UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Capacitors in series

dinkydi · 15th Jan 2012, 2:27 pm

Thanks for that GMB, I think we are in agreement.

Electrolytic capacitors are certainly robust. It has not been mentioned that they have surge-voltage ratings which allow their maximum working voltage to be exceeded by about 50%, for a short time! Also, they can be run continually at high temperatures with a core in the vicinity of 100 degrees C or more. The considerable surface area of the larger sizes means they can dissipate substantial power. While the leakage currents of electrolytics are normally low, circuit designs must nevertheless be able to cope with possible high leakage currents of 10s of mA for medium size, to 100s of mA for very large capacitors.

If you understand this robust nature you can appreciate why those using new-old-stock or recycled electrolytics, and who think that cap oxide reforming is a lot of nonsense, can get away with soldering them straight into a circuit without reforming. Most circuits by default limit the reforming current and the electrolytic is soon purring after reforming itself in situ. However, an occasional exception is in a high-current circuit, directly after a rectifier, for example. If you don't bother with reforming, check the temperature of the just-installed cap with your finger after a few minutes running (don't forget some caps may be at high voltage!). If the cap is warm keep monitoring it until it settles in.

Peter

15th Jan 2012, 2:27 pm	#41
dinkydi Retired Dormant Member Join Date: Feb 2011 Location: Sydney, Australia Posts: 277	Re: capacitors in series - pitfalls? Thanks for that GMB, I think we are in agreement. Electrolytic capacitors are certainly robust. It has not been mentioned that they have surge-voltage ratings which allow their maximum working voltage to be exceeded by about 50%, for a short time! Also, they can be run continually at high temperatures with a core in the vicinity of 100 degrees C or more. The considerable surface area of the larger sizes means they can dissipate substantial power. While the leakage currents of electrolytics are normally low, circuit designs must nevertheless be able to cope with possible high leakage currents of 10s of mA for medium size, to 100s of mA for very large capacitors. If you understand this robust nature you can appreciate why those using new-old-stock or recycled electrolytics, and who think that cap oxide reforming is a lot of nonsense, can get away with soldering them straight into a circuit without reforming. Most circuits by default limit the reforming current and the electrolytic is soon purring after reforming itself in situ. However, an occasional exception is in a high-current circuit, directly after a rectifier, for example. If you don't bother with reforming, check the temperature of the just-installed cap with your finger after a few minutes running (don't forget some caps may be at high voltage!). If the cap is warm keep monitoring it until it settles in. Peter