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I just want to share the repair progress of the small SMPS welder i was dealing with about a month ago and get some opinions .
So after checking the PWM IC i get a stable square wave at the output , now the thing that was causing the short was actually the replacement IGBTs (60N100) that were handling more power than the original ones , i don't know how they could make those shorts happen ; But after replacing them with originals ( G30N60) and a leaky start up resistor , i worked with the welder just fine with no BANG .
Are you saying you had a win?
If so, are you saying the replacement mosfets were wrong for the job.
If so, I will have a look at the specs to see what's what.
i guess 60n100 is 60 amp 1000v and 30n60 is 30 amp 600 volt. If so, I would be looking at the thermal resistance. But get back with the answers to my questions and will have further look for you.
Are you saying you had a win?
If so, are you saying the replacement mosfets were wrong for the job.
If so, I will have a look at the specs to see what's what.
i guess 60n100 is 60 amp 1000v and 30n60 is 30 amp 600 volt. If so, I would be looking at the thermal resistance. But get back with the answers to my questions and will have further look for you.
hello rumpfy !
Well its a win since everything went very well on the welding process .
And yes the mosfets were not good even with higher ratings ( very strange ) according to a friend of my father ; He told me that the kind of welders am trying to repair need replacement parts identical to the original ones , and it seems that he's right on that .
The 60N100 has a thermal resistance of 0.69 deg C / watt and the 30N60 has 0.50 degC/watt.
The 60N/100 has an input capacitance of 6000 pF and the 30N60 has 1920 pF max.
Both these parameters are better in the 30N60. The switching characteristic of the 60N100 would be slower and device dissipation could be worse and the thermal resistance being worse in the 60N100 would allow it to overheat under working conditions.
I found these two parameters quickly; there may be others but I would choose the 30 N60 over the 60 N100.
In device comparison, you need to look past the max volts/max current figures and look at
- Vce sat vs collector current
- input capacitance
- thermal resistance
- switching times/switching losses
So its not always essential to get EXACTLY the same device number, but it is important to get the same characteristics. With high speed switching devices, device dissipation can increase to excessive levels if care in selection isnt good enough. The heatsink design is based on device dissipation.
I'm not exactly sure why your alternates failed (apparently so quickly) but I would have NOT selected the 60N100 because of the potential problems with increased device dissipation.
Hope this helps a bit.
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