I have an amp that is connected directly to the positive terminal of the battery using the heavy gauge wire supplied with an in-fuse holder.

 

The holder came with a 20amp blade fuse which is what i have used but noticed the other day it had melted part of the plastic part of the fuse and the holder on the battery side of the fuse.

 

It lost the circuit but not with the fuse blowing but the fuse melting so the blade was not in contact with the sacrificial link. strangly enough if i turned the amp off and on again it would come on for a second then die.

 

I dug out most of the melted plastic, tried a new fuse and tried to make sure it wasnt in a hot area of the engine bay but the same thing soon happened.

 

Is the 20amp fuse too low rating or is the fuse holder too close to the battery (about 8" of wire seperating them) or have i got a shorting problem somewhere?

Its earthing out somewhere mate, pull the wiring out and re run it with new wiring.

 

Also make sure your amps eathing and key live are run ok with no rips in the insulation

A 20A fuse is enough for approx a 240w amp, running at full wack and assuming it's 100% efficient. Assume it's 66% efficient then it's down to 160w. Depending on what amp you have (and how deaf you now are), then you may have another problem.

A 20A fuse is enough for approx a 240w amp, running at full wack and assuming it's 100% efficient. Assume it's 66% efficient then it's down to 160w. Depending on what amp you have (and how deaf you now are), then you may have another problem.

 

 

Cant remember the exact Wattage of the amp but it is nothing extreme or tiddly. It is running a sub and rear replacement speakers. It was on pretty loud (ipod running into RCA into the stereo so stereo wacked up to get any volume) and for quite a long period (1 hour - 45 mins).

 

What amp fuse would it need if it was not running efficiently? higher or lower that 20A?

 

I guess shorting out would be the most obvious thing but it is going to be a pain pulling up all the carpets.

Wouldnt a short cause the fuse to blow rather than this heat build-up on the battery side of the fuse. What use is the fuse if it doesnt blow when the circuit is shorted??

 

I should also mention there is another in line fuse (20A) further down in the connection running under the dash but this has had no problems. Would this suggest the problem lies between this fuse and the battery?

In all honesty, pull the lot out, get down Maplin and buy some good grade wire and ONE inline fuse.

 

Re run the lot.

 

For the sake of £50 dont risk blowing your system up or setting your car on fire.

Cant remember the exact Wattage of the amp but it is nothing extreme or tiddly. It is running a sub and rear replacement speakers. It was on pretty loud (ipod running into RCA into the stereo so stereo wacked up to get any volume) and for quite a long period (1 hour - 45 mins).

 

What amp fuse would it need if it was not running efficiently? higher or lower that 20A?

 

I guess shorting out would be the most obvious thing but it is going to be a pain pulling up all the carpets.

Wouldnt a short cause the fuse to blow rather than this heat build-up on the battery side of the fuse. What use is the fuse if it doesnt blow when the circuit is shorted??

 

I should also mention there is another in line fuse (20A) further down in the connection running under the dash but this has had no problems. Would this suggest the problem lies between this fuse and the battery?

 

You can work it out easily, amps = watts / voltage, therefore 120 w / 12v = 10 amps etc etc

 

If part of the wiring near a joint is getting hot then look for a bad connection at that point. If a section of wiring is getting hot then assume that wire is too low a rating.

 

A short will normally blow a fuse, but, depending on the fuse, could melt a wire first.

maybe it is the joint in the fuse holder then and as it getting more melted and screwed up it gets worse. I think i will cut out this fuse holder so it runs through the the 20A fuse under the dash for protection. The only problem i have with that is that i have heard it is best to have the fuse as near to the battery as possible. I am not sure of the reasoning behind this but this fuse will be in about the middle of the wire connecting the batt to the amp.

The only problem i have with that is that i have heard it is best to have the fuse as near to the battery as possible. I am not sure of the reasoning behind this but this fuse will be in about the middle of the wire connecting the batt to the amp.

 

Can't think of any real scientific reason for that, the fuse will blow wherever it is assuming the rating is right. Should be about 50% of the wire rating and about 25-50% above what the amp needs.

the reason for fusing near the battery as possible is that the wire between the battery and the fuse is unprotected. so if your only fuse is under the dash and the wire from the battery snags on the chasis (say where it goes through the bulkhead) and shorts out then the fuse will not blow but the wire could melt, or your car could catch fire , or your battery could be damaged

 

some of the "high current" blade fuse holders about are the cheapest piece of junk with very poor elecrical connections. so as you say it is probably a poor conection in the fuse holder getting hot rather than a fault in your wiring. certainly once the holder has melted i would not reuse it. personally i changed the blade holder that came with mine to one of the plastic tube with screw end caps and a fuse that looks like a standard domestic one. you can get them in halfords (or cpc if you have an acount are much cheaper)

Good info, more a practical than a scientific reason, but totally valid.