OK... Here is what happened to PLCProf's 180w brick (and keep in mind that he has made a great sacrifice to the cause):
First thing to know is that an "angry pop" is a short in the 120v side. (See https://ogrforum.ogaugerr.com/t...ly=69425981492981028 for a factoid #2 that explains why the current involved is between 100 amps and 1000 amps. My post is 12th one down, similar to my post above here on cascade protection, except I had added some useful things to know.)
So what destroyed the Light Country rocker switch type RA1 (formerly R19A) of 6A 250v UR rating? A current of somewhere between 100 and 1000 amps passed through it. If the house 120v panel breaker did not open, then the switch or some part of the circuit board on which it was mounted was blown to pieces, or the point of short was burned clear. This switch is on-off, and one of a family of 2A--6A--15A switches. Being Chinese-made you don't get much more than it will switch 6A, meaning open 6 amps. How much it will carry while closed is not stated, but it has silver contacts so likely will carry 20A without a problem (8w heating at contacts). I'd even hazard 50A for a short period. But not 1000 amps. How far away (on a scale of 10 to 100 feet (which roughly corresponds inversely to the 100 to 1000 amps) was the service panel from the wall outlet?
But in all likelihood this switch (SW2) was not the problem, but the victim. Of what?
Well, the secondary coil carried 45 amps for a very short while, which was approached slowly (slowly in electrical terms). The rate of heat generation in the low voltage load side coil would be about 800w. The line-side coil would have carried about 6 amps (isn't that a coincidence?) with a heat rate of about 120w. As a general rule, in this situation you want the insulation in the primary coil (line-side 120v) to fail first. That is so you get a breaker opening on the wall outlet before you get a transformer fire.
The "bricks" are low reactance transformers. This is accomplished by winding one coil entirely over the other. Which? Well, you wind the 120v coil under the 18v coil. That way its heat is trapped and its insulation fails first. BAM! 120v short and the Light Country switch SW-2 is blown to pieces, through no fault of its own.
Meanwhile, the progressive destruction of the circuit board due the 45A short on the output is halted.
It would be interesting to break open R-1, the Millionspot 15A relay, and see if this exercise welded its contacts together...
There is at least one case of a brick with welded R-1 contacts in the historical record of 86 failures of the unfused first TUI's that I investigated about 16 years ago. I immediately opened a 135w brick lying to hand and understood at a glance (10-amp sugar-cube sized R-1 relay) what trouble cutting the special plug was causing. So I chased down a copy of UL 697 ($600+/40-odd pages those days to buy one) and confirmed this was a UL-approved cascade protection arrangement.
Cascade protection actually works, if done correctly. If done correctly. Your modern house service panel actually has the smaller breakers in cascade with the master breaker, in most cases.
About every two years I take another stab at trying to explain this situation here on the OGR board, totally without success. But given the rate at which equipment is generously being destroyed in this discussion, and number of rather skilled people looking at all the pictures of the wreckage, I have renewed hope.
--Frank
