EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: aargee on December 24, 2012, 01:55:40 am
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I've got some RGB Christmas lights. These are bauble types with each LED cycling through RGB. The lights are powered by 24V AC through a transformer.
The lights have suffered some corrosion, but on dismantling them to do a bit of fixing (because they are aesthetically pleasing to SWMBO), I've found a 4.7uF/50V polarised electrolytic cap stuck across the incoming 24VAC (yes it is AC). The LEDS are constructed in a few series strings then in parallel with the AC (and cap). What function would this capacitor have? Is it there for when the LEDs are all conducting as some sort of filtering?
I know the Chinese manufacturers wouldn't throw a cap in there if they could get away with it.
- Rob.
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Are you basing the 24V AC on the fact they come with a 24V AC transformer?
Check the wire between the transformer and the first light. It's very common to have a diode bridge contained in a small lump in that section.
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I'll have a look tonight when I get home but I'm pretty sure there are no other components apart from the LEDs and capacitor.
Such a suitable task for Christmas eve :)
- Rob.
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Yeah.
Either it's got a diode/diodes somewhere or it was intended to be run on DC.
It's pretty common for china to ship stuff that's wired wrong.
As long as it actually works they don't care about much else.
They probably ran out of DC powerpacks.
So after plugged in an AC one and seeing the lights work they started shipping them that way.
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Yes, you were right. There are two diodes built into the connector, the cap is near the first LED. So it's half wave rectified DC, no wonder corrosion was such a problem.
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Yeah.
Either it's got a diode/diodes somewhere or it was intended to be run on DC.
It's pretty common for china to ship stuff that's wired wrong.
As long as it actually works they don't care about much else.
They probably ran out of DC powerpacks.
So after plugged in an AC one and seeing the lights work they started shipping them that way.
...and sometimes they don't even check that they'll work safely for any length of time. (http://www.howtospotapsychopath.com/2012/04/06/catches-fire-would-buy-again-aaa/)