With the shortage of fusible links...

[Dave 2000]

Are the ampere ratings shown for the fuses or the conductor size? The information under the node appears to have been added afterwards. The reason I ask is that I believe a fusible link will not have a true ampacity rating other than one that is shown to protect the conductor insulation (I don't know and is the reason why I am asking). That rating (insulation) is far lower than when a conductor will actually fuse. A small conductor, as an example may be rated for 30A (to protect conductor insulation) and a fuse rating (melting point of the conductor itself). Depending on the amount of current available (short circuit current which is essentially based upon the size/output of the battery).

The ampere rating of the conductor (before the conductor insulation is damaged) would not only be based upon the conductor diameter and conductor type but the insulation rating, the ambient temperature, as well as other environmental conditions. The point at which the conductor will fuse will be fairly constant, regardless of the above but will be influenced by length, ambient temps and conductor alloy, time as well as available battery current.

A conductor used as a fusible link has disadvantages, namely that they are harder and more expensive to find. A fuse can be tailored to fit a specific application and are easier to find and replace than the link.

You pretty much lost me with this post, it might be me, I have had bits of my brain removed.

First the fuse must be capable of carrying the amperage that will be drawn by the part needing it and this alone varies for example, a 100 watt fuel pump in theory will need to have a minimum 8 amp fuse, that is 100/12 = 8.33. But as the pump only tends to be running when the engine is running then the amperage the fuse would need to carry during normal running condition will be less for example, 100/13.8 = 7.2

Sounds simple enough but unfortunately this is not the case, the pump has a start up load, there will also be a slight voltage drop on the cable over the length of the vehicle, so the cabling choice from battery - fuse - switch - relay - pump would be typically expected to be capable of carrying around 16 amps, so to fuse this circuit correctly would be a rating of 10 amps, this rating would for the typical vehicle run the fuel pump under start up conditions, be sufficient for continuous running and a 16 amp cable would be safe in the event of a short circuit protected by the fuse, and assuming we are using my example of the fuel pump, then voltage drop to the pump at the rear of the vehicle would be minimal.

In simple terms a fuse should be rated at being lower than the cable size but large enough to carry the load under start up and normal running conditions.

The use of fusible links on older cars is purely a case of being right at the battery positive terminal, in other words the safest place they can be, modern cars now typically place a fuse box on top of the battery using midi fuses again right next to the positive of the battery.

Regards

Dave

 

[Azca]

You pretty much lost me with this post, it might be me, I have had bits of my brain removed.

First the fuse must be capable of carrying the amperage that will be drawn by the part needing it and this alone varies for example, a 100 watt fuel pump in theory will need to have a minimum 8 amp fuse, that is 100/12 = 8.33. But as the pump only tends to be running when the engine is running then the amperage the fuse would need to carry during normal running condition will be less for example, 100/13.8 = 7.2

The fuse can be tailored to the load. A time delay fuse will allow the pump (motor) to start during the high in-rush (startup) of the motor. This will also provide better protection as the size of the fuse can be smaller than an instantaneous fuse which may have to be sized as much as 6 times the ampere rating of the motor to allow starting. Automotive systems are not my expertise but, electricity is electricity, it doesn't know the difference between a home, highrise or a vehicle.

There are different types of time delay fuses in automotive and building systems. In building systems they classes, in order of fastest and least tolerant of high inrush currents are generally Class T, J, RK-1, and RK-5 for smaller systems 400 amperes or less. Class T fuses should not be used where the load has a significant amount of motor loads as nuisance tripping may occur. If memory serves, most fuses in automotive systems are a class R fuse (not sure if the subclass exists or not).

Sounds simple enough but unfortunately this is not the case, the pump has a start up load, there will also be a slight voltage drop on the cable over the length of the vehicle, so the cabling choice from battery - fuse - switch - relay - pump would be typically expected to be capable of carrying around 16 amps, so to fuse this circuit correctly would be a rating of 10 amps, this rating would for the typical vehicle run the fuel pump under start up conditions, be sufficient for continuous running and a 16 amp cable would be safe in the event of a short circuit protected by the fuse, and assuming we are using my example of the fuel pump, then voltage drop to the pump at the rear of the vehicle would be minimal.

Agreed, voltage drop in 12v systems is a significant concern however, this will not have the impact on fuse size you would think. When connecting a time delay fuse to a larger conductor, the larger conductor acts as a heat sink and removes heat from the fuse. The overload component of the fuse then will not see the overload as quickly as it is triggered by heat. The reverse is also true, when a fuse is installed in a hot environment (under the hood) the fusible elements will be hotter and react more quickly to an overload. This may cause nuisance tripping (opening) of fuses when, in reality, there is no problem with the load at all. It may be necessary to compensate for this by increasing the fuse size. Again, the manufacturer's specs and temperature curves must be reviewed for proper protection and is made even more complicated when the fuse and the motor or load are in different ambient locations. This is obviously more complicated than can be discussed here.

I would still size the fuse as close as possible for the load served so that if the fuel pump winding shorted out, as an example, you limit the clearing of the fuses to the circuit closest to the pump (account for the above first). In other words, system coordination. If you had a bunch of small loads, say 1 amp each, all fused separately with a 10 amp fuse that connected to a distribution block protected by another 10 amp fuse, and one of the loads shorted, you likely would open the fuse to the load as well as the one feeding the distribution block. This may be true even if the block was fed by a 20 or even 30 amp fuse. The only way to assure that only one fuse blows (the most desirable action) is to overlay the time current curves from each device to make sure the upstream device will not open before the downstream device.

In simple terms a fuse should be rated at being lower than the cable size but large enough to carry the load under start up and normal running conditions.

Generally agree. I am not sure if motors in a vehicle have thermal overloads (I am doubting the fuel pump does as an example but certainly could be wrong) but many winches do. Where thermal overloads are provided, the fuse is really only providing short circuit protection, not overload protection and can be sized much higher than you would think and still provide very good protection.

The use of fusible links on older cars is purely a case of being right at the battery positive terminal, in other words the safest place they can be, modern cars now typically place a fuse box on top of the battery using midi fuses again right next to the positive of the battery.

Agreed, limiting the length of unprotected conductor is very desirable. Unprotected defined as not protected against overloads or short circuits.

Regards

Dave

 

[Broski]

I was merely calling you out for talking out of your ass about part numbers. That’s all.

I just hate f***ing misinformation about Toyota part numbers which is what you engaged in mainly because you are ignorant, knowingly or not.

But everyone is a parts expert it seems because the internet says you are.

90982-08264 is nowhere close to being NLA.

You might want to get your blood pressure checked.

 

[NexusD]

So should we start a fuseable link delete thread?

 

[Dave 2000]

@Azca

I simplified the post a little to make it easier for the less electrically savvy or informed (not less intelligent) members of the forum without any real jargon. You point out that the fuse should be tailored to the load, which is close but not correct. You point out electricity is electricity AC or DC would be correct fuse wise however, the 240 volts that arrives in an electrical socket in (most countries in Europe ) is so tightly regulated it rarely varies and whilst it may drop it never goes over that, but in a typical car this is not the case because there are too many variables to choose an accurate rating, my fuel pump analogy explained this. Remember the amperage in this instance could be as high as say 10 amps and yet as low as 7 when the engine is running due to the running voltage the alternator produces will be varying, so lets go back to my my first post which needed no explanation.

Where you 'generally agree' I would say you are again close, for example you say a fuse can be rated ' much higher' and still provide protection. At the end of the day regardless whether a winch is used or a single light bulb, the cabling is what must be protected, this is where fires start and the vehicles life invariably ends.

Regards

Dave

 

[Azca]

@Azca

I simplified the post a little to make it easier for the less electrically savvy or informed (not less intelligent) members of the forum without any real jargon. You point out that the fuse should be tailored to the load, which is close but not correct. You point out electricity is electricity AC or DC would be correct fuse wise however, the 240 volts that arrives in an electrical socket in (most countries in Europe ) is so tightly regulated it rarely varies and whilst it may drop it never goes over that, but in a typical car this is not the case because there are too many variables to choose an accurate rating, my fuel pump analogy explained this. Remember the amperage in this instance could be as high as say 10 amps and yet as low as 7 when the engine is running due to the running voltage the alternator produces will be varying, so lets go back to my my first post which needed no explanation.

Where you 'generally agree' I would say you are again close, for example you say a fuse can be rated ' much higher' and still provide protection. At the end of the day regardless whether a winch is used or a single light bulb, the cabling is what must be protected, this is where fires start and the vehicles life invariably ends.

Regards

Dave

Agree with everything you have said. In my original response was a question as to the information posted in the line diagram showing the ampere rating of the fusible links. Not sure if the ratings were added later or not. I was curious as to how these links were rated or sized. When using a fuse to replace the link it is important to understand it is not just the size of the wire that must be taken into account.

Also agreed on the "less savvy" response. I am not an expert by any stretch of the imagination when it comes to a vehicle's DC system and looking for information from the well informed forum's membership. I relate this to the difference between a brain surgeon and a heart surgeon; both are well trained individuals but I don't want the brain surgeon working on my heart, or vise versa, if I can help it. Nor do I want either one working on my cruiser (arguably the most important part of my life!). They are not idiots, just lack the technical savvy in another discipline. The wealth of knowledge here for us less informed people is irreplaceable.

 

[Dave 2000]

Agree with everything you have said. In my original response was a question as to the information posted in the line diagram showing the ampere rating of the fusible links. Not sure if the ratings were added later or not. I was curious as to how these links were rated or sized. When using a fuse to replace the link it is important to understand it is not just the size of the wire that must be taken into account.

Also agreed on the "less savvy" response. I am not an expert by any stretch of the imagination when it comes to a vehicle's DC system and looking for information from the well informed forum's membership. I relate this to the difference between a brain surgeon and a heart surgeon; both are well trained individuals but I don't want the brain surgeon working on my heart, or vise versa, if I can help it. Nor do I want either one working on my cruiser (arguably the most important part of my life!). They are not idiots, just lack the technical savvy in another discipline. The wealth of knowledge here for us less informed people is irreplaceable.

OK.

Regards

Dave

 

[Fullscale]

Question for those that know fuses well:
Midi fuses have been mentioned on this post as good alternative to the fusible links, but can someone clarify specifically which ones? I'm assuming the slow-blow/time delay versions but just want to be clear.

Also, what about MRBF fuses? they appear to have surge characteristics from their graph charts, but I'm not an expert and am considering them. Thinking about a terminal block setup (at, or very close to the battery) with 3 separate MRBF fuses (30a,80a,100a) may be a tidy solution, but only if they have the proper surge properties, which I'm unclear on.
Would something like these (below) work well?

 

[Broski]

It’s probably just me.
But I just don’t see it. The fusible links from Mr. T Are designed and packaged for just what they do.
Zero guess work and readily available.
At $18 apiece they’re a fraction of the cost.
If you replace your fusible link every time you replace your battery you should never have an issue with it.
Easy enough and cost-effective to just carry the one you take out as a spare in your bag that’s what I do.
Again JMHO

 

[NCFJ]

I have been using the MRBF type fuses for years. I generally use the double off of the battery to a secondary Bussman Relay/Fuse block from there. The are compact, a clean install and are widely available, just not at your local auto store.

 

[gummycarbs]

I looked into fusible links recently and learned that when you start asking questions beyond the "four numbers smaller AWG and no longer than six inches", you quickly find out the you need an actual engineer to assess the needs of the entire electrical system.

It's truly a complex topic. Toyota paid engineers to come up with these fusible links as a last-ditch method to prevent fires. Just order a spare and spend your time working on other stuff.

 

[smritte]

Toyota paid engineers to come up with these fusible links as a last-ditch method to prevent fires. Just order a spare and spend your time working on other stuff.

Not only Toyota but pretty much the entire auto industry. No so much last ditch but a long time industry standard.
Question is, why don't they still use them? Even though they still work, fuse and fuse box technology evolved in the auto industry.
I started seeing fuse links disappear starting in the early/mid 90's with most of them gone by the late 90's. Auto reset circuit breakers disappeared (thank god) a little earlier.

Fuse links work great. For years in the shop we had spools of it and had to make our own (American cars). As long as the fuse link isn't subjected to movement they last. Most American cars didn't have plug in types, you have to splice one in. One can replace our Toyota fuse links easily. If you mod the crap out of your electrical system (like mine) you can still run fuse links (if you know how to calculate them). I prefer fuse blocks. I have also spent four decades doing custom automotive wiring professionally.

Bottom line, if you don't know what your doing, leave it alone. You don't want to "guess wrong".

 

[Perfected]

Got my popcorn out. This thread is juicy.

 

[cruiserdan]

Got my popcorn out. This thread is juicy.

Popcorn is many things but I never considered it juicy.

More like "Dryer than a popcorn fart".

 

[Dave 2000]

Apologies in advance to vendors.

First let's look at the mechanics of the fusible links, they move and they weaken and break, they were perfect in the day but they are now 'old hat'. If you are about keeping your 80 'original' then they will do the job and of course you keep a spare set. The most often cause I have seen is a battery not clamped down properly for whatever reason, the wrong battery fitted, the clamp goes missing (trust me a bungy cord is not a good substitute!) so the fusible links become the battery 'anchor' and they break.

Now lets look at the electrical side of things, they do the job, if there is a short they burn out, and being right next to the battery they are correctly placed, so this would seem that Mr T had your cars arse covered.

So you are driving down the tarmac and your cars electrics die, easy enough to sort, you get out your multimeter (because you always carry one right, and of course know how to use it right?) And you find the fusible link has burnt out (because you saw it on the forum or internet) so you check what section does what by looking at the workshop manual, wow you are good for keeping that in the car as well! And you start looking through the wiring diagram. "How long are you going to be John the kids are hungry!" "Not long Janet will you please stop the kids crying?" "They are bored honey, how long is this going to fix?" "I will have it sorted soon darling, I have a spare fusible link in the tool box." (Impressed huh?) So you fit the new set and it blows again. "Susan need a diaper change and I don't have a spare with me, I thought we were only going the store and you decided we would 'go for a short drive'?" "It's OK but I can't concentrate on the wiring diagram with the kids screaming, can't you take them for a walk?" "No I fuc*king can't it's a 100 degrees are you crazy?" "OK...OK I think I have found it........well I think I have.....er...I have no more fusible links....it's OK I will call the breakdown truck." "Well they had better hurry up, Steven's got a tummy ache......oh too late he has crapped his pant's where is the toilet roll so I can get him cleaned up?" "Jeez! There are some tissues in the glove box." "Oh yeh a whole two of them...fu*king great" "Well if you had let me get the shop to change out the fu*king fusible links (Saw that on the forum right?) I could have kept a whole bunch of fu*king fuses in the tool box!" "Well perhaps if you did not spend all that money getting the shop to fit that fu*king big bumper and spotlights, and of course those stupid big wheels which make it so sodding difficult for me to climb in and out of the car, perhaps you could have had them change out the f..ff.....link...whatever the fu*k is that's broke, oh damn I am covered in sh*t"

I know it is a bit of fun but it does happens in real life, and unless you have had an old car that may be getting tired (which the 80 is) and you have a baby and a toddler (which I did) and of course you are a mechanic (but your not) then get the FL's sorted and you can carry a bunch of fuses that mimic the FL ratings, then it would be easier to just pull the blown fuse (which you can see has blown) and then pull circuits and perhaps carry half a dozen fuses which are cheap, you might just get back on the road and go home.........and of course you don't take the family when you go 'off road' and go camping.....do you?

Regards

Dave

 

[mudgudgeon]

Apologies in advance to vendors.

First let's look at the mechanics of the fusible links, they move and they weaken and break, they were perfect in the day but they are now 'old hat'. If you are about keeping your 80 'original' then they will do the job and of course you keep a spare set. The most often cause I have seen is a battery not clamped down properly for whatever reason, the wrong battery fitted, the clamp goes missing (trust me a bungy cord is not a good substitute!) so the fusible links become the battery 'anchor' and they break.

Now lets look at the electrical side of things, they do the job, if there is a short they burn out, and being right next to the battery they are correctly placed, so this would seem that Mr T had your cars arse covered.

So you are driving down the tarmac and your cars electrics die, easy enough to sort, you get out your multimeter (because you always carry one right, and of course know how to use it right?) And you find the fusible link has burnt out (because you saw it on the forum or internet) so you check what section does what by looking at the workshop manual, wow you are good for keeping that in the car as well! And you start looking through the wiring diagram. "How long are you going to be John the kids are hungry!" "Not long Janet will you please stop the kids crying?" "They are bored honey, how long is this going to fix?" "I will have it sorted soon darling, I have a spare fusible link in the tool box." (Impressed huh?) So you fit the new set and it blows again. "Susan need a diaper change and I don't have a spare with me, I thought we were only going the store and you decided we would 'go for a short drive'?" "It's OK but I can't concentrate on the wiring diagram with the kids screaming, can't you take them for a walk?" "No I fuc*king can't it's a 100 degrees are you crazy?" "OK...OK I think I have found it........well I think I have.....er...I have no more fusible links....it's OK I will call the breakdown truck." "Well they had better hurry up, Steven's got a tummy ache......oh too late he has crapped his pant's where is the toilet roll so I can get him cleaned up?" "Jeez! There are some tissues in the glove box." "Oh yeh a whole two of them...fu*king great" "Well if you had let me get the shop to change out the fu*king fusible links (Saw that on the forum right?) I could have kept a whole bunch of fu*king fuses in the tool box!" "Well perhaps if you did not spend all that money getting the shop to fit that fu*king big bumper and spotlights, and of course those stupid big wheels which make it so sodding difficult for me to climb in and out of the car, perhaps you could have had them change out the f..ff.....link...whatever the fu*k is that's broke, oh damn I am covered in sh*t"

I know it is a bit of fun but it does happens in real life, and unless you have had an old car that may be getting tired (which the 80 is) and you have a baby and a toddler (which I did) and of course you are a mechanic (but your not) then get the FL's sorted and you can carry a bunch of fuses that mimic the FL ratings, then it would be easier to just pull the blown fuse (which you can see has blown) and then pull circuits and perhaps carry half a dozen fuses which are cheap, you might just get back on the road and go home.........and of course you don't take the family when you go 'off road' and go camping.....do you?

Regards

Dave

You forgot the bit about it being dark, and starting to rain

 

[mudgudgeon]

Question for those that know fuses well:
Midi fuses have been mentioned on this post as good alternative to the fusible links, but can someone clarify specifically which ones? I'm assuming the slow-blow/time delay versions but just want to be clear.

Also, what about MRBF fuses? they appear to have surge characteristics from their graph charts, but I'm not an expert and am considering them. Thinking about a terminal block setup (at, or very close to the battery) with 3 separate MRBF fuses (30a,80a,100a) may be a tidy solution, but only if they have the proper surge properties, which I'm unclear on.
Would something like these (below) work well?

View attachment 2932740

View attachment 2932745 View attachment 2932746

I looked into these a few months back. I started a thread about alternatives to fusible link for exactly the same reasons as the OP here. I was drawing a blank on sourcing replacements. And wanting to replace the janky inline blade fuse holder. 100amp blade fuses aren't sitting on the shelf in many shops either.

@Dave 2000 scenario is along the lines of why I started looking at other options,

There was some good discussion about alternatives, but also incomplete info on a technical subject.

I think the MRBF are a good option, but less readily available than a midi fuse, so you'd need to have a bunch on hand.
Also a bit pricier.
They are available with different characteristics.

Midi fuses seen to be the choice for car audio system installs, so a bit more widely available

 

[mudgudgeon]

Thread 'replacing fusible link with breakers. What do i need to know' replacing fusible link with breakers. What do i need to know - https://forum.ih8mud.com/threads/replacing-fusible-link-with-breakers-what-do-i-need-to-know.1267592/

 

[Azca]

This is exactly why a coordinated system is important. The fuse closest to the circuit is the only one to blow. Of course, trying to fully coordinate your electrical system would be, well, worse than getting caught in the mess @Dave 2000 has.

 

[jonheld]

In my original response was a question as to the information posted in the line diagram showing the ampere rating of the fusible links. Not sure if the ratings were added later or not. I was curious as to how these links were rated or sized.

I added the colors and amp ratings of the fusible links to my diagram. Fusible links are rated by the color of the flameproof insulator and is a standard in the industry.
A US spec 80 Series has 3 fusible links. PINK, BLACK, and BLUE.

PINK is 30 amp (FL AM2)
BLACK is 80 amp (FL AM1)
BLUE is 100 amp (FL MAIN)