30A fuse blown (2 Viewers)

[KNWH]

I noticed my two leisure batteries had died the other day (one showing no charge and the other less than 10v) despite being on hook-up at home. They were around 5 years old, so bought a pair of new ones and just fitted them.
Control panels still dead, so started investigating and eventually found the main 30A fuse in the cable from the leisure batteries had blown.
Have new ones on order, but wondered why it had blown?
Everything was fine when it last used the Motorhome (2019 Bailey 68-2). Could trying to charge two dying batteries have pulled more than 30A? Seems unlikely. I will fit a new fuse when they arrive, but wary it could blow again. I’ll turn off all circuits and then turn each one on in turn.
Everything works fine if I switch to 240v.

 

[Bustup15]

I would test your old batteries after a full charge. They may be OK.
Main fuse between leisure batteries and what had blown?

 

[donkey]

To prevent using up more new costly fuses to diagnose fault. Find the biggest wattage 12v bulb you can find. With the fuse removed, wire the bulb across the two vacant fuse terminals. Now you can turn the power back on, if there is a short the bulb will illuminate brightly, otherwise it will just glow as you test al systems.

Geoff

 

[KNWH]

I would test your old batteries after a full charge. They may be OK.
Main fuse between leisure batteries and what had blown?

I took the old ones in re recycling when I collected the new ones, but I did try charging them when I first took them out. One didn’t take any charge and the other soon dropped off again after charging. The fuse is in the positive cable from the batteries, so the power wasn’t going anywhere! Thanks for the suggestion though.

 

[KNWH]

To prevent using up more new costly fuses to diagnose fault. Find the biggest wattage 12v bulb you can find. With the fuse removed, wire the bulb across the two vacant fuse terminals. Now you can turn the power back on, if there is a short the bulb will illuminate brightly, otherwise it will just glow as you test al systems.

Geoff

Interesting idea Geoff, thanks. I have got some new fuses arriving Thursday, but because we are supposed to be going away in the Motorhome in the next few days I was keen to try and find what the problem was ASAP.
I found that Halfords did a fuse that, although not quite the same design, could be modified to fit, so to speed things up I’ve just fitted that and it seems to be OK so far. At least it didn’t blow immediately. I’ve turned stuff on and again it seems OK but I’m still curious as to what the original fault was.

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[donkey]

Did the original fuse blow cleanly or melt due to overheating? Remember that for some time the charger has probably been delivering maximum output continuously, trying to charge two faulty batteries. With the new batteries it will have a much easier time.

 

[donkey]

Interesting idea Geoff, thanks. I have got some new fuses arriving Thursday, but because we are supposed to be going away in the Motorhome in the next few days I was keen to try and find what the problem was ASAP.
I found that Halfords did a fuse that, although not quite the same design, could be modified to fit, so to speed things up I’ve just fitted that and it seems to be OK so far. At least it didn’t blow immediately. I’ve turned stuff on and again it seems OK but I’m still curious as to what the original fault was.

I have used the idea to test for short circuits for some 60 years. Always used to carry a pre-wired sealed beam unit (remember them?) in a box with foam cushion. If testing a high current circuit, I would join main & dip together.

Geoff

 

[Lenny HB]

I took the old ones in re recycling when I collected the new ones,

Some people love throwing money away. £10 to £15 each at the scrapie.

 

[DavidG58]

although not quite the same design, could be modified to fit

I am intrigued how you ‘modify’ a fuse

Genuine question not challenging you

 

[KNWH]

Some people love throwing money away. £10 to £15 each at the scrapie.

Actually I don’t like throwing money away, but I now know, so thank you

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[KNWH]

Did the original fuse blow cleanly or melt due to overheating? Remember that for some time the charger has probably been delivering maximum output continuously, trying to charge two faulty batteries. With the new batteries it will have a much easier time.

Picture of fuse attached. Not sure if you can tell how it failed from looking?
Hopefully it was just the failing batteries pulling too much current as you suggest.

 

[donkey]

Picture of fuse attached. Not sure if you can tell how it failed from looking?
Hopefully it was just the failing batteries pulling too much current as you suggest.



View attachment 918376

I think you are right.

Geoff

 

[KNWH]

I am intrigued how you ‘modify’ a fuse

Genuine question not challenging you

Picture of the correct fuse at top (they just arrived, a day early, yippee)
Middle is Halford fuse (it was a mixed pack, so that is actually the 40A one) and bottom is the blown one.
The two piece plastic surround provides some additional strength to the fuse (pins locate in the holes in the fuse) and also helps contain the molten metal if it fails)
I just had to file away non-critical parts of the Halford fuse so it didn’t foul the pins and I could fit the plastic surround to contain the bits if it blew.
I’ve just checked this morning and fuse still OK and batteries up to 13.4v so will fit the correct fuse and keep my fingers crossed

 

[DavidG58]

Interesting fuse, is it screwed in place ?

 

[Lenny HB]

Interesting fuse, is it screwed in place ?

It's a standard midi fuse avalible in 30 up to 150 amps a larger version is a mega fuse they go from 100 amps up to 500 amps.
Very common in vehicles and used quite a bit in Motorhomes.

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[DavidG58]

It's a standard midi fuse avalible in 30 up to 150 amps a larger version is a mega fuse they go from 100 amps up to 500 amps.
Very common in vehicles and used quite a bit in Motorhomes.

How are they fitted? Our equivalent is in its own holder, not seen one like this

 

[Lenny HB]

How are they fitted? Our equivalent is in its own holder, not seen one like this

My Carthago has a Mega fuse inline with the battery, Hymer use a Maxi blade fuse which have a habit of melting under high current.

 

[KNWH]

How are they fitted? Our equivalent is in its own holder, not seen one like this

It fits in an inline plastic holder. Cover here hinged open.