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Old 09-07-2012, 06:30 PM   #1
theflry
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Inline fuse for our amp, necessary with battery in trunk?

I had my system hooked up by a professional with the same car as mine. When installing my 5 channel amp, he did not use an inline fuse on the 4awg power line (even though the Rockford Fosgate amp came with one included).

This was 3-4 years ago. I recently discovered this when my RF amp unmounted, fell on its face, and burned alive. I hooked up my new Alpine amp using the same power, ground, and leads from the professional install and have not had any problems yet.

Should I even bother putting an inline fuse into the wiring now? It went so many years without an issue. I read that an inline fuse is very important, but I have also read that the chance of our E46 trunk batteries/power leads short circuiting due to an accident is nil.

I'd appreciate some honest advice from anyone who has been in the same situation as me.

Thank you all.
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Old 09-07-2012, 06:43 PM   #2
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Yes. Always use an inline fuse for the power from your battery to amp. The fuses on the amp are only to save the amp, but they won't protect the main power line, battery, etc if something goes totally wrong like a bad short, etc. It's always good insurance for your electrical system and sound equipment.
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Old 09-07-2012, 07:34 PM   #3
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If you imagine how much power can be flowing to the amp, you'll understand why having an inline fuse is a very, very good idea.
Keep it as close to the battery as reasonably possible, generally within 18".
If a professional installed an amp without a fuse, I'd never go back. It's simply dangerous.
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Old 09-08-2012, 02:53 AM   #4
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Definitely use an inline fuse. If the amp shorts out, or the power lead somehow were to short out, the positive lead would continue to heat up and the wire could very likely light on fire. I have seen this personally, being a professional installer for 15+ years. Your wire catching on fire or your amp burning up isn't the worst part. There is carpet and possibly other flammable materials in your trunk that could come in contact with the flame/heat being produced from this short, and before you know it your whole car goes up in flames. And all because you didn't bother to install a $15 dollar fuse that you seemed to never need before. YES!!! Put a fuse in it please.
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Old 09-08-2012, 03:27 AM   #5
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Not necessary, but good practice anywhere you can cause an electrical fire near a person. Good general wiring practices are easily a safer bet than relying on a fuse though. This is why you'll see very critical electronics (think military, medical, etc.) not having fuses because they are additional points of failure and liability, but tons of prevention instead. As the saying goes, an ounce of prevention is worth a pound of cure. Use your judgement.
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Old 09-09-2012, 02:19 AM   #6
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I respectfully disagree. You can wire a device up as perfect as can be, but internal components can fail, cause a short, and cause excessive current draw, which could then possibly result in a fire. When you mention military and medical devices, I conclude that you mean AC powered devices. Even though they may not have inline fuses on the device itself, the circuits that supply them power have "circuit breakers", which act as a type of fuse.
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Old 09-09-2012, 07:58 AM   #7
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YES! ABSOLUTELY! Install a fuse, within 12 inches of the battery. Not sure how the hell it became unmounted, but that, and the fact that he didn't bother to use the fuse, makes it sound like it wasn't a professional installation to me. A fuse probably would have prevented the "burning alive" part. LOL
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Old 09-09-2012, 12:24 PM   #8
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Quote:
Originally Posted by benzovs View Post
I respectfully disagree. You can wire a device up as perfect as can be, but internal components can fail, cause a short, and cause excessive current draw, which could then possibly result in a fire. When you mention military and medical devices, I conclude that you mean AC powered devices. Even though they may not have inline fuses on the device itself, the circuits that supply them power have "circuit breakers", which act as a type of fuse.
Nope, I'm talking about DC devices as well. This isn't just from guessing, but from past experience circuit breakers and fuses have a pretty high chance of failure compared to most other components, and will NOT prevent fires.

I'm not advising against fuses, but I think a lot of people put way too much trust in them. Take an amplifier like what OP is talking about and lets give the failed internal part situation like what you mentioned. If the unit has a 30 Amp fuse just to function, that means you can have a 20 Amp continuous draw and the fuse won't do anything. 20 Amps is enough to actually TIG weld thin pieces of metal together, and can easily start a fire. Also, if the person added a 30 Amp fuse but didn't crimp wires right(very common since most people don't have the right tools), you may just end up with a large cable that slips out of the inline fuse and causes a much more serious problem then likely would ever happen with an amp that had an internal failure.

With some of the stuff I deal with, and actually probably some of the competitive sound system people deal with, normal operating currents can be around 100 Amps with 200+ Amp spikes. If you use a fuse big enough not to blow during normal use, then you also have a fuse that is so big it's not going to do anything even if a wire is doing a short circuit in most situations.

In short, good practice prevents fires. Fuses and circuit breakers protect components.
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Old 10-02-2012, 10:45 AM   #9
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Pardon me if I'm asking this question in the wrong place. I have a 2001 m3 with an aftermarket system installed by BMW (amp, sub, headunit, etc.). My battery had to be replaced recently and since then, I'm getting no sound from the speakers. The head unit is turning on, but no sound. I started my search regarding the fuse and it brought me here. Any idea what the problem could be and where I should begin troubleshooting?
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Old 10-02-2012, 02:18 PM   #10
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Can you see the amp? Does it have an led to indicate that it is on? It's common practice to take the fuse out of the power cable when you are servicing the battery, that way you are not dealing with a live circuit. So they just most likely did not replace it. Start there.
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Old 10-02-2012, 03:42 PM   #11
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Thanks for your reply.

The lights on the amp are not turning on. The huge fuse running from the black cable to the battery is fine. The amp has 3 small fuses (like the small ones cars use) and they look fine too. Are there any other fuses I should be looking for?
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Old 10-02-2012, 07:00 PM   #12
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The only fuses that the amp should have is one on its main power line that goes directly to the battery(typically this cable is red or blue in color), and the ones that are on the amp itself. The fuse that is on the main power line, is that a tube shaped glass fuse (AGU)? Or is it a maxi blade type? Well, if it is the glass type, they are notorious for looking intact, but actually being defective.

The solder connection that is made internally gets weak and no longer makes the connection from within the fuse. So the metal strip on the inside looks as if it is fine, but the fuse still conducts no current. If the fuse is in fact %100 fine, then my next question to you is; do you have multi/voltmeter? And do you know how to use it? We can continue with the trouble shoot if you answered yes to atleast the first question.
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Old 10-02-2012, 07:48 PM   #13
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I think the fuse is AGU. The metal strip does look fine. I have a multi/voltmeter, but I am a complete novice with it. Let me know what you think I should do next. And thanks much for the advice.
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Old 10-02-2012, 07:55 PM   #14
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Check the remote trigger wire as well. This is usually a small gauge blue wire. If this isn't connected, the amp won't turn on. And of course, make sure the power cable and ground cables to the amp are connected properly.
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Old 10-02-2012, 08:14 PM   #15
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You don't have to be an expert with the mm (multimeter) to do these simple tests. What I want you to do is test for 12v + at the amps main power input, and at the remote turn on input. Set your multimeter to dc voltage and for the proper range (12 volts). Then place your black probe ( negative) on the ground of the battery and your red probe (positive) on both of those terminals of the amp.

The positive terminal will show you 12v + no matter what position the ignition is in, it is a constant power source. The remote turn on, will show 12v + when the radio is turned on, sometimes techs will improperly install this wire to a ignition switched 12v +, so the remote wire will have 12v + whenever you turn the vehicle on instead of the radio. Either way, make sure both of those terminals on the amp show 12v + when the radio is on. Check those out and let me know what you come up with, then we will move on.
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Old 10-02-2012, 08:57 PM   #16
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I went to use the meter and may have discovered the problem. The AGU fuse you were speaking about - it is inline on a thick grey cable that is attached to the black terminal of the battery. Should that line need to be connected to the red? The reason I ask is that the black ground coming from the amp is connected to the frame of the car. I never even considered this as a mistake because I would think the battery installers would know the right thing. Also, my red batter terminal has the main car connection and a second red connection which I am assuming would be the alternator. Perhaps this alternate red connection made them think the other one had to go to the black terminal?
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Old 10-02-2012, 09:23 PM   #17
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That was it. Everything is cool and the system works like normal. I think because the 12v wire coming from the amp was a big thick dark grey wire, and that it dissappears between the amp and the battery area, the person installing the battery assumed it should have went to the negative terminal. Now that it's hooked up to the positive terminal the stereo is back in business. Also just wanted to say thanks to everyone (especially The Don and Benzovs) for being such great resources. We would all have to spend more time and money if it wasn't for all you great guys on the forum. Thanks again.
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Old 10-02-2012, 10:26 PM   #18
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Glad to hear it was something simple and free to fix. That is the whole purpose of this forum, to help other fanatics whenever we can.
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