"TRU POWER"

[ChevyBoy 10+ year member]

I know this question has been asked before but how can an amp with a 80 amp fuse make 1400 watts of power. Like for instance a pg tantrum 1200..or maybe a hifonics with a 120 amp fuses creates 1500 watts....i know some amps are more efficent than others but i thought it took 10 amps to create 100 watts of power..and so if an amp had such a small fuse ,shouldn't they blow after a couple of minutes.I see amps like rockford fosgates 1501 and jl 1000/1 and there rated correctly with 150 amp fuses and 100 amp fuses...I'm not doubting the pg tantrums power ,maybe i'm just confused somewhere?????

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[Logikalliquid 10+ year member]

well watts is amps x volts first off. that still leaves you a little short of power even at 14.4v though. i've noticed this discrepancy before as well and still havent found the answer. hopefully someone can point it out.

 

[namster44 10+ year member]

Fuses are just a estimate. The amp in question can actually pull more current. And assuming most d class amps are about 70%(give or take) efficient. 1500 = .7(14.4 * 149).

Just look at the D2 Earthquake amp, modded it can do about 2500 watts with 60(could be wrong, but I know it's low) amps for fuse(s).

 

[helotaxi 5,000+ posts]

It all has to do with the way a fuse is rated. The standard for a fuse is 110% of rating for 4 hrs, 135% for a max of 60 minutes and 200% for a max of 2 minutes. Based on that an amp can make a lot more power than its fuse rating would seem to allow, it just can't do it forever.

 

[Fr0sty51 10+ year member]

Ya ive read on a few Phoenix Gold Tantrums that their efficeincy was only like 60%

 

[cjj2d 10+ year member]

so what does this mean if their efficiency is only 60%?

 

[Randy Savage 5,000+ posts]

40% is dissipated in heat...

 

[cjj2d 10+ year member]

meaning what? that it is not putting out the stated power? or what.

 

[Randy Savage 5,000+ posts]

40% of the current drawn by the amplifier is dissipated heat...

 

[maylar 10+ year member]

Standard practice is to fuse a circuit with 150% of actual expected load current. Some designers will go 125%, some 200%.

Power input = power output / efficiency. If an amp outputs 1000 watts and is 60% efficient then it's input power is 1000/.6 = 1666 watts. The current it would draw at 14.4 volts would be 115 amps. I would expect a 150 amp fuse at least.

2 channel amps that can be bridged ususlly have separate power supplies for each channel. The example above might have 2X80 amp fuses.

To answer your original question, 80 amps at 14.4 volts is 1152 watts. Even if the amp was 100% efficient (impossible), you can't get 1400 watts output from it without blowing the fuse. Assuming a 125% fuse overload and 80% efficiency (Class D) the amp is probably designed for about 750 watts RMS.

Note however that music has about a 5:1 peak-to-average ratio. The amp could very well be capable of 1400 watts and the designers figured the fuse rating conservatively based on expected duty cycle. A slow-blow fuse needs about 10 seconds at rated current before popping.