Transformerless Power Suppply

[psdayama]

It's not cost saving, but size too...

When this thread started, I put forward an example of a Fan Controller. This fits inside a standard size wall recess which can be as shallow as 15mm. They just don't make transformer bobbins that small - and consider you have to wind around 8,000 turns of 0.01 or 0.008mm wire for a 0.5VA transformer primary - and even then it'll run warm because you really need about 12,000 turns at that rating and you quickly discover that there are minimum sizes for sensible transformer manufacture. Wire that thin is scary stuff to work with as it's so fragile.

Cost of course is a factor. A small Capacitor, a Diode and an Opto-isolator makes for a simple 'Fuse Blown' or 'Power Fail' detect circuit. Whilst a Transformer is nice, it just takes up too much PCB space - and you can't do it for 20 cents.

Finally, my choice of X2 Capacitors is deliberate. If you correctly chose your Capacitor, series Resistors are unnescessary. In all the years I've been designing these kinds of circuits, I've never had any failures of X2 Capacitors. Actually, I can't ever recall having a defective X2 Capacitor in any circuit. Chose your components wisely from reputable sources and you'll not have any troubles.

Your very first statement is exactly opposite to end one.
Check size of X2 capacitor and normal metallised film capacitor. You will
find X2 atleast 2times bigger than normal. Obivously no manufacturer can
provide X2 at same price so they are atleast 3times expensive.
Metallised film caps which are supplied by UL approved manufacturers will
NEVER short. They may become open with overload. So either way the
argument is pointless! A serries resistor costs less than a cent and it is
wise to limit inrush current.(In all situations). You may have not recieved any complaint with
X2 capacitor as they if not used properly become open circuit SLOWLY. If
anybody notices difference in EMI after 6months or years later, it will be
sheer accident!

I have designed and made a fridge controller (Blind type) with 555 and
similiar transformerless power supply some 3-4 years ago. I have used
normal 680n / 250V capacitor --( our system is 240V 50Hz) and those are
working nicely last 3-4 years and saving 100s of Rs. every month for the
users without any recall.

[sayzer]

...

I have designed and made a fridge controller (Blind type) with 555 and
similiar transformerless power supply some 3-4 years ago. I have used
normal 680n / 250V capacitor --( our system is 240V 50Hz) and those are
working nicely last 3-4 years and saving 100s of Rs. every month for the
users without any recall.

Now it would be a good time to post that schematic here.

BTW; let me remind you that Melanie has a Klingon cloaking device.


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[Melanie]

Take a hundred engineers and give them the same problem, and you're likely to get a hundred different solutions, and each will argue that thiers is the best approach. I think this thread has been pretty much done to death, and there's more than enough information here for anyone but the most inept to design their own. And they, through natural selection when playing directly with the supply mains, will ensure that the standards remain high for the rest of us on the forum.

[dhouston]

Now it would be a good time to post that schematic here.

Just do a web search for X-10 schematics. They've been using a metallised film cap and series resistor for many years in the millions of UL approved switches and modules they've sold.

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[Luciano]

Hi,

About the resistors:

(Click to enlarge the picture).

Best regards,

Luciano

[psdayama]

Now it would be a good time to post that schematic here.

BTW; let me remind you that Melanie has a Klingon cloaking device.


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Hi sayzer,
well here is the schematic. Im not so good in drawing like U.
I had a fridge which had thermostat gone bust. So I made this ckt and
saved lot of energy 0.75KWHr /day instead of 5KWHr/day. I also found
that most of fridges have improper settings evenif the thermostat is OK and
there is lot of frost and they consume abt 3-4 KWHr/day. So making a
commercial unit costing Rs.400/- ( $9 appx.) have installed in abt 20-30
homes and they are all saving energy down to 1KWHr/day.
The consumption of unit is less than 05VA and there is no area even feeling
warm. I cant afford to use X2 capacitors in this as that will push cost of unit.

[Pic2008]

Can someone explain to me how the 240VAC after rectification can come down to +12VDC?

[financecatalyst]

Can someone explain to me how the 240VAC after rectification can come down to +12VDC?

Are you kidding me? I have enjoyed the arguments a lot, and from the first post to the third last (subtracting yours & mine of course), I have come across 2 to 4 circuits all making 12VDC. Check them out going back few posts (Remember to use X2 capacitors with mains - else Melanie would not like it - in case she comes across your circuit )