Electrical Near Miss - Melted 80A fuse

gerry mcg

gerry mcg

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I’m posting this for discussion as to what might have happened as a near miss on my electrical system following my B2B install
I’m at a bit of a loss to be honest - so please feel free to discuss.

this is an 80A fuse (bought from amazon? that i put in in place of a 50A fuse in the starter battery compartment fuse holder to fuse the 50A B2B on 16mm (110A cable)
it was melted but still live and conducting power

334631D1-D384-41ED-9B52-6CFE32E5D890.jpeg

I only found it by accident as i went to change the wiring between the starter battery this evening and the B2B for new 16mm cabling and fit a 80A MIDI fuse holder and fuse

I guess the question us what the hell went on here? Why did the fuse melt? Why did it melt And not blow?

the B2B has only run for about 1hr total since fitting with the 80A fuse (the Std 50A one was blowing) (perhaps 30min drive, les maybe 30 min idle when i was testing it.

I have just added a Votronic VCC 1212-50 B2B - see thread here. https://www.motorhomefun.co.uk/forum/threads/wiring-votronic-b2b-through-an-ebl119.253516/

wired direct from the Starter battery using the existing thin wall 16mm +ive cabling between starter battery and B2B (fuse increased from 50A to 80A) then new Flexible 16mm +ive cabling between B2B and 200AH lithium battery (1.5m, fused at 60A) and 16mm -ive cabling to negative ground shunt terminal as per below
0DB9F358-CD8D-41E9-8971-6F22ED2F8303.jpeg

With wiring and cablding according to manual for 16mm2 cables (cable runs are short (2m)
68E1B9BD-BB42-48DF-B170-F8D434769C47.jpeg

The area with the melted fuse was here in the battery compartment (behind the 20A fuse) - that is the factory wired EBL119 power source.
802BE6BB-7174-4A60-B392-F77245C9ABE9.jpeg

And it is now cabled and fused with new 16mm2 cables and a 80A midi fuse (the thin red cable in teh foreground is 1.5mm2 battery voltage cable fused at 5A)
9B72C04C-6FA7-4889-9A98-DE0906463FB7.jpeg

I dread to think what could have happened if i had not happened upon it by accident :(
 
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Cable getting very hot but current insufficient to blow the fuse?
 
steveh57 said:
Cable getting very hot but current insufficient to blow the fuse?
Click to expand...
The factory cable appears to be 16mm thin wall cable that should be rated to 110A, so I thought that unlikely?

They plastic fuse holder is OK and unmarked

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Yeah there have been stuff about ddgy gear via amazon etc but they look to be well rated

Boom boom
 
Could be poor connections in the fuse holder leading to overheating? Worth replacing with a midi fuse like you have by the leisure battery perhaps as these don't have iffy contacts unlike the blade fuses.
 
paddymcc said:
Could be poor connections in the fuse holder leading to overheating? Worth replacing with a midi fuse like you have by the leisure battery perhaps as these don't have iffy contacts unlike the blade fuses.
Click to expand...
I had already fitted a 60A midi fuse at the leisure battery end. It was always my plan to do the starter end as well, but I was utilising the existing maxi blade fuse setup as a short term solution to establish proof of working
 
If you want to risk using the fuses you have you could use some contact cleaner on the fuse holder and blades. Perhaps stand over it with the engine running tho to check that it's not heating up....

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paddymcc said:
If you want to risk using the fuses you have you could use some contact cleaner on the fuse holder and blades. Perhaps stand over it with the engine running tho to check that it's not heating up....
Click to expand...
I'm not convinced it want anything to do with these fuses after this! They are all Bin bound! Just not worth the risk.
 
Not uncommon with blade maxi fuses. If the socket is not a good tight connections that often happens. Also there are a lot of crap blade fuses about made from poor quality alloys always best to buy branded fuses by a known manufacturer like Littlefuse, especially when buying blade fuses, that's why they are two to three times the price.

I would replace it with a midi fuse like the ones in the photo of your battery.
 
Lenny HB said:
Not uncommon with blade maxi fuses. If the socket is not a good tight connections that often happens. Also there are a lot of crap blade fuses about made from poor quality alloys always best to buy branded fuses by a known manufacturer like Littlefuse, especially when buying blade fuses, that's why they are two to three times the price.

I would replace it with a midi fuse like the ones in the photo of your battery.
Click to expand...
Already replaced it with the midi fuse - that is the replacement wiring and fuse in the photo 👍
NicM said:
Do you have an amp meter to see the amps going though it?
Click to expand...
no i don’t - (could get one tho) what perplexes me is why the fuse melted rather than blew if it was a high current issue.
i would have thought the fuse should have blown before melting - so either the fuse melted at <the fuse rated 80A, or the fuse didn’t blow when the current was >> than the rated 80A.
neither are a comfortable position!

Ive taken the wiring / fuse and fuse holder in question completely out of the system and replaced the B2B starter battery power with new 16mmm2 wiring rates at 110A and a 80A midi fuse with proper crimped 16mm2 M5 and M6 copper battery terminals
 
gerry mcg said:
Already replaced it with the midi fuse - that is the replacement wiring and fuse in the photo
Click to expand...
Missed that in the photo, have you been working all night. :LOL:

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gerry mcg said:
Already replaced it with the midi fuse - that is the replacement wiring and fuse in the photo 👍

no i don’t - (could get one tho) what perplexes me is why the fuse melted rather than blew if it was a high current issue.
i would have thought the fuse should have blown before melting - so either the fuse melted at <the fuse rated 80A, or the fuse didn’t blow when the current was >> than the rated 80A.
neither are a comfortable position!

Ive taken the wiring / fuse and fuse holder in question completely out of the system and replaced the B2B starter battery power with new 16mmm2 wiring rates at 110A and a 80A midi fuse with proper crimped 16mm2 M5 and M6 copper battery terminals
Click to expand...
If you buy a clamp meter make sure it does DC current. A lot advertise as 'DC clamp meters' but they only measure DC volts.

Here's the one me and Lenny use:

UNI-T UT210E True RMS AC/DC Current Mini Clamp Meters w/ Capacitance Tester Amazon product ASIN B00O1Q2HOQ
 
Richard n Ann said:
If you buy a clamp meter make sure it does DC current. A lot advertise as 'DC clamp meters' but they only measure DC volts.

Here's the one me and Lenny use:

UNI-T UT210E True RMS AC/DC Current Mini Clamp Meters w/ Capacitance Tester Amazon product ASIN B00O1Q2HOQ
Click to expand...
I made that mistake a while ago 🤦‍♂️- hence why i don’t have one! (my one only does AC current) 🤦‍♂️
 
Jim What's going on every other post I make today is posting the message 3 or 4 times. On a fairly fast Win10 PC with 40mb/s broadband.

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I don’t have a thermal imaging camera, but I do have a IR thermometer that picks up hot spots fairly easy. It’s very handy in situations like this. That fuse holder could of melted even with 30a flow, if was loose. I agree to use only reputable brand fuses, specially high power ones. If they are not properly tested and accredited, it could turn ugly. One main reason I stay away of those Chinese thermal resettable breakers.
Well done for spotting and rectifying the fault.
 
As a retired engineer, in my opinion the melting and heat was due to the blades of the fuse arcing,. Although the fuse was rated at 80 amps, the actual contacts of the blades would probably only be good for about 50.
 
I don’t know for sure on automotive fuses. But it’s worth looking at the curve and spec of fuse used. I have some midi that blow at 1,6 times the rated current. Most anl and fusible fuses blow on current way above the rating. Type of fuse may be the clue in the rating.
That’s why I’m not a fan on upping the fuse. Papa John has a point, the 80a it may be to much for a 16mm cable.
 
pappajohn said:
A clue might be the fact you changed from a 50a to an 80a fuse .
Current too high for a 50a but not high enough for an 80a to blow so it gets very hot instead.

Find the reason for the 50a blowing then put a 50a back in
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The 50A fuse only blew when i swapped the feed from the battery from the EBL to the B2B.
I would have expected the EBL to make a lower current demand (20A) than the B2B (50+A). And i hadn’t upped the fuse to the specified 80A when i initially wired to the B2B
so the 50A fuse blowing with the B2B isn’t exactly unsurprising / unexpected

Votronic manual suggested 16mm2, fused to 80A is OK (the 16mm2 cable is 110A rated)

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I had a Votronic 30A b2b and it pulled 47Amp and they get very hot. I wouldn't be surprised if a 50A b2b pulled around 80Amp. The fuse working near its limit will get hot and the type of plastic it is cased in is not a high temperature material. Seen it before with cheap see through fuses. The bin is the best place for them.
 
Fuses get warm when in use, especially when the current is near the rated current. Maybe the plastic had a melting point that was too low.

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