melted fuses

[saysomestuff 0]

Hey all.

 

I've been checking over my new '88 8v passat GT and I've found two melted fuses, not blown, just the plastic has melted off them , anyone had this problem with cheapo fuses or is there something a bit more sinister happening?

 

it's the rear demister and the central locking fuses.

[nocrap 0]

If they're getting that hot the fuse should have way broken before that!

Sounds a bit scary too me!!

 

I assume the correct amps are used? i deffo start by getting a new set of fuses though!

[GIXXERUK 0]

yeah as nocrap, says i would check you've got the correct rated fuse in there and i'd change them to be sure , you dont want a fire or getting high off plastic fumes :-)

[khurrado 0]

My last valver had melted fuses, took it to design dubs and they told me it was prob from water leakage above the box, or a wiring problem. They replaced the fuse box, and no problems since.

[GIXXERUK 0]

it should blow the fuse before it melts anything though , thats why they are there :? unless they are over rated ,the rear demister does draw a lot of current

[nocrap 0]

it should blow the fuse before it melts anything though , thats why they are there :? unless they are over rated ,the rear demister does draw a lot of current

 

Indeed it does, the worrying one in the central locking! that one really shouldn't draw enough current to melt the fuse, even if it did because of a fault, like GixxerUK said, it should blow the fuse

[saysomestuff 0]

ok the central locking fuse is definitely getting totally unecessarily hot, tried loads of different, non-cheap fuses.

 

With key off, it's drawing 48.2 with the multimeter set to 200mA - would anyone mind nipping out to check what it should be for me? Just whack the multimeter across the fuse terminals.

 

Probs best on an 8v golf or passat.

 

 

EDIT - i think it's number 21 - runs clock, c/locking, interior lights.

[saysomestuff 0]

quick bump for anyone back from work :)

[Toad 0]

48.2mA? when off?

 

that's not that much I suppose.

[yalan 0]

it should blow the fuse before it melts anything though , thats why they are there :? unless they are over rated ,the rear demister does draw a lot of current

 

Not necessarily.

Lots of heat doesn't necessarily mean excess current through the fuse.

It means localised heat - probably caused by a poor connection and therefore high resistance - either of the fuse within the fusebox or connections to the fusebox itself.

 

I'd say Very unlikely to be anything to do with the quality of the fuses - but you never know. Happened to me on my Audi - on the Fan circuit where the AC was on too. High power circuit, high current draw - poor connections equals.......

 

I replaced the fusebox and circuit lucas connectors to the fusebox. Symptom didn't re-surface. HTH

[GIXXERUK 0]

It means localised heat - probably caused by a poor connection

 

shouldnt a poor connection that causes heat blow the fuse ? Poor connections consist of high resistance generating heat but A fuse is an intentionally included sacrificial weak link current conductor, carefully sized such that under normal circuit operation it will pass current just fine...however exceeding its current rating will cause it to heat up to a point where it will melt, opening the circuit, causing the current to stop flowing, thereby saving other conductors in the circuit from the same fate

an overrated fuse can cause problems by not blowing when it should as can introducing a conductor such as water/damp

[yalan 0]

yes but a fuse blowing is caused by an excess current flowing across the sacrificial link - overloading that part and causing heat.

 

A poor connection will mean an electrical junction is not able to pass the current efficiently causing high localised resistance and heat. The metal in the fuse then conducts the heat and can melt the fuse body. All this well under the fuse's rated levels.

[saysomestuff 0]

Not necessarily.

Lots of heat doesn't necessarily mean excess current through the fuse.

It means localised heat - probably caused by a poor connection and therefore high resistance - either of the fuse within the fusebox or connections to the fusebox itself.

 

hmm, once melted, both blades of the fuse are very hot (still not blown), have checked the reistance across the fuse and it's 0, so do we reckon it's an area of high resistance nearby?

 

EDIT - just spotted your last post yalan - will whip it all out tomorrow and check the circuit for areas of high resistance.

 

Just to also back up the low current draw argument, the car hasn't been touched for over a week and battery still fine.

[GIXXERUK 0]

saysomestuff,

I've found two melted fuses

 

were they close together ?

 

yalan,

A poor connection will mean an electrical junction is not able to pass the current efficiently

 

i see where you're coming from mate

[saysomestuff 0]

saysomestuff,

I've found two melted fuses

 

were they close together ?

 

Hello mate - no, numbers 11 and 21 I think - but their wiring may be closer within the fusebox?..

[yalan 0]

When it happened to me, I called round a few reputable auto electricians and they all suggested that I do what I'd already done (ie check out connections nearby and replace the fuseboard (I got mine from a local breakers for £11 including most relays and fuses!)).

 

A number of fuses doing the same thing could be as a result of shared common hardwiring in the fuseboard? In fact come to think of it, there were 3 showing signs of overheating on my board too.

[saysomestuff 0]

thanks mate - you've been really helpful - it's always worth going through it with others, hopefully I'll find the culprit through resistance testing - if not, will whack a new fuseboard in.