Transformerless Power Supply from a Rechargeble Torch

Pavi98

Member
Hello,
I have a small rechargeble torch and when I tried to recharge it (from 230V), its smoothing capacitor was blown. As the capacitor was blown I couldn't read the exact value and voltage of the capacitor (C2). I replaced it with a 220uF 50V new capacitor and after few minitues, it also damaged again. But this time, I removed the output of the ccircuit (the 4V rechargeble battery) before powering the circuit. Is that the reason to damage the capacitor?

Thank you
 
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Pavi98 said:
Can you please explain this more? If the battery is not recharging properly, can it be a reason to explode the capacitor?
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The ONLY thing stopping the capacitor exploding is the battery - it limits the voltage across the capacitor to the charging voltage of the battery. If the battery is faulty, and not drawing any current, or the battery is disconnected, then the capacitor will explode.
 
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Pavi98 said:
Can you please explain this more? If the battery is not recharging properly, can it be a reason to explode the capacitor?
Click to expand...
Yes, because it is a lead-acid battery, if it breaks down, the current will not be loaded, and the power supply of the transformerless will cause the necessary voltage drop for the current it loads.
 
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As drawn, there is no limit on the output voltage, without a battery. C2 will explode.
I question the placement of the LED.
I added a Zener diode to limit the voltage. Mayve 6.3V or even 12V, something!
Did you design this circuit?
Do you want the LED to come on when the battery is charged, or do you want to see the charging current in the LED?
It could be that the LED+resistor works like the Zener to limit the voltage, but the LED is in the wrong place.


The charger will work just fine without C2. (assuming there is something to limit the voltage) Some battery chargers do 120 (or 100) pulses/second charging. Pulse charging is just fine.
 
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Pavi98 said:
Thank you. Now I understood this. But what will happen in a situation when the battery is fully charged and not drawing any current? Will it cause the capacitor to explode?
Click to expand...
It will always draw current, there's no mechanism to stop it charging - it's a really crude and nasty charger.
 
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The LED should turn ON when the power is supplied. The output voltage will be maintained constant, lower level as long as the battery is connected as I learned. Therefore, a zener diode will not be needed. Is that correct?
 
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If the first 400V capacitor is really 2.5uF then you are charging at 150mA? What charging current do you want?
edited: wrong numbers. Corrected, I hope.
 
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Pavi98 said:
The LED should turn ON when the power is supplied. The output voltage will be maintained constant, lower level as long as the battery is connected as I learned. Therefore, a zener diode will not be needed. Is that correct?
Click to expand...
If you remove the battery the voltage goes to 200V. (no battery, no Zener)
 
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I have a simulation running of your circuit. If the battery voltage is in the 0 to 12V range the current is a constant 150mA. If your battery can withstand that there is no problem. Small batteries and some types are not happy to be over charged. You may need to add a timer to cutoff after some time. Or add a voltage, over charge detector.

Note the current changes with frequency, 50hz or 60hz and the current changes with line voltage.
 
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