Electrical Fuse/Fusible Link Wire Question

[Zeus51]

Hey guys, Let me start by saying I have an '86 CUCV K30 6.2L Diesel and I have done the glow plug resistor bypass, installed a Napa ST85 glow plug relay and I'm using AC 60G glow plugs.

I am thinking about wiring in either a fuse or breaker into the 4 gauge wire I have feeding the glow plug relay so I easily get rid of the fusible wire and I can separate my diamond shaped 12 volt block from my glow plug relay using two seperate wires.

I have poured over all the threads and internet and I have read the differing opinions on how many amps the plugs collectively pull (either it doesn't matter if you use a wire coming from the positive of the front battery or they pull amps of 10-20 amps per glow plug meaning it might be between 100-215 amps depending on brand glow plugs), and now that brings me to my question.

If the ST85 relay is a 12 volt relay that is rated for 80 amps, then wouldn't that be the max amperage that the relay allows the 8 collective glow plugs to receive? Meaning, that's the MAX amount of amp fuse or breaker I'd want to install into my single dedicated line to the glow plug relay?

All opinions are welcome. If you disagree, please provide an explanation so I may learn the error of my ways. Thanks!

 

[richingalveston]

not a real necessity in my opinion if you have that much stuff that is running at startup then a separate fuse block directly to the front battery would be a better solution to your accessory needs. run both the + and - to the battery and you will get the least amount of noise in your equipment.

The glow plugs only operate at start up and thus the load is not on the 12v block for most of the vehicle operation.

going to a fuse or breaker might require a slow blow and could get expensive. just running two wires (one to relay, one to 12v block) each with fuseable links at end would be cheap and over kill. It is also easy to carry some extra fuseable link wire and not so easy to have large expensive fuses or breakers.

I carry an extra st85 and some fuseable link material.

I have two 6 position blocks inside under the dash. each with their own wires to front battery. one is hot always and the other runs through and st85 relay to the other block and is hot via the ignition on. I am using the st85 for this fuse panel so that I only need to carry one type of spare.
just my 2 cents
Rich

 

[Zeus51]

Thanks Rich, I'd love to see a photo of the engine so I can see how you did it. How would you replace the fusible wire on the trail? That's why I was thinking of using an easily replaceable fuse or flip a breaker switch. I'm not saying you're wrong, I just want to hear your rationale so it can educate me.

I was thinking of a circuit without fusible wire that does the following: starting at the front battery positive terminal of the 24 volt system to 4 gauge wire to a 4 terminal 12volt block located 13" to the left then one terminal would supply the glow plug relay with an 80 amp fuse at the beginning of it and one terminal would supply the diamond shaped 12 volt block with a 100 amp fuse at the beginning of the wire.

I have never fixed a wire that has fusible link wire in it. I've been under the impression that there is crimping and soldering involved. Am I wrong?

 

[richingalveston]

I carry tools always. especially when on trails. all you need is a pair of wire crimpers a butt connector and ring terminal. All of these can fit in glove box.

when I splice the fusable link at my shop, I solder the conection and heat shrink with di-electric grease in the heat shrink. This keeps the corrosion out. In the field just splice in a new piece and put a new end terminal on it.

Fusable links do not change over time except when the connections get corroded or the wire insulation gets damaged. most resettable fuses/breakers get weaker with every trip and thus once it starts tripping, it just starts to trip sooner. Heat under the hood can also cause a resettable breaker type to have a short life.

I would spend my money on getting the load off of the existing wiring harness by adding LED lights where possible and a headlight relay kit. I have all LED marker lights except my front two blinkers. Leaving two regular blinker bulbs in place allows the standard flasher to work and a digital flasher is not needed. I would not add anything new to the 12volt terminal block, I would add an additional fuse panel inside the truck that has wires directly to the battery. you can put a relay on this so it is only on when the key is on.


Remember all of the existing wiring in the truck is 30 years old. it will work for another 30 years if the connections are cleaned and the load reduced with the newer LED bulbs.

The stock system works fine as it is with the exception of the head light circuit. The glow plug operation is active less than 1% of the time the truck is running and in all the cucv's I have owned, I have never had a fusable link fail. The only time the fail is when not maintained or when they are supposed to due to a problem down stream of the link.

what you want to do will work, however it will cost some money that could be spent on load reduction and other improvements.
My truck is in pieces right now getting a new 6.5 GEP motor installed or I would send you some pictures of my addition fuses and wiring.

Rich

 

[pjwest03]

Zeus51,

The glow plugs are generally around 1.2 ohms when new. So, I = V / R and that gives us a 10 amp draw on a 12V supply (12 / 1.2). The relay is rated 80 amps continuous but will tolerate a much higher load for short duration. As a starter relay, the ST85's take several hundred amps of inrush when the stater first engages.

You always have to remember that the circuit protection device (fuse, link, breaker) is there primarily to protect the wire from overheating and possibly starting a fire.

It's always best for high current loads to have the most direct path to the source with the fewest number of connections. Every connection is a fail point.

 

[Chief_919]

Thanks Rich, I'd love to see a photo of the engine so I can see how you did it. How would you replace the fusible wire on the trail? That's why I was thinking of using an easily replaceable fuse or flip a breaker switch. I'm not saying you're wrong, I just want to hear your rationale so it can educate me.
I was thinking of a circuit without fusible wire that does the following: starting at the front battery positive terminal of the 24 volt system to 4 gauge wire to a 4 terminal 12volt block located 13" to the left then one terminal would supply the glow plug relay with an 80 amp fuse at the beginning of it and one terminal would supply the diamond shaped 12 volt block with a 100 amp fuse at the beginning of the wire.

I have never fixed a wire that has fusible link wire in it. I've been under the impression that there is crimping and soldering involved. Am I wrong?

I would put at least a 100A fuse/fusible on the glow plugs. In perfect math they are an 80A draw but you want the fuse to blow when a draw higher than normal is applied, not a normal load. There is some variance in resistance even on new plugs and if your glow plugs draw just 10% higher then the nominal, still within spec, you have a 90a draw and your fuse blows. Best idea is to actually measure the draw of the circuit to know what it really uses and base your fuse sizing by going about 10% higher.

As for the diamond terminal block, if you are going to put a fuse there I would just replace the whole block with a mega fuse holder like this one and the right size fuse. That will make a cleaner install and give you capability for anywhere from a 60a to 250A fuse. In fact I would use that style fuse and holder on both.

The marine rated holders like I linked to above are a bit more expensive than others, but have longer terminals designed for multiple wires so you can use it to replace that terminal block and the covers on those will accommodate multiple wires on each side where other ones made for automotive use often have covers molded for just one wire on each terminal.

 

[Warthog]

AntennaClimber did a great glowplug write up in the CUCV Helpful Treads sticky. There areeven a couple of fusible link site ups as well.