Hi all,
I'm doing a project where I must constroll the speed of an AC motor. I'm using a random phase triac driver (MOC3020) to fire a triac (BT136-600) and change the speed as I want. All ok here.
I started by using the snubber circuit recommended in the MOC3020 datasheet for inductive loads:
The fan I'm controlling is a 57W, 230Vac motor. The grid here is 230V, 50Hz.
I'm using an arduino to trigger the MOC and I confirmed in the oscilloscope that my zero cross detector was equivalent to a zerocross in the grid and also confirmed that the arduino was triggering the MOC in the expected time. The problem was that if I increased the trigger angle, the speed of the fan was not changing linearly; Increasing the trigger just a little bit would get my motor full speed or super slow or even stopped it.
I solve this problem by changing the capacitor from 0.1uF to 0.33uF. I read someone that did this and worked out... I did the same and worked out aswell. That was ok but WHY did this solve the problem? I can't figure it out and it is bothering me not knowing why a larger capacitor solved this. On the internet I read a lot of recommended snubber circuits and they get 33ohms and 0.01uF.. Why do I need such a large values for my RC snubber if I'm triggering such a "small" motor?
Another "problem" are the resistores (180ohms and 2.4kohms). They need to be power resistores but this isn't mentioned in any place.. I've got 5W resistores and measured the voltage across them. I get 68V across the 2.4k resistor and 20V across the 180ohm resistor.. This is a lot of heat! They heat up until about 80ºC (2.4k) and 100ºC (180 ohms). I know they are suposed to burn power and transform it into heat but.. so much? Are this temperatures safe? Can I lower them easily?
I can get the snubber circuit off by using a snubberless triac like a T405-600H and I saw this configuration:
I have the moc already installed so.. can I do this?
(I don't actually need the MOC.. I could use another optocoupler?
Thanks in advance for your help.
Regards
I'm doing a project where I must constroll the speed of an AC motor. I'm using a random phase triac driver (MOC3020) to fire a triac (BT136-600) and change the speed as I want. All ok here.
I started by using the snubber circuit recommended in the MOC3020 datasheet for inductive loads:
The fan I'm controlling is a 57W, 230Vac motor. The grid here is 230V, 50Hz.
I'm using an arduino to trigger the MOC and I confirmed in the oscilloscope that my zero cross detector was equivalent to a zerocross in the grid and also confirmed that the arduino was triggering the MOC in the expected time. The problem was that if I increased the trigger angle, the speed of the fan was not changing linearly; Increasing the trigger just a little bit would get my motor full speed or super slow or even stopped it.
I solve this problem by changing the capacitor from 0.1uF to 0.33uF. I read someone that did this and worked out... I did the same and worked out aswell. That was ok but WHY did this solve the problem? I can't figure it out and it is bothering me not knowing why a larger capacitor solved this. On the internet I read a lot of recommended snubber circuits and they get 33ohms and 0.01uF.. Why do I need such a large values for my RC snubber if I'm triggering such a "small" motor?
Another "problem" are the resistores (180ohms and 2.4kohms). They need to be power resistores but this isn't mentioned in any place.. I've got 5W resistores and measured the voltage across them. I get 68V across the 2.4k resistor and 20V across the 180ohm resistor.. This is a lot of heat! They heat up until about 80ºC (2.4k) and 100ºC (180 ohms). I know they are suposed to burn power and transform it into heat but.. so much? Are this temperatures safe? Can I lower them easily?
I can get the snubber circuit off by using a snubberless triac like a T405-600H and I saw this configuration:
I have the moc already installed so.. can I do this?
(I don't actually need the MOC.. I could use another optocoupler?
Thanks in advance for your help.
Regards