Surge protector

A

Alex C

Guest
How do i add a surge protector to a sensitive device (AC powered motion
sensor)? can I just wound a few round of copper wire on a ferrite rod?

Apprecaite if can reply through my email e_mc2@pacific.net.sg as I seldom
have access to newsgroup..
thanks
 
Somehow you think a little ferrite is going to stop a
destructive surge? Start with specs for that ferrite bead or
rod? At what frequencies does it even start working? And how
much impedance? Up front, you must put numbers to your
transient and to what is going to stop or block that
transient.

Lets use a toggle or keyed panel switch as example.
Typically, switches are rated for 20K volts. However I
touched one, static shocked it, and crashed the computer.
Human body should not generate more than 20K. But that 20K
isolation spec has conditions - default knowledge. One does
not typically stop or block transients. Transients are
diverted. If the static shock or transient occurs, nothing
was going to stop it. We avoid failures by diverting.

That switch body was isolated from metal chassis by epoxy
paint. Solution - an internal washer was required to ground
that key switch, through paint, into metal chassis so that
switch could withstand 20K volts.

Same applies to your sensor. Solution is to divert a
transient so that transient does not have both an incoming and
outgoing path through sensor. That means incoming path must
make some path to what the surge seeks - ground. This path is
either by a direct connection (ie the internal washer and
metal chassis) or by making same connection via a surge
protector. The latter is necessary when a direct (hardwire)
connection cannot be made. The latter must also consider
other parameters such as let-through or threshold voltage,
parasitic capacitance of that protector device, and isolation
voltage at sensor so that voltage will pass through protector
and not through sensor.

Basic concept. One can build a dam and see transients
(floods) overwhelm and destroy same. Or one can build dikes
to divert flood downstream. That is how transient protection
is installed. Any transient that has an incoming path to
sensor, but does not have a good outgoing path from sensor,
will not pass through or damage sensor. You must provide path
for destructive transients that does not pass through sensor.
Trying to stop a transient with a ferrite rod and looped wire
is - well look at the numbers. You would be only fooling
yourself - and not the transient.

Your sensor must be properly installed so that even human
static electricity 20K volts will not interfere with sensor
operation. BTW, this analysis must consider both differential
and common mode transients as well as numbers for every type
transient.

Alex C wrote:
How do i add a surge protector to a sensitive device (AC powered
motion sensor)? can I just wound a few round of copper wire on a
ferrite rod?

Apprecaite if can reply through my email e_mc2@pacific.net.sg
as I seldom have access to newsgroup..
thanks
Click to expand...
 
thanks tom, for the point, I'll look into it...

Thanks!

"w_tom" <w_tom1@hotmail.com> wrote in message
news:41872FBA.638B98A9@hotmail.com...
Somehow you think a little ferrite is going to stop a
destructive surge? Start with specs for that ferrite bead or
rod? At what frequencies does it even start working? And how
much impedance? Up front, you must put numbers to your
transient and to what is going to stop or block that
transient.

Lets use a toggle or keyed panel switch as example.
Typically, switches are rated for 20K volts. However I
touched one, static shocked it, and crashed the computer.
Human body should not generate more than 20K. But that 20K
isolation spec has conditions - default knowledge. One does
not typically stop or block transients. Transients are
diverted. If the static shock or transient occurs, nothing
was going to stop it. We avoid failures by diverting.

That switch body was isolated from metal chassis by epoxy
paint. Solution - an internal washer was required to ground
that key switch, through paint, into metal chassis so that
switch could withstand 20K volts.

Same applies to your sensor. Solution is to divert a
transient so that transient does not have both an incoming and
outgoing path through sensor. That means incoming path must
make some path to what the surge seeks - ground. This path is
either by a direct connection (ie the internal washer and
metal chassis) or by making same connection via a surge
protector. The latter is necessary when a direct (hardwire)
connection cannot be made. The latter must also consider
other parameters such as let-through or threshold voltage,
parasitic capacitance of that protector device, and isolation
voltage at sensor so that voltage will pass through protector
and not through sensor.

Basic concept. One can build a dam and see transients
(floods) overwhelm and destroy same. Or one can build dikes
to divert flood downstream. That is how transient protection
is installed. Any transient that has an incoming path to
sensor, but does not have a good outgoing path from sensor,
will not pass through or damage sensor. You must provide path
for destructive transients that does not pass through sensor.
Trying to stop a transient with a ferrite rod and looped wire
is - well look at the numbers. You would be only fooling
yourself - and not the transient.

Your sensor must be properly installed so that even human
static electricity 20K volts will not interfere with sensor
operation. BTW, this analysis must consider both differential
and common mode transients as well as numbers for every type
transient.

Alex C wrote:
How do i add a surge protector to a sensitive device (AC powered
motion sensor)? can I just wound a few round of copper wire on a
ferrite rod?

Apprecaite if can reply through my email e_mc2@pacific.net.sg
as I seldom have access to newsgroup..
thanks
Click to expand...
 
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