Minor new year emergency. Help please.

[davedindubai]

Typically, when I have an issue, it’s New Years morning with a boat full of family and I’m in the middle of changing a babies nappy!

This morning whilst on daddy duties I smelled smoke in our starboard hull (Lagoon 450 owners cabin). Obviously the first job is to get the little one upstairs and then I secured the batteries as the smoke alarm sounded. I then opened the window above the bed and the little window aft of the bed as I knew it was coming from the battery compartment. When I’m working under the bed the fastest way to access there is to tie a line thru the aft window onto the foot of the slated bed base to pull the mattress, topper, bedding etc all out of the way in one go. As I did a small amount of burnt plastic smoke came out. It was quite obvious that it was coming from the clear plastic cover over the mega fuse.

Here’s our set up:

Victron Quattro 5000
840ah lead acid battery bank
1000w solar
750a fuse from batteries to inverter on positive side.

We’re currently in a marina with shore power but I like to occasionally run on battery using the inverter during the sunny hours to cycle the batteries a bit so I was on inverter. We regularly see 4000w on the Victron Color Control when boiling the kettle, heating the hot water tank, making water etc but this morning I was running 2 oil filled heaters 1000w and 2000w and heating the hot water tank 1400w. Total draw approx 4,400w. Plus some other small 240v appliances.

The inverter didn’t trip at any point.

The 2x positive cables are 95mm2 and were red hot to touch hence the melting fuse.

I’ve checked the cables all the way from the fuse up to the inverter and all looks good, nothing is melted and it’s all cooled down now. There’s a small amount of damage to the inverter side of the fuse.

I’m guessing I was trying to run too much current for too long but other than obviously not using the oil heaters on the inverter what else should I be doing from now on?

Should I replace the 750a fuse with a 500a?
Should I replace the mega fuse holder?
Should the fuse have blown?

I’m no electrics expert (quite the opposite) so please be gentle with my nievity and of course I never leave the boat unattended with any 220v power source on.

I’ve been running 3 oil filled heaters, 4000w total from the 16a shore power and also the boats electrics but if I want to boil the kettle for example I’ll turn off the 2000w heater.

Thanks for reading and Happy New Year.

[Reefmagnet]

The burnt looking stud had a bad electrical connection ( most likely not tight enough) and this caused resistance which overheated the connection and adjacent areas. Not enough current to blow the fuse, though, if it got hot enough it should have open circuited due to melting of the link at some point. Replace the fuse holder and fuse. It might even be a good idea to replace with multiple parallel fuses of a lower rating to increase the protection against this kind of issue if possible.

[davedindubai]

Thanks for the reply (especially today).
I’ve checked and the 4 nuts on the fuse are all bar tight.
I’ll replace the fuse and holder as soon as I can and will remain on shore power.

[NYSail]

With the bad stud that reefmagnet mentioned..... make sure there were no washers in the wrong place. Washers should not be between connections as this will add significant resistance.

Good luck!

[GrowleyMonster]

Well, you are sort of over fused. 500a x 12v is 6kw, nominal. 750a would be 9kw.



I bet your connection at the fuse had a high resistance. Otherwise you would not have a concentration of heat there. Make sure there is plenty of ventilation behind that fuse cover, too.

[Chotu]

Clean those connections and make sure they are tight. That's probably the cause. Bad connection.

[_andi_]

Hi,



12V System?

I'd try to get hold of a professional, can't really tell from the pictures but there's some stuff I'd have a closer look at:

• crisscrossing of red&black wires, potentially unfused. Chafe might lead to boat burning down.
• fuse on wooden panel.
• maybe overfused, depends on cable thickness&length
• check the insulation of the cables, might be cooked and fall off soon
• Also be aware of fuse datasheets, most can run quite some over-current for some time

And yeah, it has to be "high" resistance on the connection. At 4kw and 12V the load resistance is around 0.36 ohm, so a bad connection at 0.018 ohm might be plenty to get it red hot. (back of the envelope new years calculation, wouldn't trust these numbers...).

Andi

[_andi_]

Originally Posted by davedindubai

Should the fuse have blown?

No. I strongly recommend to read up on fuses and their purpose. Short summery: They protect the wires from melting in case of a short. In these scenarios the might melt at some point due to the boat burning but not through electrical current.

[ullar]

Originally Posted by NYSail

With the bad stud that reefmagnet mentioned..... make sure there were no washers in the wrong place. Washers should not be between connections as this will add significant resistance.

Good luck!

+1
From pictures, there seems to be a washer below fuse. Should not be. Like NYSail said, additional resistance and hence heat up under heavy current.

[_andi_]

Originally Posted by NYSail

Washers should not be between connections as this will add significant resistance.

Good catch! Also you might get some electrolytic corrosion, for example with stainless steel washers on (tinned) copper.

[KTP]

Remember, power dissipated in a connection goes up with the square of current.

At 700 amps that is 490,000 x the resistance of the connection. With that much current even a connection with 0.0001 ohm resistance will have 49 watts heating it up, which is like holding a good soldering iron to the metal. No wonder the plastic was melting.

[Terra Nova]

Originally Posted by ullar

+1
From pictures, there seems to be a washer below fuse...

The entire installation appears to be an amateur hack job. There should be no conductor exposed outside the fuse block's protective cover. The cable has been stripped back WAY too far. And no attempt has been made to install shrink sleeve over the terminal and insulation.

[_andi_]

Originally Posted by KTP

With that much current even a connection with 0.0001 ohm resistance will have 49 watts heating it up, which is like holding a good soldering iron to the metal. No wonder the plastic was melting.

Funny coincidence, 0.1mOhm is the design resistance of the fuse (or more specific for the 500A version)...

https://www.victronenergy.com/upload...holders-EN.pdf

[Kelkara]

Not an instant fix ... but if you're regularly using that kind of current ... perhaps you are a candidate for upgrading to a 24V system in the future ... 1/2 the current and 1/4 of the heat generated.

[_andi_]

... and come to think of it, stainless is a crappy heat conductor, so if the washer under the cable is stainless it might have been overheating of the fuse because it couldn't sink the heat into the cables... So I might have been wrong with "high resistance" after all. But then again, stainless is also a crappy electrical conductor.