What fuse do I need?

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ifrythings

ifrythings

Member
Joined 2005
I have a 80VA toroid transformer that goes to a bridge rectifier than to, two 8200uF caps to give me +/-37V and runs 2 LM3875 Amp's.

What size fuse should I use to proctect the supply but not die on turn-on?

Should the fuse be slow-blow or fast-blow?

Thanks

Dave

P.S transformer markings are:
Primary:115V, blue-brown, 115V, blue-brown
Sec:0-25.7V @ 1.7A yellow-black-yellow

Transfomer has two(2) primaries(tied together for 115V operation) and secondary is 25.7-0-25.7@1.7A(tested) (Just to clear things up)
 
A

AndrewT

R.I.P.
Joined 2004
Hi,
transformers (and motors) usually require a fuse of about three times it's rated capacity to allow start up surges.

This implies 3*80VA/supply voltage. 240Vac >= T1A and 120Vac>=T2A.

the "T" = time delay = slow blow = anti-surge.

"F" = fast.

You may find it will start reliably with a slightly smaller fuse, it's worth trying because close rated fuses provide more protection in event of a mishap.

A fuse that is stressed by repeated start ups will fatigue and will eventually blow. This nuisance blowing could be weekly (try the next size up) or annually (is this tolerable?) or even longer.
 
ifrythings

ifrythings

Member
Joined 2005
AndrewT said:
Hi,
spend the money and time to research your requirement.
Click to expand...


As in try fuses and which ever one stops blowing should be the one I use? (if not then you need to explain what you mean.)

alimaj, I'll be fusing the primary of the transformer, the local mains here is 120V+3% and the transformers is 80VA (as stated above), so what would the formula be then?

Thanks

Dave.
 
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