Induction heater

[foxi1528]

Hi everyone. I am new here but looking for little help. Tried to fix an induction heater who was burn out the fuse. I've changed one of four IGBT who was burn, and the big diode between rectifier and IGBT. But I stupidly tried without safety lamp and the fuse burn out again. Now I get decision to change the both capacitors 4,7 nF 2kV and also discovered two burnt diodes who are in series and stay after collector of IGBT. Their sign is CU310 but I can't find anything for them and what replacement I can to use. Does someone know something about them? I began to be sceptical about that repair on that heater

 

[BradtheRad]

Two diodes in series... likely needed because one diode has insufficient voltage rating? Perhaps in the area of 2kV similar to the capacitor rating you mentioned.

As for an unknown Ampere rating, the diode's physical size is a clue. Plain silicon 1N4007 is rated 1kV 1A. Or perhaps yours is larger, then investigate diode Amp ratings in the same physical size. Consider an even greater Ampere rating since your unit burnt the existing diodes.

--- Updated Dec 15, 2023 ---

 

[foxi1528]

That, with the voltage was a good input. The 1N4007 is twice as narrow as this. In the photo you can see the two missing, a little further down and to the left are the two on top of each other for the other pair of IGBTs. The two collectors of one pair are connected to the working coil of the inductor and to these two diodes and to the resonator capacitor 0.25 microfarad 800V. The other two collectors of the other pair respectively to the other two diodes and the other end of the capacitor and coil. And these capacitors that I will replace are connected to the collector by means of a 4.7 ohm resistor and the capacitor goes to so as I look at the IGBT drivers. I assume some kind of feedback. And I ordered diodes for 400 volts... I don't know if they will burn out. There are rectifier diodes and Schottky diodes in this case

, I have no idea what their role is even there... However, one thought has entered my head, why does the machine short out and burn the fuse only when plugged into the network without actually starting the machine. Tomorrow I will connect through a load lamp to see voltages here and there, but in general my ideas are coming to an end...

 

[tepalia02]

For the capacitors (4.7nF, 2kV), it's essential to use capacitors with similar ratings. Ensure they are rated for the same voltage and capacitance. Using components with different specifications could lead to further issues or failures.

 

[foxi1528]

I changed them because they had difference in the capacity. The new are double smaller , and came 50 in one pack. I just grab two but didn't check their capacity. I hope they will be same value.

 

[foxi1528]

Guys can you explain me something. Two couples of IGBT working together. When I measuring with ommeter between collector and emiter give me almost zero ohms. But if I removed them from the board the values are normal. This happened only with one of the couple. Also if the main inductor isn't connected the test lamp not running. But if I connect the inductor the lamp running at full power, so that means there is short circuit. If it possible the problem to be with IGBT.

 

[D.A.(Tony)Stewart]

CU310
CMR3U-10
Central Semiconductor
DO-214AB
Diode
U-fast recov. rectif, 1000V, 3A, Vf<1.7V(3A), <100ns

 

[foxi1528]

CU310
CMR3U-10
Central Semiconductor
DO-214AB
Diode
U-fast recov. rectif, 1000V, 3A, Vf<1.7V(3A), <100ns

Yes I used almost same. The case is same DO -214AB. At previous posts I was showing what I got.

 

[BradtheRad]

Also if the main inductor isn't connected the test lamp not running. But if I connect the inductor the lamp running at full power, so that means there is short circuit.

I guess the heating unit is a large coil (inductor)? And it presents a load (medium impedance) to high frequencies? But suppose it's getting only a low frequency (or mains frequency 50/60 Hz), then it offers low resistance. Maybe carrying sufficient Amperes to blow a fuse immediately as well as a few components in the power supply.

Can you diagnose whether a high frequency oscillator is operating in the unit? If that is malfunctioning then you must fix that besides the other components you worked on.

 

[foxi1528]

Can you diagnose whether a high frequency oscillator is operating in the unit? If that is malfunctioning then you must fix that besides the other components you worked on.

Yes, that's right, almost identical to an induction hob. Unfortunately I don't have an oscilloscope to check what is coming to the gate of the transistors. However, there are two transformers for operating voltage, for the control board and for the operation of the transistors. When I isolate them and apply power only to the power part, two of the four transistors are unblocked. This confuses me, only one pair gives a short between C and E but if I remove them from the board and test them one by one there is no short. I ordered the other three to make sure it wasn't one of them. The other thing that confuses me a lot is that the device burned out when it was simply connected to the network but in non-working mode. Schematically, +310V is available even when plugged into the outlet. The two operating transformers also operate continuously. And something happened, with the effect of burning the IGBT (one of the other pair) and the power diode between the rectifier and the IGBT. I have two theories, one is that the IGBT gave a problem and caused the short, and the other is that the IGBT control gave a false signal that turned on the IGBT when the machine was not running.