Brown out protection.

[Control Freq]

Hi,
Recently, I experienced a Cisco firewall device break during an
electricity power failure. The power went off, came back up briefly,
then suffered a brown out then went off again.

Inspection of the device showed that the power supply transformer
device had broke, not the firewall iteself. We got a new firewall
device (and transformer) to get our systems up and running again.

Anyway, I was wondering how a brown out could have caused this
problem. The device is connected to a surge supressed mains outlet!

So, what is the usual way of protecting sensitive equipment to this
sort of failure?

All of our computers are connected to UPS, and they don't (yet) suffer
from problems with power failures, but all of our network hubs/
switches are not on UPS, only surge supressors.

Can someone fill in the blanks in my knowledge.

Thanks in advance.

 

[Brendan Gillatt]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Control Freq wrote:

Hi,
Recently, I experienced a Cisco firewall device break during an
electricity power failure. The power went off, came back up briefly,
then suffered a brown out then went off again.

Inspection of the device showed that the power supply transformer
device had broke, not the firewall iteself. We got a new firewall
device (and transformer) to get our systems up and running again.

Anyway, I was wondering how a brown out could have caused this
problem. The device is connected to a surge supressed mains outlet!

A brownout is the opposite of a surge - too *low* voltage for safe use.
Any sensitive, CMOS circuitry inside a complex piece of kit (such as a
cisco device) can be damaged by a brownout just as much as a surge.

So, what is the usual way of protecting sensitive equipment to this
sort of failure?

UPS

All of our computers are connected to UPS, and they don't (yet) suffer
from problems with power failures, but all of our network hubs/
switches are not on UPS, only surge supressors.

Then get another UPS! They're cheaper than Cisco firewalls ;]

Can someone fill in the blanks in my knowledge.

Thanks in advance.

- --
Brendan Gillatt
brendan {at} brendangillatt {dot} co {dot} uk
http://www.brendangillatt.co.uk
PGP Key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xBACD7433
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[Meat Plow]

On Wed, 03 Oct 2007 11:29:29 -0700, Control Freq wrote:

Hi,
Recently, I experienced a Cisco firewall device break during an
electricity power failure. The power went off, came back up briefly,
then suffered a brown out then went off again.

Inspection of the device showed that the power supply transformer
device had broke, not the firewall iteself. We got a new firewall
device (and transformer) to get our systems up and running again.

Anyway, I was wondering how a brown out could have caused this
problem. The device is connected to a surge supressed mains outlet!

So, what is the usual way of protecting sensitive equipment to this
sort of failure?

All of our computers are connected to UPS, and they don't (yet) suffer
from problems with power failures, but all of our network hubs/
switches are not on UPS, only surge supressors.

Can someone fill in the blanks in my knowledge.

Put all your networking gear on a UPS.

 

[Rich Grise]

On Wed, 03 Oct 2007 11:29:29 -0700, Control Freq wrote:

Recently, I experienced a Cisco firewall device break during an
electricity power failure. The power went off, came back up briefly,
then suffered a brown out then went off again.

Inspection of the device showed that the power supply transformer
device had broke, not the firewall iteself. We got a new firewall
device (and transformer) to get our systems up and running again.

Anyway, I was wondering how a brown out could have caused this
problem. The device is connected to a surge supressed mains outlet!

As others have said, put the stuff on a UPS - the same one if it
has the capacity, and another if it doesn't.

As to why it broke, when the undervoltage happened, the power
supply was struggling to regulate its output, and with less
voltage available, it needed to draw more current from the mains,
which exceeded the input tranny's ratings.

Hope This Helps!
Rich

 

[Phil Allison]

"Control Freq"

Recently, I experienced a Cisco firewall device break during an
electricity power failure. The power went off, came back up briefly,
then suffered a brown out then went off again.

** The brown out part is what sometimes does the damage.

Inspection of the device showed that the power supply transformer
device had broke, not the firewall iteself. We got a new firewall
device (and transformer) to get our systems up and running again.

Anyway, I was wondering how a brown out could have caused this
problem. The device is connected to a surge supressed mains outlet!

** The Cisco DC supply is a switching type (ie no iron transformer) with
a wide operating range of 100 to 240 volts AC. For that to stop working or
be harmed, the normally 240 volt AC supply must have been below 100 volts.

Such failures are still unusual and only a post mortem on the particular
supply will reveal the cause.

So, what is the usual way of protecting sensitive equipment to this
sort of failure?

** When a sustained brown out occurs - turn everything off.

Specially any fridges or air conditioners as it can burn out the motors.




........ Phil

 

[Michael A. Terrell]

Control Freq wrote:

Hi,
Recently, I experienced a Cisco firewall device break during an
electricity power failure. The power went off, came back up briefly,
then suffered a brown out then went off again.

Inspection of the device showed that the power supply transformer
device had broke, not the firewall iteself. We got a new firewall
device (and transformer) to get our systems up and running again.

Anyway, I was wondering how a brown out could have caused this
problem. The device is connected to a surge supressed mains outlet!

So, what is the usual way of protecting sensitive equipment to this
sort of failure?

All of our computers are connected to UPS, and they don't (yet) suffer
from problems with power failures, but all of our network hubs/
switches are not on UPS, only surge supressors.

Can someone fill in the blanks in my knowledge.

Thanks in advance.

The power supply is likely to be a small 'Switched Mode Power
Supply', or SMPS, like those used in your computers. As the supply
voltage drops, the 'on time increases, and draws more current trough the
switching transistors. If the design is marginal, it can cause one or
both transistors to short out, or blow an internal fuse. You need to
run them from the nearest UPS, or put them on one of their own.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[w_tom]

Brownouts do not cause electronics damage. That was an industry
standard even long before the IBM PC. Low voltage must not harm
electronics. Many even forget what happens when powering off
electronics. Electronics suffer a brownout - then eventually a
blackout - and without damage. Many will say otherwise based only
upon assumptions, observations, or popular urban myth. For example,
they saw the brownout but failed to see a reason for that brownout -
such as a preceding overvoltage. Many of your replies are based on
speculations. They assume; therefore it is a fact?

A UPS is to maintain power during blackouts and extreme brownouts.
Electronics must remain operational for a short time as that UPS
disconnects from AC mains and connects to the battery. Why is that
switchover time significant? Because the destructive surge could
repeat 100 times before that switchover occurs - the switchover takes
that long and surges are that short. A UPS connects electronics
directly to AC mains when not in battery backup mode. A UPS cannot
disconnect from a surge fast enough. The typical UPS does not even
claim to protect from typically destructive surges. It simply switches
to battery when AC voltage gets too low.

Usual way of protecting that Cisco is the same and simple solution
found in the telephone CO (central office). Any destructive surge is
earthed before it can enter the building. Do same with one properly
earthed 'whole house' protector. Such devices are not sold under
brand names of lesser companies such as Belkin, Tripplite, or APC.
Effective protectors are sold under responsible brand names such as
Siemens, Intermatic, Leviton, Square D, Cutler-Hammer, and GE.

Review spec numbers for that UPS. Chances are its joules are even
inferior to a paltry circuit found in power strips. That is near zero
protection. Those who recommend a UPS for surge protection often do
not even know how the UPS works and did not even first consult spec
sheets. They know only from half truths promoted on color glossy
sales brochures.

All electronics contain internal protection. Computers tend to have
protection numbers well in excess of other appliances. A surge that
might harm some appliances may also be irrelevant due to protection
inside a computer.

Protection inside any electronics can be overwhelmed. So we install
one 'whole house' protector to earth the rare and so destructive
surge. If properly earthed, that rare surge will not overwhelm
protection inside maybe 100 household appliances.

How many electronics fortunately were not damaged this time? Did
you lose furnace controls, dishwasher, smoke detectors, bathroom
GFCIs, or dimmer switches? Some of those electronics devices are more
critical to your safety. All have internal protection. Internal
protection that may be overwhelmed should the rare and destructive
surge not be properly earthed. We earth any incoming surge so that
even internal protection in every appliance (includeing that Cisco
power brick) is not damaged.

Brownouts only harm electronics where someone saw a brownout,
assumed no surge preceded it, and proclaimed their assumption as
fact. This 'cherry picked' reasoning also proved Saddam had WMDs.
Even 35 years ago, industry standards required electronics not be
damaged by brownouts. Chances are the brownout was preceded by a
surge. A surge sufficient to damage only some items and not
sufficient to overwhelm protection in others.

Phil Allison makes an important point. Such failures are unusual
and only a post mortem can provide further definitive facts.
Potentially destructive surges average maybe once every seven years -
and can vary significantly even without same town.

All electronics must either work just fine even when lights are
dimmed to 40% intensity, or shutdown without damage if that voltage
drops farther. It is an industry standard so old ... and yet how many
posted in denial of well known industry standards? Any power supply
damaged by a brownout was defective when designed. Brownouts do not
damage electronics.

On Oct 3, 2:29 pm, Control Freq <n...@nhthomas.freeserve.co.uk> wrote:

Hi,
Recently, I experienced a Cisco firewall device break during an
electricity power failure. The power went off, came back up briefly,
then suffered a brown out then went off again.

Inspection of the device showed that the power supply transformer
device had broke, not the firewall iteself. We got a new firewall
device (and transformer) to get our systems up and running again.

Anyway, I was wondering how a brown out could have caused this
problem. The device is connected to a surge supressed mains outlet!

So, what is the usual way of protecting sensitive equipment to this
sort of failure?

All of our computers are connected to UPS, and they don't (yet) suffer
from problems with power failures, but all of our network hubs/
switches are not on UPS, only surge supressors.

Can someone fill in the blanks in my knowledge.

Thanks in advance.

On Oct 3, 2:29 pm, Control Freq <n...@nhthomas.freeserve.co.uk> wrote:

Hi,
Recently, I experienced a Cisco firewall device break during an
electricity power failure. The power went off, came back up briefly,
then suffered a brown out then went off again.

Inspection of the device showed that the power supply transformer
device had broke, not the firewall iteself. We got a new firewall
device (and transformer) to get our systems up and running again.

Anyway, I was wondering how a brown out could have caused this
problem. The device is connected to a surge supressed mains outlet!

So, what is the usual way of protecting sensitive equipment to this
sort of failure?

All of our computers are connected to UPS, and they don't (yet) suffer
from problems with power failures, but all of our network hubs/
switches are not on UPS, only surge supressors.

Can someone fill in the blanks in my knowledge.

Thanks in advance.

 

On Oct 4, 7:11 pm, w_tom <w_t...@usa.net> wrote:

Brownouts do not cause electronics damage. That was an industry
standard even long before the IBM PC. Low voltage must not harm
electronics. Many even forget what happens when powering off
electronics. Electronics suffer a brownout - then eventually a
blackout - and without damage. Many will say otherwise based only
upon assumptions, observations, or popular urban myth. For
example,
they saw the brownout but failed to see a reason for that brownout
-
such as a preceding overvoltage. Many of your replies are based on
speculations. They assume; therefore it is a fact?

I suggest you go get a Variac and try some experiments on your own
computers and TVs. Since you say it causes no problems, you have
nothing to lose. I, however, would not bet on your success.

GG

 

[Stephen J. Rush]

On Thu, 04 Oct 2007 19:11:40 -0700, w_tom wrote:

A UPS is to maintain power during blackouts and extreme brownouts.
Electronics must remain operational for a short time as that UPS
disconnects from AC mains and connects to the battery. Why is that
switchover time significant? Because the destructive surge could
repeat 100 times before that switchover occurs - the switchover takes
that long and surges are that short. A UPS connects electronics
directly to AC mains when not in battery backup mode. A UPS cannot
disconnect from a surge fast enough. The typical UPS does not even
claim to protect from typically destructive surges. It simply switches
to battery when AC voltage gets too low.

A truely uninterruptable supply always drives the load from the inverter,
with the battery floating on the inverter input. There is no switching
time. Standby supplies are for people who can't afford a real UPS.

 

[Phil Allison]

<stratus46@yahoo.com
w_tom

Brownouts do not cause electronics damage. That was an industry
standard even long before the IBM PC. Low voltage must not harm
electronics. Many even forget what happens when powering off
electronics. Electronics suffer a brownout - then eventually a
blackout - and without damage. Many will say otherwise based only
upon assumptions, observations, or popular urban myth. For
example, they saw the brownout but failed to see a reason for that
brownout - such as a preceding overvoltage. Many of your replies
are based on speculations. They assume; therefore it is a fact?


I suggest you go get a Variac and try some experiments on your own
computers and TVs. Since you say it causes no problems, you have
nothing to lose. I, however, would not bet on your success.

** I'll take a bet on there being a particular AC supply voltage that
does, if held long enough, cause damage or fuse blowing to one of the items.

You will needed to fit a amp meter in line to find the "bad" voltage.



......... Phil

 

[Michael A. Terrell]

stratus46@yahoo.com wrote:

On Oct 4, 7:11 pm, w_tom <w_t...@usa.net> wrote:
Brownouts do not cause electronics damage. That was an industry
standard even long before the IBM PC. Low voltage must not harm
electronics. Many even forget what happens when powering off
electronics. Electronics suffer a brownout - then eventually a
blackout - and without damage. Many will say otherwise based only
upon assumptions, observations, or popular urban myth. For
example,
they saw the brownout but failed to see a reason for that brownout
-
such as a preceding overvoltage. Many of your replies are based on
speculations. They assume; therefore it is a fact?

I suggest you go get a Variac and try some experiments on your own
computers and TVs. Since you say it causes no problems, you have
nothing to lose. I, however, would not bet on your success.

GG

+-------------------+ .:\:\:/:/:.
| PLEASE DO NOT F :.:\:\:/:/:.:
| FEED THE TROLLS | :=.' - - '.=:
| | '=(\ 9 9 /)='
| Thank you, | ( (_) )
| Management | /`-vvv-'\
+-------------------+ / \
| | @@@ / /|,,,,,|\ \
| | @@@ /_// /^\ \\_\
@x@@x@ | | |/ WW( ( ) )WW
\||||/ | | \| __\,,\ /,,/__
\||/ | | | jgs (______Y______)
/\/\/\/\/\/\/\/\//\/\\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
==============================================================
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[w_tom]

On Oct 5, 12:17 am, stratu...@yahoo.com wrote:

I suggest you go get a Variac and try some experiments on your own
computers and TVs. Since you say it causes no problems, you have
nothing to lose. I, however, would not bet on your success.

I was doing that decades ago which is only one in a long list of
reasons why we know brownouts do not damage electronic appliances.
But again, what is a power off? A brownout followed by a blackout.
Putting a Variac on electronic designs and lowering voltage is
standard for all designs because industry standards DEMAND no damage
on brownouts.

What industry standards? You don't ask? Why not? Your replies
never provide numbers or industry standards. So how do you know
anything? Notice what the chart states in the brownout region: No
Damage Area. The standard applies internationally. One copy is
page 3 at:
http://www.itic.org/archives/iticurv.pdf

How do appliances fail when this CBEMA standard (and many other
standards) have existed for over 30 years? Urban myths are widespread
- and are posted without facts or numbers.

Those who knew by doing used that variac and therefore knew long ago
that brownouts must not cause electronics damage. One example is
"Motheboard Problem? Post Problem?" in alt.certification.a-plus on 7
Sept 2001 by Tom MacIntyre

We operate everything on an isolated variac, which means that I
can control the voltage going into the unit I am working on from
about 150 volts down to zero. This enables us to verify power
regulation for over and under-voltage situations. A linear supply
(many TV's) will start to lose its regulation from 100 volts down to
maybe 90, and the set will shut off by 75 volts AC or so.

... the best I've seen was a TV which didn't die until I turned the
variac down to 37 VAC! A brownout wouldn't have even affected
the picture on that set.

Notice how he was routinely damaging electronics with that variac?
Oh. No damage. How curious.

Routine design means determining the actual brownout voltage that my
design will cut out at (obviously without any damage). All 120 volt
electronics must operate at 105 volts and work for many seconds at 96
volts. But computers must even startup and work at 90 VAC - another
industry standard. Everything I design ran just fine until voltage
dropped to 85 volts. Did we damage electronics doing these variac
tests? Never. Obviously not. When that voltage drops below 85
volts, electronics just turn off. What is required of all designs?
No damage ever from brownouts. Electronics must work just fine or -
as even industry standards demand - cut off in the "No Damage Area".

Please take your own advice - get a variac and start learning by
doing. Then learn what designer must conform to - industry standards
as even on Page 3. Brownouts only cause electronic damage when urban
myths are promoted by those who never did this work and cannot post
numbers.

Industry standards are old and blunt: brownouts must never cause
hardware damage - see that chart on page 3. Intel standards for
computers demand even better. How many reasons here demonstrated
brownouts don't cause damage? Too many - with numbers, industry
citations, and justified contempt for those who would know without
first learning such facts. Brownouts must not cause electronics
damage - which is even common sense. Otherwise an appliance would
self destruct when powered off.

 

[w_tom]

On Oct 5, 12:59 am, "Stephen J. Rush" <sjr...@comcast.net> wrote:

A truely uninterruptable supply always drives the load from the inverter,
with the battery floating on the inverter input. There is no switching
time. Standby supplies are for people who can't afford a real UPS.

Which means most every UPS is not a true UPS. Those UPSes without
switching are $500 retail and higher. UPSes being discussed here
connect electronics directly to AC mains when not in battery backup
mode. Then the power to electronics is a clean sine wave.

Some in the UPS industry are quite good at promoting these myths.
Many only assume a UPS always powers from battery because propaganda
gets promoted as fact. The typical UPS connects electronics
directly to AC mains AND exposes electronics to some of the 'dirtiest'
electricity when operating from battery. Why is UPS electricity so
'dirty'? That inverter is as cheap as possible so that UPS need not
cost closer to $500.

So a relay can disconnect from a power surge? Of course not. Notice
the switchover time - about 10 milliseconds. Just another reason why
UPSes list (in numeric specs) near zero protection and another reason
why the UPS does nothing useful for Control Freq's problem. The UPS
provides temporary power during extreme brownouts and blackouts that
would otherwise power off that appliance.

 

[Control Freq]

Well, that was, erm, quite an answer. Thanks.

I wonder what Victor Frankenstein would have made of it all !


Regards

 

[Rich Grise]

On Thu, 04 Oct 2007 19:11:40 -0700, w_tom top-posted:
[top-post repaired]

On Oct 3, 2:29 pm, Control Freq <n...@nhthomas.freeserve.co.uk> wrote:
Hi,
Recently, I experienced a Cisco firewall device break during an
electricity power failure. The power went off, came back up briefly,
then suffered a brown out then went off again.

Inspection of the device showed that the power supply transformer
device had broke, not the firewall iteself. We got a new firewall
device (and transformer) to get our systems up and running again.

Anyway, I was wondering how a brown out could have caused this
problem. The device is connected to a surge supressed mains outlet!

So, what is the usual way of protecting sensitive equipment to this
sort of failure?

All of our computers are connected to UPS, and they don't (yet) suffer
from problems with power failures, but all of our network hubs/
switches are not on UPS, only surge supressors.

Can someone fill in the blanks in my knowledge.

Thanks in advance.

Brownouts do not cause electronics damage. That was an industry
standard even long before the IBM PC. Low voltage must not harm
electronics.

Sorry, but that seems to have been what took place.

And don't top-post.

Thanks,
Rich

 

[Jamie]

w_tom wrote:

Brownouts do not cause electronics damage. That was an industry
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Not true, Sorry..

Still today, PSU's are still made where if a brown out occurs, the osc
circuit will deadlock (stop) and things like the power transistors
will sit there and heat up and most likely be damaged before the unit
will shut down from temperature over load, if it even has that
protection in it.

It's what you call cheap and dirty;
Out the door by 4:30;



--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

[w_tom]

On Oct 6, 1:28 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Still today, PSU's are still made where if a brown out occurs, the osc
circuit will deadlock (stop) and things like the power transistors
will sit there and heat up and most likely be damaged before the unit
will shut down from temperature over load, if it even has that
protection in it.

When the oscillator stops working, then no current flows; controller
shuts down. Do you really think those PWM chip designers are so
stupid as to design as Jamie has just posted? Of course not. Doing
it to meet 30+ year standards is routine. The brownout region was long
ago called the "No Damage Area". Either a power supply must provide
DC output voltages; or power supply shuts off. Nothing new about this
reality.

What happens in a PC when a brownout is so major? Power supply even
signals the computer of a shutdown. Does that signal announce a
hardware failure? Of course not. A most extreme brownout simply
creates a power off. Supply even signals the computer of a shutdown.

If a power supply controller was designed as Jamie posted, then
normal power off could create damage. Industry standards demand that
brownouts never cause electronics damage. Just one of numerous
functions standard inside power supplies.

How curious. Testing new designs in a brownout is normal design
practice. Strange how damage never results. According to Jamie,
damage should be routine. If a brownout ever caused damage, then
instead a major design failure is solved. Electronics perform as those
old and blunt industry standards demand. Those who actually design
stuff would know brownouts must not cause electronics damage - ever.

So how extreme is a brownout? Well Intel specs demand that a fully
loaded computer even start up normally when voltage is so low that
incandescent bulbs are at well less than 40% intensity - a brownout.
Either it must work just fine or shutdown. What Jamie must and fails
to dispute are industry standards. Why does he post speculation AND
ignore industry standards? Even 30 years ago, brownouts must not
cause hardware damage. Suddenly we are making inferior designs
because Jamie says so? Yes, but only where speculation must also be
fact.

Brownouts can cause electric motor failures. Many heavy appliances
(ie air conditioner compressor) now include circuits to power off
motors should a brownout be excessive. Curious how even electric
motors are made resistant to brownout damage. Why are appliances that
need not meet those industry standards doing so anyway?

So how often are electronics damaged by bad breath? No standards
define bad breath induced failures. Therefore bad breath damage is
possible? Of course. Myths can claim anything when justified by no
numbers and no facts. However even old standards are quite blunt
about brownouts - the "No Damage Area". Bad breath damage? Anybody
can make claims only on speculaton.

 

[Jamie]

w_tom wrote:

On Oct 6, 1:28 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Still today, PSU's are still made where if a brown out occurs, the osc
circuit will deadlock (stop) and things like the power transistors
will sit there and heat up and most likely be damaged before the unit
will shut down from temperature over load, if it even has that
protection in it.


When the oscillator stops working, then no current flows; controller
shuts down. Do you really think those PWM chip designers are so
stupid as to design as Jamie has just posted? Of course not. Doing
Yes, there are crap electronics out there.

Cheap and dirty..
I've replaced a good many smps with better brands do element that
problem.
Being in the industrial field, i've repaired a good
many smps that took out the bipolar and power fets (depending on the
voltage at stake) just because of an electrical brown out that cause the
PS to stop outputting and over heat the transistors if the smps wasn't
repowered up in time to get the driving OSC started.

it to meet 30+ year standards is routine. The brownout region was long
ago called the "No Damage Area". Either a power supply must provide
DC output voltages; or power supply shuts off. Nothing new about this
reality.
That's crap. You haven't been around enough have you?

There are many bad designs out there that depend on the OSC circuit to
operate. when this circuit fails to start or stalls. driving bias can
be at it's highest point where normally the OSC circuit be working in a
state of pulling this bias down.

It's a common problem with bad and cheap designs. Get over it.

Most of the supplies we use now have a watch dog timer in it now
to element burn out of components. They work very good how ever,
you won't find to many of those in the cheap throw away classes.

Take my word for it. Bad designs still exist on the market!
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

[Phil Allison]

"Jamie"

There are many bad designs out there that depend on the OSC circuit to
operate. when this circuit fails to start or stalls. driving bias can
be at it's highest point where normally the OSC circuit be working in a
state of pulling this bias down.

It's a common problem with bad and cheap designs. Get over it.

Most of the supplies we use now have a watch dog timer in it now
to element burn out of components. They work very good how ever,
you won't find to many of those in the cheap throw away classes.

Take my word for it. Bad designs still exist on the market!

** SMPS are not the only products that can misbehave when the AC supply
voltage is very low.

I have come across transistor amplifiers (a Peavey bass guitar amp) that
will blow their AC fuse if slowly brought up on a Variac. This happens at
about 50% of rated AC voltage.

A Carver C-500 stereo power amp, I tested on the bench just recently,
cannot control its output voltage until the AC supply is at least 25% of
normal. When the AC supply is between 20 - 24 % of rated, both channels
output a DC voltage ( plus hum) of 20 volts into the load.

The Carver amp itself is not harmed by this, but any connected speakers (
read expensive hi-fi woofers ) could be expected to go up in smoke.

The same amp makes only a tiny " plop " noise when switched on the normal
way and a small "click" after being switched off. The DC offset at the
output was normally under +/-10 mV.

BTW:

Industry design standards that cover the entire electronics manufacturing
industry, world wide, DO NOT EXIST.

The Chinese have simply never heard of them......



....... Phil

 

[Jamie]

Phil Allison wrote:

"Jamie"

There are many bad designs out there that depend on the OSC circuit to
operate. when this circuit fails to start or stalls. driving bias can
be at it's highest point where normally the OSC circuit be working in a
state of pulling this bias down.

It's a common problem with bad and cheap designs. Get over it.

Most of the supplies we use now have a watch dog timer in it now
to element burn out of components. They work very good how ever,
you won't find to many of those in the cheap throw away classes.

Take my word for it. Bad designs still exist on the market!



** SMPS are not the only products that can misbehave when the AC supply
voltage is very low.

I have come across transistor amplifiers (a Peavey bass guitar amp) that
will blow their AC fuse if slowly brought up on a Variac. This happens at
about 50% of rated AC voltage.

A Carver C-500 stereo power amp, I tested on the bench just recently,
cannot control its output voltage until the AC supply is at least 25% of
normal. When the AC supply is between 20 - 24 % of rated, both channels
output a DC voltage ( plus hum) of 20 volts into the load.

The Carver amp itself is not harmed by this, but any connected speakers (
read expensive hi-fi woofers ) could be expected to go up in smoke.

The same amp makes only a tiny " plop " noise when switched on the normal
way and a small "click" after being switched off. The DC offset at the
output was normally under +/-10 mV.

BTW:

Industry design standards that cover the entire electronics manufacturing
industry, world wide, DO NOT EXIST.

The Chinese have simply never heard of them......



...... Phil


Yes, I agree there, I have seen damaged voice coils from voltage

drop outs when the coils were already hot from max operation.

Many designs do not allow for this problem.

That reminds me.
I have 2 Carvin amps that do 800 Watts RMS (bridged)each, that was
nicely given to me in working order. Now what to do with them


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
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