How to check fault in transformer?
Posted: Sun May 22, 2011 3:42 am
On Friday I did a booboo. I have a 600V/600mA old fashioned linear electrophoresis supply, in which both sides of the output are isolated. I caused the outputs to float high and they probably [can't tell for sure - no part of the system is intentionally grounded] ended up going 5kV to ground.
(There's a lesson in there for deciding when to tie to ground and when not, I guess, but it was an experiment and if I knew exactly what was going to happen then it wouldn't be!! )
Well, a transformer-type humming started up and then the fuse blew. I was hoping it was a short to ground of a small part, but oddly, after desoldering each part in turn to trace, the fault appears to be in the isolation transformer itself.
What is odd is that there is no short to ground in it, but it seems to be a short in the secondary. The resistances all look OK on the terminals so I suppose what has happened is that a couple of turns into the secondary coil something has fused making an alternative 'few-turn' coil causing very high current internal load that I can't see.
Does this make sense? And perhaps it just gave up (being 40 years old) and was unrelated to terminal float?
(There's a lesson in there for deciding when to tie to ground and when not, I guess, but it was an experiment and if I knew exactly what was going to happen then it wouldn't be!! )
Well, a transformer-type humming started up and then the fuse blew. I was hoping it was a short to ground of a small part, but oddly, after desoldering each part in turn to trace, the fault appears to be in the isolation transformer itself.
What is odd is that there is no short to ground in it, but it seems to be a short in the secondary. The resistances all look OK on the terminals so I suppose what has happened is that a couple of turns into the secondary coil something has fused making an alternative 'few-turn' coil causing very high current internal load that I can't see.
Does this make sense? And perhaps it just gave up (being 40 years old) and was unrelated to terminal float?