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#1
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Inrush Surge pics
** Hi tubeheads, these JPEGs were taken late in 2009 using my Rigol DSO. The first is a 1kVA step down ( 240V to 120V) E -Core transformer with no load. http://sound.au.com/tmp/surge-002.jpg The second is a commercial powered speaker with in built 200 watt SS amplifier using a 300VA toroidal tranny. http://sound.au.com/tmp/surge-001.jpg The smaller current peaks are due to filter electros charging. The moment of switch on was close to a zero crossing of the AC supply - with the voltage going positive. See the captions. Note how the transformer current surges are all the same polarity and peak as the AC voltage is crossing zero. .... Phil |
#2
Posted to rec.audio.tubes
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Inrush Surge pics
"Phil Allison" wrote in message ... ** Hi tubeheads, these JPEGs were taken late in 2009 using my Rigol DSO. The first is a 1kVA step down ( 240V to 120V) E -Core transformer with no load. http://sound.au.com/tmp/surge-002.jpg The second is a commercial powered speaker with in built 200 watt SS amplifier using a 300VA toroidal tranny. http://sound.au.com/tmp/surge-001.jpg The smaller current peaks are due to filter electros charging. The moment of switch on was close to a zero crossing of the AC supply - with the voltage going positive. See the captions. Note how the transformer current surges are all the same polarity and peak as the AC voltage is crossing zero. Apparently, the huge curent surges are due to the core saturation. To avoid them one must turn power switch on the peak(!) of the sinewave, not at the zero-crossing. But then we will have possibly huge surges from charging of the filter caps. However the later are easier to control by adding small R or R+L in series with the diodes. So which is the lesser evil? |
#3
Posted to rec.audio.tubes
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Inrush Surge pics
"Alex Pogossov" "Phil Allison" ** Hi tubeheads, these JPEGs were taken late in 2009 using my Rigol DSO. The first is a 1kVA step down ( 240V to 120V) E -Core transformer with no load. http://sound.au.com/tmp/surge-002.jpg The second is a commercial powered speaker with in built 200 watt SS amplifier using a 300VA toroidal tranny. http://sound.au.com/tmp/surge-001.jpg The smaller current peaks are due to filter electros charging. The moment of switch on was close to a zero crossing of the AC supply - with the voltage going positive. See the captions. Note how the transformer current surges are all the same polarity and peak as the AC voltage is crossing zero. Apparently, the huge curent surges are due to the core saturation. ** Just like pulling the iron core half out of the transformer for a few mS. To avoid them one must turn power switch on the peak(!) of the sinewave, not at the zero-crossing. ** Bit of a special skill, that one. But then we will have possibly huge surges from charging of the filter caps. ** Yep - but rather less peak current for a bit longer and on each half cycle. Cos the secondary copper losses are then involved, as well as the primary ones. However the later are easier to control by adding small R or R+L in series with the diodes. ** There is no issue with silicon diodes or elector caps during start up - both can easily cope with huge surges. The problem is with the AC supply fuse !!! Cos it forces you to use a much bigger rating fuse than would reliably protect the tranny from burn out. ..... Phil |
#4
Posted to rec.audio.tubes
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Inrush Surge pics
On Jun 4, 4:45*pm, "Phil Allison" wrote:
** Hi tubeheads, these JPEGs were taken late in 2009 using my Rigol DSO. The first is a 1kVA step down ( 240V to 120V) E -Core transformer with no load. http://sound.au.com/tmp/surge-002.jpg The second is a commercial powered speaker with in built 200 watt SS amplifier using a 300VA toroidal tranny. http://sound.au.com/tmp/surge-001.jpg The smaller current peaks are due to filter electros charging. The moment of switch on was close to a zero crossing of the AC supply - with the voltage going positive. See the captions. Note how the transformer current surges are all the same polarity and peak as the AC voltage is crossing zero. ... *Phil OK, if you are getting 115 peak amps at tranny turn on and mains source resistance = 1.1 ohms, then at the max peak charge current there is 126.5 Vpk across the source resistance. The winding input *impedance* at the max peak current point would appear to be very low. So what is the voltage being applied to the tranny, allowing for phase shift? less than 340V pk probably. Your test tranny must have very low winding resistance, and with the absence of any magnetic field the voltage sees a short circuit at the instant of turn on until the magnetic field establishes itself, no? The tranny winding resistance in models appears in series with a primary winding. If one had a 5 ohm resistance in series with the tranny, then would not the peak current 340Vpk from the source be much limited? If primary coil input Z = 2 ohms, then total Z + R might be 6 ohms with added R and peak I max = 340/6 = 56A. ARC VT100 have 5 ohms resistance with a relay to shunt the resistance after turn on. But I've found sucha small R ineffective to limit the longer lasting inrush current to rail capacitors. I have one amp with +/- 70V rails and a total of 200,000uF so inrush to charge C up will blow mains fuses unless the fuse value is high, maybe 10 A for 240V input. Hence my prefered use of perhaps 100 ohms with relay shunting after 4 seconds when rails have come up to about 2/3 full value. I guess the 100 ohms cops about 3 amps at the first cycle of 240Vrms applied. The instant power in such an R = 900 Watts, but only for less than 0.02 seconds. I've used 20W rated R with no troubles. Even if one has not calculated or measured all the input currents one soon finds the R value and type which won't fuse open and which will last and which will allow a smaller and more useful fuse value offering more sensitive protection to excessive current draw from the mains in a fault condition. Patrick Turner. |
#5
Posted to rec.audio.tubes
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Inrush Surge pics
"Patrick Turner" Even if one has not calculated or measured all the input currents one soon finds the R value and type which won't fuse open and which will last and which will allow a smaller and more useful fuse value offering more sensitive protection to excessive current draw from the mains in a fault condition. ** That 115 amp surge from the step down tranny is not big enough to blow a 15 amp wire fuse or trip a 16 amp ( thermal magnetic) breaker as fitted to domestic AC supply circuits here in Australia. But it IS big enough to blow a 4 or 5 amp slo-blo glass fuse as would be needed to protect the tranny. Adding a permanent series resistor is not practical - it would dissipate far to much heat. The obvious and simple answer is to use a thermal breaker, rated at 4 or 5 amps - these have long opening times and will ignore most any half cycle surge, eg: http://au.element14.com/te-connectiv...-5a/dp/9659080 If it ever does trip, just push to re-set. Avoids the possibility of users fitting an oversize fuse too. ...... Phil |
#6
Posted to rec.audio.tubes
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Inrush Surge pics
"Phil Allison" wrote in message ... "Alex Pogossov" "Phil Allison" ** Hi tubeheads, these JPEGs were taken late in 2009 using my Rigol DSO. The first is a 1kVA step down ( 240V to 120V) E -Core transformer with no load. http://sound.au.com/tmp/surge-002.jpg The second is a commercial powered speaker with in built 200 watt SS amplifier using a 300VA toroidal tranny. http://sound.au.com/tmp/surge-001.jpg The smaller current peaks are due to filter electros charging. The moment of switch on was close to a zero crossing of the AC supply - with the voltage going positive. See the captions. Note how the transformer current surges are all the same polarity and peak as the AC voltage is crossing zero. Apparently, the huge curent surges are due to the core saturation. ** Just like pulling the iron core half out of the transformer for a few mS. To avoid them one must turn power switch on the peak(!) of the sinewave, not at the zero-crossing. ** Bit of a special skill, that one. But then we will have possibly huge surges from charging of the filter caps. ** Yep - but rather less peak current for a bit longer and on each half cycle. Cos the secondary copper losses are then involved, as well as the primary ones. However the later are easier to control by adding small R or R+L in series with the diodes. ** There is no issue with silicon diodes or elector caps during start p - both can easily cope with huge surges. The problem is with the AC supply fuse !!! Cos it forces you to use a much bigger rating fuse than would reliably protect the tranny from burn out. I can see two ways of killing of the inrush currents. 1. To avoid saturation on turn-on at zero-crossing a transformer shall be so designed that the core would not reach saturation after one half-sine wave, not after a quarter. In other words, the transformer primary shall have double of turns per volt -- inrushless transformer shall be designed say for 240Vac to work in the US 120V environment or to 460Vac to work in Europe. Of course this will make the beast inefficient, twice heavier. larger and costlier for the same wattage. Bean counters would scream! Since you are keen on experimenting, take two identical trannies, connect theis primaries in series (to simulate one tranny with double turns/volt) and do the in-rush test as before. You will see NO INRUSH at all! Not just it will be halved. No. Not at all! Hobbyists perhaps could afford designs where two identical trannies with primaries and secondaries in series are used instead one tranny. But it will be inrush free! 2. How to deal with capacitor charge in-rush. Well, Patric uses a delay relay, others -- thermistors, SS current limiters, just series resistors, etc... A real answer is to reduce C in the filters. You guys seem to use hundreds and even thousands of uFs in staggered RC or LC filters in the tube amplifiers. It is crasy. In fact, you need only one big cap of a value of about 1uF per 1mA of peak load current. It will keep ripple at about 10V. You can feed output plates from it. 90% of the home brewed amps can do away with 100uF or 220uF at worst. For all the other loads use active filters based on large R, relatively small C and a Hi-V darlington of MOSFET. These can be taken from dumped TVs. Typically they are in the nice insulated TO-263s and can be bolted to chassis. (Note: transisors from the line deflection usually have 50R built-in resistor between base and emitter. Use a lower power transistor in front.) This is another instance where transistors could be put to a good use in valve designs, not just for making current sources (as Partick does). Regards, Alex |
#7
Posted to rec.audio.tubes
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Inrush Surge pics
On Jun 5, 7:57*pm, "Alex Pogossov" wrote:
"Phil Allison" wrote in message ... "Alex Pogossov" "Phil Allison" ** Hi tubeheads, these JPEGs were taken late in 2009 using my Rigol DSO. The first is a 1kVA step down ( 240V to 120V) E -Core transformer with no load. http://sound.au.com/tmp/surge-002.jpg The second is a commercial powered speaker with in built 200 watt SS amplifier using a 300VA toroidal tranny. http://sound.au.com/tmp/surge-001.jpg The smaller current peaks are due to filter electros charging. The moment of switch on was close to a zero crossing of the AC supply - with the voltage going positive. See the captions. Note how the transformer current surges are all the same polarity and peak as the AC voltage is crossing zero. Apparently, the huge curent surges are due to the core saturation. ** Just like pulling the iron core half out of the transformer for a few mS. To avoid them one must turn power switch on the peak(!) of the sinewave, not at the zero-crossing. ** Bit of a special skill, *that one. But then we will have possibly huge surges from charging of the filter caps. ** Yep *- *but rather less peak current for a bit longer and on each half cycle. Cos the secondary copper losses are then involved, as well as the primary ones. However the later are easier to control by adding small R or R+L in series with the diodes. ** There is no issue with silicon diodes or elector caps during start p *- both can easily cope with huge surges. The problem is with the AC supply fuse *!!! Cos it forces you to use a much bigger rating fuse than would reliably protect the tranny from burn out. I can see two ways of killing of the inrush currents. 1. To avoid saturation on turn-on at zero-crossing a transformer shall be so designed that the core would not reach saturation after one half-sine wave, not after a quarter. In other words, the transformer primary shall have double of turns per volt -- inrushless transformer shall be designed say for 240Vac to work in the US 120V environment or to 460Vac to work in Europe. Of course this will make the beast inefficient, twice heavier. larger and costlier for the same wattage. Bean counters would scream! Since you are keen on experimenting, take two identical trannies, connect theis primaries in series (to simulate one tranny with double turns/volt) and do the in-rush test as before. You will see NO INRUSH at all! Not just it will be halved. No. Not at all! Hobbyists perhaps could afford designs where two identical trannies with primaries and secondaries in series are used instead one tranny. But it will be inrush free! 2. How to deal with capacitor charge in-rush. Well, Patric uses a delay relay, others -- thermistors, SS current limiters, just series resistors, etc... A real answer is to reduce C in the filters. You guys seem to use hundreds and even thousands of uFs in staggered RC or LC filters in the tube amplifiers. It is crasy. In fact, you need only one big cap of a value of about 1uF per 1mA of peak load current. It will keep ripple at about 10V. You can feed output plates from it. 90% of the home brewed amps can do away with 100uF or 220uF at worst. I like to use 470uF caps in PSUs because they are small, and do a fine job to reduce Vripple at a CT to negligible values. ARC uses far more C than I do, but anyway, in class AB there is no CMRR in the OP stage and in each class B wave cycle you have Vripple in series with OPT load and anode signal so unless the amp works in pure class A you need the CT voltage to be clean. The CT must also be bypassed to 0V with a low impedance to allow good AB operation, and what better than about 470uF which is 34 ohms at 10Hz. Its easy to allow for inrush currents. For all the other loads use active filters based on large R, relatively small C and a Hi-V darlington of MOSFET. These can be taken from dumped TVs. I've found source follower used for B+ rails to be fragile. Too many fail mysteriously after awhile. Better are more rugged BU208 or BU108 HV rated bjts, but they have very low hfe so you need to dalington connect them and put all sorts of diodes and series resistances in to prevent excessive currents into base and through collectors. I try not to use any active regulation in B+ rails for input/driver stages and just rely on good old RC filters. I don't have problems with any motorboating, ie, LF oscillations. Patrick Turner. Typically they are in the nice insulated TO-263s and can be bolted to chassis. (Note: transisors from the line deflection usually have 50R built-in resistor between base and emitter. Use a lower power transistor in front.) This is another instance where transistors could be put to a good use in valve designs, not just for making current sources (as Partick does). Regards, Alex- Hide quoted text - - Show quoted text - |
#8
Posted to rec.audio.tubes
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Inrush Surge pics
On Jun 5, 1:57*pm, "Phil Allison" wrote:
"Patrick Turner" Even if one has not calculated or measured all the input currents one soon finds the R value and type which won't fuse open and which will last and which will allow a smaller and more useful fuse value offering more sensitive protection to excessive current draw from the mains in a fault condition. *** That 115 amp surge from the step down tranny is not big enough to blow a 15 amp wire fuse or trip a 16 amp ( thermal magnetic) breaker as fitted to domestic AC supply circuits here in Australia. *But it IS *big enough to blow a 4 or 5 amp slo-blo glass fuse as would be needed to protect the tranny. Adding a permanent series resistor is not practical - it would dissipate far to much heat. The obvious and simple answer is to use a thermal breaker, rated at 4 or 5 amps *- *these have long opening times and will ignore most any half cycle surge, eg: http://au.element14.com/te-connectiv...d/w28-xq1a-5/c... If it ever does trip, just push to re-set. Avoids the possibility of users fitting an oversize fuse too. ..... *Phil The full link is http://au.element14.com/te-connectiv..._merc h=true& Not a bad price, and not a bad device to be sure, which will fit somewhere easily on any amp. I didn't suggest a permanent series resistor ever be used to lower the input current you mentioned. The consequent continuous current would indeed fry such a resistance, which I like to shunt with a timed relay after 4 seconds when the rails have come up to nearly the full B+/B- value. The series R I've used seems to survive the high turn on surge for the first few 50Hz cycles and the charge up currents needed for massive capacitors. Once the caps are "full" the amp will rarely produce huge mains current draw unless there is a serious fault. Where multiple output tubes are used, complete bias failure in one output tube may not increase mains draw enough to blow even a sensitive fuse - especially if you have 12 x output tubes like in my 300W amps. Its in cases like such amps where mains fuses have limited abilities and responsibilities so one must use fuses in each cathode to 0V circuit, or have active sensing so that if one or more tubes conducts more than 3 times the Idc for longer than 4 seconds the amp is turned off by a relay interupting the mains supply to the primary. I fit such protection even when only 2 output tubes are used. Such protection saves OPTs and PTs from ever being over heated for some length of time by a tube which has become saturated from bias failure. A bright spark like yourself could give thought to designing a circuit module which monitors amplifier output voltage and current and applies the info to a chip based circuit which determines if the load connected is below a setable value of say 2 ohms. If RL 2 ohms is detected, even at low level, even for say 0.1 seconds, then the amp is turned off by a relay and the red fault LED turned on. This would protect all amps against shorted speaker cables, arcing ESLs and so on, all of which cause many amp failures. Such a protection measure is exactly what is missing from most protection circuits which dismally fail to protect an amp against a low RL at very low signal levels when excessive device currents are not large enough to make any fuse blow but are large enough to overheat and destroy the devices within seconds or minutes. I would suggest it could be lucrative. Patrick Turner. |
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