1st posting! I'm a mechanical eng'er with some electronics knowledge and get called to repair old 5v & 15v Linear Power Supplies (Lambda LOD-W 152, Power One HC5, Coutant HSC5 etc). Usually, the large electrolytic capacitor has leaked but for good measure I replace the lot. However, there are so many types (series FK FC M YK etc etc) of smaller cap's that I don't know which to use. RS Components used to list the application the cap was best suited to, but not any more it seems. Whether I pay 15p or 50p makes no difference I just need to know which series (or technical spec / esr / ripple etc) I should be using. Thanks in anticipation.

 

hi,
This may help with the smaller type capacitors.

E

EDIT:
Added 2nd pdf

 

Thanks Eric, but that's way too much info for me to digest. What I'm really after is.... is there a rule of thumb for types of capacitors suitable for (5v & 15v Linear Power Supply Units). For Panasonic the choices include M, FC & FM series and say for Rubycon you have YK, PK, ZL & YXJ. Or.... Provided it is the correct capacitance & voltage will any capacitor do? Ahh I've just spotted the "Product Information" tab on RS Website that gives a description of the typical usage of the capacitor ~ so I may have answered my own question!

 

You aren't working with an inverter or a high speed switching supply. ESR isn't as important in linear supplies. I'm not even sure ESR was invented when I was designing them, 40 years ago.

Electrolytic caps leak.
Mark the original capacitance and voltage on the chassis or circuit board. Buy the same voltage and capacitance or higher, but not much higher, never more than 2X the original size or voltage. If there is any suspicion that these will be in a warm place, get 105 C temperature rating, or do that "just in case". Make no attempt to get tiny capacitors. The physical size is how they get rid of heat. Modern capacitors are always smaller than they were 10 or 20 years ago. Don't bother with the little ceramic or polywhatever caps. They almost never fail, even after 50 years. Watch for the lead spacing so they will fit the holes. That's about it.

ps, try a good vendor (not radio shack) http://www.mouser.com/

 

Ta' for the info, some of which I knew already, like using higher voltage caps if the correct one is not available ~ however someone told me it's okay to go lower PROVIDED it's not lower than the output voltage of the PSU but I wasn't aware of the never exceed twice the voltage 'rule'. Thanks also for the heads up on 'long life' ceramics et al.

 

someone told me it's okay to go lower PROVIDED it's not lower than the output voltage of the PSU.

That only applies to one capacitor, the output capacitor. The primary filters will always be higher voltage than the output voltage. "Someone told me" goes right out the window here. You're dealing with the pros now...if you can spot which ones they are.

 

I suspect you are not in the U.S.
Please go to "User CP" and type in some description of where you are so we can tell you that Maplin stinks as badly as Radio Shack.

 

I'm in the UK and buy my bits from RS Components ( uk.rs-online.com ) or Farnell (uk.farnell.com ).

Radio Shack's UK High Street operation "Tandy" closed down a long long time ago. The Maplin store is 3 minutes from my house but I don't use them.

thanks once again.