Fuse rating vs. RMS question

[SPLaudio 5,000+ posts]

200 percent of 80 amps is 160 amps,3 secs. i have seen 4krms burped off a single 100amp fuse. ask meca guys about fuse ratings,lol...

 

[squeak9798 5,000+ posts]

Fuse rating also depends on if your amp is High Voltage/High Impedance versus High Current/Low Impedance.

That has pretty much nothing to do with it. It's going to take X power input to reach Y power output for a given efficiency regardless of what impedance the amp is driving.

I have an amp that does 400 watts RMS @ 8 ohms with a tiny *** 25 amp fuse! Of course the rail voltages inside of that amplifier are high enough to pack a serious wallop to them!

Try running a sine wave at full power out of that amp for a period time......fuse will go pop.

For listening with music, however, it's probably sufficient fusing because as was mentioned you need to exceed the fuse rating by a reasonable amount for a substantial period of time (as far as musical peaks/dynamics are concerned) before a fuse will blow.

Trying to base power output on fuse rating is pretty meaningless unless it's an extreme example, such as 25A fusing on an amp claiming 2.5kw of output.

 

[GregU 10+ year member]

FYI -

Fuse Rating = X

X = RMS Watts/Voltage

i.e. 1000 RMS Watts and 13.5 volts = 74amps, use 80 amp fuse.

 

[Notloud00 10+ year member]

true but i bet its not clean power.and your saying that an 80a fuse will need to see 240a for 3 seconds to blow?//content.invisioncic.com/y282845/emoticons/wow.gif.23d729408e9177caa2a0ed6a2ba6588e.gif

i ran 1kw and could never blow 80amps worth of fusing but i could blow 60 or so i like 5 sec in meca.....

 

[n2audio 5,000+ posts]

It's hard for me to believe people actually want to try to nit pick a general rule of thumb. It's not perfect -- I think that is pretty obvious.

This has never been a way to determine the ACUTAL power an amp can produce to any respectable degree of accuracy, but if a newb is looking at a pyramid at the local pawn shop that says 2000 Watts Of MIND blowing POWAH, but it has a pair of 25's -- it is plenty accurate to tell them they should probably walk away, or at least recognize they're probably looking at 500-600w of usable power.

Recently someone's been dealing with a Quantum qsa1000d. It's a class a/b with a pair of 30's rated for 1000w. It is pretty safe to say it's not going to do 1000w.

10-12w/A IN GENERAL. IT is a GOOD rough ESTIMATE.

Why people want to drag 5 or 10% efficiency variations into the mix, or 13.8v vs 12v vs 14.4v, or how this one amp only had a 1A fuse but my buddy's uncles roommate clamped it at 68 octillion watts Etc etc etc is BEYOND me.

Don't debate it.

Deal with it.

 

[stocker08 10+ year member]

Every amp is going to have variables that change the Fuse to RMS relation, but for the most part, all amps are going to fall in the same general area when it comes to the relation between the two.

 

[SWFL 10+ year member]

my zx850.4 has 3 fuses and its 40 amp fuses so 120amps

 

[Zellner 10+ year member]

the cadence txa-1000d has a built in 80A fuse but i heard it benched a little over 1100 rms?

 

[Lakota 5,000+ posts]

It's a rule of thumb....

It's not a law or anything. You can just use it to approximate if a amp is somewhere within its rating...

jeez..

 

[Undisputed King 10+ year member]

Exactly, I just say 10w per A. Its not exact, but its usually on the ball give or take 10%.

I was running a GP3000D at 3/4 tilt on a 100A fuse and never blew it, it played for 10 minutes at a time. That was just testing it before I installed my 1/0 kit.

 

[roarzorz 10+ year member]

Yes this is a good general rule. It's not approximate but in the ball park.

The formula is volts x amperes / efficiency = actual power output in watts. A lot of people forget the efficiency part or just take a wild clueless guess.

 

[bananablack 10+ year member]

my 1000/1 is blowing 100a fuses. I was told to use a 180a. but that sounds insane.

 

[SPLaudio 5,000+ posts]

ur clipping the crap out of the jl to blow a 100 amp fuse. turn ur bass boost off and ur gain down...

 

[manofthehour123]

I have a cadence TXA-1000D and blew a 60A fuse at about 70% power and an 80A fuse all the way turned up lol. Talked to a friend who knows a little in the field of electric stuff and he said the fuse I had was cheap... Got it from DB Link looked relatively well made, but obviously not... just thought I'd throw that out there. Bought a different fuse holder and fuse for the amp today and got a 40A, 60A, 80A, and 100A fuses with it. Obviously the 40A and 60A are no gos, but I put the 80A in to see how well it would do. Another important thing when looking at fuses is looking at how much amperage your wire can actually take. The 0/1 gauge I just ordered from Knu Koncepts to do the Big 3 and put in a second battery said no more than 250A so I bought 250A fuses and holders... Putting more amperage may cause the wire to catch fire... or something like that. Hope that helps clear some stuff up. And hopefully I got my facts straight lol.

 

[Papermaker85 5,000+ posts]

you simply cannot go on fusing for output.. your better off opening the amp up and looking at the transistors to approximate power.

i can put 3 40 amp fuses in a 1kw amp and claim 1200 RMS @ 12.8 volts doesn't mean its going to do it if the transistors won't supply the current needed..

as for class Ds there ruffly 65-75% efficient at its lowest load at full power..

fuses are not all made the same and there not made to blow instantly when you exceed its rating.. as mentioned eariler some power supplies will draw more current on demand while others use larger cap banks and pull current in a much more constant form..

take for example the RF 15000 kw.. it constantly pulls 300 or so amps too keep the bank charged even if your only getting 200-300 watts of output on the other hand MMats amps do the opposite and only draw the amount of current necessary for the output/load..

its no secret thats amperage x voltage will give you power in wattage but you simply cannot say amp A has 2 25s and b has 2 30s and B is stronger..

also if you multimeter isn't designed for inrush current it simply won't provide your with a RMS number.. again this goes back to the power supply..

its easier when you have a constant load when measuring output..