On Thu, May 27, 2004 at 11:13:29AM -0400, Dave Tweed wrote:
> Charles Craft <chucksea@MINDSPRING.COM> wrote:
> > A search on "transformerless" at www.microchip.com brought up 5 documents:
> > AN236 - X-10 Home Automation Using the PIC16F877A  Release Date: 10/30/02
> > TB008 - TechBrief Tranformerless Power Supply  Release Date: 8/26/97
> > DD2016 - Freezer Protector  Release Date: 4/22/98
>
> Three of these documents recommend connecting the circuit to the grounding
> (safety) conductor of a 3-wire plug, and then putting a fuse or other
> component between the grounding conductor and the grounded (neutral)
> conductor.
>
> THIS IS A MAJOR SAFETY RISK AND IS BLATENTLY ILLEGAL IN THE US AND
> PROBABLY ELSEWHERE AS WELL!
>
> The grounding conductor must never intentionally carry load currents.
> This type of transformerless power supply must be completely isolated
> from the safety ground!

Agreed. Also it'll trop GCFI systems which specifically detect current in
that leg. It's really bad engineering.

So let's get back to the issue. I have a simple engineering question: Why
isn't the neutral available? Other than an academic exercise, I can't conceieve
of a situation where you only have the hot wire and no physical access at all
to the neutral. Even in a 3way or 4way switch situation, both hot and neutral
are available right?

You'll have to leak current through the load like this.

Hot -> Control -> X1 -> Switch -> X2 -> Load -> Neutral

Where X1 and X2 are connected so that the control and switch can be powered
through the load even when the switch is disengaged leaking a minimal amount
of current through the load. You can even use a resistor or cap and a zener
to limit the voltage and current going around the switch so that the load
doesn't get enough power to activate.

But again other than the academic exercise, why bother. Connect X1 directly to
the neutral and be done with the task.

Or am I missing something significant?

BAJ

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