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  1. #41
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    Re: Driving Induction motor using TRIAC

    Quote Originally Posted by KlausST View Post
    Hi,

    Why optocoupler? In my eyes they are useless.

    Relays don't need the capacitors...but if you want to stabilize the voltage then you are free to add capacitors.

    Klaus
    Why optocoupler? In my eyes they are useless. For this only I asked.Shall we use optocoupler with ULN ic



  2. #42
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    Re: Driving Induction motor using TRIAC

    Hi,

    Why do you ask again and again?
    The answer is already given.

    ***
    * The ULN datasheet does not say you need optocouplers.
    * Iīve already twice said they are useless here.

    --> Only you showed the schematic with the optocouplers.

    Iīve already asked you twice why you used the optocoupler. --> No answer. (If you donīt know the answer - who else should know why you used them?)

    Thus I have no reason to change my mind in this.

    Klaus
    Please donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



  3. #43
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    Re: Driving Induction motor using TRIAC

    Quote Originally Posted by KlausST View Post
    Hi,

    Why do you ask again and again?
    The answer is already given.

    ***
    * The ULN datasheet does not say you need optocouplers.
    * Iīve already twice said they are useless here.

    --> Only you showed the schematic with the optocouplers.

    Iīve already asked you twice why you used the optocoupler. --> No answer. (If you donīt know the answer - who else should know why you used them?)

    Thus I have no reason to change my mind in this.

    Klaus
    I'm having separate power supply for ICs(+5VDC) and Relays(+12VDC),so for isolating purpose I used optocouplers.



  4. #44
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    Re: Driving Induction motor using TRIAC

    Hi,

    OK, 5V supply and 12V supply.

    The question now is:
    Do the supplies need to be isolated?
    (Technically there is no need to. Every PC power supply has 5V and 12V, but they are not isolated.
    But maybe your application needs. Thus only you can answer this)

    * Yes, your application needs isolation:
    Keep the optocoupler

    * No, no need for isolation:
    connect 5V_GND with 12V_GND, omit the optocoupler.
    The ULN is happy with 5V input signals while switching 12V output signals. Read the datasheet, look at countless ULN example circuits.

    Klaus
    Please donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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  5. #45
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    Re: Driving Induction motor using TRIAC

    Quote Originally Posted by KlausST View Post
    Hi,

    OK, 5V supply and 12V supply.

    The question now is:
    Do the supplies need to be isolated?
    (Technically there is no need to. Every PC power supply has 5V and 12V, but they are not isolated.
    But maybe your application needs. Thus only you can answer this)

    * Yes, your application needs isolation:
    Keep the optocoupler

    * No, no need for isolation:
    connect 5V_GND with 12V_GND, omit the optocoupler.
    The ULN is happy with 5V input signals while switching 12V output signals. Read the datasheet, look at countless ULN example circuits.

    Klaus
    Apart from this,in which condition shall we use optocouplers..?



  6. #46
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    Re: Driving Induction motor using TRIAC

    Hi,

    Itīs all said from my side.

    Klaus
    Please donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



  7. #47
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    Re: Driving Induction motor using TRIAC

    Click image for larger version. 

Name:	dc_snubber.jpg 
Views:	5 
Size:	48.5 KB 
ID:	152676

    Is this circuit is suitable for DC loads..?
    Last edited by venkates2218; 28th April 2019 at 06:43.



  8. #48
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    Re: Driving Induction motor using TRIAC

    How's DC load related to thread topic?

    General points:
    - rated relays DC switching power must be sufficient for the load
    - if inductive load, a freewheeling diode is much more effective than a snubber
    - no problem to keep the RC snubber as is



  9. #49
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    Re: Driving Induction motor using TRIAC

    Quote Originally Posted by FvM View Post
    How's DC load related to thread topic?

    General points:
    - rated relays DC switching power must be sufficient for the load
    - if inductive load, a freewheeling diode is much more effective than a snubber
    - no problem to keep the RC snubber as is
    1.The load is 2A DC and I'm using 5A/G2R/+12VDC relay.
    2.It's like an buzzer which used in the factory for alert



  10. #50
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    Re: Driving Induction motor using TRIAC

    Click image for larger version. 

Name:	relay_diode.jpg 
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ID:	152827

    Placing the diode like this is correct..?



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  11. #51
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    Re: Driving Induction motor using TRIAC

    A freewheeling diode must be connected across the load (solenoid valve), not the relays contact.



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  12. #52
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    Re: Driving Induction motor using TRIAC

    If we are using RC network means,the circuit in POST:47 is correct..?



  13. #53
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    Re: Driving Induction motor using TRIAC

    We need to know what capacitors are connected to your motor? e.g. start or RUN caps

    if the triac turns on at mid mains the current peaks into these caps will kill it as will the high currents - so you need to start gradually from the volt zero crossing and allow turn off as the CURRENT falls to zero - you are likely using too small a triac, with no di/dt limiting choke and not enough snubbing ...

    - - - Updated - - -

    Sorry - I didn't see this:
    Snubber with TRIAC is working fine without any issue.Thanks for all your supports...
    new thread needed I think ...



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