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Why Does My Amp Keep Blowing Fuses?

When a car amplifier keeps blowing fuses, troubleshooting the problem starts with figuring out the reason why the fuse bit the dust. This is assuming, of course, you know which fuse is blown.

A car amp fuse can blow for a number of reasons. Figuring out why is an easy job for the most part if you know what you’re doing.

In this article, we’ll walk you through the troubleshooting process to figure out what’s wrong, how to rectify the problem, and how to make sure the fuse doesn’t blow every little while.

Before we move forward, a quick note:

While it is pretty straightforward to visually inspect the element in a fuse to see if it has blown, a multimeter is the more precise way to go about it. You need to check the voltage at both sides of each fuse, starting with the main fuse (battery fuse).

If a fuse has the same voltage on both terminals, that means it’s good. If it has battery voltage on one side but not the other, that means it’s blown.

Amp Blowing Fuses Troubleshooting

First and foremost, it must be noted that there are two or three different types of car amp fuses in a typical installation, so figuring out the root cause in any given situation entails figuring out which one blew and then narrowing down the causal factors of why it did so.

In installations where an amplifier is directly connected to the battery, there will be an inline fuse (also known as main fuse) that can blow in addition to the internal amp fuse. In other installations where power is drawn from a distribution block, there will be another fuse on the distribution block.

So, essentially you’ll be dealing with a variety of different fuses, depending on how your amp is wired into the electrical system.

The troubleshooting process depends on which fuse is constantly blowing: main fuse, distribution block fuse, or internal amplifier fuse.

After you have determined what fuse you’re dealing with, you can move on to the next step.

1. Diagnosing a Blown Internal Amp Fuse

First of all, it must be noted that fuses usually blow when too much current is drawn through them than they can handle. In other words, they blow more easily when they’re hot. Furthermore, a hot fuse can handle way less amperage than a cold fuse.

Therefore, while diagnosing a blown fuse problem, it’s highly recommended to never replace a blown fuse with one that has a higher amperage rating. The reason why is because the original fuse was almost certainly hot when it blew, so replacing it with a new fuse that has the same or higher rating may allow an amp that has already suffered some type of internal damage with the original fuse to draw even more current than it did prior to blowing the old fuse, which could make things worse, bringing further damage to the internal components of your amp.

So, by replacing the blown fuse with a smaller one during the diagnostic procedure, you’ll still be able to figure out the problem, but you’ll be less likely to bring further damage to the amp.

With all of that being said, if the problem still persists, the problem is almost certainly in the amplifier itself.

Bear in mind that the timing here plays a major role in detecting the reason why that happens. I mean, think about it, a car amplifier has two power sources: a main source of power from the battery that becomes available as soon as the ignition key is in or in run position, and a “remote turn on” voltage from the head unit.

If your amp’s fuse blows while the radio is turned off – meaning that there was no power in the the remote turn-on wire -, then it’s highly likely that the problem relies in the amp’s power supply. In other words, your amp is probably connected with reverse polarity (positive/negative connected backwards), or you connected a speaker or multiple speakers in such a way that their overall impedance load is beyond the capabilities of your amp, or simply you have a faulty component that’s arising from time and normal use…etc.

If the fuse only blows right after the head unit is turned on – meaning there is power in the remote turn-on wire -, then you’re probably looking at a problem with the amp’s output transistors, rectifiers, transformer winding, or other components. Actually, a bad speakers or something as simple as faulty speaker wiring can also cause this type of fault — if the fuse only blows when the volume on the radio is cranked up.

To sump it up, here’s a rundown of all the reasons why the fuse keeps blowing in your amp:

1. Reversed polarity

If you’re powering up your amp after doing some re-wiring, but it keeps popping fuses, there’s a good chance you reversed the polarity. This may be elementary, but that doesn’t mean it’s not worth checking if power and ground aren’t hooked up backwards. It never hurts to be thorough.

Some car amp manufacturers put a diode across the + and – input lands on the circuit board. Its key function is to control the direction of current-flow. Current passing through a diode can only go in one direction.

Better built amplifiers usually have a reverse polarity protection feature and won’t allow the amp to work when the polarity is reversed.

2. Impedance mismatch

If your amplifier is presented with an impedance load that’s beyond what it can handle, it will try to draw more current than its power supply is designed to deliver, making it overheat, or go into protect mode.

The fuse in an overtaxed amplifier might also blow to make the amplifier shut itself down before it causes too much damage.

With all of that being said, we can’t stress enough how important it is to abide by the amp’s manufacturer recommendations. A car amplifier that’s built to be stable at 2 ohm, for instance, should not be driven beyond that.

It goes without saying that if the impedance of your speakers is matched to the impedance the amplifier is designed to drive, you shouldn’t have any problems.

3. Excessive heat building up (as a result of clipping)

Excessive heat build up and distortion in the form of clipping go hand in hand with incorrect gain setting.

If you start adjusting the gain knob while listening to your music playing, you will notice an increase and decrease in volume. This is the reason why most inexperienced car audio enthusiasts often confuse the gain settings with volume controls, and max out the gain.

Essentially, amp gain refers to the input sensitivity adjustment necessary to match an amplifier’s input to the receiver’s output. By adjusting the gain properly, you’ll reduce background noise, and prevent your amp from “clipping,”.

An amplifier that’s pushed way too hard (because of impedance mismatch for example) will introduce distortion in the form of clipping. Eventually, it’ll overheat, blow the fuse, or jump into protection mode to protect itself from serious damage.

Clipped audio signal itself doesn’t only make your speakers and subwoofers sound weak, but it also makes them surpass their thermal or mechanical failure rate by doing things they’re not designed to do. This leads to overheating and, eventually, blowing out.

4. Small wiring kit (insufficient power and ground wire size)

It goes without saying that for an amp to operate efficiently, its power and ground wires must be large enough to accommodate its demand for electrical current.

An amplifier that is not getting enough power will have a hard time trying to drive your speakers/subs. Not only that, but the amp may also experience thermal shutdown, blow the fuse, or go into protect mode when bass hits hard.

So, invest in good amp wiring kit to make your amp operate efficiently. As a general recommendation, use the chart below as a quick reference in determining the appropriate wire gauge for your amp.

Wire Gauge SizeTotal Amplifier RMS Wattage
0/1 AWG1000+ Watts
4 AWG400-1000 Watts
8 AWG200-400 Watts
10 AWG100-200 Watts

 

5. Faulty speaker or damaged speaker wiring

If your amp keeps popping the fuse and you’ve ruled out all the potential causes we listed here so far, there could be a problem with your speakers or the speaker wiring. This is especially true if the fuse only blows when the volume is turned up high.

If one of your speakers is blown out or grounded to the chassis of the vehicle, the amp will still try to put power to it. When it does, it “sees” a condition that makes it get hot fast, blow the fuse, or go into protection mode to prevent serious damage.

6. Faulty amplifier

If you’ve ruled out everything that could cause the the fuse to pop, but you still couldn’t figure out the root cause, it is more than likely that the problem lies within the amplifier itself.

There’s a variety of things that could go wrong with an amplifier including but not limited to blown/shorted output transistors, faulty power supply …etc.

7. Improper or loose grounding

When mounting an amplifier in your car, the ground wire can make or break your sound system. A bad ground can cause all sorts of problem you can think of starting with dimming headlights, all the way up to amplifier damage. Therefore, in order to ensure good functioning and stability of your audio components, it is crucial to properly ground the wire to the car’s chassis.

The best connection point for attaching a ground wire is usually sanded or bare metal, or a screw or a metal nut that is attached directly to your car’s chassis. You do not want the ground wire touching paint or any preexisting nut or bolt.

Furthermore, your ground should be secured tightly. If the ground is loose and allowed to move in the slightest, it could cause the fuse to pop or the amplifier to shut off.

8. Wrong fuse size

Fuses are used to protect your equipment. Therefore, it’s highly recommended to always use the right car amp fuse size. If you use a fuse that’s too small, it will blow during normal operation, whereas if you use a fuse that’s too big, you could end up dealing with blown amp or an electrical fire.

If your amplifier has an internal fuse, then your main fuse should be a bit larger. For instance, you might want to use a 45 or 50 amp main fuse if your amp has an internal 40 amp fuse.

In case your amplifier has no internal fuses, you’ll need to check its power rating to determine the right size for your inline car amp fuse.

If you’re dealing with multiple amps that don’t have built-in fuses, you should consider using a fused distribution block.

2. Diagnosing a Blown Distribution Block Amp Fuse

If the main fuse is intact and passes current but one of the fuses in the distribution block is blowing, the problem is certainly beyond the distribution block. So, either the wire feeding the amplifier is shorted or there is something wrong with the amplifier. There are a few ways to determine which one is the culprit, depending on where the amp is mounted and how the wires are routed.

Basically, what you want to do is carefully check the entire length of the power cable that connects the distribution block to your amp, and make sure it’s fully intact.

If the wire is routed in such a way that makes it almost impossible to inspect, disconnect it from your amp and see if the fuse blows when it’s inserted into the fuse holder. If it does, then the power wire is the culprit, and replacing it will almost certainly fix the problem. However, if the fuse doesn’t blow with the power wire disconnected from your amp, that’s a sign that the wire is fine and there’s probably something wrong with the amplifier.

A faulty amp is more complicated to diagnose, let alone to fix, unless, of course, you’re good with electronics. So, you’ll probably end up taking the amp to a certified professional, or just replace it with a new one in case it’s unrepairable. If it’s still new, it may still be under warranty.

3. Diagnosing a Blown Car Amp Battery Fuse

If you determine that your main fuse is blowing, it’s crucial to pay close attention to when that happens. If the battery fuse blows immediately as soon as it’s inserted into the fuse holder with both the headunit and amplifier being turned off, the problem could be anywhere in the power line.

If you have a distribution block between the battery fuse and the amp, and its fuses aren’t blowing, the problem is likely a direct short to ground between the main fuse and the distribution block. It’s not likely beyond the distribution block, because if it were, the fuses in the distribution would blow first.

If there’s no distribution block, then you’re probably dealing with some kind of short in the power cable between the main fuse and the amplifier.

What you want to do in this case is to check if the power cable is in good condition – inspect it for cracks, tears and any other visible damage. In some cases, a power cable with deteriorated casings or insulation may only come in contact with the ground when the vehicle is moving, resulting in a fuse that blows every time you run over speed bumps or rough terrain.

Additionally, trace the ground wire to where it is attached to the chassis, and make sure it’s securely fastened to your bolt in the grounding point. Loose grounding could cause the fuse to blow or the amplifier to shut off.

Alex Brown

Hey There, my name is Alex Brown, I'm an LA-based sound engineer with over 10 years experience installing, troubleshooting, and repairing commercial, automotive, and household sound equipment. I've installed highly competitive car audio systems, and everything from navigation systems to full car stereo systems, remote starters, alarms and beyond. I enjoy creating solutions and simplifying everyday needs. I also love helping people get great sounding gear, thereby, saving the world from bad sound one customer at a time.

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