Sealer is a heat sealing device suitable for small businesses and home use. Usually 220V AC power supply, heating power of hundreds of watts. Sealing machine produced by the various manufacturers circuit is similar, is to FR-200-type sealing machine, for example, analyze the working principle of the circuit and repair examples.
Circuit see the photo. The machine nominal heating power 350W, sealing the maximum length of 200mm. It has an operating handle, its role has two: First, press the operating handle, the plastic bag to be sealed in the heating bar, the second is to press the power switch K to close. When the switch K is closed, the AC power by R1, R2 buck, diode D1 rectification. Capacitor C1 filter to provide local power supply. The power by R4, VR to C2 charge. Early charge, C2 on the voltage is very small, transistor Q is off, the collector is high, the resistor R6 and LED trigger triac SCR, transformer T was energized. The other is to power the heating element RL, which is sealed by the heat being applied to the plastic bag on the RL. C2 charge to be turned on the transistor Q, collector voltage decreases, not enough to trigger SCR, RL stop heating, lift the handle, remove the plastic bag, the seal will be completed. After the handle is lifted, the switch K is disconnected and C2 is discharged rapidly via D2 and R3 to prepare for charging once. LED Tube LED During RL energization, the LED is used for indication. Adjustable potentiometer VR can change the length of each seal plus time, the specific adjustment of the power supply voltage can be based on the work and the thickness of plastic test is determined.
Common reasons for the local failure of the transformer burned, SCR damage, such as heating bar fracture.
Example 1: Press the handle, the switch K is closed, RL energized and heated, and finally the plastic bag sealing site heating fuse; welding repaired thyristor measured with a multimeter found T1 and T2 have been breakdown between the electrodes. After the replacement of silicon can be repaired. SCR selection 3A / 600V, such as TLC336A.
Example 2: After pressing the handle, the BL can not heat the seal. Open the visual inspection of the shell found transformer has been burned, measuring transformer primary coil has been broken. Available at this time the secondary voltage of about 25V, power and the same transformer can be replaced after the original repair. The local transformer work intermittently, so its power capacity of about 350W. If the temperature is too high, or continuous use of time is too long, it may cause damage to the transformer, which should be used in the attention.
Example 3: After the handle is pressed down, the heating temperature can not be adjusted while heating. Maintenance, the main check potentiometer VR, because VR is often rotated, leading to damage to the VR of the carbon diaphragm. With the new VR for it, you can.