Fuse Rating

jwatts · 5th January 2004, 08:29 PM

I need to fuse a loudspeaker to prevent overpowering it. Can anyone help me relate the correct fuse current and voltage value to the loudspeaker watt value?

Richard C · 5th January 2004, 11:54 PM

This should give a workable minimum value for a fast-blow fuse:

Fuse (amps) = 1.414 X sqrt (Power rms / Impedance)

A good trick for protecting a speaker from over-cooking is to connect it in series with a filament bulb.

Ron E · 6th January 2004, 12:07 AM

Fuses don't always protect well. You don't say if you are protecting a single driver (what size) or a whole system.

Best is to start with a low current rating (voltage doesn't matter as long as it is more than your amp can put out) and increase it a bit if it blows too often.

I have a 250Watt, 4 ohm speaker that came with a 2 amp slow-blow fuse on the input. 250 watts into 4 ohms is sqrt(250/4)=7.9 amps. I have blown a tweeter before the fuse blew....

Also look at polyswitches and other types of protection devices. I think Parts Express sells something like this.
http://www.partsexpress.com/webpage....ctGroup_ID=568
http://www.partsexpress.com/webpage....ctGroup_ID=237

jwatts · 6th January 2004, 08:37 PM

Thanks for the help!

5th January 2004, 08:29 PM	#1
jwatts diyAudio Member Join Date: Jan 2004 Location: Erwin, Tennessee	Fuse Ratting I need to fuse a loudspeaker to prevent overpowering it. Can anyone help me relate the correct fuse current and voltage value to the loudspeaker watt value?

6th January 2004, 12:07 AM	#3
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	Fuses don't always protect well. You don't say if you are protecting a single driver (what size) or a whole system. Best is to start with a low current rating (voltage doesn't matter as long as it is more than your amp can put out) and increase it a bit if it blows too often. I have a 250Watt, 4 ohm speaker that came with a 2 amp slow-blow fuse on the input. 250 watts into 4 ohms is sqrt(250/4)=7.9 amps. I have blown a tweeter before the fuse blew.... Also look at polyswitches and other types of protection devices. I think Parts Express sells something like this. http://www.partsexpress.com/webpage....ctGroup_ID=568 http://www.partsexpress.com/webpage....ctGroup_ID=237 __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Science is a way of thinking much more than it is a body of knowledge. --Carl Sagan

6th January 2004, 08:37 PM	#4
jwatts diyAudio Member Join Date: Jan 2004 Location: Erwin, Tennessee	Fuse Value Thanks for the help!

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5th January 2004, 11:54 PM	#2
Richard C diyAudio Member Join Date: Jul 2003 Location: Nottingham, England	This should give a workable minimum value for a fast-blow fuse: Fuse (amps) = 1.414 X sqrt (Power rms / Impedance) A good trick for protecting a speaker from over-cooking is to connect it in series with a filament bulb.

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