Using a 3 terminal capacitor

[revtintin]

Hi,

I'm in the middle of building a PSU, and I ended up ordering a pair of 3 terminal capacitors (instead of the 2 I'm familiar with). I wired up and tested them just using one of the +ve terminals and the readings were as per the book I'm following.

What's the extra +ve terminal for? Also, I'm supposed to have used "phenolic strips" to mount the capacitors, providing a "3 chassis mount insulated tie points" for them... but I don't quite understand. Does anyone know what kind of hardware these would be? A link to some actual parts in say Mouser/Digikey would be very helpful.

Thanks!

[David Hess]

What's the extra +ve terminal for?

The extra terminal is to make the capacitor polarity unambiguous; a three terminal capacitor can only be wired up one way.

Also, I'm supposed to have used "phenolic strips" to mount the capacitors, providing a "3 chassis mount insulated tie points" for them... but I don't quite understand. Does anyone know what kind of hardware these would be? A link to some actual parts in say Mouser/Digikey would be very helpful.

That sounds like these.  They mount to a chassis and provide several insulated terminals.

http://www.mouser.com/Connectors/Terminals/_/N-5g5uZ1yzvvqx?P=1yztjf0&FS=True

[Phoenix]

I ended up ordering a pair of 3 terminal capacitors (instead of the 2 I'm familiar with).

Do you have a link to what you ordered?

[Zero999]

What sort of capacitor is it? I can think of two types of capacitor which have three terminals.

[revtintin]

The ones I ordered are: http://www.mouser.sg/Search/ProductDetail.aspx?R=401X442U050AK8virtualkey59850000virtualkey598-401X442U050AK8

[wraper]

Did you ever open the datasheet at all? It obviously says "no internal connection" on 3rd pin, it's there solely for mounting robustness.

[revtintin]

Did you ever open the datasheet at all? It obviously says "no internal connection" on 3rd pin, it's there solely for mounting robustness.

I'm ashamed to say I didn't! Thanks for pointing that out. I am still curious if this is the case for all 3 terminal capacitors .

[wraper]

Not always, it may have 2 capacitors inside with one common connection. But this was common it the past, not nowadays. I cannot remember when I've seen  such last time.

[Zero999]

Not always, it may have 2 capacitors inside with one common connection. But this was common it the past, not nowadays. I cannot remember when a saw such last time.

Or it could be one capacitor, with two pins to either the positive or negative, in which case they should be connected together. Always check the data sheet.

[revtintin]

Thanks all. I will definitely study the data sheets more from now on.