Car stereo question

Alaric · Post by **Alaric** » Thu Mar 29, 2012 6:41 pm

So lemme start by saying i know nothing about electrical. That said I have the following thisng that happened to me last week and Im trying to figure out WHY??

I went to get a new car battery. Got back to the shop to install it. Now Im the idiot as I put it in the same way as the old one but epically failed to notice the posts were reversed. So I go to hook it up and poof, there goes the fuse due to reversing the polarities. Thats fine and dandy, pretty typical and was an easy fix. But here is the part I simply DO NOT understand:

I have a 60 amp fuse right off the battery for the amp for my stereo. It goes from that to a capacitor then from the cap to the amp, then there are 2 more 30 amp fuses on the amp itself. SOMEHOW when I hooked up the battery the wrong way the current bypassed ALL the fuses and fried my amp.
I had the battery wire go into the cap, then from the cap to the amp. I disconnected the negative from the cap to prevent the cap charging until I could charge it properly. So there was no way for it to ground. I was under the impression that if a current powerful enuff to fry my amp would be caught by the fuses as I was under the impression thats what fuses are for.

If you can tell me why the hell 3 fuses got bypassed you will have my eternal gratitude. Ive done alot of searching online and have come up with squat.

I dont go on alot of forums so Im hoping one of you guys may have an answer or can point me to an answer. Thanks

[Edited on 3-29-2012 by thetiebers]

ijon · Post by **ijon** » Thu Mar 29, 2012 7:19 pm

short circuit. a car battery delivers up to 1000 Ampere for a short moment. the fuses literally melt. if you only fried your amp, you are lucky.

Alaric · Post by **Alaric** » Thu Mar 29, 2012 7:32 pm

but that still doesnt explain why the fuses were untouched. I blew the CAR fuse but all the stereo fuses were bypassed somehow. Thats what Im wondering is why..

Capt_Caveman · Post by **Capt_Caveman** » Thu Mar 29, 2012 7:38 pm

first off i'm an electronics repair tech for 25+ years (so i'm not just feeding you B.S.)

inside the amp is a large diode wired reverse polarity across B+ and ground
it's designed to short and blow fuse if power is reversed, to protect the rest of the circuitry.
find it, clip it out, replace fuses and give it a try.

Alaric · Post by **Alaric** » Thu Mar 29, 2012 7:45 pm

You rock! Thanks man. I was more concerned about WHY it happened, just seemed so odd that it bypassed the fuses, will that always happen if the polarity is reversed?

ijon · Post by **ijon** » Thu Mar 29, 2012 8:32 pm

didn't get the 'bypassed' part. sorry.
how do people manage to blow up their equipe and even melt cables doing what alaric did? or is that from the past.

Capt_Caveman · Post by **Capt_Caveman** » Thu Mar 29, 2012 8:38 pm

all the car audio i've worked on has this design feature.
it's intended to make you bring it in to the repair shop to be checked over
in case of other problems. (liability issues)

Post by **DaveK** » Fri Mar 30, 2012 7:21 am

From post: 134065, Topic: tid=9146, author=Alaric wrote:but that still doesnt explain why the fuses were untouched. I blew the CAR fuse but all the stereo fuses were bypassed somehow. Thats what Im wondering is why..

60A and 30A for fuses sound BIG - they would need time to heat up and melt; little transistors and chips would fry first, cutting off the juice and so protecting the fuses . . . which leads to an electronic definition . . .

"a circuit board is an electronic device designed to burn out quickly and so save your fuses from damage"

Capt_Caveman · Post by **Capt_Caveman** » Fri Mar 30, 2012 1:45 pm

amazing how much smoke can be packed into such a small componant lol

Star King · Post by **Star King** » Fri Mar 30, 2012 2:40 pm

I use to run a company that manufactured automotive alternators and generators for Ford, GM, Chrysler, Autozone, Advance Auto Parts, etc....

Electricity travels at almost the speed of light, so hopefully your quick fuse protection will help save you but most of the time other electrical components get damaged.

Hopefully, you didn't toast your voltage regulator in the alternator or toast your vehicle's computer system. I hope your lucky and it's just the fuses. Your vehicle has fusible links and not just fuses.

Alaric · Post by **Alaric** » Mon Apr 02, 2012 3:09 pm

Nah cars just peachy. Just the amp suffered. And Yah the smoke was significant. The trunk still smells like a cooking fire lol. I gues 30amp was too big...and thats the size of fuse IT CAME WITH...figures lol. Electrical has always hated me.
Thanks everyone for your input.