# Fuses on the amp



## Vital (Feb 23, 2010)

I see this mentioned all the time - look at fuses on this amp (4x40A, 3x50A....) before you even look at rated wattage. Fuses will tell you how powerfull amp really is.

Is that true? Somewhat true? bs?


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## minbari (Mar 3, 2011)

I would put it in the somewhat true dept. if your amplifier has a 50A fuse then it will have a theoretical max of 720 watts @14.4V. will it do that? not likely, it would blow the fuse. it certainly wouldnt do more than 720watts.

but here is the kicker, even though it has a 50A fuse, it might be rated for 500watts. just because it has a larger than necessary fuse doesn't mean it will put out that much. fuses are for protection not current limiting, lol.


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## jimbno1 (Apr 14, 2008)

That is interesting. Consider the JL HD 600/4. Recommended fuse is 50A and input voltage is 11-14.5 V. At 11 V the max to be 550W, not the 600W advertised. Also that assumes 100% efficiency. On the other hand fuses do not instantaneously blow at their rated amperage. Even fast blow fuses will pass much higher current for short time. Sustained high current will open the fuse. So you do have some leeway built in.


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## DaveRulz (Jun 22, 2006)

It's a quick and dirty way to see how much the amplifier manufacturer is bending the truth on the silskcreened number on the heatsink. 

For example: it is a pretty good bet that an amp with 2000w shown on the front that has a 30 amp fuse is not going to make rated power, it's against the laws of physics.


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## AKheathen (Sep 10, 2011)

well, looking the fusing is somewhat of a quick "rule of thumb" way about it. generally, each amp is 10watts, or close. you will not find 90+% efficiency from an amp, and some rare cheap amps have even thrown oversized fusing in there, though it's not what you will normally find. and some have low efficiency, and will not reflect power output good. i have seen efficiency in the 60's. it's just the easy quick reference. so, that 2k with 30a, is more like 300rms, but that 1200d with 3-40a fuses is probably right around rated


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## 14642 (May 19, 2008)

I'd say that checking the fuse rating against the power stated on the box is a quick way to confirm that something that appears to be BS is, in fact BS. a 20A fuse and a 2000W rating obviously don't go together. Neither do $99 and 2000W. 

Unfortunately, amplifiers are designed to produce god ratings when driving continuous sine waves into resistors, which is different than playing most music. Amplifiers that are designed to drive speakers other than subwoofers would be better designed to provide huge instantaneous peaks but low RMS power. there are designs that do this, but they're most often used in powered speaker systems where the power rating isn't the primary selling spec. For amplifiers designed to do that, the fuse rating would be calculated for the average durrent draw over the time it takes the fuse to blow--the amplifier would store energy at high voltage to be dissipated quickly during peaks in the music.


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## stopdrpnro (May 15, 2008)

I had a thread about this not too long ago and although it maybe a nice quick look tool its not a concrete method to finding true power. I've seen plenty of amps that have been bench tested old and new that put out more power than their fuses would lead you to believe. Nearly every old school orion amp I had produced much more power than the fuse amperage x voltage x eff formula. I can say the same about a few of the newer amps too sundown,treo , arc etc.


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