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Electrolytic Capacitors in Power Supply
Hi everyone, I'm back again...
As you aware about S-100 chassis with linear power supply uses large physical electrolytic capacitors to smooth DC. These components are more difficult to find nowadays and more expensive. In many vendors have zero in stock.
For example, I have 4700uF @ 25WVDC electrolytic capacitor blew out due aged. The label stated "Sprague 673D". This capacitor made in 1979 which obvious the electrolytic materials inside already dried out and generate heat buildup in the core. This also same with huge capacitors such as 45,000uF @ 15WVDC for my TEI S-100 mainframe was impossible to find the replacement. I switched the linear power supply for switching power supply and was very successful.
I was thinking about 4700uF @ 25WVDC capacitor replacement. It sounds like that was very easy to replace with any 4700uF from vendors. NO, because the Sprague 673D capacitors are larger than standard one because they handled very high ripple current. I discovered my original one handle about 8 amperes compared with standard one only handle up to 2 amperes current. Obviously, the standard one will generate heat much quick and then blow up.
Wonder if I can solve this situation by use 5 pieces of 1000uF @ 30WVDC, all negative hooked up with negative bus from center-tap transformer to ground. The positive bus from full-wave bridge to multiple +12v voltage regulators. the capacitors are in parallel connect but on positive side of each capacitor connect with 9 ohms 10-watt resistors then other side connect with positive bus. This method will make current into divide and reduce to 2 amperes into capacitor. So then, five capacitors will handle up to 10A current on positive bus side without risk increase capacitor's cores temperature.
Do you think this scheme will work properly? Suggestion?
Thank you very much,