Hi,
I am repairing a bench linear power supply which also had small corrosion here and there, mainly on the inside of the metal base of the case and a bit on the metal core of the transformer.
I took the supply apart, cleaned the components the best I could and I am now putting everything back together.
When doing these things, I usually check for the resistance between the earth pin on the mains input socket of the unit and the various parts of the supply that are supposed to be earthed.
And, while the transformer is mounted directly to the metal base of the case using metal brackets and metal screws, when measuring the resistance betwen the earth pin and the metal core of the transformer, I get a value of about 500 Ohms.
Measuring the resistance between the earth pin and the metal base of the case itself, I get close to 0 Ohms.
The questions I have related to the transformer core somewhat floating (i.e. 500 Ohms to earth) are:
- Does this pose any kind of risk?
I wouldn't think so, since, even if there was a failure with one of the windings and the metal core would become live, a person would not normally come into direct contact with it, when the supply is fully assembled. - Could it affect the performance of the power supply?
I am thinking of things I personally can't fully grasp (yet), but wonder whether they might be relevant here: e.g. parasitic capacitance and coupling.
Thanks!