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Just over a year ago, I purchased a 25 pack of direct replacement LED's from a well-known seller of these bulbs who attends York regularly. They were replacements for the 1445 bayonet bulb and are rated for 18 volts. The problem is that 16 out of 25 bulbs have now failed in just over a year.

I decided to open one up and see what's inside.  There are 3 components: bayonet base, 8mm "straw-hat" type LED, and a 300 Ohm resistor.

What's making these bulbs fail? They are installed in lamp posts running at a steady 10 VAC using a postwar ZW.  Is it just my bad-luck?  Is it a defective lot of bulbs? Is there an inherent problem such as reverse-voltage breakdown, overheating on pulsed AC, or an incorrectly sized resistor?

Has anyone else had similar experiences with direct replacement LED's?

IMG_8049IMG_80508MM LED

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@Ron045 posted:

You could make your own.  I re-did my bayonet bulbs with Christmas lights and they are still running bright since 2016.  Some might also suggest a diode when using AC.

https://ogrforum.ogaugerr.com/...or-lionel-260-bumper

Have Fun.

Ron

Thanks for the good advice, Ron. I love recycling LEDs' also. I recently did an ERR upgrade on a loco using LED's scavenged from one of Harbor Freight Tools free flashlights. Although I enjoy doing LED upgrades on some accessories to improve performance, I just don't have an interest in custom building 50 of these bayonets from scratch. I suppose I could crawl under the layout and insert some diodes in-line at various locations, but it may be easier to pop in the old incandescents bulbs again.

@shorling posted:

I would suggest contacting the vendor and recant your experience.  They have been most helpful with any of their product issues I have encountered.

When the bulbs first arrived, 4 were dead right out of the box. The vendor was very helpful and sent replacements right away. They have always been good to work with. But with  these bulbs dying off like flies, I don't want to make an ongoing nuisance of myself by asking them for more and more free replacements. Ultimately, choosing to go in a different direction may be appropriate. 

I'd try adding a general purpose rectifying diode ("normal") (1/2 wave/pulsed dc) or a bridge rectifier (dc).  LED are dc devices only. Any AC LED is rectified internally or has more resistance to ACs negative wave, it still functions on DC internally.Some LED can handle a certain amount of ac, but dc is easier on them in general.

  Over voltage will burn an LED near instantly too.  A surge can wipe them out. 

Plus with future replacement, you can use a wider variety of LED on 1/2 wave or dc.  Incandescents can still be used if a diode is on the circuit.

 Voltage will drop by about 0.75v after the diode..no big deal really. (diode amps have to exceed the total amp draw of bulb(s)/LEDs. Voltage rates should be higher too (much higher= safer from surges... say 35v or more)  Làrger amp diodes stay cooler as well. (A Brdge Rectifier is just 4 diodes in one package, already arranged to make dc from ac).   

  Price them all in small bulk from an electronic supplier & you may save quite a bit.

I like incandescent's look best, but it is hard to argue with the life and low draw of LED done right.

ANY car should be able to have LEDs added. Very few conditions would rule it out.

@GregR posted:

...

I decided to open one up and see what's inside.  There are 3 components: bayonet base, 8mm "straw-hat" type LED, and a 300 Ohm resistor.

What's making these bulbs fail? They are installed in lamp posts running at a steady 10 VAC using a postwar ZW.  Is it just my bad-luck?  Is it a defective lot of bulbs? Is there an inherent problem such as reverse-voltage breakdown, overheating on pulsed AC, or an incorrectly sized resistor?

That you identified the resistor as being 300 Ohms tells me you probably have a meter?  Your photo suggests the resistor is in good shape (not charred/toasted) but a simple meter test will confirm that.

I'd say the failure is because they did NOT install a 1-cent diode to protect the LED from reverse-voltage breakdown from applied AC voltage.

In this recent OGR post regarding a wedge-style plug-and-play LED replacement for an incandescent, they include the diode.  I'd contact the manufacturer and refer them to this thread!  In bulk the diode will cost them less than a penny.

Separately, and I realize you're running at "only" 10V AC, but a 300 Ohm resistor is suspicious.  Your photo shows a 1/2 Watt LED.  Let's say it's operated at half of that since it's AC...so 1/4 Watt.  The math is a little more involved with AC operation but if operating at its rated 18V and dropping that down to ~3V as per a typical white LED...that means the resistor is absorbing several times the power of the LED and that looks like only a 1/4W resistor.

I did have a couple of issues with the subject direct replacements.  I had incandescent lamp posts powered by 14 VAC through a dimmer.  I changed to direct replacement LEDs and some of the LEDs didn’t work because I didn’t pay attention to lamp post wiring polarity since it was AC.  The dimmer output was chopped and basically DC.  But it looked like I had bad bulbs at the start.

I also had what looked like shorted direct replacement LEDs.  Turned out it was the lamp post socket.  On some sockets the center contact was slightly off center.   The direct replacement LED base created a short with the offset socket contact.  No bad LEDs here either just bad lamp post sockets.

 

 

 

@stan2004 posted:

That you identified the resistor as being 300 Ohms tells me you probably have a meter?  Your photo suggests the resistor is in good shape (not charred/toasted) but a simple meter test will confirm that.

I'd say the failure is because they did NOT install a 1-cent diode to protect the LED from reverse-voltage breakdown from applied AC voltage.

In this recent OGR post regarding a wedge-style plug-and-play LED replacement for an incandescent, they include the diode.  I'd contact the manufacturer and refer them to this thread!  In bulk the diode will cost them less than a penny.

Separately, and I realize you're running at "only" 10V AC, but a 300 Ohm resistor is suspicious.  Your photo shows a 1/2 Watt LED.  Let's say it's operated at half of that since it's AC...so 1/4 Watt.  The math is a little more involved with AC operation but if operating at its rated 18V and dropping that down to ~3V as per a typical white LED...that means the resistor is absorbing several times the power of the LED and that looks like only a 1/4W resistor.

Yes, I did meter test to confirm the resistor value (which matched the banding). I also suspected the resistor was undersized. The whole bulb casing may well be acting as a heat sink. As you and others have suggested, I think reverse-voltage breakdown is the culprit.

I have a sleeve full of 1.0A diodes. I just crimped one onto the end of the wire that powers the light in my 445 switch tower. It was easy enough and I just trimmed and inserted the end of the diode into the spring clip.

Now for my string of Lionel No. 70 lamp posts: Will a 1.0A diode be good for a string of 3 LED bulbs, or would each lamp require a 1.0A diode? I'm the wrong kind of engineer for making these calculations.

IMG_8052

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Last edited by GregR
@shorling posted:

The vendor must have sold tens of thousands of these direct replacements.  If there was a fundamental design issue I suspect they would have been out of business a long time ago.  My issues in my previous post were all application related.

Just because they've sold thousands doesn't mean there isn't a basic design flaw.   Lots of products have major flaws, yet massive quantities of them are shipped before the flaws surface.

The diode is a basic precaution running LED's on AC voltage, the reverse voltage rating of most LED's is around 5V peak.  A 10 VAC source has a peak reverse voltage of 14 volts to the LED, almost three times it's rating.

Once again, though you should expect it, Stan is spot on with his analysis, they needed the diode.

@GregR posted:
Will a 1.0A diode be good for a string of 3 LED bulbs, or would each lamp require a 1.0A diode? I'm the wrong kind of engineer for making these calculations.

Yep, unless these are REALLY high power diodes, the 1A diode is plenty.

conundrum1

By happenstance, GregR photographed what appears to be some kind of marking on the outside of the bayonet that might indeed be at the same point where a few seconds of huge-heat is applied to the exterior wall. 

However your answer is incomplete.    To earn a gold star, you must articulate whether they apply (1) a blob of solder to the end of the LED lead, or (2) a blob of solder to the inner wall of the bayonet, or (3) both 1 and 2...  before final assembly.  Or identify some other method.  I'm nominating GregR to be the arbiter.   To be clear, I do not know the answer!

I guess my point is if they indeed go thru such machinations to install a resistor-LED combo, it would be only a minor incremental effort to add the 1-cent diode.  A 64% failure rate (16 out of 25) after 1-year is no way to run a railroad...

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