LED lamp

I destroyed an LED lamp so I removed the bottom part of it. It's this lamp -> http://www.waz.com.br/lampada-led-7-5w-e27-branca-806-lumens-6-500k-bivolt-philips-25-000h-114293.html?gclid=CjwKEAjw_6XIBRCisIGIrJeQ93oSJAA2cNtMMLnyljXdWMyNYFvnfywAYKBz9AVSuT7FVKA8sG-1gBoCZ5Hw_wcB

The bottom part of the LED lamp is this picture I taken -> https://goo.gl/photos/79y5uwPTDG2divgA6

So I connected this to a wall socket (220v) and measured the CC (not AC) voltage across those 2 wires that you can see in the picture I taken. It's freaking 127v! I was lucky that I didnt touch those wires cause I thought they would be something close to 12v.

So what is going on? This bottom part was connected to 16 small leds (surface mount LED), how are those 16 leds being powered by such enormeuous voltage? If every led forward voltage was 3 (which is pretty high), the 16 LEDs (in series) would consume at most 50 v. Did I measured this right?

batata004:
So I connected this to a wall socket (220v) and measured the CC (not AC) voltage across those 2 wires that you can see in the picture I taken. It's freaking 127v!

I think when you destroyed the LED, you first destroyed the power electronics that regulated the voltage to the LED. I'd say the whole unit has been fried - can't just replace the LED.

batata004:
If every led forward voltage was 3 (which is pretty high), the 16 LEDs (in series) would consume at most 50 v. Did I measured this right?

Did you measure the diode forward voltage for each diode BEFORE you fried them? Usually the forward drop is 0.6-0.7 volts, not 3 volts.

batata004:
how are those 16 leds being powered by such enormeuous voltage?

LEDs are current controlled, not voltage controlled.

Power_Broker:
Did you measure the diode forward voltage for each diode BEFORE you fried them? Usually the forward drop is 0.6-0.7 volts, not 3 volts.

Whatt?! A white led indeed drops around 3V, not 0,6V...

But indeed, leds are current controlled. And that's probably what the driver does as well. So if there is no load connected the voltage will go up.

And even if the voltage wasn't that high it's still a very bad idea to touch it... Those drivers are not isolated from mains. So although the voltage between the wires isn't high, referenced to earth that can be the full 230V...

Are those the 6-pin SMD LEDs? the ones with three elements in each? Maybe they put them all in series...

3v * 3 elements * 16 LEDs = 144v - if the per-element voltage was a little lower, that'd be just about right.

Or it's a low current, unregulated supply that relies on the output being under load to get any voltage close to normal operating current.

I see a transformer, so it's an SMPS - I suspect it is actually isolated from mains, or is supposed to be.

Hi my friends,

This is the LED part (that I removed): https://goo.gl/photos/qcrXpxVebXHBES9EA

In the lamp those 2 wires (that I show you in the first thread) were connected to the 2 spots in the middle of this little LED board SO I assuem all the LEDs were in series, no parallel.

At first I just wanted to run this LEDs from 12v so I connected 2 pairs of 3 leds in series and 2 pairs of 4 leds in series and after that I connected the 4 sets of leds in parallel to 12v. I know this is not recommended and I should burn all the LEDs if one of them (in the 3 leds series) burn, but HEY IT WORKS!

So do you still think it's normal my bottom part of the LED produce 127v CC? Or I damaged the board when removing the leds?

Quite possible that it's normal. If you care enough, put a resistor across it (500-1000 ohms, preferably a large (high wattage) one), fire it up, and (carefully) measure the voltage across the resistor.

I will do that! So you assume the voltage will drop quickly after I start using the LEDs? Just a question, do you think CC would cause any harm at 120v?

To you, if you touched the wires when it wasn't under load? Ya, probably would. Don't do that. I wouldn't touch it at all without verifying that it was isolated, and verifying that the voltage it was putting out was low enough to not hurt.

Thanks man for your suggestion, I will treat this with the most care!

Just one final question: is ther a way to know for sure that:

  1. the current is indeed CC and not AC in those 2 wires? I used CC in my multimeter to measure the voltage but I think it would still produce some reading if it was AC right?

  2. the circuit is "isolated" from the AC 220v wall supply? How do I verify this? Visual inspetion?

Do you mean DC when you say CC?

  1. Yes, the voltage is DC although it might have considerable ripple which will measure as a AC (component).

And like I said, the supply is probably a constant current source. Because you need to drive leds with current, not voltage. So without leds the voltage might be very different.

  1. Yeah, by figuring out the cir circuit. But I wouldn't count on it being isolated. Isolating it is more expensive and normally you can't touch it so why should a manufacturer do it?

Sorry, really sorry. I meatn DC you are correct.

I agree with you that LEDs are driver mostly by DC and the output of my 2 wires should be DC. BUT is there a way I can test it to make sure it's indeed DC? Cause I may have damaged the buld and for some reason it may be outputing AC and if it's the case I will thorw this away cause I dont wanna get killed.

I thought that to check isolation I could use a multmeter or something else, but I will assume it's not isolated and treat it with respect. :slight_smile:

How sure do you want to be? Really sure, take a scope. Reasonable sure, get a true RMS DMM. Kind of sure, use a random DMM.

And the getting killed part has nothing to do with DC or AC :wink:

You can check with a DMM if it's not-isolated. But because the output will go through components (which might switch but do not isolate) not measuring continuity doesn't mean isolation for sure. Just put the DMM and measure between input and output in BOTH polarity. So 8 checks in total. If you see any resistance lower then let's say 1M there is no isolation.

I have none of those equipments you said :frowning: Ayway I tahnk you so much for being kind to help me, I learned a lot and will take care when playing with this "harmless looking" lamp.

batata004:
I have none of those equipments you said :frowning: Ayway I tahnk you so much for being kind to help me, I learned a lot and will take care when playing with this “harmless looking” lamp.

It’s cheap chinese crap that’s connected to mains and is designed in a way where the case would need to be removed in order to access the internals. That doesn’t look harmless to me…

Anywhere there’s mains electricity, you’ve gotta take a lot more care.

And - I thought you said you had a DMM - what were you using to measure the voltage with otherwise?