Transformer soft start with Triac and uC
in [Design]
|
Prev: If D from BC were a carpenter:
Next: Conroy - Public Enemy #1 - Re: Turn your Rigol DS1052E Oscilloscope into a 100MHz DS1102E
From: blisca on 18 Apr 2010 05:01 "Sjouke Burry" <burrynulnulfour(a)ppllaanneett.nnll> ha scritto nel messaggio news:4bca23a5$0$14132$703f8584(a)textnews.kpn.nl... > 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. Thanks,probably this will be an unavoidable option,but very expansive in terms of space If possible I would like to solve with "intelligent" start ,without adding bulky components.
From: blisca on 18 Apr 2010 05:05 "Baron" <baron.nospam(a)linuxmaniac.nospam.net> ha scritto nel messaggio news:hqdan9$nfs$2(a)news.eternal-september.org... > 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. > > -- Thanks Baron, I tried NTCs,and they do have a limiting effect,but in case of repetitive ON the NTC becomes useless
From: blisca on 18 Apr 2010 05:11 "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> ha scritto nel messaggio news:kkhks59bovn5bsr8lhnhg4r3q9k0odqhl3(a)4ax.com... > On Sat, 17 Apr 2010 22:47:23 +0200, "blisca" > <bliscachiocciolinatiscalipuntoit> 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 > > > > > > It's tricky using a triac in series with a transformer primary. It can > be both hard to keep them on, and hard to turn them off. RC snubbing > is critical, and gate drive may have to be sustained, not just pulsed. > > NTC inrush limiters work well. They look like big black disk ceramic > capacitors. Simple. > > You can also switch in a series resistor with one triac or relay, to > let things charge up/demagnetize, then use another for the direct > connection. But that's hard on resistors. > > Toroidal power transformers can be tricky that way. We had one > amplifier that, when you switched it on, you could hear the wires in > the wall jump. We were peaking around 1000 amps sometimes. !!! > > These transformers should have an auxiliary primary winding for > startup. Maybe 20% extra primary turns but lots of copper resistance. > > > John >
From: blisca on 18 Apr 2010 07:07 "Martin Riddle" <martin_rid(a)verizon.net> ha scritto nel messaggio news:hqdvlc$7n2$1(a)news.eternal-september.org... > > > "blisca" <bliscachiocciolinatiscalipuntoit> wrote in message > news:4bca1e61$0$1122$4fafbaef(a)reader3.news.tin.it... > > 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 > > > > Toroids like to hold their magnetic state longer that EI cores. > might be turning on the core in the same direction that it was last > magnetized. An inrush current limiter should help, long enough for the > core to walk back to a balanced state. Thanks,Martin I hoped that feeding the primary with a growing "time slice" of current ,inverted in direction at every semiperiod was equivalent to alternatively start by a codition of alternatively growing induction,i.e. at semiperiod T1 B=1,then B=-2;then B=+3 and so on. My impression is that rather i start every time by B=0;but i'm not shure > EI cores have a natural gap that help eliminate this effect. > In larger equipment that is pulsed, such as X-ray, there is usually some > sort of means to record the last magnetized state of the primary > transformer. So that the core does not saturate and put stress on the > SCR's. > > Cheers > > >
From: blisca on 18 Apr 2010 07:10
"whit3rd" <whit3rd(a)gmail.com> ha scritto nel messaggio news:81a21783-2454-4d1e-84e7-e0e0522b1ba7(a)j21g2000yqh.googlegroups.com... On Apr 17, 1:47 pm, "blisca" <bliscachiocciolinatiscalipuntoit> wrote: > 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. Yep, that's why you shouldn't ever use zero crossing for the first cycle of turnon of an inductive load. Turn on at 90 degrees (voltage peak) instead, and KEEP it on by continuous gate drive on the triac, Thanks, Probably i'm wrong,but powering at 90 degree i still have peaks,but let me try again If you must, for isolation, use a transformer to drive the triac, consider replacing it with a relay. It's more power-efficient, anyhow. |