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Old 6th April 2010, 05:50 PM   #1
Join Date: Nov 2006
Location: Torpoint
Default What fuses to use

I am building a 80Watt / Channel Class A Amplifier based roughly on a Mark Levinson design.

The PSU uses 2 x 500VA Toroidal transformers ( 4 x 45V secondarys) feeding bridge rectifiers then nearly 0.5F (yes 1/2 a Farad) of capacitors each. So each secondary has a capacitive load of about 0.5F.

The transformers are rated at 5.1A per secondary.

So far every fuse that I have tried has blown (10A Time Lag) and (5A Anti Surge). The fuses are in the secondary supplies to the bridge rectifiers. The rectifiers are rated at 35A and neither the transformers nor the regulators have come to grief.

What size, and what type, fuses would you recommend?

The amplifiers are expected to pull about 4A at full output.

Intuition states that I should use 4 x 1.3 = 5A Anti-Surge but these can't survive the inrush current of the huge capacitors.

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Old 8th April 2010, 04:45 AM   #2
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Location: Portland,Oregon
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With that much capacitance,I'd think it's time to consider a soft-start circuit!
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