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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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problem with triacs with neon transformer loads
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 |
#2
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problem with triacs with neon transformer loads
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#4
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problem in triac circuit with neon transformer loads
Winfield Hill wrote: 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. -- Thanks, - Win 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 |
#5
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problem with triacs with neon transformer loads
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#6
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problem with triacs with neon transformer loads
"Winfield Hill" = an asinine, ivory tower lurking, ****ing 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 ****ing 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 |
#7
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problem with triacs with neon transformer loads
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#8
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problem in triac circuit with neon transformer loads
writes:
Winfield Hill wrote: 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. -- Thanks, - Win 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/ +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. |
#9
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problem with triacs with neon transformer loads
On 19 May 2006 04:18:15 -0700, wrote:
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 -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice480)460-2350 | | | E-mail Address at Website Fax480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
#10
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problem with triacs with neon transformer loads
Winfield Hill 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. Thomas |
#11
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problem with triacs with neon transformer loads
Zak writes:
Winfield Hill 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. 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. |
#12
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problem with triacs with neon transformer loads
On Sat, 20 May 2006 16:23:43 +0200, Zak wrote:
Winfield Hill 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. 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 -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice480)460-2350 | | | E-mail Address at Website Fax480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
#13
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problem with triacs with neon transformer loads
"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 |
#14
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problem with triacs with neon transformer loads
Sam Goldwasser wrote in
: 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/...re/ta/9115.pdf Regards, Mike Monett |
#15
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problem with triacs with neon transformer loads
Zak wrote...
Winfield Hill 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. -- Thanks, - Win |
#16
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problem with triacs with neon transformer loads
"Mike Monett" http://relays.tycoelectronics.com/ap...fs/13c3206.pdf http://www.allanson.com/Product%20PD...ating_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 |
#17
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problem with triacs with neon transformer loads
Winfield Hill wrote:
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. Thanks, - Win OK, it's clear due to the phase lag of an inductor, switching an inductive load at a zero-cross will give high inrush current. It should be switched at the peak, or some other method should be used to limit the inrush current. But I was still having problems understanding the inrush current due to remanence. Modern transformers use low-remanence steel, so why should there be a problem? I finally found an article that offers an explanation. It shows the inrush current superimposed on the BH curve for two values of remanence, and describes the efforts needed to find a better low-cost steel: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~ Today's grain-oriented steels work with a fraction of the losses, at higher permeability, and they can be driven harder at elevated induction levels. But there are consequences. The magnetizing curve is no longer soft and round, because it has turned square and hard. However coincidental, the combination of high permeability and square loop comprise a major component of the formula for inrush. Improved steels have enabled smaller, lighter and less costly transformers. Yet, those same improvements have created a generation of transformers that draw immense amounts of current at start up. Although it probably was not a problem in 1954, inrush current is definitely a problem today - one that concerns every primary circuit designer. http://powerelectronics.com/mag/404PET20.pdf ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~ This makes sense. I just salvaged the transformers and magnetrons from a dozen old microwave ovens for a high power heating experiment. The transformers in the oldest ovens were huge and heavy monsters, but the later versions were much smaller. Regards, Mike Monett |
#18
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problem with triacs with neon transformer loads
In article ,
Winfield Hill wrote: [.. neon sign xformer ..] The problem with switching transformer primaries with triacs is the high inrush current that can develop. Yes, but not, I think for the reason you suggest. The secondary capacitance of the transformer reflects back into the primary. There is a primary leakage inductance that is intentionally built into the transformer to limit the current secondary to under (IIRC) 6mA. Between these two effects, you end up with a funny ring when the switch closes. It could be that something in this is getting his triac. Also the OP didn't say anything about snubbing. The triac may be refiring on the dv/dt when it switches off. -- -- forging knowledge |
#19
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problem with triacs with neon transformer loads
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#20
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problem with triacs with neon transformer loads
"Mike Monett" OK, it's clear due to the phase lag of an inductor, switching an inductive load at a zero-cross will give high inrush current. ** Absolute nonsense. The inrush surge is caused by *core saturation* and consequent temporary LOSS of primary inductance. The core saturates because of the DC component ( really a low frequency transient) generated by switching a sine wave. It should be switched at the peak, or some other method should be used to limit the inrush current. ** A rapid "fade up" using a triac with phase control is one way. But I was still having problems understanding the inrush current due to remanence. Modern transformers use low-remanence steel, so why should there be a problem? ** Where it exists, it just makes the worst case inrush surge larger. The peak surge current approaches the zero inductance situation in many cases. So, I pk = V pk / R primary Eg. A 1 kVA transformer ( R primary =1 ohm) can be expected to exhibit 300 amp peak surges on a 230 volt supply. .......... Phil |
#21
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problem with triacs with neon transformer loads
wrote:
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 Try swapping the connections to the triacs and see if the problem stays with the MOC3083 driver or BTA41 triac. Here are the datasheets for the triacs: http://www.st.com/stonline/products/...7469/bta40.pdf http://www.ortodoxism.ro/datasheets/...la/MOC3082.pdf Did you know the optocoupler is a zero cross? Here's the description: "The MOC3081, MOC3082 and MOC3083 devices consist of gallium arsenide infrared emitting diodes optically coupled to monolithic silicon detectors performing the function of Zero Voltage Crossing bilateral triac drivers." In the datasheet, there is a statement near Figure 8: "*For highly inductive loads (power factor 0.5), change this value to 360 ohms." but I can't see what it refers to. Maybe there is a way to make it switch at the voltage peak for inductive loads. This might help reduce the inrush current and reduce heating in the BTA41 triacs. Regards, Mike Monett |
#22
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problem with triacs with neon transformer loads
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#23
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problem with triacs with neon transformer loads
In article ,
Mike Monett wrote: (Ken Smith) wrote: In article , Winfield Hill wrote: [.. neon sign xformer ..] The problem with switching transformer primaries with triacs is the high inrush current that can develop. Yes, but not, I think for the reason you suggest. The secondary capacitance of the transformer reflects back into the primary. There is a primary leakage inductance that is intentionally built into the transformer to limit the current secondary to under (IIRC) 6mA. Between these two effects, you end up with a funny ring when the switch closes. It could be that something in this is getting his triac. Also the OP didn't say anything about snubbing. The triac may be refiring on the dv/dt when it switches off. Here's the original post: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~ 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? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~ He has two triacs connected to one flasher channel. It worked for 4 months. Then one channel failed while the other continued working. Both worked when he took it to the lab. Returned to service, same problem after two weeks. Do you think a ringing problem or dv/dt could give these symptoms? Yes: The dv/dt problem prevents the traic from ever turning the transformer off. Every time it switches off, the dv/dt turns it right back on again. There may be some smallish change in the output voltage but the light would remain on. The ringing can be passing a large current spike through the triac. The triac is now, in fact, damaged. When you damage a BJT or a triac, often the first sign is that the breakdown voltage is reduced. The effect is often progressive. This could cause a breakdown firing problem at high mains voltage. -- -- forging knowledge |
#24
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problem with triacs with neon transformer loads
(Ken Smith) wrote:
Yes: The dv/dt problem prevents the traic from ever turning the transformer off. Every time it switches off, the dv/dt turns it right back on again. There may be some smallish change in the output voltage but the light would remain on. The ringing can be passing a large current spike through the triac. The triac is now, in fact, damaged. When you damage a BJT or a triac, often the first sign is that the breakdown voltage is reduced. The effect is often progressive. This could cause a breakdown firing problem at high mains voltage. forging knowledge So why does one channel fail in the field after some period of time, work in the lab, then work in the field but fail again after another delay? And the other channel apparently works fine. That's what I was referring to when I asked if you thought a ringing problem or dv/dt could give those symptoms. Somehow it deoesn't seem possible that a ringing or dv/dt problem could heal itself, then fail again after a delay. Especially when you describe ringing as a progressive reduction in breakdown voltage. Regards, Mike Monett |
#25
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problem with triacs with neon transformer loads
Hi
Look for SGS-Thomson application note "Control by a triac for an inductiv load" You will find the solution in using an alternistor instead of a triac for this purpose. Schematics included alternistor = TPDV 640 .... 1240 Ton Visch wrote: wrote: 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 Firstly as has been mentioned switch on at the AC maximum to reduce the inrush. Triacs are not good for this application since they go off at the current zero crossing point which is when the voltage is near maximum. This sudden application can cause the triac to conduct during the current "off" time so when the current tries to reverse you get conduction once again. Large snubbers can help out but its marginal at best, this is why sometimes it works and sometimes doesnt. The solution is to chuck out the triac and use two thyristors instead. |
#26
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problem with triacs with neon transformer loads
In article ,
Mike Monett wrote: (Ken Smith) wrote: Yes: The dv/dt problem prevents the traic from ever turning the transformer off. Every time it switches off, the dv/dt turns it right back on again. There may be some smallish change in the output voltage but the light would remain on. The ringing can be passing a large current spike through the triac. The triac is now, in fact, damaged. When you damage a BJT or a triac, often the first sign is that the breakdown voltage is reduced. The effect is often progressive. This could cause a breakdown firing problem at high mains voltage. forging knowledge So why does one channel fail in the field after some period of time, work in the lab, then work in the field but fail again after another delay? And the other channel apparently works fine. That's what I was referring to when I asked if you thought a ringing problem or dv/dt could give those symptoms. Somehow it deoesn't seem possible that a ringing or dv/dt problem could heal itself, then fail again after a delay. Especially when you describe ringing as a progressive reduction in breakdown voltage. The OP hasn't stated whether it starts working again if he stands on his left foot or the neighbor turns on his toaster. I assume the circuit is right on the edge of the working/not working bondary. Regards, Mike Monett -- -- forging knowledge |
#27
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problem with triacs with neon transformer loads
(Ken Smith) wrote:
The OP hasn't stated whether it starts working again if he stands on his left foot or the neighbor turns on his toaster. I assume the circuit is right on the edge of the working/not working bondary. forging knowledge Then any degredation should make it fail permanently. Anyway, Fred thinks the post is a hoax. Regards, Mike Monett |
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