list57 at top.geek.nz
Tue Nov 20 07:38:21 GMT 2018
> Here is a start on snubbers : https://en.wikipedia.org/wiki/Snubber
> with link to https://en.wikipedia.org/wiki/Arc_suppression
Yes. It's a capacitor and resistor parallel to the relay contacts,
which take up the energy stored in the inductance when switching off.
There are numerous other circuit variations.
> For a mains application an X rated 0.1uF cap in series with 100R 1W
> resistor might be a good start (across contacts which need
> protection). This is for a slightly inductive load. Ambiguity
> indicates uncertainty, as in most cases...
> Anyone got any better rules-of-thumb on the subject ?
No, but there's just the 350 page book on snubbers:
RC Snubber circuits
Some calculation methods:
RC SNUBBERS (SMPS)
Snubber Circuit Design Analysis
RC snubber circuit design for TRIACs
Designing RC snubbers
The first trouble is that I have no idea what the inductance might be...
so the formula is guess in, guess out. There is mention of ringing, and
careful component value calculation. It wouldn't be engineering if it
was easy ;-)
Btw you mean X2 rated cap? Those are permitted between neutral and
phase, but connection to earth requires a better Y2 rated cap. Both are
designed to take a hammering from spikes and component failure is not
unexpected. The Y2 ones are required to fail open. The X2 ones may fail
closed, which will blow the fuse.
You might want a Y2 in snubbers, because if that cap fails closed your
resistor is a fire risk.
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