Capacitor polarity - UK Vintage Radio Repair and Restoration Discussion Forum

baff1957 · 19th Jul 2020, 11:11 am

Please excuse my ignorance but i thought capacitors always have a polarity? i have to replace two capacitors (C102 and C103 please see pdf attached). The Old capacitors are the wax type and i can see no markings as regards polarity and the replacements are not marked or they are from left to right as viewed positive at the left (the E of Electrica) and negative the other??

Would really appreciate some help, don't want to get wrong.

snowman_al · 19th Jul 2020, 11:29 am

They are not polarised. They can be fitted either way round, it will make no difference.
Only 'polarised' capacitors, electrolytics etc, need to be connected Plus (+) to plus and minus (-ve) to minus. Example in your diagram C1, C2, C3 and C130 etc.

baff1957 · 19th Jul 2020, 12:48 pm

Quote:

Originally Posted by snowman_al

They are not polarised. They can be fitted either way round, it will make no difference.
Only 'polarised' capacitors, electrolytics etc, need to be connected Plus (+) to plus and minus (-ve) to minus. Example in your diagram C1, C2, C3 and C130 etc.

Thank you so much for your prompt reply and sorry for my ignorance. Something else to my memory bank.

Radio Wrangler · 19th Jul 2020, 1:03 pm

Electrolytic capacitors are polarised. They are formed electrochemically after assembly, and running them with a reverse polarity DC voltage across them undoes the forming operation and the capacitor will fail. Quite dramatically for high power ones.

Non-polarised capacitors are simply two strips of foil rolled into a swiss-roll. There are two strips of paper or plastic between the foils to insulate them. The paper or plastic is the dielectric of the capacitor, the bit that does the real work. These capacitors are totally symmetrical and can have voltage across them in either direction. Paper capacitors are failing a lot nowadays due to the ingress of moisture.

Some makers of non-polarised capacitors put a marking band around one end. This tells you which ens is connected to the outermost foil. This is helpful because in sensitive circuits you can get better screening with this connection at the less sensitive point in the circuit.

David

19th Jul 2020, 11:29 am	#2
snowman_al Octode Join Date: Dec 2018 Location: Llandeilo, West Wales, UK. Posts: 1,092	Re: Capacitor polarity They are not polarised. They can be fitted either way round, it will make no difference. Only 'polarised' capacitors, electrolytics etc, need to be connected Plus (+) to plus and minus (-ve) to minus. Example in your diagram C1, C2, C3 and C130 etc. __________________ Never Leave Well Enough Alone...

19th Jul 2020, 1:03 pm	#4
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,901	Re: Capacitor polarity Electrolytic capacitors are polarised. They are formed electrochemically after assembly, and running them with a reverse polarity DC voltage across them undoes the forming operation and the capacitor will fail. Quite dramatically for high power ones. Non-polarised capacitors are simply two strips of foil rolled into a swiss-roll. There are two strips of paper or plastic between the foils to insulate them. The paper or plastic is the dielectric of the capacitor, the bit that does the real work. These capacitors are totally symmetrical and can have voltage across them in either direction. Paper capacitors are failing a lot nowadays due to the ingress of moisture. Some makers of non-polarised capacitors put a marking band around one end. This tells you which ens is connected to the outermost foil. This is helpful because in sensitive circuits you can get better screening with this connection at the less sensitive point in the circuit. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done