Fuse Question

[TurboVS]

Hi, my cousin has a Clarion Amp with 3x40amp fuses and also a Blaupunkt with 2x25amp fuses. Will a 150amp wafer fuse do the job at the battery?? I know you are meant to use a higher fuse at the battery then all of the fuses on the amps added together. But just want to see what people reckon. Thanks

[teK]

Wafer fuses aren't cheap so I'd recommend you get the right value unless you're made of money :). Ideally the fuse at the battery is the sum of all fuses at the amps plus a small 10% or so of headroom to save blowing fuses often. It all depends on how you are running the speakers off the amps and how much current is then being drawn. E.g. if you are running the amps at low impedance and at high volume then it will be drawing close to the fused limit.

Fuses don't blow instantaneously except for fast-blow types, they take a sustained overlimit current of a few seconds. You could try a 150A fuse and if it doesn't blow after cranking the system hard for a few minutes you will be OK. Ideally you will use the smallest fuse possible since it gives greatest protection against overload. This is determined by total amp power and gauge of your power cable. For 150A you should be running at least 4GA and preferably 2GA.

Alternatively you can use a circuit breaker which seem expensive at first but are available up to 200A+ and respond to power overload/short in fractions of a second :).

[tandy ass]

I hear galvanised roofing nails are rated at approximately 180 amps :)

[robgs13k]

yes i`m pretty sure that a 150amp fuse will be enough.its pretty hard to draw that much current anyway,he will need to be putting out more than 1050wrms to blow that fuse. volts x amps = watts divide by 2 coz most amps only have around 50% thermal effeciency (generalization unless its a class D amp)
i have 2 sub amps with 4x25amp fuses each and another for the splits with a 40amp fuse (total 240amps) and they havent blown my fuse yet (also 150 amp wafer fuse) fair enough the sub amps are barely working coz the subs cant take that much but it gives you an idea.
Rob

[tandy ass]

You're very unlikely to even blow a 70 amp fuse at full power with RnB or dance/techno music. However change that to alternative and grungy stuff with heaps of guitar and so forth and the fuse will be on edge.

The average power output for music with a heavy drum beat is about 10-20% of the amplifiers maximum continuous RMS output. The bass takes up all of the available power then the time between it is almost quiet.

Dont forget to factor in the amplifier has an inbuilt inverter, or power supply if you call it that. These DC-DC converters have a typical efficiency of about 65-80%. This is where they're scamming you on the MOSFET term, most amplifiers still use BJT (Bipolar Junction Transistors, ie your standard NPN and PNP type) in the amplifier stage and use MOSFETs in the power supply stage - this makes absolutely no difference to the sound output but I am digressing here...

Most class AB amplifiers have a typical efficiency of about 30-40%. Pump a pure sinewave through it at maximum power into a resistive load (ie not a speaker) most amplifiers will overheat within minutes.

Class B amplifiers are very seldom used since there is considerable crossover distortion as the signal passes through zero volts. Class A amplifiers aren't used since they consume full power the moment they're switched on. Class AB is a blend - the positive and negative driver transistors are partially biased into each others range to make the amplifier have minimal distortion while using a small amount of standby power with no signal.

[TurboVS]

Sweet thanks for all your comments

[AutokaT]

Originally posted by Bozz
I hear galvanised roofing nails are rated at approximately 180 amps :)

LMAO....I prefer the nickel finish nails myself..look much nicer in the custom install moit!