Power Wire Grounding out after fuse


Jersey2816

CarAudio.com Newbie
Feb 27, 2021
2
1
MO
I have a cheap 800 watt amp in the work truck that keeps blowing fuses at the battery, when i hook up the tester to the fuse box it shows that the power wire is grounded on one side and the other side is hot. I put in a new 4ga power wire, took all the screws out of the amp that were touching the metal of truck, all the wires coming into the amp are nice and neat, not overlapping or touching each other. I'm out of ideas on where to look to fix this problem. The amp runs for about 20 mins then the 20amp fuse blows up by the battery. Any Ideas?
 

Coolhand20th

CarAudio.com Elite
Mar 27, 2019
1,231
329
Wisconsin
Not too mention the kind of wire as well. Cheap wire could cause issues like this as well. I also have a 2nd fuse a few inches before my amplifier as do many others these days.
 

Coolhand20th

CarAudio.com Elite
Mar 27, 2019
1,231
329
Wisconsin
Kickstand mentioned fuse size figured I didn't have to if someone else did. Good grief! Don't like the response that is not my problem. Why mention it when someone else already did right above me. You however can take your smart ass comment someplace else.
 
Last edited:

Jersey2816

CarAudio.com Newbie
Feb 27, 2021
2
1
MO
  • Thread Starter Thread Starter
  • #8
I was wrong, it's a 600Watt, Dual DA6002D. The old one was 800 watts that worked fine for 2 years then started blowing fuses so i bought the new one after finding nothing wrong with the wiring. I went with a 20amp fuse because that's what's in the amp from factory. I'm only powering two 6 by 9's so you can hear the music over engine. The wiring is a soundbox 4ga amp power/ground wire.
 
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Squirrel!

Curmudgeon
Feb 26, 2020
332
56
Ohio
You have a cold solder joint or other internal short. Toss the POS and get another. They are that inexpensive for a reason. :sneaky:
 

metalheadjoe

Registered User
10+ year member
Oct 21, 2007
349
205
ND
If there is a short in the line after the fuse by the battery then your amp might take the brunt of it.
This doesn't make any sense. If there is a short after the fuse, the fuse opens and the line after the fuse is dead. Current is constant in a series circuit.
 

Kickstand

CarAudio.com Well Known
Jan 1, 2021
323
86
Maple Ridge
If you get a short between the fuse and the amp you can get a surge.
Yes it will probably blow the fuse but not before it goes to the amp.
I lost an old school RF Power 800a2 to this
There was a quarter sized hole in the board after and my car smelled like burnt electronics for a week
I have pictures somewhere but there on an old hard drive in a stack of like 20 of them.
I gave up after the 3rd drive
 

metalheadjoe

Registered User
10+ year member
Oct 21, 2007
349
205
ND
Your amp died of something else. A power cable shorted to ground causes a current spike between the battery and ground. It doesn't cause any additional current to the amp. If an amp has an internal fault, it might draw enough current to blow the fuse in your power wire, but a shorted power wire doesn't do anything downstream of the short besides kill power.

Really sorry about your amp situation though. Burnt electronics is a painful smell.
 

metalheadjoe

Registered User
10+ year member
Oct 21, 2007
349
205
ND
Wouldn't the fuse installed in the amp protect the amp?
Fuses in the amp prevent the amp from causing a fire. Fuses in power wires prevent the power wire from causing a fire. It's as simple as ohm's law. Current is based on supply voltage and total resistance. It's a law, not a theorem. If an amp draws enough current to cause damage, it's because the amp has an internal short, meaning lower resistance. Your battery can't randomly defy ohm's law and throw more current at the amp just because there is a new parallel load (the short) in the circuit.
 

LsGuy

Manila Gorilla
Sep 11, 2020
407
108
Ohio
Fuses in the amp prevent the amp from causing a fire. Fuses in power wires prevent the power wire from causing a fire. It's as simple as ohm's law. Current is based on supply voltage and total resistance. It's a law, not a theorem. If an amp draws enough current to cause damage, it's because the amp has an internal short, meaning lower resistance. Your battery can't randomly defy ohm's law and throw more current at the amp just because there is a new parallel load (the short) in the circuit.
That is mostly correct, however there are factors outside of a battery that can cause current spikes...like the alternator. This is why the computer in a newer vehicle will detect overcurrent and prevent its self from frying. This happened to me in a new alt install where the diodes were failing at high temps. Car ran great, 20 minutes into the drive it would start randomly going dead and then springing back to life.
 

metalheadjoe

Registered User
10+ year member
Oct 21, 2007
349
205
ND
That is mostly correct, however there are factors outside of a battery that can cause current spikes...like the alternator. This is why the computer in a newer vehicle will detect overcurrent and prevent its self from frying. This happened to me in a new alt install where the diodes were failing at high temps. Car ran great, 20 minutes into the drive it would start randomly going dead and then springing back to life.
Please specify what's not correct. I used "battery" as a generic term for supply voltage. My sentiment stands. A shorted cable doesn't cause a current surge downstream of the short.
 

LsGuy

Manila Gorilla
Sep 11, 2020
407
108
Ohio
I never said shorted cable, I asked if the fuse in the amp would protect the amp. You said it's there to prevent the amp from causing a fire. However, that fuse should also pull duty protecting the amp in the event of overcurrent.
 

metalheadjoe

Registered User
10+ year member
Oct 21, 2007
349
205
ND
I never said shorted cable, I asked if the fuse in the amp would protect the amp. You said it's there to prevent the amp from causing a fire. However, that fuse should also pull duty protecting the amp in the event of overcurrent.
I thought I was being helpful with a descriptive answer. Apparently i was wrong. The short answer to your question is NO.

I must not be making myself clear enough...
THE FUSE IN THE AMP DOES NOT PROTECT THE AMP. THE ONLY THING THAT BLOWS THE FUSE IN THE AMP IS AN INTERNAL ISSUE. IF THAT FUSE BLOWS, IT'S BECAUSE THE AMP HAS AN INTERNAL ISSUE. THE FUSE IS THERE TO PREVENT THAT INTERNAL ISSUE FROM STARTING A FIRE.

Again, refer to ohm's law. Overcurrent can't defy ohm's law. It's really that simple. The fuse in the amp doesn't protect internal issues. It prevents the amp from causing a fire should an internal issue occur for whatever reason.
 

LsGuy

Manila Gorilla
Sep 11, 2020
407
108
Ohio
So it is some sort of fancy one way fuse then? If the fuse blows to stop power from exiting a device, wouldn't blowing said fuse also stop power from entering the device?
 
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