a little help with capacitive power supply values

[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.

[Dennis]

Steve...

Ah yes the tongue tip taste !! There is something tantalizing (addictive perhaps) about the tongue tip taste for a battery (up to 9volts DC) not so ?

And then there's something thats very off-putting like the shock delivered working older monitors and some TV's and getting a nice belt from the LOPT or finding out from the other side of the room as an apprentice with your mentor laughing at you afterwards about the fact that the chasis of one such monitor was live.
Something so different between a shock from DC and one from AC.

Many years back I heard about an incident at a nearby college where a student had used the tongue tip test on a PC PSU (when they still had live coming to the front power switch)...they lived but couldn't do anything but mutter and waffle for quite a while afterwards !

We were always taught to use things like the right hand rule and have a friend nearby (some lecturer's actually joked about it and said the friend was there to laugh at your stupidity or have them test the circuit first :-))

Dave ...
How does one learn without experimenting ?

Keep well

Kind regards

Dennis

[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

[Pic_User]

This is an interesting idea.
Transformerless Power Supply of 1A at 5Volts!
Thanks to Ioannis!
http://www.picbasic.co.uk/forum/showthread.php?t=12249
-Adam-

[Dennis]

Adam Thanks for that :-)
Saw it when it was first posted ... I don't want to use a bride rectifier or transformer and 1 amp is way more that I need :-)

All I want the pic to be able to do is act as and intelligent switch

AC IN --->> PIC >>> LOAD

Make sense ?

Kind regards

Dennis

[amgen]

the capacitor reactance (resistance for ac voltage) is
1/(2 X pi X freq X Cap(micro-farad)) ohms,

for 50MA from power supply, 220V/.050 = 4400 ohms....
the required resistance provided by cap for 50HZ at 220V.

then,
Cap= 1/(314 X 4400) equal aprox .7 micro-farad cap (>250 VAC rated)
works out to about .15 micro-farad per 10MA.
See attached diag.