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Old 04-07-2007, 10:33 PM   #1
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Default fuse at the battery

Yeah so anyway I am wondering what size fuse I need to install at the battery.

I am using Punch amps and they have no fusing.

My Mid Amp: 100x2 @ 4 ohms

My Sub Amp: 125x2 @ 4 ohms

Any help is 'Preshaded

Tim
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Old 04-07-2007, 11:03 PM   #2
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a 40A would be MORE than sifficient, i would likely run a 30
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Old 04-08-2007, 01:40 AM   #3
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Thanks Oats. Does it matter that I am running the sub amp 4 ohm bridged? It'* putting out around 500 watts to one sub. It may not make a difference but I thought of it after I had posted.

anywho thanks,

Tim
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Old 04-08-2007, 03:55 AM   #4
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Are there any fuses showing in the side of the 2 Amplifers ?
If not check the specs in the manual or check the website.

If so add up the fuse ratings and fuse your wire for 10 amps extra.

For example:
Amplifer #1, has a 30 Amp fuse
Amplifer #2, has 2 x 40 Amp fuses
Add the fuses together from the 2 Amplifers (30 + 40 + 40) = 110 Amp draw

Also you have to fuse your power wire so that it can not exceed the max power handling limits of the wire.

Example:
8 Gauge wire can only handle a Max of 100 Amp draw (before the wire gets to hot) over an average of 20 - 25 feet.

See this link & look at the table on the bottom right corner:
http://www.the12volt.com/info/recwirsz.asp

This is why fuse blocks are nice because you can fuse the main power wire for close to the max, and fuse the amps individually at the fuse block just before the amps.

Hope this helps,
Dutch
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Old 04-09-2007, 02:48 PM   #5
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An easy way to figure what size fuse to use is to divide the output power by the battery voltage and then multiply by the number of channels. Do that for each amplifier and then add them together.

For example in your case:

sub amp ~ 500 watts / 13.8 volts = 36.23 amps (one channel)
mid amp ~ 100 watts / 13.8 volts = 7.24 amps x 2 channels = 14.48 amps

total ~ 36.23 amps + 14.48 amps = 50.71 amps

I would use a 60 amp fuse in your case to compensate for the occasional power spikes.
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Old 04-09-2007, 08:36 PM   #6
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Thanks alot gang. All this info really helps.


Tim
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Old 04-10-2007, 01:45 AM   #7
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Civic Guy, while your method is a good way of guessing, it lacks precision and does not take into account the power handling of the main power wire. What happens with your method if you fuse the main power wire for more than it can handle?........it starts to melt the coating off the wire = Fire.
Always check max power handling of the main power wire.
The easiest way to judge power draw is by looking at the fuses in the sides of the Amplifers. The Amp can not draw more power than what the fuse in the side is rated for. If there is no fuse, then check the specs for draw at max power.

These are the methods used by Professional Installers & Automotive Electronic Techs for years (including myself).
I've never had anything melt down.

"Remember electronics run on smoke, once you let the smoke out it doesn't work anymore"

Dutch
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Old 04-10-2007, 04:11 AM   #8
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First of all, thats not guessing, it'* ohm'* law. Second, he wanted to know what size fuse to use and that'* what I was was answering. Your way would work but if there are no fuses in the side of the amp or you don't have the paperwork for the amp, then it'* no good.

I may have only been installing car stereo systems for almost 8 years and have a degree in electrical engineering but I do know a couple things about hooking up an amplifier.
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Old 04-10-2007, 09:18 AM   #9
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I'm going to pretend I know very little about auto electronics and electricity in general for a minute and I'm going to use your method.

Lets say I have a 10,000 watt amplifer, 1 channel mono block.
10,000 watts \ 13.8 volts = 724 amp draw

I think I will run this off an 8 guage power wire. Also I'm going to try and find a fuse this size. Should work correct ? This is Ohms Law correct ?

The problem with this is it does not take into account max power ratings for power cables.
If I knew very little and wired up my amp used in the example above this could be dangerous.
The inline fuse is to protect the run of power cable & the factory electrical system, not the devices attached, thats what a fuse block is for.

While Ohms Law is a good tool and has its uses, it can't be your basis for all electrical connections.

As far as my method being "no good, without the specs for the amp" this is were we have to do our homework and do some research to find the specs.
If I couldn't find the specs then I would still fuse the power cable for just below max handling and I would still be safe.

Dutch
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Old 04-10-2007, 02:37 PM   #10
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Your missing the whole point Dutch. He asked what FUSE size to use...thats it. I am totally aware of the wire issue. Personally I would not run anything smaller then 4 gauge for any system. But I would have said something about the wire size if you had not already brought it up in your first post.

Also as far as researching the specs, sometimes it'* not that easy. Say you get an old amp from a friend with no paperwork and it'* so old you can't anything online about it. Then what do you do? The point i'm trying to say here is, either way is not bad but sometimes one way may be easier then the other one.

Matt
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