Heat on terminals.

[Sennen]

When my system was under an extended 150a load, I went to check on wiring for warmth. The negative busbar connection was room ambient temperature, but the connection at the fuse and the fuse itself was warm.

I say connection, but thermals indicate the crimps are potentially not solid. However, I removed one of these and tested by attaching to my workbench and giving it a hearty tug. No movement. At all other junctions, there are no thermal issues.

So I have to ask; is this normal at fuse connections? All connections are torqued to provided spec from Blue Sea.

 

[WindWizard]

I would get a multimeter and then measure the voltage drop at 150 amp load to test the crimp connections, fuse, wires etc. This will tell you where the heat is being generated. I do not like it when things get warm or hot.

 

[hwy17]

I mean it's nothing over 45C. 60C, 75C, 90C, are the usually thresholds for operational concern in electrical.

But it does make you wonder if double stacking lugs contributes to it.

The heat in the Class T is unavoidable and normal I think. That has to be high resistance in order to be halfway to melting.

 

[mushhead]

Is the the hot spot in the 2nd picture of something metal? And if so, did you correct for it's emissivity for the temp read out? The technique I use for reading metal temps with IR is to put a strip of black electrical tape on the metal, and then read that to do away with the emissivity issue.
As for warm fuses after a sustained 150A load... fuses get warm under high loads... warm enough to melt the internal metal at their trip point. But it's still good to check things out.

 

[Skypower]

I’ve seen weird things about surface emissivity. Note the shiny nickel Blue Sea mounting surfaces read cooler than the red heat shrink and cable body or the center fuse body insulator. The exposed parts of the copper lugs show cool yet right next to it the heat shrink is warmer? I don’t think so, especially if there’s been so time to spread the heat out. The metal exposed parts should appear hotter so I think you are seeing a bit of emissivity anomaly. I’m guessing by your detail for neatness that you have your lugs well crimped (hex corners crisp) and quality lugs and appropriately matched to cable. The following old photo has daisy chained jumpers and nickel plated cell buss and shows the same thing. That was a test with different approaches to crimping and conductive substances like carbon. Bottom line, a clean, shined up lug barrel and straight strands was measurably better than out of the bag lugs and random strands, but not that big of a deal.

 

[Sennen]

Thanks for the replies. Based on the above comments, I think the heat is radiating from the fuse assembly into the wires but since the fuse/bolts/fuse bus are all shiny, it appears to be the crimp.

I’m guessing by your detail for neatness that you have your lugs well crimped (hex corners crisp) and quality lungs and appropriately matched to cable.

Thanks for noticing. After 15 years of doing car audio, I am well practiced in the art of clean wiring. And yes, temco hydraulic crimper with temco lugs. This is the only area that's warm.

 

[Sennen]

And the only noticeable voltage drop in the system is across the blue sea switch. It's not feeling warm, though. 20mv drop

 

[Skypower]

I don’t think that you can do better with the cable, lug and crimp quality. A single crimp with that hydraulic crimper for that lug type is optimal. Note: repositioning the die and re crimping on the same hex is actually counter productive. On “power lugs” at least two crimps are needed, but for our purposes if done correctly “starter lugs” (shown) are fine.
I have modified the dies on a few of my crimpers (four crimpers) every set is different so it must be determined for each application to get that perfect crimp. I like Blue sea stuff but not the disconnect on 48+ volt systems. I want something that won’t have the potential for arc damage if I must disconnect under load .
.

 

[OzSolar]

And the only noticeable voltage drop in the system is across the blue sea switch. It's not feeling warm, though. 20mv drop

Did you measure across the entire system?

I think that’s about the best you can do across a fuse. Breakers are a bit worse than fuses if I remember correctly.

.2v x 150 amps = 30 watts of heat being generated.

 

[Sennen]

I’ve seen weird things about surface emissivity. Note the shiny nickel Blue Sea mounting surfaces read cooler than the red heat shrink and cable body or the center fuse body insulator. The exposed parts of the copper lugs show cool yet right next to it the heat shrink is warmer? I don’t think so, especially if there’s been so time to spread the heat out. The metal exposed parts should appear hotter so I think you are seeing a bit of emissivity anomaly. I’m guessing by your detail for neatness that you have your lugs well crimped (hex corners crisp) and quality lugs and appropriately matched to cable. The following old photo has daisy chained jumpers and nickel plated cell buss and shows the same thing. That was a test with different approaches to crimping and conductive substances like carbon. Bottom line, a clean, shined up lug barrel and straight strands was measurably better than out of the bag lugs and random strands, but not that big of a deal.
View attachment 201333
View attachment 201329

At 120Amps with nylon tape on the fuse block Fuse is definitely the hot spot.

Did you measure across the entire system?

I think that’s about the best you can do across a fuse. Breakers are a bit worse than fuses if I remember correctly.

.2v x 150 amps = 30 watts of heat being generated.

Just measured at 120 amps.
38mV drop across switch
32mV drop across fuse
<6mv drop across each section of wire

Not sure if I should swap out the switch for a more robust relay as the switch is technically rated for 48v.

 

[Skypower]

If I had a “do over” this is what I’d get. I have a clone, but this is a ridiculous over kill for a reasonable price. They have this new model in all kinds of current ranges. So it’s more than just a switch, you could size it as a last ditch over current.
https://a.co/d/3pp1zWJ