Fuse housing melting but fuse not blowing, ppi amp - diyAudio
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Old 31st July 2008, 12:54 AM   #1
rawadia is offline rawadia  United States
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Default Fuse housing melting but fuse not blowing, ppi amp

I have a ppi4100 which I have connected into 4 ohm loads, fronts are 100x2 rms and rear go to a sub, 400x1 rms. I've a attached a poorly drawn schematic of my how my system is wired.
So here is the problem. Sound sometimes cuts in and out. One day it cut completely out, so I looked at the amp and there was not any power to it, then I saw that my 60 amp fuse was in pieces, pics to be attached. The fuse never melted, but it looks like the wire started to melt on the side that goes to the the amp (looks black and burnt, the housing completely melted apart, and the fuse has some dark looking liq residue inside but still conducts.

Here are some of my ideas on what I think might be happening:

1. I recently repaired the amp, where a leg off the power inductor had broken off, since I could not solder it back to the board, I soldered a wire to the board and then the leg of the inductor to the wire. I haven't taken the amp apart yet to check, but maybe that wire is touching the heatsink occasionally, which kicks on the protection and my sound goes in and out, then it also causes a lot of current to flow which heats up the wire, but not enough to blow the fuse since it happens intermittently.

2. The 8 guage wire is too small, so wire heats up, and fuse doesn't blow. But then should the entire wire melt? Maybe as the housing starts to comeapart is the reason for the amp cutting in and out?

3. Similar logic to #1, but instead of inductor short, short is in speaker wiring is causing amp to cut in and out, and then leading to fuse housing failure.

would really like to figure out whats going on here. thanks!
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Old 31st July 2008, 12:57 AM   #2
rawadia is offline rawadia  United States
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fuse holder
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Old 31st July 2008, 12:59 AM   #3
rawadia is offline rawadia  United States
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side view, notice blackness of wire where it connects to the fuse holder
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Old 31st July 2008, 01:00 AM   #4
rawadia is offline rawadia  United States
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notice residue in fuse, but still works
also hard to see, but the metal part still inside the main fuse housing has a black melted spot, what would have caused that since it seems like all the damage is on the other side?
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Old 31st July 2008, 01:10 AM   #5
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The fuse is poor quality (too much resistance in end caps), the fuse holder has too much resistance where it connects to the fuse, you didn't tighten the set screw sufficiently or all of the above.
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Old 31st July 2008, 05:32 AM   #6
ppia600 is offline ppia600  United States
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That amp draws WAY too much current for that fuse holder type. Use an anl wafer type fuse holder, WAY better. Those glass (agu) types can have a lot of resistance and build up heat, melting the solder loose inside the fuse. Then it can act like a circuit breaker and cut power off and on randomly. Also, I can't believe you are using an 8 gauge for that amp. Do it justice and use at least a 4 gauge, that thing needs voltage to give you clean wattage.
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Old 31st July 2008, 06:24 AM   #7
luka is offline luka  Slovenia
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Hi

Which amp? that 4x100w one? I have 1.2kw amp on this fuse, 80A and it works great + 4 channel amp!
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Old 31st July 2008, 04:33 PM   #8
ppia600 is offline ppia600  United States
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His amp is rated to run 800w rms when fully loaded. It would be drawing approximately 1500w through the fuse and wiring. He can not get that wattage through a tiny 8 gauge and a fuse holder with weak high resistance contacts. (maybe if the amp was only 15" from the battery, lol) They are going to phase that type of holder out anyway, because of the reliablility issues. The anl and mini anl (manl) never have those issues and only blow the fuse if the current drawn exceeds the fuse's rating. I haven't used an agu fuse holder since the early 90's. AGU FTL
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Old 31st July 2008, 04:52 PM   #9
luka is offline luka  Slovenia
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I know what you mean, I do use only it because I didn't think I will get so "big". About 1500w is about the same as I have now (probably). And I have about 4gauge, 20mm^2... Anyway, not the best fuse and holder for this kind of powers
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Old 31st July 2008, 04:53 PM   #10
rawadia is offline rawadia  United States
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Just to make things clear, I am running 4 gauge the length of the car, the 8 guage section is less than 2ft (from the distribution block to the amp), which, from what I have read, should be sufficient for the amount of current. Correct me if I'm wrong on that assumption.

I had this setup running since last october, no problems till June of this year, so granted that the fuse is faulty, what I need to figure out is whether the fuse itself was the cause of the 'cutting out' or did something else cause this, and its repercussions were seen in the fuse holder getting hot at its weakest point (highest resistance), which would be the connection point of the fuse holder to the wire.

Now to add to this saga, I connected another fuse and fuse holder. I just slipped some heat shrink over the end connectors, but I didn't have a heat gun available so it was 'un-shrunk.' I also used to look at it everyday. It was working fine for about two weeks. Then a couple days ago the 'cutting in and out' started again, I popped my trunk and looked at the fuse and saw that one end had 'shrunk,' as shown in the pic.

Unfortunately, I've never been able to look at the amp and catch it in the act of 'cutting in and out' so I don't know if it completely loses power (which would point to the fuse shorting out) or if the protection circuitry is engaging ( which would point to a short in the amp or in output wiring)

Since the 'cutting in and out' occured again, with and different fuse, fuse holder, and fully tightened screws, there must be something more going on.
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