Author Topic: LED Fluorescent replacements  (Read 3550 times)

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Offline westfwTopic starter

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LED Fluorescent replacements
« on: February 27, 2024, 09:06:06 am »
So... I've been replacing fluorescent tubes with LEDs, and I have a relatively simple question that came up as I dissect some of the tubes that have stopped working.

The tubes I have are rated 14W, contain 4 parallel chains of 28 ~3V white LEDs, and have simple electronics - a bridge rectifier, filter, and some current limiting resistors.  Presumably the bulk of the current limiting is supposed to happen in the fluorescent ballast that you're supposed to leave in.
So each LED should be running at approx 14/(28*4) = 0.125W, or about 40mA.  That seems ... very reasonable; I thought consumer LED lamps regularly overdrive the LEDs?  Am I missing something?
(the LEDs are all mounted on a thin, single-sided glass/epoxy PCB, which slides into an aluminum channel.  So while it's not very well attached, there is some heat-sinking as well.)
(At least one of the failed lamps seems to have had the failure mode of the current-limiting resistors heating up enough to de-solder themselves  (assuming I didn't break them during disassembly.) :-( )
 

Offline tom66

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Re: LED Fluorescent replacements
« Reply #1 on: February 27, 2024, 09:53:35 am »
Most LED fluros suggest removing the ballast to improve reliability.

There will be either a capacitive dropper in the lamp or, more commonly nowadays, a small switchmode power supply.  If you can't see an SMPS there, it might be a linear current regulator, though those tend to be more commonly used with long chains of LEDs to get near mains voltage.
 

Offline cosmicray

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Re: LED Fluorescent replacements
« Reply #2 on: February 27, 2024, 10:25:54 am »
You have 112 (total) LEDs. That suggests around 100mw each. Depends on the ratings on the individual devices. 2835 footprint seems very common in white LEDs used for consumer lighting.
it's only funny until someone gets hurt, then it's hilarious - R. Rabbit
 

Offline westfwTopic starter

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Re: LED Fluorescent replacements
« Reply #3 on: February 27, 2024, 10:37:20 pm »
Quote
Most LED fluros suggest removing the ballast to improve reliability.
Here (USA), there are explicitly at least three kinds of fluorescent replacements being sold:
  • Type A: designed to be used with an existing ballast.
  • Type B: designed to be directly wired to the AC supply (bypassing the ballast)
  • Type AB: can be used either way.
https://www.energyficient.com/2018/08/29/type-a-vs-type-b-led/
 


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