Electrical Near Miss - Melted 80A fuse (2 Viewers)

[gerry mcg]

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

I got my sparkly new clamp meter yesterday
I put on the grey tank heater over night to put a dent into the lithium charge - it took 40Ah out of hte battery and dropped the SOC to 70% overnight so that would allow the Votronic 50A B2B something to work with.

the B2B fires up and was putting out a solid 50A to the leisure battery and the new 16mm2 wiring fused with 80A fuse was carrying 54A adjacebt to the 80A fuse. And the current seemed to closely mirror the B2B output voltage by +2A or so as the current tailed off as one approached 100% SoC.

there was about 60A measures on the braided earth cable between the starter battery and the chassis in the battery compartment (i guess the difference is the van electrics such as fan running)

so all seems safe and well now with the new wiring and midi fuse

 

[Captain Birdseye]

We had our voltronic b2b catch fire in our old motorhome. It had been professionally fitted. My wife heard a noise like "pop, Pop, Pop" then a funny smell, then smoke. The engine was not running at the time and we had just parked in a car park and were getting the bikes off the back, so no hook up. Our dog was going to be left behind. Thank goodness that it happened just before we set off. Put out the fire after it had melted all around it including the Schrider unit controlling all electrics in the motorhome. Took out main fuse and disconnedted b2b connection from battery. That was the end of our holiday in Cornwall, so drove home to Cheshire. Voltronic had it back and said it could not be a problem with the unit, but as a gesture of goodwill sent a new unit foc. I sold the new unit on ebay. Our motorhome was repaired and part exchanged with our dealer who knew what had happened.

 

[Clive Mott]

Cheap fuses run hotter and get very hot before they rupture. Quality fuses have a low temperature melting point element and run a lot cooler. You get what you pay for.

 

[Gromett]

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.

Watts = I²R

If you have a poor connection and a resistance of say 0.5ohms was present between the blade and the terminals. At 60 amps (well below the rating) this would generate 60 * 60 * 0.5 = 1800 watts of heat
As you can see from the maths, it doesn't take a lot to generate heat in a dodgy connection. Even a tiny small rise of 0.002 ohms in the connector will cause 10 watts of losses/heating.

This heat in the terminals will very quickly build up and melt the plastic while leaving the metal intact.

I developed a habit many, many moons ago of cleaning terminals whenever I replaced a fuse.

 

[PaulandChrissy]

When it comes to higher amperage fuses, I think the solid bolt in versions are much safer. This should eliminate the poor connection which is the route cause of the failure. Push in blade fuses are generally OK when new, but in time as they tarnish, heat builds up and this is the scary result. The same can happen to any push together connectors, not just fuses. Check the 12volt high amperage connection on the back of your 3way fridge, they also melt. I’ve removed mine and made a solid bolt together connection.

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[JockandRita]

Cheap fuses run hotter and get very hot before they rupture. Quality fuses have a low temperature melting point element and run a lot cooler. You get what you pay for.

This is a genuine question Clive, ie, how does Joe Bloggs identify a quality blade fuse from a non quality one, in the absence of some identification standard like a BS or ISO number/code?

Cheers,

Jock.

 

[Richard n Ann]

This is a genuine question Clive, ie, how does Joe Bloggs identify a quality blade fuse from a non quality one, in the absence of some identification standard like a BS or ISO number/code?

Cheers,

Jock.

I (grudgingly) bought mine from halfords

 

[JockandRita]

I (grudgingly) bought mine from halfords

But how do you know they are of pukka electrical quality Richard?

Cheers,

Jock.

 

[NorwayNeil]

If the 50 amp fuse is recommended & kept blowing why replace it with an 80 amp? That's like filling up every day because you've got a leak in your fuel tank. I'd suggest looking for why more than the max current is being drawn, not why it melted ... Or put a 6" nail across it

 

[Richard n Ann]

But how do you know they are of pukka electrical quality Richard?

Cheers,

Jock.

I don't know for sure, just buying from a reputable source they look OK

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[Trevor Wbm]

I had a similar thing happen on my brand new PHEV. 12v supply from the fuse box to the 12v battery wasn't properly tightened: as it worked loose, it evidently sparked more and more, and that generated heat that melted the plastic part of a 200amp fuse, and part of the fuse box.

Probably quite close to a fire when the car died from lack of adequate 12v charge to the battery, but all worked fine even with the melted bits once the connection was tightened up, so no actual electrical fault.

New fuse and fuse box fitted after I had had a mild rant at the dealers.

 

[vzac]

Sorry to hear what's happened. I will not use Internet for purchases unless I know its a reputable company. I used to sell dewalt, and regularly received warranty claims for batteries that had set on Fire, did not work, or had gone bang. Everyone had been bought in ebay etc and were not genuine dewalt even though they looked like and gave nearly all rhe same specifications. Told them all to go back to where they were purchased from. Lesson learned.

 

[gerry mcg]

If the 50 amp fuse is recommended & kept blowing why replace it with an 80 amp? That's like filling up every day because you've got a leak in your fuel tank. I'd suggest looking for why more than the max current is being drawn, not why it melted ... Or put a 6" nail across it

The 50A fuse was the fuse fitted to the EBL supply.
THE EBL was disconnected and replaced with a 50A B2B with a 80A fuse recommendation. The original 50A fuse only blew once the B2B was brought online.
Once the 50 A fuse blew ( which was one might say predictable given the 80A fuse reccomendation) it was replaced with a 80A fuse as per the installation instructions.

To suggest the fusing was ignored is plain wrong

 

[MrTVR]

Fuses blow when the thin section of metal melts. If the failure occurs due to a short circuit (the most common failure mode) then the event will be so quick that collateral damage will be limited. However, if the fuse is operated at close to or even slightly above its rating for a prolonged period of time the heat build up can be sufficient to cause this kind of damage without being sufficient to actually melt the metal.

 

[autorouter]

Fuses blow when the thin section of metal melts. If the failure occurs due to a short circuit (the most common failure mode) then the event will be so quick that collateral damage will be limited. However, if the fuse is operated at close to or even slightly above its rating for a prolonged period of time the heat build up can be sufficient to cause this kind of damage without being sufficient to actually melt the metal.

An 80A fuse should be capable of running at 80.0A indefinitely with no damage or melting of anything. If the plastic melts at 60A, or even 80A, then the design is incorrect. This fuse design is supposed to be tested by the manufacturers to ensure this does not happen.

In this case what we don't know is whether the heating was the normal fuse heating or due to contact resistance at the blades.

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[Lenny HB]

But how do you know they are of pukka electrical quality Richard?

Cheers,

Jock.

Buy a known brand like Littlefuse.

 

[gerry mcg]

Buy a known brand like Littlefuse.

This is why i shared the issue - i had no idea that there were such a thing as “good“ or “bad” quality fuses…
i thought they were all created equal - and it has been a learning experience.

do you happen to know of UK suppliers of said Littlefuse fuses?

 

[Lenny HB]

This is why i shared the issue - i had no idea that there were such a thing as “good“ or “bad” quality fuses…
i thought they were all created equal - and it has been a learning experience.

do you happen to know of UK suppliers of said Littlefuse fuses?

Farnell

https://uk.farnell.com/c/circuit-protection/fuses-fuse-accessories/fuses/automotive-fuses?st=littlefuse

CPC

https://cpc.farnell.com/search?st=littlefuse

RS, website down at the mo.

 

[Minxy]

A fuse replacement guide for those who like to live dangerously!

 

[tonyidle]

An 80A fuse should be capable of running at 80.0A indefinitely with no damage or melting of anything

At what current would you expect the fuse to "blow"?

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[gerry mcg]

At what current would you expect the fuse to "blow"?

I think they blow at something like 125% peak (i.e. short term) current or the like

https://www.littelfuse.com/~/media/electronics/application_guides/littelfuse_fuseology_application_guide.pdf.pdf

1. NORMAL OPERATING CURRENT: The current rating of a fuse is typically derated 25% for operation at 25oC to avoid nuisance blowing. For example, a fuse with a current rating of 10A is not usually recommended for operation at more than 7.5A in a 25oC ambient. For additional details, see RERATING in the previous section and AMBIENT TEMPERATURE below.

 

[tonyidle]

I think they blow at something like 125% peak (i.e. short term) current or the like

https://www.littelfuse.com/~/media/electronics/application_guides/littelfuse_fuseology_application_guide.pdf.pdf

1. NORMAL OPERATING CURRENT: The current rating of a fuse is typically derated 25% for operation at 25oC to avoid nuisance blowing. For example, a fuse with a current rating of 10A is not usually recommended for operation at more than 7.5A in a 25oC ambient. For additional details, see RERATING in the previous section and AMBIENT TEMPERATURE below.

That sounds about right - as does the de-rated value. It is never wise to operate a fuse too close to its nominal rating

 

[MrTVR]

An 80A fuse should be capable of running at 80.0A indefinitely with no damage or melting of anything. If the plastic melts at 60A, or even 80A, then the design is incorrect. This fuse design is supposed to be tested by the manufacturers to ensure this does not happen.

In this case what we don't know is whether the heating was the normal fuse heating or due to contact resistance at the blades.

This is why proper fuses are constructed of nonflammable materials. Automobile fuses are designed for weight & (primarily) low cost and just don’t work well on the limit.

 

[MrTVR]

This is why i shared the issue - i had no idea that there were such a thing as “good“ or “bad” quality fuses…
i thought they were all created equal - and it has been a learning experience.

do you happen to know of UK suppliers of said Littlefuse fuses?

It’s probably not down to the manufacturer of the fuse but is down to the variable connection resistance of the spade connector and low temperature tolerance of the plastic fuse body.

At these high currents even a fraction of an ohm can result in significant heating of the fuse. The solution is to use a fuse manufactured from a nonflammable material (glass or ceramic) which is fastened using a screw or bolt terminal.

 

[WildBunch]

I had a look at my ISO-TECH ICM 135R clamp meter. It is a good quality meter supplied by RS (ex work meter).
But it does not have a DC current function, so I did not expect it to work on a DC circuit. I did a quick test using a battery charger connected to 12 V battery. the charging current measured by the chargers ammeter was 8 amps. The clamp meter also read 8 amps approx. Clearly there will be a discrepancy because the clamp meter is calibrated to " true RMS ". I am wondering if this will be any use when I change from lead to lithium in the near future.

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[Gromett]

It is worth noting that the fuse is there to protect the cable, it should be rated at less than the cable nominal capacity. Therefore a cable rated at say 10A should have for example an 8A fuse. The fuse should be able to carry a little more than 8A continously but blow when it exceeds this by a margin. That margin varies with fuse types and most manufacturers will provide a spec. However, rarely do you need to know the spec except in the case with equipment that has a high start up current such as motors.

 

[Gromett]

It’s probably not down to the manufacturer of the fuse but is down to the variable connection resistance of the spade connector and low temperature tolerance of the plastic fuse body.

At these high currents even a fraction of an ohm can result in significant heating of the fuse. The solution is to use a fuse manufactured from a nonflammable material (glass or ceramic) which is fastened using a screw or bolt terminal.

Agreed, see my previous post #34.

I personally do not like using the blade fuses above 10A in installs I do. Anything over this gets it's own cable fused with a screw terminal fuse. I love the mega fuses.

 

[gerry mcg]

It is worth noting that the fuse is there to protect the cable, it should be rated at less than the cable nominal capacity. Therefore a cable rated at say 10A should have for example an 8A fuse. The fuse should be able to carry a little more than 8A continously but blow when it exceeds this by a margin. That margin varies with fuse types and most manufacturers will provide a spec. However, rarely do you need to know the spec except in the case with equipment that has a high start up current such as motors.

Yip, 16mm2 cable is rated at 110A, so an 80A fuse should be adequate to protect it.

 

[Peregrinator]

I know this is old, Just like to keep this warning going, when I was working in a car parts shop before retiring, we stocked blade fuses which were made in China, almost a disaster with three burn outs, and nine melt downs, trouble was the metal had a high melting point, so became like a heating element, and some plastics caught fire, A case in point was U-Tuber "Wandering Bird Motorhome Adventures" which made a video to show what happened, this is their link, check this video out so you get an idea of what I mean: ch

 

[Nedge68]

Resistance is the enemy here, a poor blade connection or a loose screw terminal, I have found BS88 fuse holders melted together through poor connections. When using high current 50 amps a small resistance 0.01Ohms has a huge effect as power is a square of the current P= (I x I) x R
so (50x50)x0.01 = 25Watts.

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