problem with triacs with neon transformer loads

[[email protected]]

Hi,
I am designed a commercial neon lamp two channel flasher and connected
to my hotels name board. The circuit is having two parts, one is
flashing circuit and the other is the output stage, wher the phase line
is switched. In the out put stage i have used BTA 41 triacs for
switching the neon transformer, ie the phase to the transformer is
connected through the triac. The gate signal is controlled through one
MOC3083 opto triac. the output from the flashing circuit is connected
to the opto triac's(MOC3083) input (LED).
I have installed the flasher in my hotel's neon name board. there is
two transformers connected to one flasher channel. it was working for
the last 4 months. last week one channel was not flashing. only one
channel is flashing the other channel is in ON state, ie not blinking.
The next when i checked the flasher in my lab both of the channels was
flashing. again i connected the flasher to the same neon board. After
two weeks agin the same problem occured, ie one channel was not
flashing. Can anbody know the reason for that. Is that problem with
Opto triac(MOC3083) or BTA 41. Is there any possibility of humidity or
temparature cause the problem

Thanks in advance

Raseel.M

 

[Winfield Hill]

[email protected] wrote...

I am designed a commercial neon lamp two channel flasher and connected
to my hotels name board. The circuit is having two parts, one is
flashing circuit and the other is the output stage, wher the phase
line is switched. In the out put stage i have used BTA 41 triacs for
switching the neon transformer, ie the phase to the transformer is
connected through the triac. The gate signal is controlled through one
MOC3083 opto triac. the output from the flashing circuit is connected
to the opto triac's(MOC3083) input (LED).

The problem with switching transformer primaries with triacs is
the high inrush current that can develop. For example, if the
transformer magnetizing flux is strongly of one polarity when
it's turned off, and the ac line is pushing toward the peak of
the other polarity when the triac is turned on, the transformer
core will saturate and the primary will look like a section of
thick copper wire across the AC line. Very high currents will
flow for a portion of an ac cycle. Your triac is designed to
handle a little of this, but it's highly stressful and should
be minimized.

There are several solutions, including zero-crossing switching,
or a two-stage switch with a series resistor in the first path,
or both.

 

[[email protected]]

[email protected] wrote...

The problem with switching transformer primaries with triacs is
the high inrush current that can develop. For example, if the
transformer magnetizing flux is strongly of one polarity when
it's turned off, and the ac line is pushing toward the peak of
the other polarity when the triac is turned on, the transformer
core will saturate and the primary will look like a section of
thick copper wire across the AC line. Very high currents will
flow for a portion of an ac cycle. Your triac is designed to
handle a little of this, but it's highly stressful and should
be minimized.

There are several solutions, including zero-crossing switching,
or a two-stage switch with a series resistor in the first path,
or both.

HI Win,
Thanks for ur replay. Here i will explain you more about the problem.
The triac is capable of handling max 40A current. I have used the zero
crossing triggering with the help of MOC 3083. Actually the problem not
causing to damage of triacs. The same triacs i have used again. The
neon transformer has one property such that it wont saturate the core.
the windings is done in such a manner. Then wat will be the problem

 

[[email protected]]

[email protected] wrote...

The problem with switching transformer primaries with triacs is
the high inrush current that can develop. For example, if the
transformer magnetizing flux is strongly of one polarity when
it's turned off, and the ac line is pushing toward the peak of
the other polarity when the triac is turned on, the transformer
core will saturate and the primary will look like a section of
thick copper wire across the AC line. Very high currents will
flow for a portion of an ac cycle. Your triac is designed to
handle a little of this, but it's highly stressful and should
be minimized.

There are several solutions, including zero-crossing switching,
or a two-stage switch with a series resistor in the first path,
or both.

HI Win,
Thanks for ur replay. Here i will explain you more about the problem.
The triac is capable of handling max 40A current. I have used the zero
crossing triggering with the help of MOC 3083. Actually the problem not
causing to damage of triacs. The same triacs i have used again. The
neon transformer has one property such that it wont saturate the core.
the windings is done in such a manner. Then wat will be the problem

 

[Fred Bloggs]

[email protected] wrote...



The problem with switching transformer primaries with triacs is
the high inrush current that can develop. For example, if the
transformer magnetizing flux is strongly of one polarity when
it's turned off, and the ac line is pushing toward the peak of
the other polarity when the triac is turned on, the transformer
core will saturate and the primary will look like a section of
thick copper wire across the AC line. Very high currents will
flow for a portion of an ac cycle. Your triac is designed to
handle a little of this, but it's highly stressful and should
be minimized.

There are several solutions, including zero-crossing switching,
or a two-stage switch with a series resistor in the first path,
or both.

Haha- write more- Genome is having too much fun here-)

 

[Phil Allison]

"Winfield Hill"

= an asinine, ivory tower lurking, fucking IDIOT !!!!!

The problem with switching transformer primaries with triacs is
the high inrush current that can develop. For example, if the
transformer magnetizing flux is strongly of one polarity when
it's turned off, and the ac line is pushing toward the peak of
the other polarity when the triac is turned on, the transformer
core will saturate and the primary will look like a section of
thick copper wire across the AC line. Very high currents will
flow for a portion of an ac cycle. Your triac is designed to
handle a little of this, but it's highly stressful and should
be minimized.


There are several solutions, including zero-crossing switching,

** How fucking ASININE of *Winnie * the posturing pommy **** head !!

Any competent person knows that " zero switching " the AC main supply
*guarantees* consecutive maximum inrush current surges into a supply
transformer.

Is the vile puke really completely ignorant of simple physics involved ?

I hope the slimy **** chokes.





....... Phil

 

[John Fields]

Hi,
I am designed a commercial neon lamp two channel flasher and connected
to my hotels name board. The circuit is having two parts, one is
flashing circuit and the other is the output stage, wher the phase line
is switched. In the out put stage i have used BTA 41 triacs for
switching the neon transformer, ie the phase to the transformer is
connected through the triac. The gate signal is controlled through one
MOC3083 opto triac. the output from the flashing circuit is connected
to the opto triac's(MOC3083) input (LED).
I have installed the flasher in my hotel's neon name board. there is
two transformers connected to one flasher channel. it was working for
the last 4 months. last week one channel was not flashing. only one
channel is flashing the other channel is in ON state, ie not blinking.
The next when i checked the flasher in my lab both of the channels was
flashing. again i connected the flasher to the same neon board. After
two weeks agin the same problem occured, ie one channel was not
flashing. Can anbody know the reason for that. Is that problem with
Opto triac(MOC3083) or BTA 41. Is there any possibility of humidity or
temparature cause the problem

Since your load(s) are inductive, you should use a snubber across
the TRIAC.

 

[Sam Goldwasser]

HI Win,
Thanks for ur replay. Here i will explain you more about the problem.
The triac is capable of handling max 40A current. I have used the zero
crossing triggering with the help of MOC 3083. Actually the problem not
causing to damage of triacs. The same triacs i have used again. The
neon transformer has one property such that it wont saturate the core.
the windings is done in such a manner. Then wat will be the problem

Have you made any actual measurements? It could be the MOC3083, its
drive, or the BTA41 that's the problem. The actual schematic would also
be of help.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[Jim Thompson]

Hi,
I am designed a commercial neon lamp two channel flasher and connected
to my hotels name board. The circuit is having two parts, one is
flashing circuit and the other is the output stage, wher the phase line
is switched. In the out put stage i have used BTA 41 triacs for
switching the neon transformer, ie the phase to the transformer is
connected through the triac. The gate signal is controlled through one
MOC3083 opto triac. the output from the flashing circuit is connected
to the opto triac's(MOC3083) input (LED).
I have installed the flasher in my hotel's neon name board. there is
two transformers connected to one flasher channel. it was working for
the last 4 months. last week one channel was not flashing. only one
channel is flashing the other channel is in ON state, ie not blinking.
The next when i checked the flasher in my lab both of the channels was
flashing. again i connected the flasher to the same neon board. After
two weeks agin the same problem occured, ie one channel was not
flashing. Can anbody know the reason for that. Is that problem with
Opto triac(MOC3083) or BTA 41. Is there any possibility of humidity or
temparature cause the problem

Thanks in advance

Raseel.M

It always works when returned to the lab?

At the installed location try removing all power for a few minutes,
then turn it back on and see if flashing resumes.

You probably have some kind of "hang" mode in your flasher circuitry.

...Jim Thompson

 

[Zak]

The problem with switching transformer primaries with triacs is
the high inrush current that can develop.
[snip]

There are several solutions, including zero-crossing switching,
or a two-stage switch with a series resistor in the first path,
or both.

It is 'maximum voltage switching' that should be used in this case,
isn't it? Switching on at zero crossing will start with a demagnetized
core handing the full voltage * time integral, where in operation it
would start out with the opposite magnetization.


Thomas

 

[Sam Goldwasser]

The problem with switching transformer primaries with triacs is
the high inrush current that can develop.
[snip]

There are several solutions, including zero-crossing switching,
or a two-stage switch with a series resistor in the first path,
or both.

It is 'maximum voltage switching' that should be used in this case,
isn't it? Switching on at zero crossing will start with a demagnetized
core handing the full voltage * time integral, where in operation it
would start out with the opposite magnetization.

That's what I thought. But in any case, I don't believe his problem is
a matter of destroying the triacs with excessive current since the thing
works after the problme occurs when taken back to the lab or whatever.
Possibly something in the driver circuit that's not turning completely off.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[Jim Thompson]

The problem with switching transformer primaries with triacs is
the high inrush current that can develop.
[snip]

There are several solutions, including zero-crossing switching,
or a two-stage switch with a series resistor in the first path,
or both.

It is 'maximum voltage switching' that should be used in this case,
isn't it? Switching on at zero crossing will start with a demagnetized
core handing the full voltage * time integral, where in operation it
would start out with the opposite magnetization.


Thomas

In the early '80's, when I did disco stuff, I controlled neon
transformers by feeding them _complete_ cycles only (using TRIAC's).

I found, from experiment, that partial cycles or an odd number of half
cycles would ultimately smoke the transformer.

...Jim Thompson

 

[Phil Allison]

"Jim Thompson"

In the early '80's, when I did disco stuff, I controlled neon
transformers by feeding them _complete_ cycles only (using TRIAC's).

I found, from experiment, that partial cycles or an odd number of half
cycles would ultimately smoke the transformer.

** An automatic result of the large DC component inherent in half cycles or
1.5 cycles or 2.5 cycles etc.

But to minimise current surges - use whole numbers of cycles, commencing
at a peak.

Least DC component x time.

Do the math.




....... Phil

 

[Mike Monett]

The problem with switching transformer primaries with triacs is
the high inrush current that can develop.
[snip]

There are several solutions, including zero-crossing switching,
or a two-stage switch with a series resistor in the first path,
or both.

It is 'maximum voltage switching' that should be used in this case,
isn't it? Switching on at zero crossing will start with a demagnetized
core handing the full voltage * time integral, where in operation it
would start out with the opposite magnetization.

Thomas

There are a number of descriptions on the web, some worse than
others. Here's one where the scope figures bear no resemblance to
the description:

http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3206.pdf

All the photos show switching at or near the peak of the 120V
waveform. The B graph is 50 Amp per division. It shows about 40 Amp
peak current, the same value as in the A graph. The text claims the
peak is 200 Amps.

Here's one that seems to do a good job simulating the result of the
transformer inductive load while flashing neon signs. It shows the
inrush current at various points on the AC waveform, and the effect
of magnetic remanence. Unfortunately, a poor choice of colors for
the traces makes them hard to read.

The article recommends a cooling period between power cycles to
prevent destroying the transformer. It also recommends leaving the
primary turned on for at least 30 cycles. This is somewhat different
from Jim's recommendation to only use complete cycles:

http://www.allanson.com/Product PDFs/Flashing_Animating_apps.pdf

Regards,

Mike Monett

 

[Mike Monett]

That's what I thought. But in any case, I don't believe his problem
is a matter of destroying the triacs with excessive current since the
thing works after the problme occurs when taken back to the lab or
whatever. Possibly something in the driver circuit that's not turning
completely off.

Maybe a marginal design where the sign is in direct sunlight and the extra
heating in the triac increases the leakage so it won't turn off?

If so, bringing it back to the lab removes the sunlight and it now works.

One way to reduce the inrush current is to add a NTC resistor in series
with the AC line. This is used in ordinary PC power supplies, where the
inrush current charging the caps could be 50 times the normal operating
current.

Here's an article that discusses different methods of limiting inrush
current. It is slanted towards selling their new product, so some of the
numbers are skewed. But otherwise not a bad overview.

http://www.st.com/stonline/products/literature/ta/9115.pdf

Regards,

Mike Monett

 

[Sam Goldwasser]

Maybe a marginal design where the sign is in direct sunlight and the extra
heating in the triac increases the leakage so it won't turn off?

Sure, it's possible. That's why I asked in a previous post for him to
provide the schematic. Could be that the traics are very sensitive
and there's enough leakage in the driver under some conditions.

If so, bringing it back to the lab removes the sunlight and it now works.

One way to reduce the inrush current is to add a NTC resistor in series
with the AC line. This is used in ordinary PC power supplies, where the
inrush current charging the caps could be 50 times the normal operating
current.

How well would this hold up to continuous cycling?

Here's an article that discusses different methods of limiting inrush
current. It is slanted towards selling their new product, so some of the
numbers are skewed. But otherwise not a bad overview.

http://www.st.com/stonline/products/literature/ta/9115.pdf

Sure, but inrush current may not have anything to do with his problem.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
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[Mike Monett]

How well would this hold up to continuous cycling?

As the article describes, you need to allow enough time for the NTC to cool
before starting another cycle. It also recommends waiting for the
transformer to cool, so this may solve both problems.

Sure, but inrush current may not have anything to do with his problem.

Maybe it adds enough heating to the triac to make it fail in the
application. Unfortunately, these are all just guesses as the OP never
replied to your request for schematics.

Regards,

Mike Monett

 

[Mike Monett]

[...]

How well would this hold up to continuous cycling?

Good question. I did some followup and found some good NTC design
articles on the web. This gives the design process to select the NTC
resistor:

http://www.rtie.com/ntc/surggard.htm

This shows the process for transformers:

http://www.ametherm.com/Transformer_case_study.htm

The problem is cooldown of the NTC resistor. Most sites recommend 60
seconds, which may be too long for a flashing sign. One answer may
be to bring the current up in steps. The following describes the
process:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There is a design technique engineers can employ to eliminate the
problems posed by the cool-down/recovery time required for Surge
Limiters to return to their initial level of resistance.
Essentially, this involves designing inrush current protection to
drop the Surge Limiters out of the circuit after they have performed
their function. By removing them from the circuit once the initial
surge has passed, the thermistors have an opportunity to cool down,
so they are ready to respond to a subsequent surge after a power
drop-out occurs.

This technique requires the addition of either a relay or a triac in
parallel with the Surge Limiters, plus the circuits necessary to
control it. All the components of the protection circuit would be in
series with the input to the line. Once the inrush current has been
absorbed by the thermistor, then either the triac starts firing or
the relay closes. The simplest method of powering these components
is from the power supply itself. Once the power supply starts, it
closes the relay or fires the triac, dropping the thermistor out of
the circuit and allowing it to cool down and regain its initial
resistance, so it's ready to provide inrush current protection.

http://www.ametherm.com/Inrush_Current/inrush_current_faq.html

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A simpler approach might be to use fixed resistors instead of NTC.
This would eliminate any problems with ambient temperature and
allow increasing the cycle time to a rate suitable for flashing
signs.

Regards,

Mike Monett

 

[Winfield Hill]

Zak wrote...

The problem with switching transformer primaries with triacs is
the high inrush current that can develop.
[snip]

There are several solutions, including zero-crossing switching,
or a two-stage switch with a series resistor in the first path,
or both.

It is 'maximum voltage switching' that should be used in this case,
isn't it? Switching on at zero crossing will start with a demagnetized
core handing the full voltage * time integral, where in operation it
would start out with the opposite magnetization.

Thanks, Thomas, I stand corrected.

 

[Phil Allison]

"Mike Monett"

http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3206.pdf

http://www.allanson.com/Product PDFs/Flashing_Animating_apps.pdf

** The first pdf article seems to date from the late 60s or mid 70s.

The second is both desperate and dateless.

Nevermind.

The factual content is timeless anyhow.






........ Phil