Exactly What Is A PETP Capacitor?

[ToolGuyFred]

... But it's true nonetheless - switching high voltage DC will destroy switches...

My day job involves industrial control equipment. You will very often find a switch or relay contact rated at a given current for 240V AC or 24V DC. Experience also supports this recommendation. If you exceed the DC rating then the insulation bears up OK but the contacts don't last long at all. If you have to switch high voltage DC then use an appropriate MOSFET, IGBT or SCR and only ever for control: don't rely on this solid state stuff where your safety is concerned. If they fail they usually fail short-circuit.

(Edit)
On reflection, probably best to avoid SCRs for amateur use: you can latch them on OK but switching them off while they're passing DC current can be a bit of a chore...

[Grainger49]

Ed is that a 35V 2200uF inside the can of a 60V 6800?  I can't quite read the voltage on the outer can.

I have heard of counterfeit capacitors.  This is the first I have seen.

[Grainger49]

... But it's true nonetheless - switching high voltage DC will destroy switches...

My day job involves industrial control equipment. You will very often find a switch or relay contact rated at a given current for 240V AC or 24V DC. Experience also supports this recommendation. If you exceed the DC rating then the insulation bears up OK but the contacts don't last long at all.  .  .  . 

I used to work for Alcoa in a rolling mill.  The big motor was 14,000 Hp (an Westinghouse motor built in 1942).  I wish I could get a picture of the DC contractor for that motor.  It was HUGE!  It wasn't allowed to close with voltage across it.  But an emergency stop would open it under load.  It was like a cannon going off over your head.

[ToolGuyFred]

The big motor was 14,000 Hp (an Westinghouse motor built in 1942).

I used to work as an application engineer on Mitsubishi variable speed drives. Never played with anything bigger than 500 Hp (still big enough to command a certain level of respect). Even a 20Hp drive makes a fair bang when the power stage fails - not unlike a .22 rifle going off. (I was once standing next to a 20Hp servo drive when it failed - despite ear defenders my manager looked like heart failure was imminent but commented that I didn't even flinch - maybe too much time on the rifle range?)