Electrical appliances, in terms of technical performance, can be broadly classified into three categories: capacitive appliances, inductive appliances, and resistive appliances.  

Capacitive load refers to the input load that is capacitive relative to the power supply. Common examples in households include televisions, computers, and mobile phone chargers, all of which are powered by switching power supplies and can be considered capacitive loads. This is because these electrical devices all have a large filter capacitor at the input stage. Those familiar with electronics know that capacitors allow alternating current (AC) to pass through but block direct current (DC), but the capacitor current leads the voltage by 90 degrees. In other words, instantaneously, from the perspective of the power supply, it acts as a short-circuited wire. Therefore, these electrical devices exhibit an instantaneous peak value.

Inductive loads, which we commonly encounter, include fans, audio devices (which are typically powered by low-frequency transformers), water pumps, electric drills, air conditioners, and refrigerators. When connected to a power source, their inputs are inductive coils, and a coil is essentially an inductor. Those who understand electronics generally know that the voltage of an inductor leads the current by 90 degrees. This means that when it is momentarily connected to a power source, it is also short-circuited. Only after it starts up and its impedance increases does it operate stably. When we use high-power motors, we can clearly feel that the moment the motor is turned on, the lights and appliances in the entire room flicker. This is peak power, and the instantaneous peak power is many times greater than the power indicated on the motor. For example, if a 500W motor has a 3-time instantaneous starting power, it is equivalent to a starting power of 1500W.

A resistive load, commonly seen in light bulbs, acts as a pure resistor relative to the power supply, eliminating the issue of start-up surge.

How to choose a bulk DC switching power supply in China

Is it produced by a legitimate manufacturer? Legitimate products will definitely have a Chinese trademark and manufacturer, and the packaging will bear the manufacturer's address and phone number. If these are absent, it can generally be judged as a "three-no" product. There are many products in China that are labeled with a bunch of foreign characters, but lack even a trademark or manufacturer. They are even marketed as imported products. It's best not to buy such products. If there is a quality issue, you won't even know who to contact, and don't expect the seller to provide after-sales service guarantees.

Be sure to choose products with metal casings: Due to the high power and significant heat generation of car-mounted bulk DC switching power supplies from China, if the internal heat cannot be dissipated in a timely manner, it can affect the lifespan of components at the very least, and pose a fire hazard at worst. Metal casings, on one hand, have good heat dissipation characteristics, and on the other hand, they do not burn. It is best not to choose products with plastic casings. Even if a fan is added to aid heat dissipation, it increases noise during use and the fan's working life is generally relatively short, which reduces the reliability of the entire machine. If the fan stops working one day, the consequences could be serious.

One must opt for a split-type product and avoid the integrated type. There are four disadvantages to the integrated type. Firstly, due to the shallow depth of the car cigarette lighter socket, the rear of the integrated product is relatively heavy. Bumps during driving can easily shake off the bulk DC switching power supply or cause poor contact. Secondly, when the integrated bulk DC switching power supply is plugged into the cigarette lighter socket, the rear part protrudes significantly, which can interfere with the right hand gear shifting operation, which is closely related to driving safety. This must be taken seriously. Thirdly, as it is directly plugged into the cigarette lighter socket, the rear of the integrated bulk DC switching power supply cannot be used. Fourthly, the integrated shell is made of plastic, and as we all know, plastic is not heat-resistant. Therefore, when the contact part of the integrated bulk DC switching power supply with the cigarette lighter socket passes through high current, it can generate high temperatures, leading to deformation or melting of the head, and in severe cases, even causing a fire. Therefore, whether from the perspective of safety or convenience, the integrated bulk DC switching power supply should not be chosen.

Is the protection function comprehensive? A good on-board bulk DC switching power supply from China should have comprehensive protection functions to safeguard your car and power supply under various conditions. It should also feature an audible and visual alarm function to remind you to promptly address various situations. Common protection functions include input undervoltage, overvoltage protection, overtemperature protection, output overload, and output short circuit protection.

Conversion efficiency: This is a very important indicator for bulk DC switching power supplies in China. The higher the inverter efficiency, the longer the battery can last, and the less heat the bulk DC switching power supply generates. Generally, it should reach over 90%. However, users cannot test this indicator and can only rely on the manufacturer's honesty in labeling. Users can only make a simple judgment based on the heat generated by the bulk DC switching power supply when carrying a high-power load. A good bulk DC switching power supply should be able to operate for a long time without heating up when carrying a load at 80% of its nominal power.

The cigarette lighter plug should be made of bakelite material, with a thick cable and a convenient length for use. Bakelite-made cigarette lighter plugs can operate under high temperature conditions without deforming or burning. Nowadays, products on the market that do not use bakelite-made cigarette lighter plugs are rare. Due to concerns about safety, it is still important to pay attention to this. Bakelite cigarette lighter plugs have a bright appearance, while those made of plastic material appear duller and lack luster.

If the power of the electrical appliance is greater than 160W, it is necessary to use a battery clip to directly draw power from the battery: the car cigarette lighter socket can only pass a current of about 10A, so high-power bulk DC switching power suppliers in China must be equipped with an additional battery clip cable to directly draw power from the battery. Nowadays, some manufacturers, in order to save costs, do not provide a battery clip cable even for 300W products, and they even claim to have passed CE certification, which is ridiculous. Using such products can, at the very least, burn out the car wiring, and at worst, cause a fire. Car owners, please pay close attention.

How to choose a bulk DC switching power supply in China

When choosing a bulk DC switching power supply from China, we must understand the surge capacity of the electrical appliance at the moment of power-on! The surge is only manifested in inductive or capacitive negative electrical appliances. For example, for motors, because they are inductive, the surge is generally between 3 to 7 times. For a 500W motor, the power surge ranges from 1500W to 3500W. Bulk DC switching power supplies from China generally have a 2-time peak value, which means that for a 500W bulk DC switching power supply from China, there is an instantaneous power output of 1000W, 2000W for 1000W output, 3000W for 1500W output, and 4000W for 2000W output. Therefore, for a 500W motor, we should choose a bulk DC switching power supply from China with a capacity of 2000W or more. However, on the other hand, not all motors have a 7-time peak value.

We just need to understand that a bulk DC switching power supply in China can instantly output twice its rated power, and for capacitive or inductive loads, it requires 3 to 7 times the peak power for instant startup.  

Determining whether it's 3 times or 7 times the peak value is actually not difficult. Under no-load operation, it's 3 times, while under full-load operation, it's 7 times. Therefore, we can determine the peak value based on the degree of load driven by the motor. For example, when it comes to a handheld electric drill, we usually operate it under no-load conditions before drilling. So we can calculate it as 4 times the peak value (actually 3 times, with an additional 1 as a margin). For a 500W handheld electric drill, a 1000W bulk DC switching power supply from China would suffice. Other motors can be similarly judged. For air conditioners, which are purely inductive, the starting peak value is very high because the motor operates at full load every time the compressor starts. We can consider its starting as 7 times the peak value. For a 1000W air conditioner, the peak value is 7000W, and a bulk DC switching power supply from China with a peak value of 2 times would be required. Dividing 7000 by 2 equals 3500W, which means that for a 1000W air conditioner, a bulk DC switching power supply from China with a power of over 3500W is necessary for safe operation. Nowadays, air conditioners are equipped with frequency converters, so we can calculate it as 4 times the peak value. For a 1000W frequency-converting air conditioner, the peak value is 4000W, and a 2000W bulk DC switching power supply from China is required for safe operation. Therefore, for a 1000W air conditioner, we can choose a bulk DC switching power supply from China with a power ranging from 1500W to 2000W.

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