Principle and maintenance of household air purifier

The air purifier can remove dust, odor and harmful gas, kill bacteria and mold, and improve indoor air quality by means of indoor air adsorption, filtration, catalytic decomposition and release of negative ions.

1、 Working principle

Typical air purifier consists of high-voltage circuit, negative ion generator, air fan, air filter, etc. It mainly adopts infrared remote control, intermittent operation and other control methods. The filter forms include mechanical, electrostatic and mechanical electrostatic hybrid.

There are two forms of high-voltage generation circuit: one is direct boost of 220V mains power and double voltage rectification. The other is that the mains voltage is reduced and rectified by a transformer to form a low voltage DC, and then boosted, rectified and filtered by self-excited oscillation to form a DC high voltage, as shown in Figure 2. The high voltage generated by both types of circuits is between kilovolts and tens of thousands of volts. The charged dust is attracted to the positively charged electrode plate through needle electrode discharge. The air filter uses activated carbon or Euryale like ketone to absorb odor and filter out harmful substances in the air. The negative ion discharge electrode is a group of needle shaped metal bodies, as shown in Figure 3. After the power is turned on, the DC high voltage generated by the high-voltage circuit continuously ionizes the air, producing a large number of positive and negative ions. As the needle shaped emitter has a negative high pressure, it absorbs positive ions, and a large number of negative ions are repelled by the negative high pressure and blown out by the breeze fan, forming a negative ion wind to purify the air.

2、 Common troubleshooting

Example 1. The high voltage indicator does not light up and the fan does not turn.

Analysis and maintenance: the high-voltage indicator does not light up, usually because the power fuse is blown or the high-voltage generating circuit is faulty. The inspection shall be carried out in the following order:

(1) Check whether the fuse is broken. If it is broken, find out the cause and then replace it.

(2) Check whether the coil of the step-up transformer is burnt out. Use a multimeter to measure its resistance. If the coil is open or short circuited, replace it with a transformer of the same model.

(3) Check whether the rectifier tube and capacitor of the voltage doubling rectifier circuit are damaged and whether the oscillator stops vibrating. Use a multimeter to check the relevant components one by one and replace the burnt components to eliminate the fault.

Example 2. The high voltage indicator is on, but the fan does not turn.

Analysis and maintenance: the high-voltage indicator light is on, indicating that the high-voltage generating circuit of the power supply is normal, and the fan may be faulty. First, check whether the fan blade is stuck by foreign matters and whether the bearing is severely worn. If there is no abnormality, check whether the motor lead is open circuit and whether the winding is damaged. Use a multimeter to measure. If the winding is open or short circuited, replace the fan motor with the same specification.

Example 3. Ignition between electrodes of negative ion generator.

Analysis and maintenance: The ignition between the electrodes of the negative ion generator may be caused by the high humidity of the ambient air or the bending and deformation of the positive and negative electrodes. Use tweezers to correct the pole piece first. If the ignition is still on, move the air purifier to a dry place for trial use. Generally, the fault can be eliminated.

Example 4. The output concentration of negative ions is low.

Analysis and maintenance: there may be too much dust and dirt on the filter screen and electrode, and the positive and negative plates are bent and deformed; It may also be caused by the high voltage too low due to the failure of the high voltage generating circuit. First remove the dirt on the filter screen and electrode, correct the positive and negative plates, and then check the high-voltage generation circuit if it is invalid. Use a multimeter to check the step-up transformer, rectifier tube, capacitor, etc.

Note: When cleaning the dust on the fan motor and electrode, be sure to cut off the power supply, unplug the plug, short-circuit the high-voltage electrode for discharge, and use a long brush to remove the dust; Clean the electrode holder with tweezers and alcohol cotton ball; Do not disassemble the high voltage electrode of the negative ion generator.