Tag: INVT VFD

A 55KW inverter of the Envision suddenly shut down in thunderstorm weather, with no display on the panel, suspected of being damaged by lightning strikes.

Inspection: Both the input rectifier module and the output inverter module are undamaged. The switch power supply has no output, the switch tube is damaged, and the copper foil strip introduced by the power supply and the copper foil strip of the switch tube drain circuit have all detached from the substrate, indicating that this circuit has been subjected to high current shocks.
After replacing the switch tube and oscillation block 3844B, the switch power supply was first sent to an AC 220V rectifier power supply, which did not vibrate and confirmed that there was no short circuit phenomenon; Then send in a 500V DC power supply, and when powered on, the power supply will burn and fuse F1 will be introduced. Power outage measurement inspection, no short circuit phenomenon. After replacing the fuse, power on. When it is below 300V DC, it does not vibrate, but when it is sent to 500V, the fuse still burns. When there is a short circuit fault in the load circuit of the power supply, the power supply often cannot vibrate; It is suspected that there is a short circuit fault in the circuit of the switch tube after the vibration is triggered, but after measurement and inspection, there is indeed no short circuit phenomenon. Maintenance has entered a dead end.
Carefully observe the circuit board of the switch power supply. The approximately 550V DC power supply of the switch power supply is introduced through the main DC circuit, and the circuit board is a double-sided circuit board. The power supply terminal is located at the edge of the circuit board, with a+pole lead copper foil strip on the front and a – pole lead copper foil strip on the back. It was found that there is a “black wire” between the+and – copper foil strips on the edge of the circuit board! Due to humid weather, the insulation of the circuit board is reduced, causing sparks between the+and – copper foil strips and carbonization of the circuit board. When the power supply voltage is below a certain value, it will not break down. When it is above 500V, it will cause the carbonized circuit board to break down and burn out the fuse. The reason for burning the fuse is not due to a short circuit fault in the switch circuit after vibration, but rather caused by carbonization of the circuit board.

Remove carbides from the edges of the circuit board and perform insulation treatment. When fed into 500V, the fuse will no longer burn, but it will not vibrate. Check that the rectifier diode D38 (LL4148) of the 3844B power supply branch has a certain reverse resistance. After replacement, the machine tested normally.
The circuit board is broken down and carbonized after being damp, causing a fuse burning fault, which is also a relatively small fault phenomenon encountered in switch mode power supplies.