How Do You Determine Fusible Link Size

Alright, apologies in accelerate for the book I'm about to drop hither.

Trader wrote:

The rule of thumb is the fusable link is iv gauge wire size smaller and then the original usher and the length is 6" to 12". Longer length for more amps and #viii link being 8" for automotive.

The conductor should burn out before the insulation and existence a fixed length, burn out in the middle.

Perfect! That was the item I was missing that acquired me to go sideways on this whole subject. See, I was not thinking at all virtually how length of the link could be an important factor in the physical area where a break would occur. Now all the recommendations about crimping AND soldering new links makes a lot more sense. It'southward not only a affair of preference regarding a general method of making a low-resistance connection to ensure an electric fault occurs when it should. It's also to make certain the fault occurs where it should --at the middle of the length of the usher, instead of at one of the joints! Wouldn't practice much skilful to protect the harness if the link burned up at a disquisitional splice. . .

I had been unknowingly thinking of links kinda like resistance wire by assuming that the length was a factor because of the corporeality of resistance that would exist had depending on the overall length of the conductor. If information technology was too long or too curt, the resistance would change appropriately and in that location would be a corresponding impact on the function of the link. While I guess that could be true if I ran a link to the back bumper and dorsum into the engine bay, or but made it long enough to attach a terminal to each end, information technology's a high strand-count copper wire. A couple inches either fashion won't alter the overall resistance to the point where it would exist relevant.

Jmerican wrote:

Since you are choosing fuses, my advice is this. Find the max ampacity of the wire in the excursion and protect for that. It may be tricky with old wire and unknown spec. But new wire will be rated. The ampacity will be based on gauge, insulation temp rating, length of excursion Including the footing wire side. Then de rate that for bundling in a hot engine bay. And slightly more for a fused circuit. Fuses vary with how they accept overload, just similar breakers.

Likely de rate by xx-25%

Thanks for bringing this upwardly -- it helps quite a bit, particularly the advice on how much to derate by. I didn't realize that I had been getting wrapped up in factoring in the ampacity of the wire gauges, though overlooking environmental variables that are just equally important. That will salvage me from going down a rabbit hole over figuring out how much to adjust my estimates by, for certain.

6PakBee wrote:

NAPA publishes the length of the wire mode fusible links they sell.

Thanks! Pretty handy info. I had no thought that they actually specify that in their production pages.

304-dude wrote:

Yous can get a similar replacement, by feel, through hobby stores, on RC Car battery wiring kits.

I never would've considered an RC store, but that makes perfect sense, now that you mention it. If I find myself in an RC shop soon, I'll take a look at that. Even if I'm not using links at the moment, it's ever proficient to know alternate sources for stuff like that.

billd wrote:

Note where the factory used links and where they used fuses and think about it.

Excellent advice! The Gremlin was my starting point for anything automotive related, and so when I started planning the fusing for the electric organisation, I didn't accept the get-go inkling what a fusible link even was.   If I hadn't taken the time to enquiry what they are and do, and why they're present at the distribution points that they are, I easily could've ended up being one of those folks who but get out them out or put an inline blade fuse or something in their place. Not something I want to learn the hard manner!

Jmerican wrote:

Y'all are very much on the right track with your assessment of the fuses you are considering.

Whew! Adept bargain. I didn't desire to accept to start rearranging things unless I had to, haha

Jmerican wrote:

If you are building a college performing charging system, lets just say in that location is low hanging fruit to be picked.

I'chiliad not really going to exist putting much more load on the charging system than the factory design. When all is said and washed, it'll probably be a off-white degree less. The changes I've made are with an eye towards longevity and serviceability.

For case, the MEGA fuse is much easier to replace than a burned link, and if I'm non able to get a replacement, an advisable fusible and some ring terminals are all I need to safely become me to where I can get 1. The alternator type provides more current at lower RPM, which my battery volition appreciate, and is likewise more readily available in yards and parts stores (not to mention cheaper). I've also Incorporated relays for the headlights to reduce current draw and heat in the wiring loom, while as well (I suspect) extending the life of the footswitch and reducing points where a fire could occur in certain (probably unlikely) scenarios.

Basically, I'm non trying to improve things past blindly "upgrading" things. I'yard more interested in staying fairly faithful to the original design, but as it may have been done if our present options were available and if a per-unit of measurement production cost didn't take to be a deciding factor. Kinda similar how I have the iv.0L caput and manifolds with the 258 block. Perhaps a total-on engine swap would've been "better", just to get the changes I wanted, the head swap was the cheaper, simpler, and more conservative way to become.

I'm hearing ya, and in that, I'thou hearing alternator upgrade. I hearing faithful to the pattern. I hope there is no amp judge loop. I'm hearing serviceable. Then fuses. I'm hearing if price wasn't an outcome in the original. Well, it was, and voltage drop and resistance was high because of it. If you lot put in a fancy battery, it will accept more charge, quicker. A high acceptance charge per unit. That will demand more from the alt and cabling. You unloaded the factory harness with relays for lighting. Cool. Simply all the bulbs bigger? If then, more amps through alt wiring. And on. So, I don't desire to overstep, and I practice want to be helpful. But use big wire. And such. So you tin fuse for low resistance, go along the wire protected, etc.

Nah, totally fine beyond the board!  I've put so much into this motorcar that I want to make sure that the piece of work I'm doing is washed right, but more importantly, that I'yard doing the right work.  I figure whatever input is a great thing to get.

I'm still using the stock bulbs, but also have a "plug and play" HID kit in case the xanthous doesn't cut it for me out on the road.  I'm thinking of fairly remote regions where in that location aren't a lot of people, but plenty of other stuff worth seeing every bit far out as possible.  Fifty-fifty though I expect that the OE bulbs will exercise me only fine, I increased the gauge of the wire to the next largest diameter.  Actually, there aren't many runs where the wire wasn't stepped up to the next gauge, ii]at to the lowest degree.  Fifty-fifty the approximate sender wires got bumped upwards.  The merely things I can call up of offhand are pigtails that would be impractical to modify (turn betoken switch, for case).  In some cases, I remember I even went a little overboard (00 J1127 welding cable to the starter comes to mind).

I've got a yellow pinnacle Optima battery that's been running in the Eagle (my daily), but I'grand going to go it tested before I put it in the Gremlin.  The bird's RPM-related dim/bright headlight output tells me that the alternator is probably most as tired as the rest of that poor railroad vehicle.

Thanks again for your input.  It's a huge help to exist able to bounce this stuff off of other actual people, instead of running in circles, called-for hours researching, and going down dead ends until I forget entirely what I started with, haha

t

Glad things are going well. The xanthous top can and volition accept Much much more current than an standard battery, due to its construction. To take advantage of that, and to not taxation the cabling and hey, perchance a master fuse, you desire to design healthy charging cables with appropriate fusing. It also sounds like your alternator blueprint output is low at the speeds information technology's turning. If yous're interested in depression speed output, and so look into a improve part. In a low duty application like yours, usually none of this is a big deal. Just run the yellow top downward, and y'all may find that the rest won't keep up, or blows a fuse. Matching the designs of components is what you lot're later, with the removal of the penny pinching OEM.

These are all very good plans. I just cheat everything by measuring the amperage describe of each excursion, combination circuits, max amp draw and full draw to independently bract fuse where advisable and guard the most important circuits with fusible links 4-6" in length at the starter. Starter itself pulls the most amperage when turning then I figure that's a peachy place to use as a link post for all major connections.

Naught makes me more irate than seeing a ton of linked cables AT the bombardment terminals except for those battery terminals that enable that cocky-subversive scenario, complete with rusted bolts, corroded wires and bad insulation. Skilful luck if you're out of EJC#two. The starter I'g using is a manufactory 4.0L pulled from a 1000 Jeep but the screws still have blue pigment on them from the rebuild job notwithstanding many years ago. Fabricated in Mexico, or every bit I phone call it: JACKPOT.

Indicate is, as long as you're paying attention to where your power comes from, where it goes and the first problem areas, yous should be able to business relationship for them without a bunch of engine bay fuses or link posts. I still utilise all the manufactory blade fuses in my Eagle wagon and the two circuit breakers. The only other affair is that I switched most of my relays over to minis for a meliorate wiring profile in the engine bay. The full size box models draw an additional 10mA only they're so bulky that I would have to add a 2nd relay pod just to fit everything and that'due south ugly. Here's an thought: Put the source for all of your fusible links in ane primary location and then that in the result of a blown link, you lot don't have to chase then many of them. This was the case on the FACTORY +12V side of the ignition harness and it was a cobweb headache to diagnose whenever something went incorrect(unremarkably headlamps). I'1000 sure the lot of yous are competent enough to not have this problem anymore but from in that location just chase downwardly odds and ends like voltage driblet and you're good.

1971 Javelin SST
American 304 2v | FMX | AM20-3.31
1983 American Express
Jeep 4(.7)L Due south-MPFI | 1982 NWC T-5M (4.03/.76) | Dana30IFS/35-2.72

How Do You Determine Fusible Link Size,

Source: https://theamcforum.com/forum/length-of-fusible-links_topic97112_page2.html

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