Melting fuse plastic?

[-Nemesis-]

Any idea why this would happen?

I've got a Narva fuse box (about 8 fuse width) for the power in my engine bay. I don't like it because it's messy, with 8 inputs as well as 8 outlets - off topic here: Anyone know if you can get a single input (say 4 guage wire) distribution block, with multiple outputs?

Anyways, one of the fuses is for my AU Falcon thermo's. The fuse is fed by a 4 gauge cable, into about a 12g (as big as the fan factory wiring anyway), through the 30amp fuse, then into the relay, then to the fans. The fans keep running fine, but the blade fuse for it keeps (well only done this one) melting the plastic of the blade fuse, turning into a blob of red goo.

If the fuse is rated high enough for the current draw, why is it melting?


My engine bay needs a serious re-wire anyways so looking for ideas. When I put the blower in I had to relocate the battery to the opposite side, so to power everything I've got one 4g (110amp I think) cable running to the original side, then tapped into this old fuse block...

[pongo]

red goo ???? 10 amp fuse perhaps typo

am curious too, melted a few head light fuse and holders in my time using globes that are within range, am thinking bad earth but NFI really

[-Nemesis-]

red goo ???? 10 amp fuse perhaps typo

am curious too, melted a few head light fuse and holders in my time using globes that are within range, am thinking bad earth but NFI really

Hehe going off memory (bunch of colours in there) maybe it changed colour as it fries.

It's a big fuse, at least 30 amp maybe more (can't get it out or read what I used) because any less blow on startup. The big twins have a huge amp pull at start up.

[drivesafe]

Hi Nemesis, here is some better cable prices.

The second link is to a page of 12v accessories and if you scroll down you will find some 8 way blade fuse holders with a single input and 8 outputs via fuses.


Cable


12 volt accessories

[-Nemesis-]

Nice links thanks mate. That 8 way block looks the goods, I could run the big cable under the gaurd and pop it up into that box, so it's alot neater! At the moment I have all the output wires from my main cable just soldered on and taped up, looks hideous.

Just looking at that link. For the bigger accessories that run 30 amp fuses (eg), what's the disadvantage of running those circuit breakers instead? I could hide them in the inner gaurd as well. My engine bay is so tight that I could actually make needed room by moving wires lol!

[stuee]

Are you running one 30 amp fuse per fan or for both. I have a single 25 amp fuse for each fan. Basically they are wired, relayed and fused separately so if one goes I still have the other.

I also have one of those distribution blocks from drive safe but I wish I purchased it prior to doing my engine bay fuse box, would have been a lot neater (I also have a narva multi-fuse block). Instead I'm going to use it for power distribution in the back of the car from the 2nd battery.

[murcod]

I'd suggest if your fuse is slowly melting then you're running it close to it's rated current. I would suggest you wire them separately with individual fuses of 25- 30 Amps. (Changing your fuse holder will not improve the situation if you're running the fuse close to it's rated current.)

PS: I've got twin electric thermos (Spal) and run a 30 Amp fuse for each.

[-Nemesis-]

Outers to the rescue, twin fuses/relays makes perfect sense and I just slapped myself for not thinking of it. No wonder it was blowing the recomended 25a fuses on start up derrrr!


Found these last night, look the goods and crazy price

http://www.acdconline.com.au/product.aspx?ID=551

Same as this, but doesn't have much info on actual wire size etc

http://www.acdconline.com.au/product.aspx?ID=570

[pongo]

Outers to the rescue, twin fuses/relays makes perfect sense and I just slapped myself for not thinking of it. No wonder it was blowing the recomended 25a fuses on start up derrrr!


Found these last night, look the goods and crazy price

http://www.acdconline.com.au/product.aspx?ID=551

Same as this, but doesn't have much info on actual wire size etc

http://www.acdconline.com.au/product.aspx?ID=570

thought you already where using twin fuses. But why do the fuses melt rather than blow?

[-Nemesis-]

I think, back then, I had thought being a 50amp 5 pin relay I could just run the single relay for both fans. So I didn't pay attention to the fuse loading....


But yeah, still why did it melt the plastics.... The red wire has gone dark too. I guess too much current.

Hopefully this means the fans weren't at 100%, so with new overkill wiring they'll be even more efficient. Need all the air I can get with the power being made!

[murcod]

Fuses work by providing a small amount of resistance in the circuit. Current flowing through them will generate heat, the heat will depend on the fuse resistance and current flow. A fuse that blows is simply overheating from the current flow generating heat- so your fuse and (by the sounds of it) wire are heating up beyond "safe working limits" from providing too much resistance to the high current. (That's a very simplistic explanation anyway! )

Personally, I'd be going to 6mm2 wiring- which I think is the perfect size for the large yellow crimps. You'll get less voltage drop and notice a significant increase in fan speed.

[-Scott-]

But why do the fuses melt rather than blow?

A fuse is intended to protect the wires in the circuit - nothing else. In a short circuit, too much current flows and wires get hot. If it flows for too long, the insulation will melt and flow (and stop doing its job), and the wire is permanently damaged - it will need to be replaced.

A fuse is a bit of metal calibrated to melt and "fall apart" when it gets too hot, and interrupt the current before the wire it is protecting becomes permanently damaged.

At low currents, heat is dissipated easily, and the fuse conducts happily.

At high (fault / short circuit) currents the heat rises very quickly, the element blows and the current is interrupted. That's what a fuse does best.

In between is where the trouble starts.

A fuse must carry it's rated current, but not carry more - well, not for a long time. So, a fuse carrying 100% of it's rated current will get very hot, because it must melt and fall apart after (some time) at anything more.

Unfortunately, automotive fuses are not precision devices, and they're generally intended to protecting against short circuit faults, not low level overloads. So, plastic blade fuses in housings which don't dissipate heat too well can tolerate low level overloads for long enough for the plastic to melt before the metal element does.

As murcod said, install bigger wires and a bigger fuse. The bigger wires will still be protected by the bigger fuse, but the fuse will operate further from its limit, and remain cooler.

[-Nemesis-]

Personally, I'd be going to 6mm2 wiring- which I think is the perfect size for the large yellow crimps. You'll get less voltage drop and notice a significant increase in fan speed.

Even though the factory wiring (on the fan itself) would be more like 6mm OD wire?

[murcod]

I think you'll find that wire in the above link is only 4mm2 (ie. 4mm squared conductor area) rather than 4mm OD. If your current wire is 6mm outside diameter then it would be a lot heavier than the 4mm2 wire in that link.

eg. Let's just say the 6mm OD cable had 1mm thickness of insulation- that would mean 4mm of actual copper in diameter. Halve that for a radius of 2mm.

Area of a circle = pi r2 = 12.56mm2 of copper!

[rumpig89]

i would be upping the cable size a notch and adding a fuse to match (cable current carrying capacity, not size of the expected load). Remember you have to protect the smallest cable (ie. lowest current carrying capacity) so i would rewire the fans if its not too hard, eliminating any voltage drop. (voltage drop = current rise)

I realise that they have factory wiring and you would think that this would be right but just look at what car manufactures put in for headlight wiring etc and how much this is improved simply by increasing wiring size.

hope this helps a little

[its aford not a nissan]

the reason the fuse is melting and not blowing is because there is a bad connection there somewhere , this bad connection may only allow say 20 amps to pass through and the fuse being rated at 25 amps wont blow because only 20 amps is passing through it , this bad connection is now the weak point and trying to act like a fuse but because it isnt designed to blow like a fuse it just heats up and melts the wire or whatever is close to the weak point in the connection , the more it heats up the further along the wire the heat will travel

i have seen this a few times and all it is was a bad connection , although under sized wiring can also cause this but it would of happened from the start

[MightyMouse]

A little off topic but if your tempted to use the Jaycar multi way 3AG fused distribution blocks ... DONT.

They are riveted together onto a thermoplastic base - the slightest increase in resistance between the riveted components generates extra heat that softens the plastic base loosening the rivets and down hill it goes from there.

There are much better blade style blocks around imo.

[-Nemesis-]

I managed to acquire some rather fancy 6mm core double insulated wire from work, so overkill wiring here we come!

Is there such a thing as too thick a wire? Is 6mm2 (at least) too thick for thermo's and spotties etc?

[drivesafe]

Is there such a thing as too thick a wire? Is 6mm2 (at least) too thick for thermo's and spotties etc?

No mate and it will make your fans work better because of the lower voltage drop.

[-Nemesis-]

Thanks mate. What about relays, do you think I should use two seperate relays for the Falcon twin thermos?

Or would one 5 pin 40a relay be okay with a 6mm feed wire and two 6mm outs to the fans?

[stuee]

Thanks mate. What about relays, do you think I should use two seperate relays for the Falcon twin thermos?

Or would one 5 pin 40a relay be okay with a 6mm feed wire and two 6mm outs to the fans?

I'd use two relays. If your going to use two fuses and two sets of cable may as well run two relays too. This way if you loose one circuit for whatever reason you still have the other.

I run two std 30amp relays for my AU thermos.

[-Nemesis-]

See, that's the get it running quickly/shortcut side of me trying to surface it's head again!!!

2 relays, check. Thanks.

[murcod]

Yes, two for sure. I've used two 60 Amp relays on my setup (Jaycar sell them )- but everything about it is "overkill" , including using 85 Amp cable for each fan!

[-Nemesis-]

Hehe yeah this cable I've acquired (should measure it) should be at least that rating, I think I'll just use the relays I've got though lol

[stuee]

Yes, two for sure. I've used two 60 Amp relays on my setup (Jaycar sell them )- but everything about it is "overkill" , including using 85 Amp cable for each fan!

Jeezus Out of curiosity what are you spalmejig fans using current wise?

[murcod]

Yes, two for sure. I've used two 60 Amp relays on my setup (Jaycar sell them )- but everything about it is "overkill" , including using 85 Amp cable for each fan!

Jeezus Out of curiosity what are you spalmejig fans using current wise?

Around 20 Amps each going by the spec sheet: http://www.spalusa.com/pdf/30102052_SPEC.PDF#view=FitH

It makes a huge difference to the fan speed if you can keep voltage drops to a minimum- hence why I've gone the "overkill" method. I learnt the hard way with my first conversion.

[stuee]

Yes, two for sure. I've used two 60 Amp relays on my setup (Jaycar sell them )- but everything about it is "overkill" , including using 85 Amp cable for each fan!

Jeezus Out of curiosity what are you spalmejig fans using current wise?

Around 20 Amps each going by the spec sheet: http://www.spalusa.com/pdf/30102052_SPEC.PDF#view=FitH

It makes a huge difference to the fan speed if you can keep voltage drops to a minimum- hence why I've gone the "overkill" method. I learnt the hard way with my first conversion.

Interesting.

I've got 2 8g cables taking power to my distribution box that feeds Thermos, fans and spotties (originally I just had one till drive safe pointed out that the 100a rating was not for 100% duty cycle).

The lights are a massive improvement and fans run no worries but at idle when the fans come on there is a definite voltage drop across the lights. So I'm looking at changing the cables to twin 6g cables and isolating the supplies for the thermos and lights so that any drops will hopefully be less noticeable. Also if I put in higher wattage globes it shouldn't have a problem powering them.

Voltage drop at idle could also be quite easily caused by the fact that the alternator is not pumping out that many amps but meh. Big cables are cool

My actual fan cables are rated at around 50amps so I feel these are adequate.

[-Nemesis-]

Is one 4g wire equivalent to two 8g as far as ability goes?

I've got one 4g (the very fine copper OFC stuff from Jaycar - super flexible) crossing from the battery side of the bay to the passenger side. This will branch off into the cabin (what it was originally for) to feed the car stereo and bits inside.

On the outside I'm in the process of T'ing in another section of 4g that goes into one of the Jaycar gold 4g into 4x8g distribution blocks. From there the 4 8 guage wires will feed the 4 fuses for 2 xfans, 1 x spotties and 1 x thermo fans on air condition (custom rear mount condensor)

I had then planned on just tapping into the 4g before the distribution box to run the rest of the fuses, which will be basically low current switching devices/signals and the standard HID wiring harness (not gonna bother upgrading this mess) etc.

[stuee]

Is one 4g wire equivalent to two 8g as far as ability goes?

I've got one 4g (the very fine copper OFC stuff from Jaycar - super flexible) crossing from the battery side of the bay to the passenger side. This will branch off into the cabin (what it was originally for) to feed the car stereo and bits inside.

On the outside I'm in the process of T'ing in another section of 4g that goes into one of the Jaycar gold 4g into 4x8g distribution blocks. From there the 4 8 guage wires will feed the 4 fuses for 2 xfans, 1 x spotties and 1 x thermo fans on air condition (custom rear mount condensor)

I had then planned on just tapping into the 4g before the distribution box to run the rest of the fuses, which will be basically low current switching devices/signals and the standard HID wiring harness (not gonna bother upgrading this mess) etc.

Going by this: http://en.wikipedia.org/wiki/American_wire_gauge

Two 8g is a touch more than one 4g. Not by much though. Personally I would look at running your current 4g cable for the engine bay accessories and run another suitably sized cable from the battery for the interior. I'm running two 8g and notice the voltage drop when the fans come on in my lights.

You might find that with one 4g cable, when the fans kick in, that there's a noticeable voltage drop due to all the power being sourced through one cable. This voltage drop would be more noticeable on the sensitive stereo equipment I imagine. If you've got a half decent stereo I would be running a dedicated supply to the amps and even head unity anyway otherwise as accessories are flick on and off it will appear as noise on the stereo.

With my set-up I will be running a dedicated supply from my 2nd battery which is getting put in the back of the wagon. Previously it had a dedicated 8g cable for the amp running from the front battery but the stereo installers did a crap job of that.

[murcod]

Voltage drop at idle could also be quite easily caused by the fact that the alternator is not pumping out that many amps but meh. Big cables are cool

Yes, I've checked my battery voltage and it drops back to 12.4V when the fans are on at idle (and of course you can hear them slow down.) A bigger battery would probably help to some extent in that sort of situation.

As soon as the revs pick up a bit the fans can be heard to increase in speed again.

My battery's stock (560CCA roughly) and I've got no idea how old it is. I will be getting a better battery (most likely AGM) when it dies.

But I'm happy with how the thermos work- they did a fantastic job when we had a 46 degree day earlier this year. The engine was actually running cooler when sitting at the lights than what the old viscous fan could mantain. They also kept it cooler driving up a long steep stretch on the way home from work, and pull the temp down real quick at idle on high speed. (I've set them up with a low and high speed.)