Powering LED from mains power - 240 V rms using series capacitor

133

02:12:14

Using reactance of capacitor to drop the excess voltage. Because the voltage and current are out of phase ( 90° in theory ) there is very little heat generated in the capacitor.
The reactance is ( 2 x pi x F x C ) ^ ( -1 ) works out about 9K7 @ 50 Hz.

published 6 years ago

salo909

6 years ago

Hey what kind of battery or cell can be added to this to tie it to a grid of a house? If possible.

salo909

6 years ago

Is it able to scale up to bigger wattege?

gasboss775

6 years ago

salo909 : About your 1st question, do you mean as a battery charger? Might be ok for trickle charging NiCad cells at 80mA, probably not ideal for any other type of battery.

gasboss775

6 years ago

About question 2, in theory yes but you would need to use increasingly large ( and expensive compared with a transformer ) The sort of capacitors used as motor starters if you could salvage one might allow for a few watts of power to be obtained this way. The danger with this type of circuit is there's no isolation from the mains, which trends to limit its safe usefulness.

hurz

6 years ago

@gasboss775, use the formulas (which are absolut correct) and you get 188nF @50Hz as value for 20mA peak current. So why do you have here 330nF which is almost double as needed?

hurz

6 years ago

240VAC is 340Vpeak, right. (340Vp-2×diodeThreshold)/0.02A= 16.9kOhm -> 1/(2pi×f×Xc)= 188nF!

gasboss775

6 years ago

I was using the RMS figures, but I suspect the truth lies somewhere in between due to the power factor.

hurz

6 years ago

First, 188nF × 1.414 = 266nF still below 330nF. Second, LEDs do not average the power, they do not have a time constant. Filament bulbs does have. Driving LEDs so slow (milliseconds range) over max rated current does reduce its livetime drastic.

gasboss775

6 years ago

Cool man, I would never use this circuit in reality anyway.

hurz

6 years ago

Another hint to your description, a cap does not heat up, cuz it doesn't have a resistance. Its not because of 90° phase shift, this does not matter. Even a cap parallel to a voltage source and zero degree phase shift wont heatup.

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