Transformer soft start with Triac and uC
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From: blisca on 17 Apr 2010 16:47 Hi,please be patient and read the description of the situation: A friend is having lot of problems trying to switch primary winding of a 400VA toroidal transformer by a triac driven by a zero crossing optotriac. Having a bit of measuring instruments i tried to help him. The net voltage is 220V,the secondary winding is left open,no load at all. Measuring the current peaks by means of a current clamp probe and a cheap digital oscilloscope i measured current spikes over 80A. After a quick research on web i have plenty of explainations of that fact.This is a very simple one http://www.opamp-electronics.com/tutorials/inrush_current_2_09_12.htm The last image should rapresent the situation i'm dealing with. It looks like at the zero voltage starting the current from zero,rather from the negative peak,this current is able to generate enough flux to saturate the core,with expected effects. I 'm trying to implement a soft start using a random phase opto triac instead of a zero-crossing one. I arranged a zero crossing detector to trigger a microcontroller,and i can fire the optotriac and the triac in every moment during each semi-period. The first soft start attempt consists in this 1)detect the zero 2)wait until 0.1 ms before next zero(end of semiperiod) and turn on the Triac 3)detect next zero,Triac turns off a bit later,i guess,when the current reaches zero 4)wait until 0.2 ms before next zero and turn on the Triac,current flows now in opposite direction than in 2) 5)same as 3) and so on When i'm close to 90% of the semiperiods i turn off the Triac for a couple of seconds,i dont want to remain in ON state so to measure current spikes only during the "soft start" Sadly ,big current spikes are still detected. Could anyone please suggest me how a correct algorhithm should be done? I always had helps in this NG,thanks in advance Diego Italy
From: Phil Allison on 17 Apr 2010 17:06 "blisca" > A friend is having lot of problems trying to switch primary winding of a > 400VA toroidal transformer by a triac driven by a zero crossing optotriac. ** Only a total fuckwit used one of them with any kind of mains transformer. Cos it guarantees a MAXIMUM surge every, single time !!! > Having a bit of measuring instruments i tried to help him. > The net voltage is 220V,the secondary winding is left open,no load at all. > Measuring the current peaks by means of a current clamp probe and a cheap > digital oscilloscope i measured current spikes over 80A. ** Yep - that is what you get. > After a quick research on web i have plenty of explainations of that > fact.This is a very simple one > http://www.opamp-electronics.com/tutorials/inrush_current_2_09_12.htm > The last image should rapresent the situation i'm dealing with. > It looks like at the zero voltage starting the current from zero,rather > from > the negative peak,this current is able to generate enough flux to saturate > the core,with expected effects. > > I 'm trying to implement a soft start using a random phase opto triac > instead of a zero-crossing one. ** Huh ???? This wog imbecile must be on some kind of mind altering drugs. > I arranged a zero crossing detector to trigger a microcontroller,and i can > fire the optotriac and the triac in every moment during each semi-period. > > The first soft start attempt consists in this > 1)detect the zero > 2)wait until 0.1 ms before next zero(end of semiperiod) and turn on the > Triac > 3)detect next zero,Triac turns off a bit later,i guess,when the current > reaches zero > 4)wait until 0.2 ms before next zero and turn on the Triac,current flows > now in opposite direction than in 2) > 5)same as 3) > and so on ** Huh ???? This wog imbecile must be on some kind of mind altering drugs. > When i'm close to 90% of the semiperiods i turn off the Triac for a couple > of seconds,i dont want to remain in ON state so to measure current spikes > only during the "soft start" > > Sadly ,big current spikes are still detected. ** No fooling ???????????????????????????? >> Could anyone please suggest me how a correct algorhithm should be done? ** Switching on at voltage PEAKS is one option. But as mains transformers tend to have capacitive loads attached to them - even this does not solve the problem. > Diego > Italy ** You said it - pal. ..... Phil
From: Sjouke Burry on 17 Apr 2010 17:09 blisca wrote: > Hi,please be patient and read the description of the situation: > > A friend is having lot of problems trying to switch primary winding of a > 400VA toroidal transformer by a triac driven by a zero crossing optotriac. > Having a bit of measuring instruments i tried to help him. > The net voltage is 220V,the secondary winding is left open,no load at all. > Measuring the current peaks by means of a current clamp probe and a cheap > digital oscilloscope i measured current spikes over 80A. > > After a quick research on web i have plenty of explainations of that > fact.This is a very simple one > http://www.opamp-electronics.com/tutorials/inrush_current_2_09_12.htm > The last image should rapresent the situation i'm dealing with. > It looks like at the zero voltage starting the current from zero,rather from > the negative peak,this current is able to generate enough flux to saturate > the core,with expected effects. > > I 'm trying to implement a soft start using a random phase opto triac > instead of a zero-crossing one. > I arranged a zero crossing detector to trigger a microcontroller,and i can > fire the optotriac and the triac in every moment during each semi-period. > > The first soft start attempt consists in this > 1)detect the zero > 2)wait until 0.1 ms before next zero(end of semiperiod) and turn on the > Triac > 3)detect next zero,Triac turns off a bit later,i guess,when the current > reaches zero > 4)wait until 0.2 ms before next zero and turn on the Triac,current flows > now in opposite direction than in 2) > 5)same as 3) > and so on > > When i'm close to 90% of the semiperiods i turn off the Triac for a couple > of seconds,i dont want to remain in ON state so to measure current spikes > only during the "soft start" > > Sadly ,big current spikes are still detected. > > Could anyone please suggest me how a correct algorhithm should be done? > > I always had helps in this NG,thanks in advance > > Diego > Italy > > > > > > > > > > > > Use a resistor for .2 seconds when switching on? Then short the resistor. Or in other words: An inrush limiting relay.
From: Baron on 17 Apr 2010 17:55 Sjouke Burry Inscribed thus: > blisca wrote: >> Hi,please be patient and read the description of the situation: >> >> A friend is having lot of problems trying to switch primary winding >> of a 400VA toroidal transformer by a triac driven by a zero crossing >> optotriac. Having a bit of measuring instruments i tried to help him. >> The net voltage is 220V,the secondary winding is left open,no load at >> all. Measuring the current peaks by means of a current clamp probe >> and a cheap digital oscilloscope i measured current spikes over 80A. >> >> After a quick research on web i have plenty of explainations of that >> fact.This is a very simple one >> http://www.opamp-electronics.com/tutorials/inrush_current_2_09_12.htm >> The last image should rapresent the situation i'm dealing with. >> It looks like at the zero voltage starting the current from >> zero,rather from the negative peak,this current is able to generate >> enough flux to saturate the core,with expected effects. >> >> I 'm trying to implement a soft start using a random phase opto triac >> instead of a zero-crossing one. >> I arranged a zero crossing detector to trigger a microcontroller,and >> i can fire the optotriac and the triac in every moment during each >> semi-period. >> >> The first soft start attempt consists in this >> 1)detect the zero >> 2)wait until 0.1 ms before next zero(end of semiperiod) and turn on >> the Triac >> 3)detect next zero,Triac turns off a bit later,i guess,when the >> current reaches zero >> 4)wait until 0.2 ms before next zero and turn on the Triac,current >> flows now in opposite direction than in 2) >> 5)same as 3) >> and so on >> >> When i'm close to 90% of the semiperiods i turn off the Triac for a >> couple of seconds,i dont want to remain in ON state so to measure >> current spikes only during the "soft start" >> >> Sadly ,big current spikes are still detected. >> >> Could anyone please suggest me how a correct algorhithm should be >> done? >> >> I always had helps in this NG,thanks in advance >> >> Diego >> Italy >> >> >> >> >> >> >> >> >> >> >> >> > Use a resistor for .2 seconds when switching on? > Then short the resistor. > Or in other words: An inrush limiting relay. Just stuff a thermistor in series, the type used for inrush current protection. -- Best Regards: Baron.
From: Leo Baumann on 17 Apr 2010 18:18
.... i have solved that problem with a big switch-on inductance and a relay by full load. It wasn't to solve within the first sin-waves. mfG Ingenieurb�ro Baumann |