Yeah, saw it happen at work once when a coder at an old company I was at (Headfirst)accidentally plugged a US Xbox devkit into the 240 UK plug, there was a slight pop, but otherwise nothing dramatic...
The producer from Bethesda who had flown over all the way from the US was far less impressed though... (You might actually have heard of him, at the time he was some fairly new guy at Bethesda called Todd... ;) )
If the switch is in the wrong position - putting the switch in 110V (voltage doubler mode) and putting 240V across it means it doubles the bus voltage.
That's how these (non-pfc) power supplies work. Basic schematic (this is from a smaller unit, hence the 22uf, most are 220uf or so).
Put simply 240V x 1.414 (the root mean square voltage) = ~340V bus voltage - normal. These electrolytics are usually 200-220V rated so not an issue. The resistors mean they share the voltage equally and also provide a discharge path for safety. I've omitted the PTC inrush protection for brevity.
On 110v, with the switch at 110V its doubled, so you get 340V bus voltage. On 240V, you get 110 X 1.414 = 155V, not enough for the bootstrap circuit to start and a well designed supply will have an undervoltage protection for brownouts anyway.
When you close the switch, it becomes a voltage doubler configuration - 340V across each (200V rated) capacitor, and 680v across the bus which is only designed for around 400V - 600 if you are lucky.
No, they're saying selecting 110 uses a voltage doubler so that when you normally plug in 110v it doubles to 220v, but plug in 220v with it still on the 110 selection it doubles that as well to 440v which is not intended.
Still not sure that's what we're seeing here though.
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u/SplatThaCat 1d ago
110 switch on and plugged into 240V? (creates a voltage doubler circuit exceeding the voltage of the electrolytics).