Too much capacitor?
- Thread starter Michael F
- Start date
wattsabundant
Chief Journeyman
They're right on the edge voltage wise. You're asking for trouble. The common safe cap is 160V.
Not enough voltage...they will make a mess in your amp when they erupt...
wattsabundant
Chief Journeyman
With respect to the rectifier, the short answer is the cap won't hurt the rectifier. As Joe points out it will make a mess inside the amp when it vents due to over voltage.
Having done some testing, the worst case inrush current I've been able to capture on a 700B was about 150 amps on the first half cycle after power was applied. The typical 25A bridge rectifier, which is what is used in the P/L amps, can withstand 250-300 amps during the first half cycle.
The attached scope image shows the rectifier current (magenta) going into the capacitor and the secondary voltage (aqua). Current is 50Amps/division. This was taken with 20,000uf caps. In the first datasheet, surge current (Ifsm) shows 300A for the 25A bridge. The second data sheet, figure 2, shows maximum current curve over several cycles. Interesting enough, the 12A bridge has the same rating as the 25A bridge.
Having done some testing, the worst case inrush current I've been able to capture on a 700B was about 150 amps on the first half cycle after power was applied. The typical 25A bridge rectifier, which is what is used in the P/L amps, can withstand 250-300 amps during the first half cycle.
The attached scope image shows the rectifier current (magenta) going into the capacitor and the secondary voltage (aqua). Current is 50Amps/division. This was taken with 20,000uf caps. In the first datasheet, surge current (Ifsm) shows 300A for the 25A bridge. The second data sheet, figure 2, shows maximum current curve over several cycles. Interesting enough, the 12A bridge has the same rating as the 25A bridge.
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Michael F
Journeyman
Thanks for the replies Gents.
And here I was worried about too much capacitance. Are the original caps not rated 100vdc or were those ratings more conservative than modern caps?
I could have got those for $50 cdn a pair compared to $230 online
And here I was worried about too much capacitance. Are the original caps not rated 100vdc or were those ratings more conservative than modern caps?
I could have got those for $50 cdn a pair compared to $230 online
Today they stuff more capacitance in the same can size and gave up voltage margin to get that as a trade off