a little help with capacitive power supply values

[Dennis]

Tales from the crypt indeed !

So who ended up shocked and who ended up de-lighted ?

And to create a shift in the TIME-SPACE CONTINUUM .......

You could try wiring LIVE and NEUTRAL across a single pole double throw switch making sure you have the correct current rating , place the project box on the floor making sure your friend is leaning over the box monitoring the power LED (Make sure the top lid of the box is removeable - all securing screws removed) THEN plug your procjet in with the wall switch in the OFF position and THEN ....using a broomstick and jokingly tell your friend it's for safety sake and THEN...from a distance flip the switch to the ON position.
RESULT :
1 X very surprised friend
1 X totally blackened pc board
1 X extremely well toasted and burned out SPDT switch (all ratings ignored) :-)

ISOLATION ISOLATION ISOLATION !

Now try to maintain proper stabilization of this channel without creating a situation of over-modulation

Steve, Adam .. are you guys kinda volunteering yourselves to be PSU testers for this one ??
Could we get captures for each stage of testing ? one cam on you and one on the circuit ?
....and the scene begins with a skull and cross-bones with a caption saying something like DON'T DO THIS AT HOME ?

Kind regards
Dennis

[Byte_Butcher]

Steve, Adam .. are you guys kinda volunteering yourselves to be PSU testers for this one ??

Me? Sure, I'll test it. I'm not afraid. I've got an isolation transformer and know how to use it.

I suppose one of my more memorable "120V bench accidents" was repairing an old radio that had the neutral connected to its metal chassis. And an old worn 2 wire cord that could plug in backwards in certain outlets.
I managed to plug it in so that the neutral chassis was actually a hot (120VAC) chassis. When I went to clip my scope probe ground onto the chassis, there was a brilliant flash and bang. I was dazed but unharmed, and the scope probe was destroyed.

Live(d) and learn(ed)...


steve

[Dennis]

Steve :-) ....
OK .. I actually un-voluntarily spat the sip of coffee out trying to suppress the laughter :-) and am still having a good chuckle ... laughing with you not at you!
I had a similar incident on an old Zenith CGA and EGA monitors whose chasis' was live/hot.
In order to get the colours and sync right one had to use a very long trim-pot tool , sometimes we had to improvise and use a long screw-driver because all of the trim-pot tools were out of the workshop in the field with other technicians to make matter worse we would place the monitor on a metal trolley with wheels.

With the right (wrong!) combination of screw-driver and hand grips and a kinda left-hand suzuki method I very quickly was sent hurtling with an ear-piercing yell across the workshop into the bench behind me knocking my mentor straight off his feet !

Well needless to say after the initial shock was over and it was established that I was OK, the entire workshop spent the rest of the day laughing to crack their sides. And I definitely feel quite wound up after that.

There's that statement in the Star Trek intro "to boldy go where no man (or woman) has gone before"
There are some options of course
"to boldly go where no man (or woman) has come back from before"
or
"to boldly go where men (and women) have come back from before"
or
"to boldly go"
finally ..."just don't go !"

Thanks for the offer .. would you like to try the circuits a few posts ago or would you like something more finished ?

Awaiting an episode of the unexplained now I think !


By the way this was an interesting find of yours..! Definitely puts and angle on things !
I was wondering all through the article where the bleed resistors where ... and then saw them and mention of them in the last few pages !

A Capacitor-Fed, Voltage-Step-Down, Single-Phase, Non-Isolated ...
http://www.grix.it/UserFiles/Powermo...L_acfvsdsp.pdf

Kind regards
Dennis

[Dennis]

Gee suddenly this thread has quietened down :-(

There were no explosions, no loud bangs , nothing that went bump in the night...
No loud bangs, nothing burned out ...!

I decided to go ahead and build the circuit for testing ... nothing worked initially :-( the LED which I had enabled to go high every 15 seconds didn't even come on :-(
I went over it again with a fine-toothed comb..and found my 100uF and 100nF cap were in the wrong places.

I had programmed my PIC outside the board of course (no ICSP implemented yet !!) the program simply blinks an LED(GPIO.5) this would tell me the PIC has voltage and there would be no need for voltage measurements and also sets the TRIAC gate (GPIO.0) to go high for 15 seconds and the low for 15 seconds.The TRIAC in turn turns on the light buld for the same amount of time.

After correcting the capacitor issue,I put my welding glasses on and a pair of earmuffs and I used a broom stick to flip the AC wall switch :-)
Well the LED came on ..YAY :-) but the connected light bulb sadly did not !
SIGH !
The I looked back at the the circuit schematic and the calculations and it dawned on me that the TRIAC gate current may not be enough.Initially I had just popped in a 1K 1/4 Watt resistor just as a placeholder in my schematic with the idea that it may or may not work.
I quickly flipped the wall switch off, unplugged the extension cord (yes that too !) and unplugged the circuit board (strip-board for now), I made sure not to touch the large caps while unsoldering the gate resistor (R3) and replaced it with a 390R one!

Again repeating the same steps, earmuffs etc,I once again powered on the circuit .....
And to my absolute surprise the light bulb came on then 15 seconds later it switched off and the LED came on ! So when the LED is ON the LIGHT is OFF and vice-versa !
WHY ?
How could both be set to come on at the same time ?
But YAY it works :-)
There is a slight flicker when the light buld is on and I'm thinking it may be the TRIAC resistor or ??? the mind wonders...!

So now I need to test more.
The questions now are :
1.Is it the TRIAC gate resistor causing the flicker ?
2. Are there any suggestions for the the value for R3 ? (Check earlier posts for BT-139 gate current values and specs.
3.Cap C1 value is 275V and I'm thinking rather to use a 400V rated X2 instead, any thoughts on this ?
4. What's a concern is in times of NO LOAD , what will life be like for the PIC control PIN and the TRIAC gate ?
5.Other options include using an opto-isolator (possibly a MOC3023 or 30XX) in conjunction with or stand-alone ..any thoughts ?

On a final note... Please note that the attached circuit design is merely for testing and discussion purposes and has NOT been completed nor cleared for safe use of any kind and is missing several safety elements like a FUSE, MOV and a parallel bleeder resistor across C1.
Also note that this is a HIGH VOLTAGE circuit and neither I nor anyone else posting on this thread assumes any liability which may arise from any aspect of the circuit and or its development and/or use.
Working with circuits like this one are HAZARDOUS and UNSAFE and could result in serious injury and/or death !
DO NOT build this circuit unless you have HIGH voltage experience, rather use a transformer based circuit which is isolated from the LIVE AC supply.
You have been warned!

Steve ... are you ready to measure ? ;-)

Any thoughts would be appreciated

Oh .. and last but not least a popquiz question... Am I using a COMMON LIVE design or a COMMON NEUTRAL design ...and why ?

Kind regards

Dennis

[Byte_Butcher]

Gee suddenly this thread has quietened down :-(

There were no explosions, no loud bangs , nothing that went bump in the night...

Gee, that's kind of anticlimactic after all the DANGER warnings, now isn't it?
No conflagrations = Congratulations.

The questions now are :
1.Is it the TRIAC gate resistor causing the flicker ?

Maybe. Honestly, I think I'd use an opto-isolator to drive the triac. But that's just the way I am...

2. Are there any suggestions for the the value for R3 ? (Check earlier posts for BT-139 gate current values and specs.

Refer to answer #1...

3.Cap C1 value is 275V and I'm thinking rather to use a 400V rated X2 instead, any thoughts on this ?

If your mains is 220V, then I 'd use a 400V rated cap. No way, on the 275V.

4. What's a concern is in times of NO LOAD , what will life be like for the PIC control PIN and the TRIAC gate ?

Not quite sure of the question here, but I think it goes back to answer #1

5.Other options include using an opto-isolator (possibly a MOC3023 or 30XX) in conjunction with or stand-alone ..any thoughts ?

Hmmm. Yeah, I think an opto-isolator would be good.

Steve ... are you ready to measure ? ;-)

Rat's, and I just sent my nomex suit to the cleaners and loaned my 10' insulated pole to my neighbor.


Say, don't you think it might be a good idea to put a small 5 volt zener from pin 5 to ground? I know that 1M is a pretty high value resistor and the PIC pins have some protection against over-voltage, but there's something kind of creepy about just connecting a PIC port pin to that high of a voltage, even through a big resistor. Probably no big deal, but it makes me nervous connecting that pin to 220v with just a resistor.


steve

[Dennis]

Hi all

OK 8 hours of flashing a 60W light bulb and no issues yet , Im feeling a little 'strobed-out' though :-), battling to decide to watch the light or the LED :-)

I'm also more keen on the OPTO , just wondering how it will survive the capacitive 5V floating circuit on the PIC side of things ... will explain more a little later.

Regarding the PIC for zero-crossing sensor , have you read the Microchip appnote 236a ? It should make you feel a little more confident , but I can try a diode if you like ?

Now about those screen caps and measurements :-) haul out that isolation transformer and scope and let's get some more info :-)
If you are curious and have the time of course ..

Kind regards

Dennis

[Byte_Butcher]

Regarding the PIC for zero-crossing sensor , have you read the Microchip appnote 236a ? It should make you feel a little more confident , but I can try a diode if you like ?

Nope, haven't read it. But I will in the morning.
But if it's OK with the folks at Microchip, then I guess it's OK with me.

I will read the appnote tomorrow... zero crossing detector is one of those things that will come in handy for me someday.

steve

[keithdoxey]

Oh .. and last but not least a popquiz question... Am I using a COMMON LIVE design or a COMMON NEUTRAL design ...and why ?

Common Live so that the triac is switching the live supply to the load.

If the circuitry was common neutral then the triac would also be switching neutral with the result that the entire load would be live when the circuit appeared to be OFF.

[Pic_User]

I had programmed my PIC outside the board of course (no ICSP implemented yet !!)

Hi Dennis,

Great work so far. Let us know how things are going.
Especially how the ICSP works out, on the non-isolated circuit board.
This has turned into an interesting thread. A mix of past and future adventures in electricity land.
I really like the guys telling (on themselves) about the mishaps that have befallen the adventurous types. That is how we learn. Sometimes just being told carries little weight.

Oh .. and last but not least a popquiz question... Am I using a COMMON LIVE design or a COMMON NEUTRAL design ...and why ?

Good question!
I would guess the answer is: It is either a “COMMON LIVE” design OR a “COMMON NEUTRAL” design depending upon whichever way you happen to insert the plug. Why? Because “Sometimes just being told carries little weight.”

Keep us up to speed on this “excellent adventure”. Your posts are a great mix of adventure, work, learning, teaching, doing, telling, asking and just plain fun. –Adam-

[Dennis]

Hi guys
With reference to post #66 and the rest that follow and everything else prior to it.

Interesting indeed !

Keith ..AWESOME reply!

I agree with you here

triac is switching the live supply to the load.

Ok now for the beginning of the mystery and to add to this threads confusion you added this in :-)

If the circuitry was common neutral then the triac would also be switching neutral with the result that the entire load would be live when the circuit appeared to be OFF.

So from that statement we should assume COMMON LIVE is the supply of choice (in terms of being a little safer) not COMMON NEUTRAL ? Assuming of course that this circuit is indeed a COMMON LIVE circuit ?

Any comments on the above statements ?

Steve ....

Nice...! You threw in another side-winder, in fact, you mentioned something very real !
A two prong(pin) plug in most countries (correct me if I'm wrong ?) is easily reversed , in other words pluged in the other way around .. both sides same sides kind of thing so if I decide to design my PSU with the left prong as LIVE and the right prong as NEUTRAL .. all fine and dandy but then I unplug the device, put the pulg into the wall socket the other way around and suddenly everything is changed around :-)
Does this mean I should re-design my whole circuit ?
UH OH !

Well I encountered this dilemma a few nights back ... just before I got the broomstick, earmuffs and rubber gloves out and got all kitted up, I thought "Gee on this two-prong plug what happens when everything turns around ?"
"Will the circuit blow? What will the effect be? Will I need to change everything?"

So it works , turned either way around ! ( AC @ 50 Hz hmmm? )

And ..on the safety side is this circuit any less dangerous than a lamp that takes a bayonet or screw in light bulb ? Let's face it there is 110/120VAC or 220/230/240VAC right at the contacts where you screw the light in , not so ?

What about the computer AT form not so long ago which had mains voltage right at the front panel pretty much like may household appliances,TV's and radios before soft-power switches became the flavour of the day.

OK my next mission would be to alter the circuit so that the 'circuit ground' is the LIVE line in the schematic but .. do I really need to ?

Awaiting more comments and thoughts :-)

Oh and the question still remains ... is the circuit in post # common live or common neutral ? and why ?

Kind regards

Dennis