Fuses??

[Barking Mat]

I was under the impression fuses either worked, or had blown.

Over the last few days my understanding has changed.

Problem : 12 volt dc bow thruster, does not work.

Check battery, battery good, run over system with volt meter...

The motor turns both directions, operated by two relays, one one way, one the other....

Fairly straightforward...

Electricity getting to the relays, but not coming out.

24 hours later, replacement relay box.

Exactly the same issue.

Phone a colleague.

He tells me it's the fuse.

I tell him I've checked it and it seems ok.

He tells me to get a jump lead and bypass the fuse.

He's right.

It is the fuse.

What's going on here?

Here's the fuse in question.

It's going to have to get opened.

 

[dobbslc]

That's a big bugger!
Maybe it's gone high resistance and your multimeter is still picking up some continuity
Edit: did you measure it when it was still "in circuit"?

 

[Barking Mat]

Ahhh....so allows some current to pass when it blows, but not high currents.

Live and learn.....

 

[LandRoverTom]

What resistance does a multimeter show across the fuse with it removed?

That fuse looks to have a striker pin/indicator - the little red bit should project further out than that if it has blown

 

[Barking Mat]

That's a big bugger!
Maybe it's gone high resistance and your multimeter is still picking up some continuity
Edit: did you measure it when it was still "in circuit"?

Yep, it was firing the relays, but not enough I guess...?
Or enough to fire the relays, but not the motor?

 

[Barking Mat]

What resistance does a multimeter show across the fuse with it removed?

That fuse looks to have a striker pin/indicator - the little red bit should project further out than that if it has blown

I think , I have now discovered, it's a dead fuse indicator, if I look really carefully, I see red plastic.

That's the circular hole in the middle.

I'll finish this beer and dismantle.

Reads full continuity on a tester.

 

[LandRoverTom]

I think , I have now discovered, it's a dead fuse indicator, if I look really carefully, I see red plastic.

That's the circular hole in the middle.

I'll finish this beer and dismantle.

Reads full continuity on a tester.

From the picture atleast the incicator looks ok to me.
And if a multimeter is telling you there is continuity between either end of the fuse then it should be fine.

When you say full continuity what is the actual reading?

Also are you putting a link in place of the fuse? or are you bypassing the fuse holder altogether?
I have had a similarly obscure scenario that turned out to be a faulty fuse holder...

 

[Barking Mat]

Looks ok to me?

 

[Barking Mat]

Genuinely no idea.

Fuse seems ok.

Fuse holder?

I stuck jump leads from the top of the fuse holder to the bottom, problem solved.

Very curious.

 

[Barking Mat]

From the picture atleast the incicator looks ok to me.
And if a multimeter is telling you there is continuity between either end of the fuse then it should be fine.

When you say full continuity what is the actual reading?

Also are you putting a link in place of the fuse? or are you bypassing the fuse holder altogether?
I have had a similarly obscure scenario that turned out to be a faulty fuse holder...

I'll just bypass the fuse holder probably, hmmm, maybe not.

I've some 300 amp which might fit..

 

[LandRoverTom]

Yep, nothing wrong there.

Do you have any circuit diagrams you can post?

 

[Barking Mat]

Yep, nothing wrong there.

Do you have any circuit diagrams you can post?

No, this is the culprit.

On really careful examination a couple of links in the mesh are broken, but that could have been me dismantling it?

 

[Barking Mat]

I'll get some photos next time I'm in work, I'm supposed to be on weekend, but can't see that happening.

I installed it 8 years ago, I was provided with this kit, and told to go install it. Never had any problems with it , till it stopped working.

I was ready to order a 900 Euro motor.

 

[dobbslc]

Ahhh....so allows some current to pass when it blows, but not high currents.

Live and learn.....

No. If it blows that should be it. It would be dangerous to believe a fuse was blown but still able to flow something.

Yep, it was firing the relays, but not enough I guess...?
Or enough to fire the relays, but not the motor?

Mmm if the relays are switching then there could be something wrong with them or the motor. The relays might have burnt contacts, worth stripping them down for a look see.

 

[dobbslc]

I've just reread this bit,

I stuck jump leads from the top of the fuse holder to the bottom, problem solved.

It could be dirty contacts on the fuse or the holder as mentioned above ^^^

 

[Barking Mat]

I've just reread this bit,


It could be dirty contacts on the fuse or the holder as mentioned above ^^^

We will see, after the storms there was some water in that area, but would have only caused humidity.

I think, think? The fuse has cooked, but still allows some current to feed to low power things , from what I found from googling.

Need to put it back in and test it under load I guess, will that fry my tester? I'll use works.

I'll get back to you all.

 

[skotl]

I've just reread this bit,


It could be dirty contacts on the fuse or the holder as mentioned above ^^^

That's what I was figuring while reading the tale fuse is ok but not making enough contact to pass the current required.

 

[Barking Mat]

Contacts look clean I had to force it out with a 17mm spanner, it was well, well clamped in place.

 

[LandRoverTom]

Need to put it back in and test it under load I guess, will that fry my tester? I'll use works.

Do not use that fuse again. Now you've dismantled it the only thing that is good for is the bin.

We will see, after the storms there was some water in that area, but would have only caused humidity.

I think, think? The fuse has cooked, but still allows some current to feed to low power things , from what I found from googling.

I think your google-ing has lead you up the garden path - when fuses blow thats it, they don't let some current flow but not much.
The perferated metal strips inside would have burned and melted though if it had blown.

Contacts look clean I had to force it out with a 17mm spanner, it was well, well clamped in place.

Perhaps it's just the picture but the fuse contracts don't look particularly great, and it sounds like the fuse was pretty well stuck in the holder. You say it's damp after the storms, has water got in there before? Water ingress is always good for causing faults and failures on boats. Corroded terminals won't conduct well.

 

[Barking Mat]

Do not use that fuse again. Now you've dismantled it the only thing that is good for is the bin.



I think your google-ing has lead you up the garden path - when fuses blow thats it, they don't let some current flow but not much.
The perferated metal strips inside would have burned and melted though if it had blown.




Perhaps it's just the picture but the fuse contracts don't look particularly great, and it sounds like the fuse was pretty well stuck in the holder. You say it's damp after the storms, has water got in there before? Water ingress is always good for causing faults and failures on boats. Corroded terminals won't conduct well.

Thank you for all that.

Yes, I completely agree, fuses should be binary, on or off.

But give me a while, cos, I've had a few beers, that reference, refers to something..... Tomorrow , just when you're feeling pretty competent in electrics, a fuse...