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Old 15-07-2013, 11:35   #1
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Fuse didn't Blow! Nearly a Fire!!

Hi Folks,

Boat is in the tropics with plenty of sun when I smelled melting plastic.
My solar panels go into a 20 amp fuse next to the red battery terminal and the fuse holder was very hot, fuse partly melted but did not blow.



As you can see its had a hot spot, but what you cant see it the connectors crimped onto the wires are nearly burnt through.

So I have changed it to a fuse holder with a 12 AWG wire and a similar 20 amp fuse.

The fuse holder is warm but not hot.

Solar panels max at about 12 to 13 amps (with new fuse its up to 14.5 amps!?)

Any thoughts as to what I have done wrong? The old one has been in for 3 years and not blown a fuse.

Why didnt the fuse blow if it was that hot? Or can it burn before it gets to 20 amps?

Thanks for ze help


Mark
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Old 15-07-2013, 11:43   #2
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Re: Fuse didn't Blow! Nearly a Fire!!

If I understand you correctly, Mark, that fuse was connected directly to the house batteries.

That's a no-no. Only three types of fuses have high enough AIC ratings to connect directly to the house bank: ANLs, MRBFs, and Class-T. For this application, I'd use either an ANL or a MRBF type.

Your post is an excellent illustration of why the ABYC has specified Circuit Protection Devices (fuses or breakers) with at least a 5,000 amp interrupt capacity for connecting directly to a big battery bank. Devices with less than this rating can possibly fail in the closed (shorted) position which can easily cause a fire.

In your specific case, and assuming no huge transient currents (like lightning or power surges), my bet would be surface corrosion had built up on the blades of the fuse, causing significant resistance and heating.

And, yes, that can cause heat, melting, and a fire with far less than 20A current.

Bill
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Old 15-07-2013, 12:02   #3
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Re: Fuse didn't Blow! Nearly a Fire!!

Oh DRAT! I thought I had passed my cruisers electrical course!



How far from my battery bank can I use a fuse as shown?


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Old 15-07-2013, 12:02   #4
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Re: Fuse didn't Blow! Nearly a Fire!!

Fires can often be started with a poor connection and high resistance well before the fuse or circuit breaker trips.

Some of the cheap ATC fuse holders have pretty sloppy friction fits which can lead to high resistance. In line glass fuse holders are also quite prone to corrosion & high resistance. That said I fuse solar panels for the protection of the wire and for the least voltage drop in the circuit. The general rule of thumb I follow is to never load any fuse or breaker to more than 80% of its rating. You are pretty close to 75%.. I prefer to load the circuit to 50-60% of the over current protection.. My solar fuses are normally much larger as are the fuse holders..

Here are a few others that never tripped a fuse or breaker...





Class T Fuse Holder - Melted (improper lug stacking)



A crimp made to solid conductor wire. A big no-no..
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Old 15-07-2013, 12:09   #5
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Re: Fuse didn't Blow! Nearly a Fire!!

Maine is right on, as usual, and confirms my suspicion voiced above. But, hey, Maine....did you have to scare us all to death? :-)

Mark,

ABYC calls for CPDs within 7" of the batteries. That's often hard to do with ANLs. MRBFs, of course, fit right onto the battery terminals.

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Old 15-07-2013, 12:37   #6
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Re: Fuse didn't Blow! Nearly a Fire!!

Is this fuse of same current rating as drawn in the boat's schematics? I'd start, by looking at the schematics. A dab of silicone grease on terminals, will retard corrosion. Take care!

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Old 15-07-2013, 13:02   #7
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Re: Fuse didn't Blow! Nearly a Fire!!

Quote:
Originally Posted by Maine Sail View Post
My solar fuses are normally much larger as are the fuse holders..

What would you use?

The smallest ANL I can see is 50 Amps. But the max from my panels I have ever seen is under 15 amps?

Can I just bolt the ANL fuse to the battery or do I need the fuse block?

I dont think Budget Marine has the MRBF fuses/blocks.

Instead, cant I use the in-line fuse I have but further from the battery?

(Some of this stuff begins to get expensive... $279 in one catalogue)
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Old 15-07-2013, 13:02   #8
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Re: Fuse didn't Blow! Nearly a Fire!!

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Originally Posted by Teknav View Post
Is this fuse of same current rating as drawn in the boat's schematics? I'd start, by looking at the schematics. A dab of silicone grease on terminals, will retard corrosion. Take care!

Mauritz
Ha! boat schematics... that's funny!
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Old 15-07-2013, 13:12   #9
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Re: Fuse didn't Blow! Nearly a Fire!!

Hiya Cheech! How do you expect to do electrical troubleshooting without looking at the schematics first? Being an EE, I do not see anything funny about it at all! I guess some folks believe in "shotgun" troubleshooting; keep replacing parts until something catches fire or miraculously work.

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Old 15-07-2013, 13:19   #10
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Re: Fuse didn't Blow! Nearly a Fire!!

Quote:
Originally Posted by MarkJ View Post
What would you use?

The smallest ANL I can see is 50 Amps. But the max from my panels I have ever seen is under 15 amps?

Can I just bolt the ANL fuse to the battery or do I need the fuse block?

I dont think Budget Marine has the MRBF fuses/blocks.

Instead, cant I use the in-line fuse I have but further from the battery?

(Some of this stuff begins to get expensive... $279 in one catalogue)
No, you can't just use the in-line fuse further from the battery.

You need as fuse or high AIC circuit breaker, located close to the battery.

You can get ANL fuses down to 40A by special order. Use real marine ones...Blue Sea Systems....not the cheapies found in automotive stores. And, yes, you need a fuse holder for ANL fuses. The BSS ANL fuse block is #5005 and costs around $21. The 40A ANL fuse is #5165 and costs about $14.50.

You'd also need a holder for the MRBF fuses if you choose to use one of those. You can buy a fuse block for as low as $21 and a fuse for $12. Do a Google search. The Blue Sea Systems part number is 85269 for the fuse block and 5175 for the fuse.

Either way, it's about $35 for both the holder and the fuse...top marine quality. Don't skimp on this....it almost never pays in the marine environment.

Bill
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Old 15-07-2013, 13:22   #11
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Quote:
Originally Posted by Teknav View Post
Hiya Cheech! How do you expect to do electrical troubleshooting without looking at the schematics first? Being an EE, I do not see anything funny about it at all! I guess some folks believe in "shotgun" troubleshooting; keep replacing parts until something catches fire or miraculously work.

Mauritz
The humor is in the idea that the boat has schematics that relate to it's wiring to begin with. We have 6 58' Meridians of the same series that we maintain, none have wiring that is more than 50% the same, including a pair that are one digit apart(constructed one after the other).
Extrapolate that to a possibly older boat with owner made modifications and probably best to figure out what the wire is doing and why.
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Old 15-07-2013, 13:35   #12
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Re: Fuse didn't Blow! Nearly a Fire!!

Hiya Brown! I really don't know what to say! So, if you want to add more toys to the circuit, you just connect them to the battery bank and add fuses to them without any load calculations and schematics modification?

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Old 15-07-2013, 13:47   #13
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Re: Fuse didn't Blow! Nearly a Fire!!

Quote:
Originally Posted by MarkJ View Post
Hi Folks,

Boat is in the tropics with plenty of sun when I smelled melting plastic.
My solar panels go into a 20 amp fuse next to the red battery terminal and the fuse holder was very hot, fuse partly melted but did not blow.



As you can see its had a hot spot, but what you cant see it the connectors crimped onto the wires are nearly burnt through.

So I have changed it to a fuse holder with a 12 AWG wire and a similar 20 amp fuse.

The fuse holder is warm but not hot.

Solar panels max at about 12 to 13 amps (with new fuse its up to 14.5 amps!?)

Any thoughts as to what I have done wrong? The old one has been in for 3 years and not blown a fuse.

Why didnt the fuse blow if it was that hot? Or can it burn before it gets to 20 amps?

Thanks for ze help


Mark

firstly if you are pushing 14amps any distance that wire is woefully inadequate.
looks like 14G wire. you need 8G minimum. and if the run is very long your looking for 4G wire. all the wire needs to be the same size also. going from thick, to thin, to thick makes a light bulb :P if you get my point.
and where is your charge controller? its should go from the panel to your charge controller, not your batteries.......
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Old 15-07-2013, 14:05   #14
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Re: Fuse didn't Blow! Nearly a Fire!!

I want to be sure I understand the "issues" here (never know when knowing the answer may be of use):

1 - the fuse over heated, probably due to a bad connection
2 - the fuse application for connecting directly to a battery is wrong

but #2 didn't cause number 1 (which was the original problem)?

I'm feeling better of my connecting my solar controller to the house bank via a breaker on the main DC panel now instead of directly to the batteries.
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Old 15-07-2013, 14:09   #15
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Re: Fuse didn't Blow! Nearly a Fire!!

It looks like the fuseholder itself isn't rated for a 20A or higher fuse.
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