Hello,

I'm working on a repair of 8 kW Alesco A800 heater used in car/truck shops in order to loosen screws. I will start with some basic information in order to make thing a bit clearer. Device consists of a power unit, hose package and the actual induction head as can be seen on the picture bellow. Everything from the IGBT's to the head itself is water cooled. Cables that run from the device to the head are inside a tube with water. In the handle itself there is a built in transformer and the actual coil is a block at the end of a copper part which is also water cooled.


There are no errors on the device itself, but it does not heat metal at all.

I did the following in order to diagnose the problem:

1. Hi-pot test between one of the hose package wires and ground (as per the service manual).
   1. It failed at around 400 V (1000 V it's recommended maximum voltage), so Nok.
2. In order to make sure that the device itself is ok I did the following:
   1. Measure voltage on the capacitor bank.
      1. Ok.
   2. Did a diode test on the power side of the IGBT.
      1. Ok.
   3. Measured drive signals of the IGBT and here is where things get a little bit confusing.
      1. If i measure with oscilloscope while pressing the trigger I get pulses with Vmin approx -9 V and Vmax +9V, which seems about right to me.
      2. Unfortunately I was not able to connect the ground and probe directly to the Gate and Emitter of the Igbt, because I was in lack of space and stand, so that's way I used a multimeter to find an accessible component that is connected to the Emitter and put a ground lead on it.
         1. 
         2. 
      3. According to the service manual you should check the board using a multimeter as per the image bellow and the voltage on both (Hi side and Low side should be ~-9 V).
         1. 
         2. 
         3. As far as I can see I should measure this voltages without pressing the trigger, because there is no requirement to press it in the service manual.
         4. If I do so with a multimeter I get ~+9,6 V, but in the manual it's stated that it should be ~-9 V.
         5. IGBT (CM300DY-24NF) is switching between -200 V and +200 V.
            1. In a standstill state both of the channels should be open, so the voltage according to polarity on the image above should be as measured (+) and not as per service manual (-) to my understanding.

Can someone please confirm that my way of thinking is right or wrong. Hose package is expensive (1 k€ +) and there is no way to return it, so I don't want to make a mistake.

If you need any additional info I can provide it.

Thank you very much in advance.

 

Without the trigger being pressed, there is a clamping voltage applied to keep the residual capacitance of the gate on the IGBT from creeping up and possibly turning it on. The plus/minus voltage sounds about right for the driver. If you can isolate the IGBT, do a diode test to ensure it's ok. There are a million write-ups on google as to how to do this.

 

Hello @Regected424,

thank you very much for your reply. I was waiting for a possible response here for a while and than pulled the plug saying to me that I need to believe in my self. About a month has passed since the induction heater is back running. PCB and IGBT were fine, there was a problem with the hose package (water cooled cables + transformer in the handle part).
Before posting here I already checked the IGBT with diode test (results were OK), but as said the manual confused me with the wrong data so I started doubting in my understanding.