Having trouble finding suitable fuses

lordvader · 15th July 2008, 05:53 AM

Hey all.

I'm currently working on the power supply for my F3 amplifier, but am having trouble sourcing the appropriate fuses. As per the schematic, the recommended fuse is a 1.25A slowblow for a 240V primary.

My psu is going to be dual mono, so the plan was (is), to have a 2.5A slow blow fuse near the IEC inlet, then a softstart circuit, then a 1.25A slowblow per transformer.

Problem is, all I've been able to find are 1.25A fast blow, and "anti-surge" fuses. Are anti-surge fuses equivalent to slo-blow fuses ? Can I use a fast-blow considering there's already a softstart (not too keen on that one)?

The transformers are each 300VA, and there's 66000uF (33000uF, 2.2mH inductor, 33000uF) for each transformer.

I'll appreciate any input. It's taken me ages to finally get everything organised, and I definitely don't want to make any mistakes as far as fuses go !

Corax · 15th July 2008, 07:27 AM

Anti-surge fuses are a good choice. They can widthstand a 10 times greater current for approx. 10 milliseconds. So they act as a slow-blow fuse.
If you use two 300VA toroid transformers you barely need a softstart for those 'suckers' based on the high inrush current (depending on the moment they make contact to the mains voltage). And with this high capacitiv load (of 66000µF) you bet it will trigger the 'big' fuse in the fuse box of your house.
Consider to use two independent softstarts for each transformer. This way you need only two fuses for the 'final' safety stage instead of three as you mentioned for your setup. There's no need for 'double-fusing' the same circuit.

AndrewT · 15th July 2008, 08:03 AM

Hi,
time delay = slow blow = anti surge and all should be marked TxA, where x=fuse rating.
Look for T1.25A or T1.6A for each transformer.

I think it is a good idea to separately fuse the equipment incomer. 3A will probably do.

golam · 17th July 2008, 07:19 PM

Hi,

Corex is right. Anti-surge fuses can be used in lieu of slow-blow fuse.
But rating should be judged properly.
Thanks.

15th July 2008, 05:53 AM	#1
lordvader diyAudio Member Join Date: Mar 2002 Location: n/a	Having trouble finding suitable fuses Hey all. I'm currently working on the power supply for my F3 amplifier, but am having trouble sourcing the appropriate fuses. As per the schematic, the recommended fuse is a 1.25A slowblow for a 240V primary. My psu is going to be dual mono, so the plan was (is), to have a 2.5A slow blow fuse near the IEC inlet, then a softstart circuit, then a 1.25A slowblow per transformer. Problem is, all I've been able to find are 1.25A fast blow, and "anti-surge" fuses. Are anti-surge fuses equivalent to slo-blow fuses ? Can I use a fast-blow considering there's already a softstart (not too keen on that one)? The transformers are each 300VA, and there's 66000uF (33000uF, 2.2mH inductor, 33000uF) for each transformer. I'll appreciate any input. It's taken me ages to finally get everything organised, and I definitely don't want to make any mistakes as far as fuses go !

15th July 2008, 08:03 AM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, time delay = slow blow = anti surge and all should be marked TxA, where x=fuse rating. Look for T1.25A or T1.6A for each transformer. I think it is a good idea to separately fuse the equipment incomer. 3A will probably do. __________________ regards Andrew T.

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15th July 2008, 07:27 AM	#2
Corax diyAudio Member Join Date: Feb 2005 Location: south of lower saxon	Anti-surge fuses are a good choice. They can widthstand a 10 times greater current for approx. 10 milliseconds. So they act as a slow-blow fuse. If you use two 300VA toroid transformers you barely need a softstart for those 'suckers' based on the high inrush current (depending on the moment they make contact to the mains voltage). And with this high capacitiv load (of 66000µF) you bet it will trigger the 'big' fuse in the fuse box of your house. Consider to use two independent softstarts for each transformer. This way you need only two fuses for the 'final' safety stage instead of three as you mentioned for your setup. There's no need for 'double-fusing' the same circuit.

17th July 2008, 07:19 PM	#4
golam diyAudio Member Join Date: Jun 2008	Hi, Corex is right. Anti-surge fuses can be used in lieu of slow-blow fuse. But rating should be judged properly. Thanks.

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