplash

Inverter for Inductive Loads

The above are all theories, and many people may not be able to understand them. If they have the ability to understand, they don't necessarily want to study. Below, I will list the inverter power to be equipped with commonly used electrical appliances.

1. For purely resistive household appliances such as heating wires, light bulbs, and solar lamps, the power marked on the electrical appliances is divided by 0.9, for example: 100W bulbs, 100 divided by 0.9=111 , So we can use a 120W inverter safely.

2. There are two types of TV sets, one is LCD and the other is CRT. For LCD TVs, as long as the inverter is twice the power of the TV standard. For example, if the LCD TV standard is 100W, we can definitely use it with a 300W inverter. For the picture tube, because of the large capacitance, the degaussing coil is equivalent to an inductive load, and the impact force is very strong. Generally, it is calculated as 10 times the peak value, such as: 100W, the peak value is 1000W. We need to be equipped with an inverter above 500W to drive.

3. For the computer, if it is a liquid crystal display, select the LCD TV point plus 90W power (computer host power), if it is a kinescope, press the nominal power of the selected display to calculate its peak power plus 90W (the host power is generally 90W) Within) select. If it feels troublesome, just use a 500W inverter, absolutely no problem.

4. Hand electric drills are calculated as 3 times the peak value (the hole is drilled under no-load and stable operation, so the peak value is small), such as: 500W, peak 1500W with 800W inverter, 1500W, with 3000W inverter. Pumping machine, household 500W, calculated as 7 times (pumping at the start, full-load start work, peak start is large), peak value, 3500W, need to be equipped with 1800W inverter, 750W pump, and 2500W inverter for safe operation .

5. For air conditioners, the non-frequency conversion is calculated as 7 times the peak value, and the frequency conversion is calculated as 4 times the peak value. For example, for an air conditioner of 1000W per hour, 7 times is 7 is 7000W, and the peak value of a 3500W inverter is 2 times, which is just right
7000W. The frequency conversion is calculated by 4 times, the 1000W peak is 4000, and the 2000W inverter peak is just 4000W, so 2000W is also used for the frequency conversion. It is true that the rich can afford to use the inverter to power the air conditioner.

6. For some low-power electrical appliances in the family, we don't have to think too much, because a 100W inverter is only sold for 70 yuan in the market. In fact, if it is the general household appliances such as TV, computer, stereo, fluorescent tube, we can equip a 500W, the price is not high, more than 200 yuan, it is like a car refrigerator, or several appliances in the house at the same time. , Buy 1000W, the price is 400 yuan/unit.

7. For special purposes, such as juicers, mixers, impact drills, air conditioners, refrigerators and other electrical appliances, it is indeed very difficult to choose, please read the instructions from 1 to 5 carefully.

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Post time: 11-04-2021