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'[OT:] Kerzzap! Hope you had a good surge protecto'
2006\05\23@190359 by Brendan Moran

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In my area, recently, there was a power surge of epic proportions.
Someone knocked a transmission line into a distribution line.  The
distribution grid (usually 12kV) took 60kV for a few moments until the
safties kicked in, resulting in 600V being delivered to 120V circuits
for a few moments.  But those few moments were enough to toast many
appliances.

Most people lost any electronics they had connected through surge
protectors.  They're not rated to take that kind of a beating.

http://www.thenownews.com/issues06/052106/news/052106nn4.html

I have a friend whose parents live in the affected area.  As his dad was
a real gadget buff, he had 3x 19" LCDs, a nice PC, and some printers.
He had all the goodies connected through a pretty solid APC UPS.  Well,
it cooked the input circuit of the UPS, but the equipment was undamaged.

Just another case of why your PC should be on a UPS, and why surge
protectors on their own aren't good enough.

--Brendan

2006\05\24@073435 by Peter Todd

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On Tue, May 23, 2006 at 04:03:12PM -0700, Brendan Moran wrote:
> In my area, recently, there was a power surge of epic proportions.
> Someone knocked a transmission line into a distribution line.  The
> distribution grid (usually 12kV) took 60kV for a few moments until the
> safties kicked in, resulting in 600V being delivered to 120V circuits
> for a few moments.  But those few moments were enough to toast many
> appliances.
>
> Most people lost any electronics they had connected through surge
> protectors.  They're not rated to take that kind of a beating.

Quite frankly, 600V seems like something I'd expect them to be able to
protect against just fine. What's hard about designing a circuit that
shunts that shunts that excess 500V and blows a fuse in the process? For
low voltage I've seen zener diodes used of course.

Heck, power bars get advertised as protecting against (indirect)
lightning...

> www.thenownews.com/issues06/052106/news/052106nn4.html
>
> I have a friend whose parents live in the affected area.  As his dad was
> a real gadget buff, he had 3x 19" LCDs, a nice PC, and some printers.
> He had all the goodies connected through a pretty solid APC UPS.  Well,
> it cooked the input circuit of the UPS, but the equipment was undamaged.
>
> Just another case of why your PC should be on a UPS, and why surge
> protectors on their own aren't good enough.

Scary... What would the effect be on a cheap wall wart? Almost
everything I build runs off of linear or switching wall warts. Decent
ones, bought new from digikey with the usual approvals. This goes into
my circuit through a standard linear reg of some sort.

I assume in the above instance the output of my wallwart would go from,
say, 10V to 60V which the linear reg could probably handle briefly.
Sounds about right?

--
spam_OUTpeteTakeThisOuTspampetertodd.ca http://www.petertodd.ca

2006\05\24@080940 by Spehro Pefhany

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At 07:35 AM 5/24/2006 -0400, you wrote:

>I assume in the above instance the output of my wallwart would go from,
>say, 10V to 60V which the linear reg could probably handle briefly.
>Sounds about right?

No, the transformer in linear wall-warts will saturate and the output
voltage will never get that high. The primary current will be very high,
through thin wire, and the primary may open up if there is enough energy,
but the circuit should be okay if the output voltage is only 10V and a
typical 40V regulator is used.

50/60Hz transformers are actually very effective surge protectors in
themselves if the circuitry on the other side is designed a bit
conservatively.

It will probably fry every SMPS that's turned on at the time, but again
not much should get through. Could be expensive with things like large
flat-panel monitors, high end printers, and plasma TVs though.

Last time I heard of such a thing happening, the power company picked
up the tab for repairing the damaged stuff, at least for 'consumers'.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
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2006\05\24@092957 by Peter Todd

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On Wed, May 24, 2006 at 08:20:59AM -0400, Spehro Pefhany wrote:
> At 07:35 AM 5/24/2006 -0400, you wrote:
>
> >I assume in the above instance the output of my wallwart would go from,
> >say, 10V to 60V which the linear reg could probably handle briefly.
> >Sounds about right?
>
> No, the transformer in linear wall-warts will saturate and the output
> voltage will never get that high. The primary current will be very high,
> through thin wire, and the primary may open up if there is enough energy,
> but the circuit should be okay if the output voltage is only 10V and a
> typical 40V regulator is used.

Interesting, I've seen references to "1000V 1minute" tests that wall
warts have to pass to be UL listed. I always thought it was purely a
function of don't burst into flames... Now I see why the 1 minute part
of the test is important!

> 50/60Hz transformers are actually very effective surge protectors in
> themselves if the circuitry on the other side is designed a bit
> conservatively.

Could a simple 1:1 isolation transformer be engineered to provide this
effect?

> It will probably fry every SMPS that's turned on at the time, but again
> not much should get through. Could be expensive with things like large
> flat-panel monitors, high end printers, and plasma TVs though.

The tiny little transformer in a SMPS should also saturate too right? Of
course, as you say, lots of supply-side electronics are there to be
fried...

> Last time I heard of such a thing happening, the power company picked
> up the tab for repairing the damaged stuff, at least for 'consumers'.

In highschool my electronics teacher told us a story once of how in the
late 60's the electricity to his rural neighboorhood in England was
sagging. This caused a lot of motors, especially as this was farm
country, to use more current and burn out. Of course, buracracies being
what they are the local power company wouldn't admit fault, and every
time a third party tested it, they would say their equipment was out of
calibration. So one day he managed to get some equipment requition forms
(he had worked for the company before) and tricked them into installing
a perfectly good calibrated long duration voltage meter on the pole
outside his house.  Just before the standard weekly log rotate would
happen, he climbed up the pole himself and retrieved the whole thing,
including the calibration documents...

The power company repaired everyones motors for free...

--
petespamKILLspampetertodd.ca http://www.petertodd.ca

2006\05\24@103804 by Alan B. Pearce

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>> 50/60Hz transformers are actually very effective surge
>> protectors in themselves if the circuitry on the other
>> side is designed a bit conservatively.
>
>Could a simple 1:1 isolation transformer be engineered
>to provide this effect?

Yes, in a previous existence we used to use 5KVA isolation transformers with
the earth wired through as filter transformers in very noisy industrial
environments, for computer equipment that was susceptible to mains borne
spikes. The lump of iron and winding inductance made an effective low pass
resonant filter.

2006\05\24@170838 by Dwayne Reid

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At 07:31 AM 5/24/2006, Peter Todd wrote:

>Interesting, I've seen references to "1000V 1minute" tests that wall
>warts have to pass to be UL listed. I always thought it was purely a
>function of don't burst into flames... Now I see why the 1 minute part
>of the test is important!

I don't know of ANY wall-wart that will survive 1000Vac applied to
the primary for 1 minute.  I *think* that you are thinking of a
standard hi-pot test between primary and secondary.

We have 2 options when we do hi-pot testing: 1KV (or 1.2KV - don't
recall) for 1 minute or 2500 Vac for x number of seconds (also don't
recall the specifics).

We use the lower voltage, longer duration test when we are dealing
with semiconductors that might be damaged by 2500 Vac.

dwayne

--
Dwayne Reid   <.....dwaynerKILLspamspam.....planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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2006\05\25@031503 by Howard Winter

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Alan,

On Wed, 24 May 2006 15:38:02 +0100, Alan B. Pearce wrote:

{Quote hidden}

In fact a number of years ago, before small UPSs became available/cheap enough, you could get a beast called a
Constant Voltage Transformer, which was resonant at 50Hz and had very high inductance.  It would effectively
stop any overvoltage spikes getting through and "ring" to keep the voltage up through sags, although they did
run pretty hot, so efficiency wasn't a major feature!

Cheers,


Howard Winter
St.Albans, England


2006\05\25@041813 by Alan B. Pearce

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>In fact a number of years ago, before small UPSs became
>available/cheap enough, you could get a beast called a
>Constant Voltage Transformer,

Yeah, I am aware of CVTs, but these isolating transformers were cheaper, and
acted in a similar way to the spikes. We certainly did not need the CVT
feature, as the various devices had regulating power supplies in them, it
was just a filter for the enormous spikes from welding and motors that
needed filtering out, and these transformers worked a treat.

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