DIYbanter - View Single Post - A wall-wart alternative

wrote:
Don K wrote:
wrote:

0.047 uF @400 V
1K || |
----www----||---------------------|------------
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| | 3V
120 VAC --- --- to clock
^ _
0.047 uF @400 V | |
|| | |
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Unlike a wall-wart, it will require special precautions not to accidentally
touch anything when you go to change the battery...

same precautions as any mains device, all nonisolated parts must be
protected from touch. The danger with this system lies not in the
design itself, but in putting into the hands of people that dont know
what theyre doing with it, and might use it like a wall wart. Since the
safety R has been added, it can be used perfectly safely, but only when
its issues are understood and appropriately addressed.

Smoke detectors could be used hapily with it if a screw were added to
prevent opening.

There's nothing to limit the current when capacitors fail, so that failure
will cause a fire.

X rated capacitors use fusible coatings, so a short causes a burn out
of the conductor around the short. The overall capacitance is not
noticeably affectde, IOW its self healing.

I doubt that. The diodes will probably open, and I used really skinny wire.

Very fine wire sounds like effective fusing to me.

There's no transient voltage protection, so the odds of capacitor over-voltage
failure is pretty high.

Or diode damage. So... I added a 1K series resistor. This would also work:

Yes, though again you need the R and C in the live. The days where you
could scatter proetction devices between L and N lines is long gone -
at least in our part of the world anyway.

If youre using non polarised plugs on this, you'd need an R in both
lines imho. These need to be safety Rs, not the kind that catch fire
and carbonise.

Personally I'd make the R as high as is possible, so it responds
effectively to any fault throughput incease.

NT