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Switching Led

Discussion in 'General Electronics Chat' started by willeng, Jul 4, 2014.

  1. willeng

    willeng Member

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    Hi Kiss,
    Well here goes nothing?
    I am sure you will correct me of I am wrong here as I am not quite sure to be honest.

    At full power with a Resistive Load--No Current Lag we fire the Triac at the beginning of Quadrants I & III at half power with 5mS delay on the gate pulse we are firing in Quadrants II & IV.
    Is that correct.
    With an Inductive Load everything seems like it is firing at the wrong time, hence the Pulse Train to catch things at the correct time?

    With an Inductive Load can we correct the Current Lag with a Capacitor without going so far as to get into resonance?
    As I mention a long while back it seems better to use Zero Current not Zero Voltage.

    If you or someone else has time to explain more about this especially if I am totally wrong about things, I would appreciate it greatly.

    Cheers
     
    Last edited: Jan 14, 2016
  2. willeng

    willeng Member

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    I just noticed on the MOC3021 Datasheet that the values of the resistors & the capacitor on the output side are different for an inductive load.
    They quote values for 60Hz so the capacitor value for 50Hz would be slightly different.
    Obviously the Capacitive Reactance would be a little different, is this a critical value, meaning should I Calculate Xc for the 60 Hz then choose a capacitor with the same Xc for 50Hz.
    Or are the values quoted close enough?

    http://pdf1.alldatasheet.com/datasheet-pdf/view/27236/TI/MOC3021.html

    I also should have mentioned the correct load for the Secondary side of the Transformer, I wrote a 100uF Cap & 6Ω resistor as the load instead of 38Ω which is approx 315mA.

    Cheers
     
  3. willeng

    willeng Member

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    Obviously I was very wrong with my replies about Quandrants & how the Triacs actually work.

    My first thought was to relate the Quadrants to the Sine Wave which made some sense at the time but there is NO relationship between Triac Quadrants & the Sine Wave.

    This made it VERY confusing to work things out.

    As I understand now, with a Positive Gate Pulse from my drive circuit it would trigger Q I when in the Positive half cycle & Q IV in the Negative half cycle.
    If I was using a Negative Gate Pulse I would be triggering Q II in the Positive half cycle & Q III in the Negative half cycle.
    Is this correct.

    Please let me know if I am on the right track!
    Cheers
     
    Last edited: Jan 14, 2016
  4. dave

    Dave New Member

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  5. willeng

    willeng Member

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    I had a look at the Transformer today & realized that before (A Year Ago) when I set this transformer up properly in a case for safety I fitted a Thermal Fuse which I had forgotten about & this is what is wrong with it, it is rated at 130 deg 3A & it has blown. The Transformer is still good.

    Cheers
     
  6. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Quadrants:

    Here's a post defining what I mean by them: http://www.edaboard.com/thread86588.html#post378022
    It's the polarity of the gate relative to MT1.

    Back to another definition of quadrants is say a power supply:
    A NORMAL power supply can operate with positive voltage and positive current and negative voltage and negative current.
    A 4 quadrant power supply can operate in +V+I, +V-I, -V-I, and +V+I
    These are 4-quadrant power supplies and not very common. An audio amplifier operates in all 4 quadrants.
    so, here it refers to the polarity of voltage and current. See: http://powersupply.blogs.keysight.com/2012/10/what-is-bipolar-four-quadrant-power.html

    In the case of the Triac, it refers to the polarity of the gate to MT1.
    You might be OK, but the datasheet says you need 2x more current to operate in quadrant IV (100 mA vs 50 mA). Not sure if your operating there or not.

    I found this http://www.littelfuse.com/~/media/e...rol_using_thyristors_application_note.pdf.pdf which MAY be useful.

    Figure AN1003.4 talks about the power/conduction angle that you worked out. See the blurb under fig Figure AN1003.4.

    Figure Figure AN1003.22 is another thing to look at. I don't think the opto is a triac, but rather a solid state relay. e.g. http://www.digikey.com/product-detail/en/CPC1981Y/CLA203-ND/700422 It MIGHT be a better choice.

    AN1003.21, using 2 SCR's back to back was used in a all of the phase angle firing controls I used at work. They used trigger transformers.

    So, questions: Are you operating in quadrant IV?
    Comments:

    The zero cross detector may influence the maximum % on. i.e. There could be an uncertainty at some maximum conduction angle.

    Sorry, I dropped of the earth for a while. Just tired
     
  7. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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  8. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I think the Diac may be causeing problems because it's preventing you from being about to turn on when you want. I think it would mean that you have no control at low phase angles. e.g. When the peak voltage is greater than 32-34 V. Does this make sense?

    So you need to use something like fig 22 in the Littlefuse document with the 100 ohm resistors probably doubled and the cap rating doubled. The opto may indeed be a triac.
     
  9. willeng

    willeng Member

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    Hi Kiss, I was hoping you were ok, not for mine or the threads sake!
    I will have to read your posts & the links you provided properly, which I will do now.

    I understand now that the Quandrants for the Triac are Modes of operation.

    This is without reading the links provided!

    You asked if I was operating in Quadrant IV.
    Just at the moment as I understand it there would have to be a positive gate pulse in the negative half cycle to operate in Q IV.
    I have not checked the polarity of the gate pulse with the scope as once again I do not seem to have a ground connection for the scope ground clip.
    To me it seems like I would have to have NO ground connection on the probe to be able to look at the gate pulse?.

    Going by the SIMULATION only it appears that the gate pulse from the MOC3021 is Positive for the positive half cycle & Negative for the negative half cycle which as I take it at the moment would have the triac operating in Quadrants I & III.

    I'll get reading & get back to you!
    Take it easy & relax for a while!

    Cheers
     
  10. willeng

    willeng Member

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    Deleted Post
     
  11. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I think you don;t have control below about 16 degrees (<~0.9 mS) of phase angle. Am I right?
     
  12. willeng

    willeng Member

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    Hi Kiss,

    Yes, that would be about right for sure.

    I have just removed the Diac to try it out quickly, I have fitted another Thermal Fuse but I was wondering if I should use a Varistor across the primary side I have some S14 K275 Varistors.
    I also have some Thermistors as well.

    Should I limit the Inrush Current until I have this working correctly, even with just a Resistor?

    Cheers
     
  13. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Dunno, Can't hurt.

    Well, at least I did one calculation right. Basically solved 34 = 240*1.4*Sin(r) for r in radians.
    Then converted to time at 50 Hz.
     
  14. willeng

    willeng Member

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    Hi Kiss,
    Sorry don't follow what the calculation is for?

    "Basically solved 34 = 240*1.4*Sin(r) for r in radians.
    Then converted to time at 50 Hz.
    "
    Do I still need to have the 2.3k 50W Resistor across the Primary to load it. ?
    I can adjust it to 3K if needed.
    Cheers
     
  15. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    The Diac won't pass any voltage until it's greater than 34 V. So, I tried to find the time where 240 V p-p reaches 34 V.
    AND it supports your observation.

    ==

    The primary load is for a "different" problem. Basically with the gate open, the triac would pass a voltage if the load was non-existant or "small". It basically says that you would read 240 V where the load would be connected if it was just the meter. The components were randomly picked (junk box) but not calculated. I went with about 50 mA for a "typical" value.
     
  16. willeng

    willeng Member

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    Hi Kiss,

    I see, so basically you were looking at the instantaneous voltage at X degrees or what degrees a particular voltage occured..

    Ok, I have some news that may shed some light on what is happening?

    Firstly I tried without the Diac with no difference found, I then tackled it like I used to when my head worked properly & started testing what was happening.
    I also tried a new BTA16 Triac & a BT151 with no difference found.

    I think it may have something to do with the actual LOAD on the Triac like you mentioned before, let me explain, this will sound a bit stupid but it is really happening so stay with meo_O.

    I returned to the Lamp setup & with the "pot to the Arduino OFF" I get zero Voltage at the Triac output & everything works perfectly.
    With the Arduino OFF--No power to it! I have Zero volts of course.
    Lamp Resistance = 15Ω

    With the Lamp replaced with a 2.3K 50W resistor across the Triac output as a load I get "79V at the Triac output with the Arduino Turned OFF"--No Power to it!, the Triac is Triggering itself.
    Total Resistance = 2.3K

    I then connected the Transformer which I have a 150Ω 50W resistor in series with one leg of the transformer 240V input, the transformer DC resistance is 39Ω & L=2.7H
    With the "Arduino Turned OFF--No power to it!" I get 220V from the Triac output, again it is triggering itself.
    XL = 847Ω
    Series Resistor = 150Ω
    Dc Resistance is 39Ω
    Total Resistance is 1036Ω

    Don't ask me why it is happening as I have no idea but I am glad I found it.

    Cheers
     
    Last edited: Jan 15, 2016
  17. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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  18. willeng

    willeng Member

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    Hi Kiss,
    I will try what you mention now.

    In the last post I should have had 192Ω Resistance for the Lamp.
    I measured it with a DMM cold not thinking properly, sorry about that.

    Cheers
     
  19. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Don;t even try to measure the resistance of the lamp. It's like 10-15x from cold to 100%.
     
  20. willeng

    willeng Member

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    Hi Kiss,
    Yes I realized that with the Lamp after I posted the 15Ω resistance for it, when I realized I worked the resistance out from the 300W rating of the lamp which was 192Ω.

    I change the resistors as mentioned first but there was no change, I then changed the cap to .1uF & it brought the voltage down with the Transformer connected without the 150Ω series resistor on the primary leg.
    It was 220V before on the triac output with no gate signal but 51V with the .1uF cap fitted.
    I then tried a .15uF cap & the voltage raised to 75V.
    I then used a .47uF & a .1uF in series giving approx .082uF & now the voltage at the Triac output is around 40V with no gate signal.

    I will have to play with this some more to get it down even further.
    I can get it down to 25V or so with the Pot into the Arduino then it jumps to the 40V when the pot is totally off, basically I can get the secondary voltage down to near 1.5V output.

    It is much better & the signal is much more stable but still not quite right.
    It has taken that jitter of the pulse train signal away totally.

    I have taken a quick clip of the Ac output signal of the Triac into the primary side of the Transformer, does it look ok to you?
    First part with adjustment via the pot into the Arduino, you will see near zero it still goes to the sine wave & the second part just ramping down automatically to look for discontinuities like you mentioned before. Just playing basically I guess you would say?



    I'll keep at it.

    Cheers
     
  21. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Nope: capacitors in series follow the resistors in parallel rule 1/Ct=1/C1+...1/Cn; so it's less than 0.47 Caps in parallel follow Ct=C1+...Cn

    Is the amplitude changing? I really can't tell.
     

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