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Rechargeable 30 LED burns up on AC

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5arid

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Hi
I have some emergency rechargeable light :
201n67ut0gmx78b3teb6.jpg

As soon as I connect them to AC outlet 220v they burn up!

I opened one of them and saw that 2 resistors are black :
f00y0za5fmnboqtfc5gs.jpg


I drew its schematic :
7qih7dnlzisfxzscj8tj.png

Also it has a 3 state switch : Low / Off / Hi

Can anyone find out if the circuit is faulty?
Thanks in advance.
 
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That's an extremely dangerous design and there is a significant risk of electric shock if the pins on the power socket are touched, even with the AC switched off. Under no circumstances touch anything else while working on it as there is no power isolation.

The burned resistors should normally run cold so it indicates the voltage to the circuit must have risen far higher than normal. The only component that can do that is C1 so I suggest you replace it. You must use the same value and it should be rated for use at 220V AC, preferably class 'X2' for safety. Do not be tempted to use a DC rated capacitor !

Brian.
 
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    5arid

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a dangerous circuit to workwith and repair.

one is , check and replace C1(2u2) with AC and class rating.

the battery must be checked.
if battery is not connected and checked for defect , you will see the smoke.
 
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    5arid

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I tested at least 5 of these devices, all of them have the same problem.
I disconnect the battery and 30 LED array and then connect the device to AC, the same thing happened.
I think the problem is cause by the very cheap design of the circuit!
I know nothing about analog circuit, but there are some things which seem odd to me :
What is the usage of R1?! two pins of it are connected to each other directly!
The direction of G2 doesn't match the silkcreen print on the PCB.

Also I found a similar circuit here : https://www.circuitstoday.com/automatic-led-emergency-light
But still I need some more help to repair this device.
Thanks again
 

I disconnect the battery and 30 LED array and then connect the device to AC, the same thing happened.
Click to expand...
Yes, if the battery is disconnected, the full capacitor current (about 150 mA) will run through R3 and R5 and burn it. Other components may be damaged, too. I guess, it's mentioned in the operation instructions (at least it should).

There isn't any means to prevent battery overcharging and early end of life. Trash to trash.
 
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    5arid

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I found this : 5V transformer less power supply

according to this schematic :



There must be a diode zener, and without it the DC voltage will be too much high!
In my PCB D6 is missing, maybe adding it solve the problem?!
But what value should I use for it?
How much DC is needed to charge the 4v lead acid battery?
 
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I have to admit that due to the unusual way you arranged the components in the drawing on post #1, it became not too easy to clearly check the current flowing from mains to the LED, but in any case I would recommend thinking about implementing a soft-start before the LED by a RC net, as this component has an intrinsic inability to absorb spikes of energy if compared to other types of "lamps", therefore burning immediately.
 

Is it better now :



Why C2 is the wrong way around?
What are those two transistors doing?
 

The revised schematic still looks wrong to me. I would guess R1 is supposed to be across C1 and the switch is supposed to be in series with the feed to the battery rather than the LEDS. Regardless, the design is bad and dangerous. As pointed out, the voltage across the battery is almost entirely dependant on the current through it. Removing the battery will make the voltage rise to about 300V.

You could protect the circuit (but not yourself) by adding a Zener diode across the battery connections, maybe a 6.8V type, rated at 5W should do it.

Brian.
 

It is not revised! It is the same schematic as the first post, I just tried to make it easy to understand!
Please someone explain about the transistors.
Why isn't LED array connected to GND?
 

So, this is really a crap for sure, no surprise that it doesn't work!
But please explain me about the transistors, what are they suppose to do?
 

In other emergency lighting, they are used to enable the LEDs when the AC mains fails.
But the way they are connected in the schematic, they don't work.

I agree with the others, a poor and dangerous circuit design.
 

How about the transistors in this schematic :


I guess T2 is for switching between AC and battery to supply the LED Array, right?
 

5arid said:
I guess T2 is for switching between AC and battery to supply the LED Array, right?
Click to expand...

Exactly, once AC mains drop down, T2 start conducting the current from battery across the LED array.
 

What about the T1?
 

T1 is a rudimentary overcharge prevention circuit.

It is not very accurate, but it would work.
 

The circuit drawing in #5 is clearly wrong. 30 LEDs in parallel will take about 2A (each LED slightly less than 100 mA) and the current has no return path to ground (except via the base capacitors). I wonder how these two transistors are biased for operation. You need to trace out the diagram carefully with some attention paid to the legs of the two transistors.
 

The circuit is very simple, and has common components available on most libraries of free tools.
A functional simulation can help to suggest all the necessary corrections.
 
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