HI guys I am trying to modify a circuit from 18v to 12v and they told me it's too lethal even if this is sealed?!
I cannot understand this.

 

Any fault in the capacitor places line voltage at the output. It is too dangerous, given the price and availability of wall transformers.

Any transformerless power source is inherently lethally dangerous.

 

In your previous thread http://forum.allaboutcircuits.com/showthread.php?t=14458&referrerid=16292 you said you wanted to drop 240V to 12v. Is this something different...like dropping an 18V wall wart (As they suggested.) output to 12v?

Ken

 

The problem is isolation. The only component that truly provides it is a transformer, as there is NO direct connection between the high voltage side and the low voltage side. If something goes wrong you loose the transformer, which costs less than $2.

On a direct connection, on the other hand, if something goes wrong you have the full line current/voltage where you are. We are no longer talking low cost components but your own very irreplaceable self. A big difference.

Most of the old hands are nuts about safety. It is drummed into us at school, and there simply isn't anything to make us give it up in the field. What you are wanting to do isn't safe, no matter how you do it. If a company ever designed something like that and someone got hurt they would rightfully be put out of business and someone would be prosecuted for manslaughter.

That isn't to say it hasn't been done, but this site is here for fun, and if someone were to advise you to grab a 100V+ line with your bare hands I suspect they would be banned and the post erased as soon as a moderator saw it. We take safety very serious here.

Why are you so hot to go this route and not use a wall wart or internal transformer in the project?

 

Here's a transformer for you:
http://www.mpja.com/prodinfo.asp?number=7838+TR
110/220 primary, 12VAC @1A center tapped secondary, $2.75/ea. One of my favorite suppliers.

I suggest that you use a 1/10 A fuse on the primary side.

 

In school, they teach us that our primary duty as engineers is to 'protect the public'. So, how good is an engineer that tries to save two dollars at the cost of potentially killing a citizen who has no electrical knowledge?

Steve

 

HI Bill ok what you said is right but even if this circuit is sealed that no-one can touch.If something goes wrong only the bulb would blow up.
I cannot understand so much fuss about this.?????

 

Sealed doesn't mean fool-proof. Example, someone drops it and it breaks, then picks it up and electrocutes themselves. The whole point is, the engineer is supposed to protect people from accidental death where it is feasible. Paying an extra few dollars for a safety device is definitely feasible. This isn't fuss, it is the way things should be done.

Steve