On Wed, 30 Nov 2011 21:36:54 -0000, "Ian Field"
wrote:


"Colin Birch" wrote in message
. ..
Hi Folks

I've got a problem with over voltage surges taking out a switch mode PSU.
I
don't know a lot about electronics but looking at catalogues VDR/Varistors
look like they could be my friend. Basically I'm looking for a simple way
of blowing the inline 5a fuse if the input voltage goes over 240V AC.

Cost is also an issue here. Anyone got any suggestions on what I should
use

This might help;

http://en.wikipedia.org/wiki/Surge_protector

As you can see there are various options, the MOV (basically a VDR) is still
common in comercial appliances but each transient event takes a little bit
out of the device.

The more you have distributed around your mains supply wiring, the better
they work and longer they last, there are various protected socket strips on
sale, there are also single socket MOV units that the plug piggybacks onto
in the wall socket and even blank MOV protection modules - you plug them
into a spare wall socket but they have no socket holes in the top, these are
claimed to protect a ring-main as part of the house wiring.

---
None of that nebulous crap seems to be what the OP's looking for,
which is a way to keep surges from toasting his PSU when they go above
240V RMS.
---

As RG says; there are more modern devices like Tranzorbs, these are more
likely to fail S/C and blow the fuse.

---
Trying to use Rich to further your own agenda by putting words in his
mouth and supplying disinformation is ingenuous.

If you have some data which proves that Zeners configured as
surge-stoppers are somehow inferior to MOV's, I'd like to see it.

--
JF