a little help with capacitive power supply values

[Dennis]

Hi all

I would like to incorporate a transformer-less capacitive power supply in the project I am busy with.
I found this app note on the microchip site
[HTML]http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf[/HTML]

What's confusing me is deriving the values for a 220V 50Hz supply.

I can't seem to fugure out where the values for R1 and C1 are initially derived...are the just assumed and we calculate the rest from there?

Also hat is not clear is the WATTAGE for R2 1M in figure 10 nor for VR1 or the MOV.

I hope someone can offer some help here

Kind regards
Dennis

[Pic_User]

Hi all

I would like to incorporate a transformer-less capacitive power supply in the project I am busy with.
I found this app note on the microchip site
[HTML]http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf[/HTML]

What's confusing me is deriving the values for a 220V 50Hz supply.

I can't seem to fugure out where the values for R1 and C1 are initially derived...are the just assumed and we calculate the rest from there?

Also hat is not clear is the WATTAGE for R2 1M in figure 10 nor for VR1 or the MOV.

I hope someone can offer some help here

Kind regards
Dennis

Hi Dennis,

Transformerless Power Supplies are extremely dangerous and discussed in many threads.
http://www.picbasic.co.uk/forum/showthread.php?t=3265
http://www.picbasic.co.uk/forum/showthread.php?t=3898

Most here would advise against them.
-Adam-

[Dennis]

Hi Adam

Thanks for the advice and heads-up !.. I promise to wear rubber gloves and have lots of back-up components for the smoked ones and will keep a fire-extinguisher handy.

It's gotta be more fun that flying a kite in the rain with a key attached to the string and waiting for the odd lightening bolt though :-)

Kind regards
Dennis

PS .. Adam ...what interesting posts !
thanks for pointing them out to me ...and I too was confused by the App Note author's use of ground and circuit ground ..especially regarding the 3-wire system.

What I would like to accomplish is a PIR/LDR controlled security light switch using a PIC , the PIC ciruit is powered from the mains and on 'sensing ' movement or light supplies mains to the light.
Something like this

MAINS ------------|PIC circuit| ----|LOAD
| PIC port
|
Live |__________-----_________|LOAD
Neutral |_______________________|LOAD

[Pic_User]

Something like this? LOL
http://www.picbasic.co.uk/forum/show...0&postcount=33

[Dennis]

That's pricless :-)
Fell really sorry for the goldfish though ! Although I'm not sure if it's the first shock ... smelly feet or the second shock .. the high voltage :-) Well I guess they could always recover from the first :-)

Wish me luck :-)

Kind regards
Dennis

[Byte_Butcher]

You laugh....

Back in the day when electricians were REAL men (and human life was cheaper than a voltmeter...) THIS is how it was done...

http://www.weirdstuffwemake.com/swee...ages/aeh66.jpg




steve

[mackrackit]

DO NOT TRY IT !!!

Life is to short the way it is...

Buy a transformer.

[dhouston]

...and I too was confused by the App Note author's use of ground and circuit ground ..especially regarding the 3-wire system.

What's the potential of the neutral line when it's tied to earth ground?

X-10 has used capacitive power supplies in nearly all of its billions of 120V and 230V modules for 40+ years without frying too many of its customers. You can check Ido Bartana's website for 120V to 230V conversions to get values for R & C.

• http://www.idobartana.com/hakb/

If you read the Microchip app note carefully, you will find that it explains how to size R1 and C1.

Or you can Google using transformerless power supply or capacitive power supply and find suggested circuits for both 120V/60Hz and 230V/50Hz.

If the very limited current capacity is insufficient, there was a recent thread showing a design capable of 1A.

[Melanie]

> What's the potential of the neutral line when it's tied to earth ground?

Actually it can be several volts.

Consider a few kW load at the end of the wire (very easy if you consider the kind of loads encountered in a building). The wire has a Resistance depending on it's material and cross-section and length.

If you connect your DVM between the Neutral Line and Earth at your wall socket with no load on that circuit (remembering it could be connected to several outlets), then you probably will get no voltage, but as soon as you start to switch on appliances you will begin to register a voltage. Now load up with a few kW (say an electric room heater) and report back with what you find...

[Dennis]

Hi guys

Dave .. thanks a million for the extra info :-) , it is the appnote which is confusing me .. The values for R1 and C1 seem to arrive out of nowhere, unless I'm reading it wrong ?

Melanie .. thanks for the extra info too !
There ain't now way I'm gonna be measuring much after I've done the right calculations especially not when under a real load :-) ....or should I .. have you ? Have you taken pics? Video ?
And as for switch on , I will do it using a push-button and a broomstick ;-)

Kind regards

Dennis