LED bulb shorted, destroying transformer


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Old 05-01-16, 10:09 PM
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LED bulb shorted, destroying transformer

Friday, I returned from using the restroom to discover a horrible burnt smell and the three bulbs in the 12V light fixture had stopped lighting.

Investigation showed me that one of the LED bulbs was giving off the stink, and my meter showed that the transformer for the lamps was burned out.

Measuring the stinky LED showed almost a dead short between the two pins.

The LED bulbs were replacements for the halogen bulbs that were originally there.

I got a replacement fixture, but how do I keep it from happening again?

Why do they make LED bulbs that short when they fail?
 
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Old 05-02-16, 12:08 AM
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Why do they make LED bulbs that short when they fail?
Are you implying that they actually make the bulb to cause a short when it fails ?

There is a power supply inside the LED. It failed. It happens.
They could put a fuse inside but that would increase the price of the bulb.

You could put a fuse on each LED to eliminate the problem.
 
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Old 05-02-16, 01:53 AM
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I am thinking more that they don't care what happens to the fixture when the bulb fails.

An incandescent bulb usually opens when it fails,

But many LED bulbs have a bridge rectifier as the first thing in the circuit. Those usually fail by shorting, and they should know that.

A lamp that destroys the fixture when it fails is not a direct replacement.

The 120 volt lamps do have to have a fuse element to prevent a fire. Why are the 12 volt lamps exempt?
 
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Old 05-02-16, 04:45 AM
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What are the electrical requirements of these "replacement" bulbs?
Most need 12 volts DC and as I learned the hard way some automotive ones require full wave DC or they will burn out as yours did.

What do you have for a power supply?
 
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Old 05-02-16, 07:18 AM
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(off topic) Incandescent lamps can fail with a short. Once in awhile the bulb comes unglued from the base and the wires down there twist and short as the lamp is screwed into the socket.
 
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Old 05-02-16, 10:12 PM
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The bulb is an MR16 high intensity bipin lamp intended for a high-intensity desk lamp, overhead projector, or low voltage track lighting. It was sold for the purpose I used it for. The package says 12 V 60 Hz dimmable.

These desk lamps have a 12 V AC transformer built into the base. My fixture has no dimmer - just the transformer.

And like I said, it worked for over a year and a half before it failed. But it didn't last for the 200000 hours 5he package claimed. There was an electrical storm at the time the lamp failed, but I have a whole-building surge protector installed in the electric meter socket by the power company.

An incandescent lamp also fails with a high current short if the filament is not supported at multiple points. But this short, while it can take out a dimmer, usually does not last long enough to damage a transformer.

A bipin lamp does not have a glued-on base.
 
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Old 05-03-16, 05:41 AM
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Why do they make LED bulbs that short when they fail?
I think it's the nature of the technology.........LED conversion bulbs are similar to self-ballasted CFL bulbs.
My workplace had replaced at least 100 incandescent bulbs with CFLs and there have been a couple that almost caught fire when they failed.
I converted several 1156 style automotive type incandescent fixtures in my RV with offshore LED bulbs.
Did the conversion and went in the house for a coffee and when I returned three bulbs were smoking and the fixtures were ruined.
Although there were no specific usage instructions with the LED bulbs it turns out that the 12 volt DC circuit for the lighting was unfiltered, dirty DC power.
I replaced the fixtures and ordered new bulbs and reconnected the lighting circuit to a filtered DC line and the bulbs have been working fine for a year.

I got a replacement fixture, but how do I keep it from happening again?
You might want to forget about the conversion bulbs and get a fixture that is made for LED lamps.
 
 

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