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Old 29-01-2016, 08:08   #46
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Re: Faulty 12 volt power point socket Fire put out with a jar of olives in Brine

I have experienced the same problem with a powerful spot light which had to be jerked out at the worst possible time leaving me blind in a narrow channel
I also was relying on the fuse in the male plug and thinking it was safe because it was on a circuit breaker at the main panel which had too high of a rating due to how many different things were to to be run on the same circuit
What could go wrong on a circuit with two fuses ????
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Old 29-01-2016, 08:18   #47
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Re: Faulty 12 volt power point socket Fire put out with a jar of olives in Brine

Quote:
Originally Posted by sartorst View Post
I have experienced the same problem with a powerful spot light which had to be jerked out at the worst possible time leaving me blind in a narrow channel
I also was relying on the fuse in the male plug and thinking it was safe because it was on a circuit breaker at the main panel which had too high of a rating due to how many different things were to to be run on the same circuit
What could go wrong on a circuit with two fuses ????
As someone else mentioned, heat. Look at the design of a cigarette lighter plug and socket. The negative side is fine but the positive side depends on contact between two pieces of metal. There is nothing to hold them tight.

Other types of plug/socket combinations put pressure on the pins to hold them tight and there is more contact area.

When you push the male part of a cigarette lighter style plug into the female, it may loosen up and any corrosion or looseness will cause heat. Heat leads to melting or a fire.
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Old 29-01-2016, 09:33   #48
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Re: Faulty 12 volt power point socket Fire put out with a jar of olives in Brine

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Originally Posted by rwidman View Post
A fuse is, in a sense, a "short". It is a conductor intended to melt when too much current flows through it. Once it melts, it is an open circuit. A fuse can't malfunction and route current around it.
A fuse can malfunction and continue passing current through it even though it has technically tripped. Just because you've not seen it happen does not mean it can't or does not happen. This is why fuses & breakers have an AIC rating....

This 5A fuse continued passing current after it tripped. It took 12A for me to trip it again... When it tripped the fusible link wire fell against the other leg and continued passing current.. While this is extremely rare it can and does happen from time to time...

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Old 29-01-2016, 15:50   #49
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Re: Faulty 12 volt power point socket Fire put out with a jar of olives in Brine

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Originally Posted by Maine Sail View Post
It likely started as high resistance and as the plastic melted it possibly shorted.

As the springs in the male plug weaken over time, in the 12V+ tip and ground wings, the plug can develop a sloppy fit and work loose. When it becomes loose in the socket we create a point of high resistance which can begin to heat the plug and outlet to the point of fire all at well below a fuses trip point. I have seen this happen with a 15A rated fuse and the fuse never tripped because the owner was not exceeding 15A but the outlet was scorching hot and melting due to high resistance..

If you follow a few simple rules for 12V DC sockets they can be used in a safe manner.

#1 ALWAYS USE OVER CURRENT PROTECTION
#2 Max fuse size 7.5A (preferably not more than 5A)
#3 DO NOT plug in pumps, motors or search lights
#4 Choose high quality sockets rated for at least 15A (but don't run them at that)
#5 Contact points need to be kept clean (A Dremel works, 12V Power off first)
#6 DO NOT plug in small 12V to 120V inverters.
#8 If the male plug becomes loose fitting stop using it and replace it.
#9 Use only for cell phone, camera, tablet or laptop charging with 12V loads less than 5A - 7A

If you follow this you will likely never have a 12V outlet issue again. High resistance can start fires well below the fuse trip point!



Absolutely and this is a major goof. Every wire on-board your vessel, not just a 12V socket, needs to be over-current protected.

Very helpful comments with Key operational points. Following your advise First up I changed my fuses to 7.5 amps yesterday. Thanks for your experence.
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Old 29-01-2016, 16:10   #50
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Re: Faulty 12 volt power point socket Fire put out with a jar of olives in Brine

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Originally Posted by Maine Sail View Post
I would suggest finding a better socket design if you want to use a pump with a 12V outlet.. Remember that 4A rating is often an un-loaded rating and every manufacturer rates these small pumps differently..

As an example a while ago I had a brand new Rule 500 kicking around my shop so I attached it to a battery... Rule recommends a 2.5A fuse for this pump. The fuse is sized to prevent the pump from caching on fire.

Battery = Group 31 AGM Resting Voltage 12.77V

Meter = Fluke 376 w/Inrush & min/max NIST Calibrated, Fluke 289 & Fluke Infrared Pyrometer

These are the tests I ran:

12.75V - Ran pump dry for 10 minutes and saw 1F rise (Fluke Infrared pyrometer)

12.72V - No Load (spinning in air) = 0.7A with no load (in-rush/startup current current = 2.7A)

12.72V - Pumping water, open bucket rate, no head pressure from hoses 1.34A (did not test with hoses, elbows etc. but would likely be a bit higher)

12.72V - Locked Rotor with a 3A Fuse = Blew Instantly

12.71V - Locked Rotor with 5A Fuse = Blew nearly instantly (about 6 seconds)

12.71V - Locked Rotor with a 15A Fuse = No blow 10.9A continuous draw, pump getting rather hot to the touch after 90 seconds of stalled rotor. Discontinued at 2 minutes and 10.7A (heat build up in windings likely caused current to drop a bit) bilge pump was at 136F, and climbing, at 2 minutes of stalled rotor.

12.70V - Locked rotor measuring inrush with 5A ATC fuse - Inrush = 10.9A - Fuse blew

You would be well served to use a DC clamp meter, or even a DVM set to 10A scale, in series, and measure the pumps actual current draw before continuing to run it off a 12V socket. As can be seen a 4A rated pump may not be a 4A draw. If it stays below 7A when pumping water it should be fine provided all contact points are clean and the male plug fits tightly.


Thanks, very interesting set of test out comes. I will buy a DC Clamp as it has been on my back burner to do list just never urgent, now your demo shows me its importance to have one on board..

However I only use the pump to start the water flowing and disconnect the pump to let the water to siphon into the tanks this way any partials in the water will not be forced through my inline hose filters and I save battery power.
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Old 29-01-2016, 17:52   #51
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Re: Faulty 12 volt power point socket Fire put out with a jar of olives in Brine

Quote:
Originally Posted by Maine Sail View Post
A fuse can malfunction and continue passing current through it even though it has technically tripped. Just because you've not seen it happen does not mean it can't or does not happen. This is why fuses & breakers have an AIC rating....

This 5A fuse continued passing current after it tripped. It took 12A for me to trip it again... When it tripped the fusible link wire fell against the other leg and continued passing current.. While this is extremely rare it can and does happen from time to time...

If you say you observed this, I suppose it can happen but I spent over twenty years as an electronic technician going from one place to another servicing electronic systems and never saw this. I probably replaced thousands of blown fuses (after determining why the fuse blew) during that period.

I would say that you have about as much chance of walking down the street and being hit by a piano being moved from an upper story window as encountering a fuse that fails yet retains continuity.

The worry here is that you will have boaters believing this is a common occurrence and passing on this "shorted fuse" theory.
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Old 29-01-2016, 18:51   #52
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Re: Faulty 12 volt power point socket Fire put out with a jar of olives in Brine

A good solid plug that cannot be connected ass about, high amp capable- Anderson plugs, not the prettiest plug ever made but very good for the application.
Even the chinese version from flea bay is reasonably good.
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