Fuse questions

[01blkcat]

This is the first time I've ever heard this question...

Aren't all fuses the same? It's just a filament that is affected by current....

EDIT: The original message appears to have been deleted... :(

[DJcougar]

My question is...what size fuse (amp wise) should be used
for a 4 gauge power wire going to a single amp in the trunk
The fuse will be going right next to the battery

I wondered if I should use a 60 amp...or 80....etc etc
I read the faq and it said 125 amps max


Hopefully someone will reply this time

[Gary]

mines got a 60A fuse in it

[Lukydogg]

I have a pair of 60A in a block for 1 400watt amp, but it was originally for 2 500 watt amplifiers. Just my .02
Oh yeah, and 4gauge wire all over the damn place-

[Slikrthnu]

I have a 100amp Circuit Breaker, it comes in handy sometimes.

[mindtrip1016]

The fuse that goes within 6" of your battery should reflect the amount of current your amp is rated to pull. I have an amplifier that pulls 100 amps by itself and another that pulls 40. That is 140 amps of current draw total. So naturally I needed something that could hold 140 amps. The closest thing I found was a 150 amp circuit breaker. The thing about circuit breakers is if you ever need to work on your amp, all you have to do is push a button and the circuit if off. Plus it is very difficult to blow a breaker. With a fuse you have to remove the protective plastic and pull out the fuse. Then take the chance of blowing the fuse when you go to reinstall it.

[DJcougar]

How do I figure out how much current my amp draws?
I have a 600Watt rms amp with 2 25 amp fuses on it
the battery fuse was a 30 amp fuse

10 gauge wire was used throughout

I am now upgrading to 4 gauge wire...so I need to upgrade the fuse by the battery also

[mcon99]

uuuuh... you use two simple formulas

P=VI and V=IR

[DJcougar]

maybe you can elaborate a little bit

[01blkcat]

Originally posted by: DJcougar
maybe you can elaborate a little bit

He basically said:

Power = Voltage (V) * Current (A)

and

Voltage (V) = Current (A) * Resistance (ohms)

[DJcougar]

How do I figure out the resistance.....this is new to me

[Excelcier]

Go Josh with Ohms law!! Wow, you did learn something while skipping all our classes!

Quite frankly though, for the purpose of fuse determination, you don't have to go that far. You don't need to calculate the input resistance of your amplifiers.

Simply do the following. Use your multimeter set for high current input ( don't use a crappy meter as currents will be high )
and pull the mega fuse out from where your battery connection is and use your meter in place of the fuse and set it to read current.

Now go and crank up some nasty, obnoxious, bassy music to draw alot of current and measure the peak value it reads.

Now let's say it tells you it's pulling 24 amps, multiply that by 2 ( rule of thumb in the audio business ) and take the closest higher value for a fuse.

So for this example you're pulling 24 amps, doubled is 48 amps, so I think a 50 - 60 amp fuse is sufficient here.

Careful, you don't want to overfuse to be a show-off because the higher the value, the less chance it has of protecting your circuitry.

Another more annoying and costly way of doing this is start off with a smaller fuse and keep blowing it until you find a value that won't, then add a bit more on for a safety margin.... this is the Mcon99 way of doing fuses, ask him!!! " Ooops, blew another one... can you hand me another fuse please? I don't know what's wrong! "

----------------

Another fun thing you can do after you know the value of amps being drawn by your amps is find out just how much the rating of the amp is really pulling your leg... there are so many amps out there that say they are 500 watt amps, or whatever...

Go back to the 24 amps from before ( this is a standard current draw on a higher end system ) and now change the multimeter configuration back to measuring voltage and read the voltage from B+ to GND on the amplifier terminals. It should be between 13-14 volts hopefully.

Now multiply them together... 24 x 13 = 312 watts or 24 x 14 = 336 watts... alot lower than 500 watts. Most amps rate the wattage at peak value, not the true running value. A quick way of finding an amps REAL wattage is to divide the peak value by square root of 2. So if we have a 500 watt amp, divide by root 2 = 353 watts.... look kinda similar to 336 watts???


Hope you find this boring classroom math usefull now.