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Old 12-22-2005, 02:41 AM   #1
WRblueX_Guy
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Default Help figuring out what size fuse I need when adding another amp

Hi,

I currently have a 85x4 ch amp, bridged to put out 85, 85, 170W RMS. The front is powering a set of components and the rear is bridged to power a subwoofer. I have a KnuKonceptz 4 gauge 4 ch amp install kit with an AGU 80A fuse.

I will soon be installing another amplifier. It will be a 130x2 ch amp, bridged to power a subwoofer at 260W RMS. The 4 ch amp will continue to power the components with the front two channels, leaving the rear channels unused.

Edit: Forgot to mention... I will be using an Stinger 4 gauge Tee Distribution block for the power wire.

I'm not sure if this has anything to do with choosing your fuse, but the 4 ch amp has 4 20A fuses, and the 2 ch has 2 25A fuses. A couple people told me that because those 6 fuses add up to 130, I will need about a 130A fuse.

I have also read things like this that go mostly based off of RMS power.
http://www.mmxpress.com/technical/fusing.htm

Although, in the last paragraph it says take the total RMS wattage, divide it by the battery's voltage, and that should be your fuse size. Then when it gives the exact formula at the bottom, it says to multiply the RMS wattage by 2, divide by battery's voltage, add 10%, and that should give you the fuse size.

Would anyone be able to tell me how to figure out the approx. fuse size I would need, or if the 80A fuse will be enough?
If I did have to get a bigger fuse, I could get this holder with a 120 or 150A fuse for $19
http://knukonceptz.com/productDetail.cfm?prodID=FH-20

Thanks
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Last edited by WRblueX_Guy; 12-22-2005 at 02:47 AM.
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Old 12-22-2005, 02:49 AM   #2
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Id recomend a 150 ANL fuse
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Old 12-22-2005, 02:00 PM   #3
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Thanks.

Anymore opinions?
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Old 12-22-2005, 05:44 PM   #4
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truthfully you could probably run the 80 amp and be fine. it could possibly blow at high volumes.

probably be best to go with a 120 ANL or above.
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Old 12-22-2005, 06:37 PM   #5
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Add up the fuses that are on the amps and then use an fuse bigger than that.
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Old 12-22-2005, 09:23 PM   #6
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The fuses that are inline with the main power wire or in a power distro block are fusing against fires from the wires melting. You fuse based off the gauge of the wire. Go to www.BCAE1.com and I think it was topic 14 Fuses.

offset
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Old 12-22-2005, 10:19 PM   #7
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Thanks guys.

offset, I was reading the fuse section the other day, but I'm not sure I quite understand it. It says "Any fuse rated at less than ~150 amps is sufficient to protect a 4g wire and the vehicle (if the 4g wire is longer than ~15 feet long, you may want to limit the fuse to ~125 amps)." Then for 4 guage wire, it says the recommended maximum fuse size is 125A.

What would happen if I tried to use a 150A fuse with my 4 gauge wire?
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Old 12-22-2005, 11:02 PM   #8
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Default fuse size

I'd go with a 125 amp or a 150 amp anl. I don't think it will make too big of a difference. To be really accurate, you would need to find out the potential current draw of your amps using a conservative efficiency percentage. Then choose a wire whose rating accomodates this current. I think 4 ga is comfortable at about 125 amps. Then choose a fuse that is rated around the upper end of the wires current capacity. So when adding the new amp determine the cumulative current draw of both amps. Of course, the lower the fuse, the more sensitive it will be to blowing, which is a good thing because this main fuse is protecting the battery from a fire that could result from the wire overheating. For that reason, it should be as close as possible to the battery. If you think your amps will draw a max current that is rated higher than the power wire, you'd need to get larger wire. I doubt that's the case here though. I would also get a fused distrobution block to separate the power to the amps. AGU fuses should be fine here. Good Luck

Last edited by mikeyg; 12-22-2005 at 11:09 PM.
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Old 12-23-2005, 12:23 AM   #9
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I would not run more than a 125amp fuse on 4 gauge wire. I'd even try not to run more than 100amp just for some margin. If you really are pulling 125amps, you should upgrade to 2ga or better.

Let's see... 85x2, other two channels doing nothing, and 260x1, right? So not even 500w total RMS! 80A is plenty.

Don't calculate by adding up the fuses built into the amps. They're usually on the large side. Calculate for your whole system power.
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Old 12-23-2005, 01:25 AM   #10
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Quote:
Originally Posted by WRblueX_Guy
What would happen if I tried to use a 150A fuse with my 4 gauge wire?
Possibly nothing. But then again you could possibly not run any fuses and be fine. Remember that fuses aren't supposed to be limiting power under normal circumstance; only in case of a severe problem. If a wire gets pinched and grounded to the cars metal or an amp goes haywire and starts pulling obnoxious amperage it could cause the insualtion to melt and possibly start a fire with the interior carpeting. I think 125A would definately be as big as you should go, but given your amps I think a 100A fuse would be fine and more telling of problems if it were to blow.

offset
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Old 12-23-2005, 03:37 PM   #11
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Offset and Freon are right. As stated, the fuses on the amps themselves are for max power draw, not continuous. The amount of actual power that the amps are putting out are your best guide to how much juice you need:

85x2 + 260x1 = 430W

assume 50% efficiency, so 430 / 0.5 = 860W draw from battery/alternator

860W / 14.4V = 59.7A being conducted in wire

Therefore, 80A or 100A fuse is fine.

Last edited by HolyMahwah; 12-23-2005 at 03:43 PM.
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Old 12-23-2005, 04:06 PM   #12
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Awesome, thanks guys.

I think I'll stick with the 80A fuse I have for now, unless it blows. Does anyone know if they make/where I could buy a 100A AGU fuse? Or do they only make 100A ANL? If so, I would have to get a new fuse holder.
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Old 12-24-2005, 12:22 PM   #13
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Quote:
Originally Posted by WRblueX_Guy
Awesome, thanks guys.

I think I'll stick with the 80A fuse I have for now, unless it blows. Does anyone know if they make/where I could buy a 100A AGU fuse? Or do they only make 100A ANL? If so, I would have to get a new fuse holder.
If you had to go bigger than 80A you would want to step up to a good ANL fuse holder.

offset
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Old 12-24-2005, 01:28 PM   #14
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fuse's blow! get a circuit breaker. 140A, i have had a fosgate one for 3 yrs now, i think it popped once, all you do is re-set it.
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Old 12-24-2005, 01:51 PM   #15
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Default 1+ for the circuit breaker style fuse

Quote:
Originally Posted by jam69007
fuse's blow! get a circuit breaker. 140A, i have had a fosgate one for 3 yrs now, i think it popped once, all you do is re-set it.

Thats what i am using.. only use fuses internally in the amp and one right before the sub amp.

-Jason
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Old 12-24-2005, 03:52 PM   #16
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Actually the inline fuse should be at the maximum rated amperage of the wire. If your pulling more amps through the wire than the wire can handle it will melt the coating on the wire allowing it to short out, possibly causing a fire before the fuse even blows. 4 guage wire is more than enough for your setup. Just leave the current fuse in there. I was running my 1800w system through my 0 guage kit with an 80amp fuse for about two years with no problem.
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