a little help with capacitive power supply values

[Pic_User]

More sites:
Step-down rectifier makes a simple dc power supply
[Electronic Design News]
http://www.edn.com/ednmag/archives/1...98/08df_06.htm
http://www.edn.com/ednmag/archives/1...98/08df_06.pdf

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

+++++++++++++++++++ You may skip this part:

In my very best Rod Serling, Twilight Zone, imitation:

“Picture if you will; A man bent over his electronics’ workbench.
A man, with many decades of experience, working for a living, doing precisely what he is doing at this moment.
Analyzing an electronic circuit.

Not just any circuit, but a circuit made by X10.
A consumer circuit, brand new, just out of it’s pristine box, for the first time since it left the factory floor.
The device is powered through a two prong, AC, 120V (USA) power cord.

Only today, instead of analyzing the circuit to repair it, or analyzing it to modify the circuit, he is trying to learn something else.
He is attaching his multi thousand dollar oscilloscope to the X10 device, to find out how it works.
To learn the secrets of it’s communication wave form, if you will. (Rod Serling speak)
To SEE what is going on in this particular mysterious device.

He has done this countless times, to repair, to alter, to learn and to expand, on the knowledge gained by this analysis.

There is no schematic included.
The two wire cord lulls this “searcher of the truth”, into a false impression that the device MUST be isolated, MUST have a small power transformer, somewhere hidden from the casual observer.

Enter - The Twilight Zone:
He FAILS to notice, that there are NO outside connections needed, except the cord.
Just an all plastic case, with all plastic buttons. No jacks, no other cords, just a dead end for the power cord.
Cleverly designed by people who do this for a living.

Just a power cord attached to a plastic case with eight plastic switches.
The output for the device is really, signals going back down the power cord.
Signals riding on the 120V AC power line.
This is know but not thought about by the investigator at this time, overlooked.
He is not aware that this device is powered by a “transformerless” power supply.

With the standard, properly functioning oscilloscope, attached through a 100 times (100x) probe (for conservative safety), the examiner is ready to begin. He has carefully attached the probe, ground on the minus of the filter capacitor, probe on the plus of the low voltage supply.
He has done this, before he energizes the circuit, for obvious reasons.

He now, without the least hesitation, picks up the x10 power plug and plugs it directly into the 120Voutlet.

Also without the least hesitation, he watches half of the printed circuit traces disappear.
A loud bang, a bright flash, a lot of smoke are all that is left of that half of the circuit.

What does he do?
He doesn’t even examine the burnt x10. He knows what happened and why.
He unplugs the warm cord.
He wraps the cord around the unit.
He puts the burnt x10 switch back into its box.
He opens the second identical x10 unit box (an extra, back-up unit).
He opens the unit.
He places the oscilloscope probe on the identical place, only on the new x10 circuit board.
AND
He plugs the new x10 into 120V AC!

DE DE DE DE – DE DE DE DE (that’s Twilight Zone theme music, look it up)

NOT into the same normal AC receptacle, but INTO an isolation transformer. His bench-top isolation transformer.

He would have done this with the first x10 but he wasn’t paying attention.”

That inattentive investigator was... ME. This is a true story.
I had plugged the first (now ruined) x10 into the normal AC receptacle with the neutral side and the line side flipped.

This is why they make and we use line isolation transformers.
++++++++++++++++++++++

You should never service a transformerless supply without one.

-Adam-

[mackrackit]

Adam,

I am glad it was not a
Tales from the Crypt
rendition.

[Pic_User]

Adam,

I am glad it was not a
Tales from the Crypt
rendition.

Hey Dave,
It might have been, “Tales from the Crypt”, is I was a little bit more careless.
Half of MY circuit traces could have been blown off, if I had touched the circuit board anywhere.
DE DE DE DE... (I gotta stop that theme music)
-Adam-

[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

[dhouston]

To learn the secrets of it’s communication wave form, if you will.

Simpler and safer is to use a stepdown transformer connected to the powerline and view the communication wave form through it. You don't even have to open the X-10 modules. A high pass filter passes 120kHz and blocks the 60Hz.

[Dennis]

Yes agreed or use a lower AC voltage at the same frequency running completely off the mains ?

Dennis