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  • Blinds (Or Any AC Power Motor) Control 4 months ago

    Thank you so much, I think it can be very useful. I will include your image in the tutorial if you don't mind.

  • Blinds (Or Any AC Power Motor) Control 4 months ago

    Efetively. In fact I directly soldered the MOVs to the SSR board, just to the connector pins.

  • Blinds (Or Any AC Power Motor) Control 5 months ago

    In this case, is not needed to put the Snubber to neutral, because in the case of a blind motor, both lines, grey and brown, are communicated inside the motor, (both coils are connected to neutral inside) hence letting a path to the current to flow. This is equivalent with the triac open as a loop with the RC and the motor coils. So, I was wrong with my previous comment, sorry; now I wonder, what does the motor open when it reaches the limit. :?
    You are right, that in the triac datasheet they say it has a built-in RC Snubber circuit, I read it time ago, but I don't remember any description about its rating and values. One thing is clear, in that space they cannot allocate the same big capacitor needed for this application, so I believe, that Snubber shall be very modest, and anyways, all this tutorial came do to the fact, that the triacs were dying by overvoltage and the external Snubber network was the solution.

  • Blinds (Or Any AC Power Motor) Control 5 months ago

    Hi Vorbis again,
    yesterday I found out, why in first place I didn't get a shock when touching the Snubber network: it wasn't connected to mains, but between the motor lines. I just wrote a PS in the tutorial about it. I hope this also helps you with your concern about leaving the Snubber always connected.

  • Blinds (Or Any AC Power Motor) Control 6 months ago

    By luck, I found a rule of thumb for those wondering how to calculate the RC values:
    Resistor:
    1Ω per Volt power supply rail voltage;
    Sufficient power rating (eg. 2W).
    Capacitor:
    0.1μF per Ampère power supply current;
    Voltage rating in accordance with power supply voltage.

    Be aware that this is not accurate and doesn't even take into account the actual inductance of the load, but your system could work perfectly with very rough approximated values; it is not a digital thing, is about to reduce the induced voltage, and you will reduce it more or less, but reduce anyway.

  • Blinds (Or Any AC Power Motor) Control 6 months ago

    Great article, I was always wondering about the effect of different currents through the body, but never searched about it.

    In our system, I'm afraid your proposal of placing the Snubber in parallel wouldn't work: first, either you make two Snubber networks, one for each direction of the motor (remember we have in the motor neutral and two power lines, one for each direction), or you place it between the two power lines of the motor, what almost doubles the voltage at the Snubber circuit terminals. But still there may be a no-way point: when the blind reaches down or up, the motor opens the circuit itself and your Snubber may be left unconnected in one side with no effect. Anyway, you can always try and share your experience.

    About the MOV, it is 275 VAC, so yours is fine. (I'll tell you a secret, the system would perfectly work without it, but with it I can be sure I don't destroy my SSR, I already blew a few of them). With the Snubber, your SSR shouldn't suffer the high voltages peaks anymore, but I cannot guarantee it will last forever. What I can guarantee is that in my system with the MOVs it has been already a year with no issue, moving the blinds every day.

  • Blinds (Or Any AC Power Motor) Control 7 months ago

    Hi again Vorbis,

    I have to rectify myself. Yesterday I made a circuit for detecting a power outage with the RPi (by the way, whenever I have the time I will make another tutorial) and tried again the Snubber circuit on a breadboard. I don't know if the first time I tested it I didn't measure properly or what, but this time, effectively as you were suggesting, having the RC Snubber circuit connected leaves the line a bit dangerously alive. Anyway, the current is limited to 7 mA, it doesn't burn, but makes you shake (true story ;) ).

  • Blinds (Or Any AC Power Motor) Control 7 months ago

    Hi Vorbis!
    1) Although the network is always connected, it does not consume active power and, in my opinion it's not worth to worry about disconnecting it. Yesterday I even took some measurements and touch it live and nothing happened. Anyway, you can mount the system and take your own measures to take the decision.
    2) If you still want to disconnect the network, this approach should be fine. If you have spare relays and want to feel safer, then it doesn't cost you much.
    3) Even though the inertia is minimal, it moves very slow, in my sketch this cannot happen: when blinds are going in one direction, if a new command arrives either via button or radio, the next action is to stop it. This way you can leave the blinds at any height and this also means that for changing the direction you have to push twice, one for stopping and another time for making it move again; just only with the 100 ms debouncing delay it makes impossible to change the direction in less than 200 ms.
    4) If you have already that component, it will work fine. It's expensive for this solution (~2€ instead of ~0.2€), but it is still peanuts if you are not producing thousands of circuits ;) Don't worry about the peak pulse, in fact, the purpose of the Snubber circuit is to reduce that peak, you will not have such voltages anymore. The power is OK.
    And thanks to you for posting!

  • Blinds (Or Any AC Power Motor) Control 8 months ago

    It's great anyway that you pointed out this topic, I'm positive this will help someone maybe trying to control a DC motor. At the end of the day helping each other is the reason why we are here for.

  • Blinds (Or Any AC Power Motor) Control 8 months ago

    Hi Alex,
    thank you for your feedback, you also bring an interesting topic. Only to note, that flyback diodes can be used only for DC current inductances, like for instance a very common use is when feeding a relay coil. The goal of this project is to manage AC motors, but people should note that the flyback diode should be used for DC motors as you remarked. Notice, that in that case the diode would be in antiparallel to the motor, not to the relay! If any other suppressor circuit in addition is needed that's another story. See https://es.wikipedia.org/wiki/Circuitos_de_ayuda_a_la_conmutaci%C3%B3n_de_transistores (sorry, but this time the Spanish version is better than the English one, strange o_O, but schematics are universal :) )
    PD: just changed the title of the project to "(or any AC power motor)" thanks to you ;)

  • Blinds (Or Any AC Power Motor) Control 8 months ago

    Hi Gabor,

    I'm very happy that this tutorial has helped you, hopefully it can spare you all the problems I encountered, that was my motivation to write it.

    For choosing the varistor you should not surpass the rated voltage of the element you are trying to protect and at the same time, assure it does not permit the current to flow when the breaking device is open. Keep in mind the peak voltage of the AC supply. In my case 275 VAC varistor > 230 VAC installation, and 400 VDC triacs > (275 VAC * sqr(2) = 389 V).

    For the RC Snubber circuit, in order to make the calculations, you would need the inductance of the valve, but since you probably don't have it (I didn't have it either), the thing turns out to be empirical. Anyway, even if you had the inductance, it would be difficult to make a precise calculation, since it will depend also on the torque of the valve at the breaking moment, which diverts from one occasion to another, the inertia of the system... If you have an oscilloscope then is great, because you can be playing with the values, looking for the combination that damps the voltage peaks the most and find the best performance. To sum up --> try the same values I used. ;) Knowing the equivalent impedance of the RC [R + (1/(2 x Pi x f x C))] may help you to have an idea of what you are playing with. My motors are 150 W lifting 20 kg blinds, that's probably worse case than yours and works fine, so that RC values would be fine after all, increasing the resistor won't give you any benefit. If your valve is very heavy stuff you may want to decrease the resistor a bit, but take care with its power.

    Regards!

  • Blinds (Or Any AC Power Motor) Control 8 months ago

    Hi thefrost,

    you definitely make the right points. First, it's great to use the ESP8266, so you can spare the radio module. I started with Arduino so I stick to it, but I wish I had known the ESP8266 before, I already use it for remote controlled lamps.

    The cascade relays are more expensive, more voluminous and the relay contacts still suffer the live commutation. Keep in mind that relays can try to break the circuit even in the highest voltage of the sin wave. In the other hand, triacs break the current when phase is around 0 V,  minimizing the energy that has to be absorbed, probably that's the reason you saw higher values for the RC Snubber circuit if it is used for relays. MOVs in my system are 275 VAC!! because triacs are rated at 400 VDC!! So if you get higher voltage MOVs you don't protect anything. They can last an eternity in this system, because they only work during the breaking of the circuit (milliseconds), so they never get too much energy.

    The RC Snubber circuit is not an exact value, in fact you could use a range of values. I can tell you the resistors between 80 to 180 ohms work fine with these motors. The higher you put the resistor, the less you protect the circuit. But you can not go too low, because the resistor and the capacitor would absorb too much energy. With the capacitor is kind of the same, small values protect less, higher values make the equivalent impedance (1/(2 x Pi x f x C)) smaller allowing more current to flow when circuit is open (RC Snubber is always connected!).

    The experience is that within one year, running the blinds everyday I had no issues so far, and I believe there is no tear in any component. I'm confident this is the most cost effective and reliable solution.

    Regards! 

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