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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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#41
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Mains transformer goodness
"Paul E. Schoen" wrote: "Eeyore" wrote N_Cook wrote: I was trying to find a table or formula for toroidal inrush current versus power rating, but nothing found. Well of course you won't you mental retard. It depends on the exact construction of the transformer, the load and the instant at which it is switched on in the mains cycle. Why do you have to clog up these groups with your infantile questions ? If in doubt fit a Surge-Gard in series. Toroidal trannies do seem to have higher inrush currents due to remanent magnetism. If there are an unequal number of positive and negative half-cycles applied, the effect is a net DC component that magnetizes the core. Depending on the phase of the next application of voltage, this could add to the normal surge and cause very high inrush for a couple of mSec, which can trip some sennsitive breakers or pop fuses. I have tried adding series thermistors, but they only work when they are cold, and in our application we applied multiple surges that heated them and reduced their effectiveness. True, but effective in 'most' instances according to application. Another solution is to place a time-delayed relay across the surge-gard so it cools quickly again. In normal applications where power is switched infrequently, they work well. Another method is to apply soft turn-on or gradual turn-off using a triac with phase modulation to demagnetize the core or reduce the turn-on surge. Never tried the triac idea. With the relay shunt mentioned above, some people also used fixed value power resistors. Fine as long as no appreciable current is drawn before the relay closes. Graham |
#42
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Mains transformer goodness
wrote in
: On Fri, 20 Mar 2009 17:09:21 -0400, Ecnerwal wrote: In article , "Kalarama" wrote: I would really worry about inhaling/handling the slightest amount of PCBs. Especially if the unit was manufactured before the '70s. (@_@) Then you'd be somewhat less than brilliant. No mention of transformer oil was involved, and nobody is likely to uncan an oil filled transformer in their living room. A dry, varnished/lacquered transformer has no oil, so no PCBs. It ain't necessarily so. Start with this for current US regulation: http://ecfr.gpoaccess.gov/cgi/t/text...cfrbrowse/Titl e40/40cfr761_main_02.tpl . More useful for answering questions: http://en.wikipedia.org/wiki/Polychlorinated_biphenyl -- bz please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. remove ch100-5 to avoid spam trap |
#43
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Mains transformer goodness
N_Cook wrote: I thought the disjunctures between the laminations of conventional Tx set up miniature magnetic circuits They're called air gaps between the E and I laminations and cannot be completely avoided. in opposition to the magnetising field They alter the permeability of the core. and so reduced the current inrush. Toroidal formers don't have these. Indeed, toroids don't have air gaps. Graham |
#44
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Mains transformer goodness
On Wed, 25 Mar 2009 15:25:30 +0000, Eeyore
wrote: N_Cook wrote: I thought the disjunctures between the laminations of conventional Tx set up miniature magnetic circuits They're called air gaps between the E and I laminations and cannot be completely avoided. in opposition to the magnetising field They alter the permeability of the core. and so reduced the current inrush. Toroidal formers don't have these. Indeed, toroids don't have air gaps. --- http://www.google.com/search?hl=en&r...+transf ormer JF |
#45
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Mains transformer goodness
John Fields wrote: Eeyore wrote: N_Cook wrote: I thought the disjunctures between the laminations of conventional Tx set up miniature magnetic circuits They're called air gaps between the E and I laminations and cannot be completely avoided. in opposition to the magnetising field They alter the permeability of the core. and so reduced the current inrush. Toroidal formers don't have these. Indeed, toroids don't have air gaps. --- http://www.google.com/search?hl=en&r...+transf ormer Yes yes yes. If you want something special you can get it. It isn't what N Cook was talking about though. Stop obfuscating. It makes you look silly. Graham |
#46
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Mains transformer goodness
"Phil Allison" wrote in message ... "Paul E. Schoen" Toroidal trannies do seem to have higher inrush currents due to remanent magnetism. ** Nonsense. The Wiki says otherwise. And I have had a lot of experience with high power toroids and have seen the effects of high inrush current. http://en.wikipedia.org/wiki/Inrush_current If there are an unequal number of positive and negative half-cycles applied, the effect is a net DC component that magnetizes the core. ** Utter ********. I have personally observed this in our circuit breaker test sets. We take care to apply voltage at about 70 degrees phase angle to obtain an initial current peak equal to those that follow, and adjust the timing so that there are equal numbers of positive and negative half-cycles. Inrush current on successive pulses is minimal. But if there is an unequal number, and a net DC component, there is always a much higher peak inrush current. This is easily seen with short duration pulses of several cycles. In breaker testing, of course, the breaker may trip at any time, sometimes causing net DC, and the next operation usually exhibits high inrush. Some other references: http://relays.tycoelectronics.com/ap...fs/13c3206.pdf http://powerelectronics.com/mag/powe...tions_solving/ http://www.melcontransformers.info/i...ransformer.pdf Paul |
#47
Posted to sci.electronics.repair,sci.electronics.design
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Mains transformer goodness
"Robert Baer" wrote in message net... Paul E. Schoen wrote: Toroidal trannies do seem to have higher inrush currents due to remanent magnetism. If there are an unequal number of positive and negative half-cycles applied, the effect is a net DC component that magnetizes the core. Depending on the phase of the next application of voltage, this could add to the normal surge and cause very high inrush for a couple of mSec, which can trip some sennsitive breakers or pop fuses. I have tried adding series thermistors, but they only work when they are cold, and in our application we applied multiple surges that heated them and reduced their effectiveness. In normal applications where power is switched infrequently, they work well. Another method is to apply soft turn-on or gradual turn-off using a triac with phase modulation to demagnetize the core or reduce the turn-on surge. Paul Where did the trannie get the sex change? A Massive Prong was removed, forming the hole in the donut. Paul |
#48
Posted to sci.electronics.repair,sci.electronics.design
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Mains transformer goodness
Paul E. Schoen wrote in message
... "Phil Allison" wrote in message ... "Paul E. Schoen" Toroidal trannies do seem to have higher inrush currents due to remanent magnetism. ** Nonsense. The Wiki says otherwise. And I have had a lot of experience with high power toroids and have seen the effects of high inrush current. http://en.wikipedia.org/wiki/Inrush_current If there are an unequal number of positive and negative half-cycles applied, the effect is a net DC component that magnetizes the core. ** Utter ********. I have personally observed this in our circuit breaker test sets. We take care to apply voltage at about 70 degrees phase angle to obtain an initial current peak equal to those that follow, and adjust the timing so that there are equal numbers of positive and negative half-cycles. Inrush current on successive pulses is minimal. But if there is an unequal number, and a net DC component, there is always a much higher peak inrush current. This is easily seen with short duration pulses of several cycles. In breaker testing, of course, the breaker may trip at any time, sometimes causing net DC, and the next operation usually exhibits high inrush. Some other references: http://relays.tycoelectronics.com/ap...fs/13c3206.pdf http://powerelectronics.com/mag/powe...tions_solving/ http://www.melcontransformers.info/i...ransformer.pdf Paul Can a toroidal former become permanently magnetised and cause excessive current draw. ? One, in front of me from an amp, drawing excess current , does not attract a small piece of iron. I don't know what the main secondaries are supposed to provide, but can give 300 watts into 4 ohms. I've wound off the primaries (yes external to the secondaries) to try and understand what is going on with this transfornmer. Applying 70 volt ac , from a variac, across series secondaries is ok but increase to 75 volt and the current draw goes up to 1/4 amp. Should be able to take twice that voltage. Absolutely no visible problem , to the wiring or the coating of the toroid and both secondaries measure DMM the same DC. Tomorrow will apply something a bit over 70 volt with temperature sensitive labels fitted around. I will even try a TV degaussing coil. |
#49
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Mains transformer goodness
"Paul E. Schoen" "Phil Allison" Toroidal trannies do seem to have higher inrush currents due to remanent magnetism. ** Nonsense. The Wiki says otherwise. ** The wiki is totally WRONG on this one. The rather higher inrush surge of a toroidal mains tranny is explained by the nature of the wound strip core itself - not on past history. If there are an unequal number of positive and negative half-cycles applied, the effect is a net DC component that magnetizes the core. ** Utter ********. I have personally observed this in our circuit breaker test sets. ** Got nothing to do with the UTTER DRIVEL you just posted. Normal users do NOT do the weird **** to transformers that you do - yet still suffer from large inrush surges. So YOU ARE 100% WRONG - YET AGAIN. ...... Phil |
#50
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Mains transformer goodness
"N_Kook" Can a toroidal former become permanently magnetised and cause excessive current draw ? ** No. Normal use on an AC supply very quickly demagnetises the core - if it ever becomes magnetised. ...... Phil |
#51
Posted to sci.electronics.repair,sci.electronics.design
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Mains transformer goodness
"N_Cook" wrote in message ... Can a toroidal former become permanently magnetised and cause excessive current draw. ? One, in front of me from an amp, drawing excess current , does not attract a small piece of iron. I don't know what the main secondaries are supposed to provide, but can give 300 watts into 4 ohms. I've wound off the primaries (yes external to the secondaries) to try and understand what is going on with this transfornmer. Applying 70 volt ac , from a variac, across series secondaries is ok but increase to 75 volt and the current draw goes up to 1/4 amp. Should be able to take twice that voltage. Absolutely no visible problem , to the wiring or the coating of the toroid and both secondaries measure DMM the same DC. Tomorrow will apply something a bit over 70 volt with temperature sensitive labels fitted around. I will even try a TV degaussing coil. Once you apply some AC voltage to the primary the remanent magnetism should be neutralized, and you should be able to apply full rated voltage without saturation. If the winding were made of the wrong material, such as perhaps hardened steel, perhaps a powerful DC pulse could essentially make a permanent magnet which would take a reverse pulse to neutralize. That seems unlikely, but you might see the effect if you observe the current waveform on a scope. I would think you would see peaking on one set of half-cycles and not the other. Most likely you have a shorted turn, and as the voltage rises, it starts to break down. Again, if you observe current waveform on a scope, you might see spikes near the peaks. If you are talking about an audio transformer, 300 watts into 4 ohms is about 35 volts. But it has to be able to work down to about 20 Hz, so it would handle 100 volts at 60 Hz. If this is a power transformer, it probably needs to generate a +/- DC supply for direct drive into 4 ohms, which will require about 50 volts DC. Two windings of 35 to 50 VRMS would be about right. So two in series might be 70 VAC, which corresponds to your readings. Paul |
#52
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Mains transformer goodness
"N_Kook" I don't know what the main secondaries are supposed to provide, but can give 300 watts into 4 ohms. ** So the amp's DC rails are about +/- 53 volts. Means the tranny likely has two secondaries, each of 38 volts. I've wound off the primaries (yes external to the secondaries) to try and understand what is going on with this transformer. Applying 70 volt ac , from a variac, across series secondaries is ok but increase to 75 volt and the current draw goes up to 1/4 amp. ** Spot on. Should be able to take twice that voltage. ** Absolute, ****ing ******** !! Wot moronic math is this anencephalic pommy turdbrain using ? Tomorrow will apply something a bit over 70 volt with temperature sensitive labels fitted around. I will even try a TV degaussing coil. ** ****wit morons like YOU should be locked up for the safety of the public. ..... Phil |
#53
Posted to sci.electronics.repair,sci.electronics.design
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Mains transformer goodness
On Wed, 25 Mar 2009 12:46:32 +0000 (UTC), bz
wrote: wrote in : On Fri, 20 Mar 2009 17:09:21 -0400, Ecnerwal wrote: In article , "Kalarama" wrote: I would really worry about inhaling/handling the slightest amount of PCBs. Especially if the unit was manufactured before the '70s. (@_@) Then you'd be somewhat less than brilliant. No mention of transformer oil was involved, and nobody is likely to uncan an oil filled transformer in their living room. A dry, varnished/lacquered transformer has no oil, so no PCBs. It ain't necessarily so. Start with this for current US regulation: http://ecfr.gpoaccess.gov/cgi/t/text...cfrbrowse/Titl e40/40cfr761_main_02.tpl . More useful for answering questions: http://en.wikipedia.org/wiki/Polychlorinated_biphenyl While it gives good background on PCBs it does not inform on the regulatory situation. Moreover some of the background is missing, like the presence of PCBs in varnishes and potting compounds used for ballasts and transformers. Also regulation wise very nearly all uses of PCBs are now banned. |
#54
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Mains transformer goodness
wrote in
: On Wed, 25 Mar 2009 12:46:32 +0000 (UTC), bz wrote: wrote in m: On Fri, 20 Mar 2009 17:09:21 -0400, Ecnerwal wrote: In article , "Kalarama" wrote: I would really worry about inhaling/handling the slightest amount of PCBs. Especially if the unit was manufactured before the '70s. (@_@) Then you'd be somewhat less than brilliant. No mention of transformer oil was involved, and nobody is likely to uncan an oil filled transformer in their living room. A dry, varnished/lacquered transformer has no oil, so no PCBs. It ain't necessarily so. Start with this for current US regulation: http://ecfr.gpoaccess.gov/cgi/t/text.../ecfrbrowse/Ti tl e40/40cfr761_main_02.tpl . More useful for answering questions: http://en.wikipedia.org/wiki/Polychlorinated_biphenyl While it gives good background on PCBs it does not inform on the regulatory situation. Moreover some of the background is missing, like the presence of PCBs in varnishes and potting compounds used for ballasts and transformers. Also regulation wise very nearly all uses of PCBs are now banned. The wiki DOES mention the use of PCB as plasticizes in insulation, and gives a time-line for the production and use, thus gives us a good idea of which products might contain PCBs. As a chemist (BS 1970), I have some familiarity with PCBs and the hazards and regulations associated with them. As a TEA Certified Electronic Technician, I have experience servicing electronic equipment. I also have practice in reading regulations. However I still found the Wiki much more useful than the regulations. The simple fact that REGULATION WISE, the use of PCBs are now banned, in almost all cases, is easy enough to make without the reams of [almost] unreadable regulations. If there is a particular SECTION of the regulations that you found particularly illuminating and informative, PLEASE point it out to us. My quick skim of the regulations did NOT give me any useful information other than PCBs are banned and must be disposed of carefully and under carefully controlled and regulated conditions. What point were YOU trying to make by citing that reference??? -- bz 73 de N5BZ k please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. remove ch100-5 to avoid spam trap |
#55
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Mains transformer goodness
John Fields wrote: http://www.google.com/search?hl=en&r...+transf ormer Actually, the moment you put a gap there, the core is no longer geometrically a toroid any more. Graham |
#56
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Mains transformer goodness
Phil Allison wrote: "Paul E. Schoen" I have tested some toroidal trannies that seem to saturate quite slowly with increased primary voltage. ** Not true of any normal commercial toroidal sold for use with AC supply, Depends on the working flux Phil. If one had been designed for very low radiated field, it's entirely possible that effect would occur. Graham |
#57
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Mains transformer goodness
JosephKK wrote: On Fri, 20 Mar 2009 17:09:21 -0400, Ecnerwal wrote: In article , "Kalarama" wrote: I would really worry about inhaling/handling the slightest amount of PCBs. Especially if the unit was manufactured before the '70s. (@_@) Then you'd be somewhat less than brilliant. No mention of transformer oil was involved, and nobody is likely to uncan an oil filled transformer in their living room. A dry, varnished/lacquered transformer has no oil, so no PCBs. It ain't necessarily so. Start with this for current US regulation: http://ecfr.gpoaccess.gov/cgi/t/text...61_main_02.tpl This has zero relevance to the OP. |
#58
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Mains transformer goodness
"Paul E. Schoen" wrote: It would also be helpful to know how the toroid was mounted, and if the failure occurred where pressure was applied. Toroids are usually mounted either flat with washers and rubber gaskets with a single screw through the hole, or vertically in an "Omega" bracket, with some rubber cushioning material around the periphery. But in either case there may be additional pressure on a "high spot" where two windings may be crossed, and softening of the insulation from overheating may also contribute to a short. Not to mention the possibility of overtorqueing on top of that. What goes on in some places is unreal. I've even seen steel TO-3 flanges dimpled by the mounting bolts pulling into the clearance hole ! Graham |
#59
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Mains transformer goodness
"Paul E. Schoen" wrote: "Robert Baer" wrote in message Where did the trannie get the sex change? A Massive Prong was removed, forming the hole in the donut. Hilarious. ;~) Graham |
#60
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Mains transformer goodness
N_Cook wrote: Can a toroidal former become permanently magnetised and cause excessive current draw. ? Unbelievable. Graham |
#61
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Mains transformer goodness
Phil Allison wrote: "N_Kook" I don't know what the main secondaries are supposed to provide, but can give 300 watts into 4 ohms. ** So the amp's DC rails are about +/- 53 volts. Means the tranny likely has two secondaries, each of 38 volts. I've wound off the primaries (yes external to the secondaries) to try and understand what is going on with this transformer. Applying 70 volt ac , from a variac, across series secondaries is ok but increase to 75 volt and the current draw goes up to 1/4 amp. ** Spot on. Should be able to take twice that voltage. ** Absolute, ****ing ******** !! Wot moronic math is this anencephalic pommy turdbrain using ? Tomorrow will apply something a bit over 70 volt with temperature sensitive labels fitted around. I will even try a TV degaussing coil. ** ****wit morons like YOU should be locked up for the safety of the public. He certainly shouldn't be repairing electronic equipment. I'm wondering if he has the necessary qualifications. Graham |
#62
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Mains transformer goodness
"Eeyore" Phil Allison wrote: "Paul E. Schoen" I have tested some toroidal trannies that seem to saturate quite slowly with increased primary voltage. ** Not true of any normal commercial toroidal sold for use with AC supply, Depends on the working flux Phil. If one had been designed for very low radiated field, it's entirely possible that effect would occur. ** Utter ********. The sharpness of the saturation knee is NOT a function of AC primary voltage. ....... Phil |
#63
Posted to sci.electronics.repair,sci.electronics.design
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Mains transformer goodness
On Thu, 26 Mar 2009 12:40:16 +0000 (UTC), bz
wrote: wrote in : snip While it gives good background on PCBs it does not inform on the regulatory situation. Moreover some of the background is missing, like the presence of PCBs in varnishes and potting compounds used for ballasts and transformers. Also regulation wise very nearly all uses of PCBs are now banned. The wiki DOES mention the use of PCB as plasticizes in insulation, and gives a time-line for the production and use, thus gives us a good idea of which products might contain PCBs. As a chemist (BS 1970), I have some familiarity with PCBs and the hazards and regulations associated with them. As a TEA Certified Electronic Technician, I have experience servicing electronic equipment. I also have practice in reading regulations. However I still found the Wiki much more useful than the regulations. The simple fact that REGULATION WISE, the use of PCBs are now banned, in almost all cases, is easy enough to make without the reams of [almost] unreadable regulations. Gee, i did not find them unreadble. If there is a particular SECTION of the regulations that you found particularly illuminating and informative, PLEASE point it out to us. My quick skim of the regulations did NOT give me any useful information other than PCBs are banned and must be disposed of carefully and under carefully controlled and regulated conditions. What point were YOU trying to make by citing that reference??? No thanks, i already did that work twice for my cow-orkers. It was not worth it, they did not learn a darn thing. Twice burned by others whose job was to keep up with this stuff. |
#64
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Mains transformer goodness
Phil Allison wrote: "Eeyore" Phil Allison wrote: "Paul E. Schoen" I have tested some toroidal trannies that seem to saturate quite slowly with increased primary voltage. ** Not true of any normal commercial toroidal sold for use with AC supply, Depends on the working flux Phil. If one had been designed for very low radiated field, it's entirely possible that effect would occur. ** Utter ********. The sharpness of the saturation knee is NOT a function of AC primary voltage. It's a function of working flux density. A transformer designed for low radiated field might be operating at a much lower working flux than a standard commercial type, hence it would take much more magnetising force i.e. primary volts before saturation. Simple physics. Graham |
#65
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Mains transformer goodness
JosephKK wrote: On Thu, 26 Mar 2009 12:40:16 +0000 (UTC), bz wrote: If there is a particular SECTION of the regulations that you found particularly illuminating and informative, PLEASE point it out to us. My quick skim of the regulations did NOT give me any useful information other than PCBs are banned and must be disposed of carefully and under carefully controlled and regulated conditions. What point were YOU trying to make by citing that reference??? No thanks, i already did that work twice for my cow-orkers. It was not worth it, they did not learn a darn thing. Twice burned by others whose job was to keep up with this stuff. Tell me about it ! Graham |
#66
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Mains transformer goodness
"Eeyore" wrote in message ... Phil Allison wrote: "Eeyore" Phil Allison wrote: "Paul E. Schoen" I have tested some toroidal trannies that seem to saturate quite slowly with increased primary voltage. ** Not true of any normal commercial toroidal sold for use with AC supply, Depends on the working flux Phil. If one had been designed for very low radiated field, it's entirely possible that effect would occur. ** Utter ********. The sharpness of the saturation knee is NOT a function of AC primary voltage. It's a function of working flux density. A transformer designed for low radiated field might be operating at a much lower working flux than a standard commercial type, hence it would take much more magnetising force i.e. primary volts before saturation. Simple physics. Actually there are two considerations here that may prove Phil to be correct in his assertion. The first is that the transformer I tested was a custom wound unit which was essentially just a primary winding with the secondary to be bus bars through the center hole, and it had been wound for a particular output voltage on a specific size core, so it had more turns than were optimal. Before management abandoned the project (and essentially scrapped about 20 toroids), I removed about 20% of the primary turns and increased the output voltage. The second consideration is that I performed my measurements by using a variable AC source and a transformer of perhaps 250 VA with a 480 VAC secondary. So, as the voltage approached saturation, and current increased, the waveform probably became distorted, which allowed a slightly higher RMS value to be applied with less current than might have been drawn with a better waveform. But the values I posted were from my actual notes, and not from memory. Paul |
#67
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Mains transformer goodness
"Eeysore"
Phil Allison wrote: "Paul E. Schoen" I have tested some toroidal trannies that seem to saturate quite slowly with increased primary voltage. ** Not true of any normal commercial toroidal sold for use with AC supply, Depends on the working flux Phil. If one had been designed for very low radiated field, it's entirely possible that effect would occur. ** Utter ********. The sharpness of the saturation knee is NOT a function of AC primary voltage. It's a function of working flux density. ** More ********. The saturation knee curve shape is a property of the magnetic strip. As usual - you have snipped and ignored the context. ..... Phil |
#68
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Mains transformer goodness
On Fri, 27 Mar 2009 19:15:35 +0000, Eeyore
wrote: JosephKK wrote: On Thu, 26 Mar 2009 12:40:16 +0000 (UTC), bz wrote: If there is a particular SECTION of the regulations that you found particularly illuminating and informative, PLEASE point it out to us. My quick skim of the regulations did NOT give me any useful information other than PCBs are banned and must be disposed of carefully and under carefully controlled and regulated conditions. What point were YOU trying to make by citing that reference??? No thanks, i already did that work twice for my cow-orkers. It was not worth it, they did not learn a darn thing. Twice burned by others whose job was to keep up with this stuff. Tell me about it ! Graham In 'mericanese "I hear you bro" is more appropo. |
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