fuses and calculating amp draw?

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dzelaya18

Copper - Posts: 49

Joined: May 14, 2004

Posted: May 28, 2004 at 1:46 AM / IP Logged

Hey everyone,

Okay, I'm wondering how to calculate amperage draw based on the fuse sizes on an amp. The two amps I have in question are a roughly 500w RMS amp with one big fuse that has an "80" written on it, and a much, much smaller 190w RMS amp that has a little blue fuse with a "30" written on it. A guy I know told me that the amps use half of what it says on the fuse to run, so 40 and 15 respectively...is this accurate? Or is there another way to know what they run at? 500W doesn't pull 80amps does it? That seems like alot for only 500 watts...

Thanx for your help guys, I don't know where I would be without this site...---D.

dzelaya18

Copper - Posts: 49

Joined: May 14, 2004

Posted: May 28, 2004 at 1:52 AM / IP Logged

Okay, I just saw that "current draw" chart and that almost answered it...anybody know the specifics though? 'cuz the chart says that 200w RMS draws 32amps, but the 190W amp only has a fuse capable of 30amps...so it must be less than 30, right? Or have I got it mixed up somehow? ---D.

dzelaya18

Copper - Posts: 49

Joined: May 14, 2004

Posted: May 28, 2004 at 1:53 AM / IP Logged

You know, it incredible how I've been running systems in my two Nissan's for more than two years and never knew any of this stuff...the Civic's tiny power capacity has forced me to learn so much usefull info! Its like a blessing in disguise! ---D.

Ketel22

Silver - Posts: 976

Joined: August 23, 2003

Location: United States

Posted: May 28, 2004 at 3:08 AM / IP Logged

if you refer to the ohms law charts on the site and learn those good you will be set in alot of the situations you will encounter in car audio. but you take the rms output of the amp and divide by say 12.2v (normal alt. output) and that will give you the nomial amperage pulled by the amp. if you take the amps peak output divided by the 12.2 and that will give you the most your amp should ever pull and that is usually where the fuses are set at i do believe.

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dzelaya18

Copper - Posts: 49

Joined: May 14, 2004

Posted: May 28, 2004 at 12:08 PM / IP Logged

Hey thanx alot, thats works. ---D.

colaroaster

Copper - Posts: 53

Joined: May 17, 2003

Location: United States

Posted: May 28, 2004 at 7:31 PM / IP Logged

would the "cheater" amps have more amperage pull ?

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Joined: November 01, 2003

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Posted: May 28, 2004 at 7:44 PM / IP Logged

Definitely!

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Ketel22

Silver - Posts: 976

Joined: August 23, 2003

Location: United States

Posted: May 28, 2004 at 8:14 PM / IP Logged

Rob, isn't there a more complex way to find out the fuse ratings you should use? like with the efficency of the amp and the power out and the voltage or something?

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titanus_aegis

Member - Posts: 14

Joined: May 14, 2004

Posted: May 30, 2004 at 4:03 AM / IP Logged

Ohm's law:

Electrical force (Voltage)=Current(Amps) * Resistance(ohms)

Power output (watts) = Current (amps) * Force (Voltage)

Say your alt delivers 12.5 volts. Your small amp with the 30 ampere fuse can deliver up to 375 watts before the current intake becomes too large and compromises the fuse's integrity. I'm guessing it's rated 190wrms @ 4 ohms, right? @ 2 ohms that's a 380 watt output, which makes sense.

Big amp... 12.5 volts * 80 means the most power it could output is 1000 wrms before compromising the fuse. Of course most alts can deliver a bit more than 12.5 volts, although not quite the 14.4v we all wish we could get, so the max theoretical output is a bit higher in both cases.

Titanus

P.S. yeah i've been visiting BCAE .... :)

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fuses and calculating amp draw?

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