Author Topic: Current through Capacitor connected with 220VAC  (Read 11333 times)

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Offline MMDuinoTopic starter

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Current through Capacitor connected with 220VAC
« on: April 21, 2015, 06:31:14 am »
Dear All


How can i know the current output of the Capacitors connected with AC 220 V? please see attached diagram and reply if there is mistakes or there is a design better than what i attached.
 

Offline Psi

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Re: Current through Capacitor connected with 220VAC
« Reply #1 on: April 21, 2015, 06:42:46 am »
You need to calculate the reactance of the capacitor (Xc).
Basically this gets you a resistance in ohms that the cap will "appear" to be at a given frequency and capacity.

Xc = 1/ 2 * pi * f * c

so
Assuming your mains is 50hz and your 486 cap is 48uf

1/ (2x 3.14 * 50Hz * 0.000048F)

Xc = 66 ohms

220V / 66 ohms = I

So the max current though that cap is 3.33A

« Last Edit: April 21, 2015, 06:47:06 am by Psi »
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Offline PSR B1257

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Re: Current through Capacitor connected with 220VAC
« Reply #2 on: April 21, 2015, 06:46:21 am »
That circuit did not work at all.
What are you looking for?

And I'm not sure what you mean by
Quote
the current output of the Capacitors connected with AC 220 V?
There is no current output at a capacitor.
The way you have connected the diodes results in a direct current. And therefor not current is flowing at all.
In theory, there is no difference between theory and practice. But, in practice, there is.
 

Offline Psi

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Re: Current through Capacitor connected with 220VAC
« Reply #3 on: April 21, 2015, 06:48:15 am »
PSR B1257 raises a good point
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Offline Simon

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Re: Current through Capacitor connected with 220VAC
« Reply #4 on: April 21, 2015, 06:49:07 am »
you need to calculate the reactance of the capacitor (Xc).
Basically this gets you a resistance in ohms that the cap will "appear" to be at a given frequency and capacity.

Xc = 1/ 2 * pi * f * c

so
Assuming your mains is 50hz and your 486 cap is 48uf

1/ (2x 3.14 * 50Hz * 0.000048F)

Xc = 66 ohms

220V / 66 ohms = I

So the max current though that cap is 3.33A

Gee let the guy do "some" of his own homework  ;)
 

Offline MMDuinoTopic starter

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Re: Current through Capacitor connected with 220VAC
« Reply #5 on: April 21, 2015, 06:54:27 am »
Thank you very much Psi

I want to use this circuit to operate timer (by using LM339) & Relay 24V - 0.040 Amp, finally when i built this circuit and connect 2 relays, the current was not enough to switch on the 2 relays, so do you advice me to use 2 capacitors connected in parallel to increase the current?

You need to calculate the reactance of the capacitor (Xc).
Basically this gets you a resistance in ohms that the cap will "appear" to be at a given frequency and capacity.

Xc = 1/ 2 * pi * f * c

so
Assuming your mains is 50hz and your 486 cap is 48uf

1/ (2x 3.14 * 50Hz * 0.000048F)

Xc = 66 ohms

220V / 66 ohms = I

So the max current though that cap is 3.33A
 

Offline PSR B1257

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Re: Current through Capacitor connected with 220VAC
« Reply #6 on: April 21, 2015, 07:00:55 am »
Do your self a favor and and use a transformer.

What you are trying to build is obviously a http://en.wikipedia.org/wiki/Capacitive_power_supply capacitive power supply. But these supplies are only safe, if you are aware of what you are doing.
In theory, there is no difference between theory and practice. But, in practice, there is.
 

Offline Psi

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Re: Current through Capacitor connected with 220VAC
« Reply #7 on: April 21, 2015, 07:03:16 am »
As others have said, your circuit isn't correct. And the type of powersupply you're building is not for beginners. Even experienced engineers usually stay away from those things.

I also question if you cap really is 486 (48uf). 
A 48uf 220VAC cap would be the size of a large coffee cup.
« Last Edit: April 21, 2015, 07:07:04 am by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline MMDuinoTopic starter

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Re: Current through Capacitor connected with 220VAC
« Reply #8 on: April 21, 2015, 07:06:52 am »
I can't use a transformer for 2 reasons the space inside the plastic box is not enough and if use a transformer the total cost will change the idea of my project.

Do your self a favor and and use a transformer.

What you are trying to build is obviously a http://en.wikipedia.org/wiki/Capacitive_power_supply capacitive power supply. But these supplies are only safe, if you are aware of what you are doing.
 

Offline MMDuinoTopic starter

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Re: Current through Capacitor connected with 220VAC
« Reply #9 on: April 21, 2015, 07:09:09 am »
Really i'm very sorry for my mistake,,, it's not 486,,,,it's 684......it's small ceramic capacitor...

As others have said, your circuit isn't correct. And the type of powersupply you're building is not for beginners. Even experienced engineers usually stay away from those things.

I also question if you cap really is 486 (48uf). 
A 48uf 220VAC cap would be the size of a large coffee cup.
 

Offline Psi

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Re: Current through Capacitor connected with 220VAC
« Reply #10 on: April 21, 2015, 07:10:36 am »
It's unlikely you have a ceramic cap which is rated for mains.

The cap needs to be a X2 rated mains film capacitor.
« Last Edit: April 21, 2015, 07:16:04 am by Psi »
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Offline MMDuinoTopic starter

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Re: Current through Capacitor connected with 220VAC
« Reply #11 on: April 21, 2015, 07:15:27 am »
i used this one...



You cannot use a ceramic cap.
It has to be a X2 rated film capacitor 

https://www.google.co.nz/search?q=X2+film+capacitor
 

Offline Psi

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Re: Current through Capacitor connected with 220VAC
« Reply #12 on: April 21, 2015, 07:16:58 am »
That most likely is a film cap, but it's only rated from 250V DC not 220V AC which is ~315VDC.
And it's not X2 rated.
« Last Edit: April 21, 2015, 07:19:32 am by Psi »
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Offline MMDuinoTopic starter

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Re: Current through Capacitor connected with 220VAC
« Reply #13 on: April 21, 2015, 07:30:03 am »
Dear PSi

my circuit its works well with 1 relay (one trip), my idea to use same circuit (unused comparator of LM324 or LM339) with CT + Relay (my circuit it will be timer, under/overVoltage and overload protection with 220vAc 50Hz).




That most likely is a film cap, but it's only rated from 250V DC not 220V AC which is ~315VDC.
And it's not X2 rated.
 

Offline MMDuinoTopic starter

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Re: Current through Capacitor connected with 220VAC
« Reply #14 on: April 21, 2015, 08:04:39 am »
Dear PSi

My idea in future is to use PIC16F690 ;), but i'm still under beginner with microcontrollers |O |O...
 

Online Zero999

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Re: Current through Capacitor connected with 220VAC
« Reply #15 on: April 21, 2015, 08:20:48 am »
You wrote the capacitor code incorrectly on your schematic. 684 is 680nF.

It isn't unusual for capacitors designed to operate off AC to be marked with the RMS voltage rating, another possibility is it's just junk and they've undersized the parts.

Where did you get this circuit board from? It's not very good quality.

There should also be a zener diode or other kind of shunt regulator in parallel with the 1000µF capacitor, otherwise the voltage will exceed its maximum rating, causing it to explode.
 

Offline MMDuinoTopic starter

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Re: Current through Capacitor connected with 220VAC
« Reply #16 on: April 21, 2015, 08:27:51 am »
Dear Hero 999

Please read all comments ,, then you will get my point...

You wrote the capacitor code incorrectly on your schematic. 684 is 680nF.

It isn't unusual for capacitors designed to operate off AC to be marked with the RMS voltage rating, another possibility is it's just junk and they've undersized the parts.

Where did you get this circuit board from? It's not very good quality.

There should also be a zener diode or other kind of shunt regulator in parallel with the 1000µF capacitor, otherwise the voltage will exceed its maximum rating, causing it to explode.
 

Online Zero999

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Re: Current through Capacitor connected with 220VAC
« Reply #17 on: April 21, 2015, 09:03:48 am »
I did read all of your comments and you've not said anything about where you got the circuit from or a complete schematic.
 

Online Zero999

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Re: Current through Capacitor connected with 220VAC
« Reply #18 on: April 21, 2015, 09:08:56 am »
Before this guy knows what he is doing and fully understand it, let's NOT teaching him how to kill himself. A capacitive divider can easily kill if not used properly, and even used properly, inadequate loading can still results in excessive voltage, and even everything works well, you can be zapped by the residual charge.

Before knowing what you are doing, go get a xfmr is a better choice.
I agree but whether he'll listen or not is another thing.
 

Offline MMDuinoTopic starter

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Re: Current through Capacitor connected with 220VAC
« Reply #19 on: April 21, 2015, 09:10:53 am »
its not big idea Hero, it's only LM339, 4 comparators , use 1/4 - under voltage comparator, 2/4 - over voltage , 3/4 - timer, 4/4 - overload,,
but i used the Capacitor as a power source cause it's cheaper and smaller than the transformer..
thats it...

I did read all of your comments and you've not said anything about where you got the circuit from or a complete schematic.
 

Online Zero999

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Re: Current through Capacitor connected with 220VAC
« Reply #20 on: April 21, 2015, 09:17:18 am »
its not big idea Hero, it's only LM339, 4 comparators , use 1/4 - under voltage comparator, 2/4 - over voltage , 3/4 - timer, 4/4 - overload,,
but i used the Capacitor as a power source cause it's cheaper and smaller than the transformer..
thats it...
What regulates/limits the voltage across the 1000µF capacitor?
 

Offline MMDuinoTopic starter

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Re: Current through Capacitor connected with 220VAC
« Reply #21 on: April 21, 2015, 09:35:06 am »
Please see what i built...




its not big idea Hero, it's only LM339, 4 comparators , use 1/4 - under voltage comparator, 2/4 - over voltage , 3/4 - timer, 4/4 - overload,,
but i used the Capacitor as a power source cause it's cheaper and smaller than the transformer..
thats it...
What regulates/limits the voltage across the 1000µF capacitor?
 

Offline PSR B1257

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Re: Current through Capacitor connected with 220VAC
« Reply #22 on: April 21, 2015, 09:49:52 am »
Oh dear...That's a whole nother story. This circuit works since there is a resistor across the capacitor.
In theory, there is no difference between theory and practice. But, in practice, there is.
 

Offline matseng

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Re: Current through Capacitor connected with 220VAC
« Reply #23 on: April 21, 2015, 10:03:50 am »
It isn't unusual for capacitors designed to operate off AC to be marked with the RMS voltage rating, another possibility is it's just junk and they've undersized the parts.
It seems like even big brands like Panasonic are using crap parts or marginal specs.  I have replaced the 'dropping caps' for the transformerless powersupplies on the control board in 8 out of my 9 Panasonic ceiling fans. They lasted between three to four years before they gave up the ghost.  The first I replaced is soon coming up on its third birthday, so maybe they will start dying again soon. :-)
 

Online Zero999

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Re: Current through Capacitor connected with 220VAC
« Reply #24 on: April 21, 2015, 12:03:34 pm »
Please see what i built...


The 0.68uF capacitor doesn't do anything but charge up, since it has two diodes in series with it, so the current will be limited by the 560k resistor.

I suspect you've drawn the bottom diode in the wrong place.

Read the documents linked to below for information on how to properly design transformerless power supplies:
http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf
http://www.designercircuits.com/DesignNote1a.pdf
 

Offline MMDuinoTopic starter

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Re: Current through Capacitor connected with 220VAC
« Reply #25 on: April 21, 2015, 12:21:05 pm »
Thanks Hero999
It's very helpful PDFs..

Please see what i built...


The 0.68uF capacitor doesn't do anything but charge up, since it has two diodes in series with it, so the current will be limited by the 560k resistor.

I suspect you've drawn the bottom diode in the wrong place.

Read the documents linked to below for information on how to properly design transformerless power supplies:
http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf
http://www.designercircuits.com/DesignNote1a.pdf
 

Offline matseng

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Re: Current through Capacitor connected with 220VAC
« Reply #26 on: April 21, 2015, 12:53:06 pm »
Here's a nice online calculator for determining the max current and power losses in some different types of transformerless PSUs.

http://www.daycounter.com/Circuits/Transformerless-Power-Supplies/Transformerless-Power-Supplies.phtml
 

Offline MMDuinoTopic starter

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Re: Current through Capacitor connected with 220VAC
« Reply #27 on: April 21, 2015, 01:04:23 pm »
Ohh, it is very good site, :clap:
Thank you very much matseng..

Here's a nice online calculator for determining the max current and power losses in some different types of transformerless PSUs.

http://www.daycounter.com/Circuits/Transformerless-Power-Supplies/Transformerless-Power-Supplies.phtml
 

Offline macboy

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Re: Current through Capacitor connected with 220VAC
« Reply #28 on: April 21, 2015, 05:05:16 pm »
i used this one...



You cannot use a ceramic cap.
It has to be a X2 rated film capacitor 

https://www.google.co.nz/search?q=X2+film+capacitor
:palm:
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