Hey,
I was wondering if somebody could shed some light on the problems I am having.
I'm trying to build a variable speed drive. Because of some unique requirements I have been forced to make it myself instead of buying a cheap OEM version from somewhere else. Oh what a drama this has been.
Well, my latest problem was that when a motor was connected the motor would spin for maybe 1 or 2 seconds, then pause for a second or so and then keep going. Sometimes it would stall completely. Now, when I was using rectified 240VAC the motor would run no problem and exactly like I wanted. When it was powered off 415VAC (which is what I need) it had the stalling behaviour. Weird.
I tried a lot of things to fix the problem. In my efforts I connected a much larger smoothing capacitor to the DC bus. Well, actually 2 x 220uF 400V capacitors in series, giving me 110uF total. When I was running it at 240VAC I was using a 40uF capacitor.
When I turned the drive on the motor ran fine for probably 4 or 5 seconds and didn't appear to stall (it normally would have at this point). Then there was an explosion. A fairly big explosion. It tripped the main breaker (300A) to the building. It also did something I've never seen before - the IGBT driver chip (which is a 44pin PLCC) now has a nice round hole in the casing.
This was about the last thing I expected to happen from adding a larger capacitor.
And just for everyone's information, everything is rated for 1200V.
I was wondering if somebody could shed some light on the problems I am having.
I'm trying to build a variable speed drive. Because of some unique requirements I have been forced to make it myself instead of buying a cheap OEM version from somewhere else. Oh what a drama this has been.
Well, my latest problem was that when a motor was connected the motor would spin for maybe 1 or 2 seconds, then pause for a second or so and then keep going. Sometimes it would stall completely. Now, when I was using rectified 240VAC the motor would run no problem and exactly like I wanted. When it was powered off 415VAC (which is what I need) it had the stalling behaviour. Weird.
I tried a lot of things to fix the problem. In my efforts I connected a much larger smoothing capacitor to the DC bus. Well, actually 2 x 220uF 400V capacitors in series, giving me 110uF total. When I was running it at 240VAC I was using a 40uF capacitor.
When I turned the drive on the motor ran fine for probably 4 or 5 seconds and didn't appear to stall (it normally would have at this point). Then there was an explosion. A fairly big explosion. It tripped the main breaker (300A) to the building. It also did something I've never seen before - the IGBT driver chip (which is a 44pin PLCC) now has a nice round hole in the casing.
This was about the last thing I expected to happen from adding a larger capacitor.
And just for everyone's information, everything is rated for 1200V.