From: James Cameron <quozl@laptop.org>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Mon, 20 Jan 2020 18:49:19 -0800
Subject: Re: [EE] Diode bridge failure
Thread-Topic: [EE] Diode bridge failure
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That's interesting.  I agree an external connection to board 0V seems
the most likely.

But also possible is current high enough for the MOV not to shunt
enough of it, leading to failure of bridge and an arc between the
traces.  MOV can shunt but not appear failed afterwards.

I'm thinking of fire or lightning ionisation path down a dual-voltage
transmission line pole, or when high voltage transmission lines fall
from a pole onto low voltage lines.

On Tue, Jan 21, 2020 at 12:14:56PM +1000, David Duffy (AVD) wrote:
> I have a bit of a mystery on my hands. A client of mine has a board that=
=20
> monitors the output of a 24V transformer.
>=20
> The inputs to the board go to a 56V MOV then on to a 0.5A 600V diode=20
> bridge.=A0 The - output of the bridge goes to the board's 0V and the +=20
> goes via a resistor divider to a buffer opamp, then off to the micro.
>=20
> I've just had several boards from one site come in where the traces=20
> between the MOV and the bridge are vapourised.=A0 The bridge AC terminals=
=20
> are now shorted, but no other damage has been found so far. The original=
=20
> board blew in service and the others went as soon as the system was=20
> powered up.
>=20
> I can't imagine that a transient caused the bridge to fail as the MOD is=
=20
> still ok.=A0 The only other thing I can think of is that the transformer=
=20
> output is somehow referenced to the board 0V by an external fault.=A0 Thi=
s=20
> would effectively put one of the bridge diodes across the transformer.
>=20
> Any other ideas?
> David...
>=20
> --=20
> ___________________________________________
> David Duffy        Audio Visual Devices P/L
> Unit 8, 10 Hook St, Capalaba 4157 Australia
> Ph: +61 7 38235717      Fax: +61 7 38234717
> Our Web Site: www.audiovisualdevices.com.au
> ___________________________________________
>=20
> --=20
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
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--=20
James Cameron
http://quozl.netrek.org/
--=20
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