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Driving Induction motor using TRIAC

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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
 

Hi,

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

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

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

I´ve already asked you twice why you used the optocoupler. --> No answer. (If you don´t know the answer - who else should know why you used them?)

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

Klaus
 

Hi,

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

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

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

I´ve already asked you twice why you used the optocoupler. --> No answer. (If you don´t 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.
 

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
 

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..?
 

Hi,

It´s all said from my side.

Klaus
 

dc_snubber.jpg

Is this circuit is suitable for DC loads..?
 
Last edited:

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
 

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
 

relay_diode.jpg

Placing the diode like this is correct..?
 

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

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

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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