Half Blown Fuse?

[BurbMan]

Boy this was weird. Was fooling with my LED lights in the fixture over the dinette, they had unstuck from the fixture base and were laying in the lenses (dual light). I guess I didn't realize how hot these had gotten, it's been raining and I've had these on all day. At any rate the insulation on the wiring going to the bulb chip is soft, the wires cross and short out as I fiddle with the bulb chip. I figured I blew the fuse, but the PD 12v center has the LEDs that light when a fuse goes, and they were all still off.

The LEDs in that fixture still work but they are very dim. Same with two of the other LED fixtures on that circuit. No blown fuse but very dim. One other LED fixture is still on at full brightness but I figure it's on a different circuit.

I turn on the fixture over the couch that still has incandescent wedge bulbs and it doesn't light, but now I see an LED light on in the load center.

When I pull the fuse and that last LED fixture that was on at full brightness goes out!! WTH?? Install a new fuse and all is back to normal. So it looks like fuse "blew" but was hanging on by enough of a thread to let a small amount of current pass...

I have never seen a fuse not blow all the way out...anybody else?

[dan-nickie]

My guess is there is something in that LED array that is causing the issue.
Like a short.
I would replace that LED to make sure it does not give trouble in the future.

[tvman44]

Just the low current draw of the LED fixtures. 🙂

[ledcomp]

I think it has to do with the LED in the PD. That LED is wired across the fuse. When the fuse is good there is a very minimal drop across it and not enough to turn it on. When the fuse blows the LED will see battery voltage on one side, it will see ground through the load. Because it is now wired in series with a very small load (the LED) the LED lights and LED indicator in the fuse box see 12 volts divided by the 2 lights. Replace the fuse, it is blown.

[BurbMan]

I think that's right...thanks for clarifying!

[vermilye]

Chris Bryant wrote:
I would suspect the fuse holder, rather than the fuse itself.

2X. When you replaced the fuse the scraping of the connection probably cleaned up some corrosion, making a good connection. LEDs draw so little current that you may have had dim fixtures due to the current the load center blown fuse indicator passes.

[Roadpilot]

A fuse doesn't half blow. But an AC rated fuse when used in a DC application can malfunction because when the link burns the residue ends up on the glass and can arc internally. Higher voltage DC rated fuses use a polymer that melts with the link and quenches an potential internal arcing. Automotive fuse won't arc after they blow because the voltage is too low.

[Chris_Bryant]

I would suspect the fuse holder, rather than the fuse itself.

[BurbMan]

Interesting....no voltage ratings on these fuses, just "15A" from the auto parts store. These are the mini blade fuses.

[WRBARTZ]

Yes. Absolutely. If you use a 250 volt fuse in a 12 volt circuit it will not blow (separate) the element far enough.