inductive or resistive load

[Cepowak]

Hi, all. This is my first post in this group.
I'm trying to make a board for controlling AC loads. I mean to be
able of swithing on/off the AC power supply. I have seen a lot of
examples around the internet, and most of them use the typical I/O pin
+ opto-triac+triac, for example, this one:

http://www.iearobotics.com/personal/ricardo/proyectos/opto-triac/download/opto-triac-sch.pdf

I made a very similar board but it didnt work and i dont know why. I
used MOC3011, BT16A, and a GPIO from a microprocessor.I would like to
be able of a remote turning on and off some of the equipments of my
lab, and most of them are powered by classical AC/DC adaptors, so I
want to turn on and off the AC input of every adaptor of the
equipments. The first question is: what kind of load is an AC/DC
adaptor, assuming that the total consumption of the equipment that it
feeds is about 50 watts: inductive or resistive? Since they usually
have a transformer as the first component that sees the AC input, I
supposed it's inductive... am I right?
Another question about the triggering. If the led is always lightning
(feeded by a gpio, for example), the final triac should be at on-state
so that the adaptor would be powered on? A while after, if I drive low
the gpio turning off the led, should the adaptor power off??? Is it
an optimal approach for this problem? What is the real benefit of
using zero crossing detectors? I read a lot about controlling the
amount of power given to lamps or other devices, but i dont want
controlling the amount, but only the on/off state.

Thanks in advance.

 

[Jamie]

Hi, all. This is my first post in this group.
I'm trying to make a board for controlling AC loads. I mean to be
able of swithing on/off the AC power supply. I have seen a lot of
examples around the internet, and most of them use the typical I/O pin
+ opto-triac+triac, for example, this one:

http://www.iearobotics.com/personal/ricardo/proyectos/opto-triac/download/opto-triac-sch.pdf

I made a very similar board but it didnt work and i dont know why. I
used MOC3011, BT16A, and a GPIO from a microprocessor.I would like to
be able of a remote turning on and off some of the equipments of my
lab, and most of them are powered by classical AC/DC adaptors, so I
want to turn on and off the AC input of every adaptor of the
equipments. The first question is: what kind of load is an AC/DC
adaptor, assuming that the total consumption of the equipment that it
feeds is about 50 watts: inductive or resistive? Since they usually
have a transformer as the first component that sees the AC input, I
supposed it's inductive... am I right?
Another question about the triggering. If the led is always lightning
(feeded by a gpio, for example), the final triac should be at on-state
so that the adaptor would be powered on? A while after, if I drive low
the gpio turning off the led, should the adaptor power off??? Is it
an optimal approach for this problem? What is the real benefit of
using zero crossing detectors? I read a lot about controlling the
amount of power given to lamps or other devices, but i dont want
controlling the amount, but only the on/off state.

Thanks in advance.

first thing you must do is place a volt meter across the LED diode of
the isolator.. See if you're getting the required drive voltage.
Also, I assume you're leaving the trigger signal on at all times until
you want to turn it off ?
Putting that aside, you may also want to check a couple of other
things, and that is the resistor you have going to the coupler that
drives the gate.. The gate current needed for trigger may be more than
what your giving it.

Things to ponder on..

 

[Cepowak]

I think the LED is well powered. It has 1.15 volts across it. The
datasheet of the opto-triac shoes that the Vd should be 1.2 so i think
it's right. I have 2 resistors of 100ohms in series ( i hadnt another
type when i made the experiment) with the gate of the triac. Maybe I
should use lower values?

Thanks

 

[Jamie]

I think the LED is well powered. It has 1.15 volts across it. The
datasheet of the opto-triac shoes that the Vd should be 1.2 so i think
it's right. I have 2 resistors of 100ohms in series ( i hadnt another
type when i made the experiment) with the gate of the triac. Maybe I
should use lower values?

Thanks

put your ma meter in series with the LED feed and see what current
readings you're getting..
You maybe just on the threshold of it.
Also, If you jump the gate of the Triac to the feed side of the
isolator, you can determine if the resistors you're using have
sufficient current for the TRIAC..
Use this approach to determine the problem. If the TRIAC is comes fully
on, then, this means you have an Optical coupler issue.
if it does not turn on, then you have insufficient gate drive..
You also need a minimum load of course on the output to test this.
You need to get above the holding current of the TRIAC..
for now, You could use a incandescent lamp as your test load.

 

[Cepowak]

put your ma meter in series with the LED feed and see what current
readings you're getting..
You maybe just on the threshold of it.
Also, If you jump the gate of the Triac to the feed side of the
isolator, you can determine if the resistors you're using have
sufficient current for the TRIAC..
Use this approach to determine the problem. If the TRIAC is comes fully
on, then, this means you have an Optical coupler issue.
if it does not turn on, then you have insufficient gate drive..
You also need a minimum load of course on the output to test this.
You need to get above the holding current of the TRIAC..
for now, You could use a incandescent lamp as your test load.

Ok i will try that, but, do you know the answer of the question about
if an AC/DC laptop adaptor is an inductive or a resistive load?

Thanks in advance.

 

[Phil Allison]

"Cepowak"

Ok i will try that, but, do you know the answer of the question about
if an AC/DC laptop adaptor is an inductive or a resistive load?

** It is neither.

The load is " non linear ".

Current is drawn in pulses at the time of the each sine wave peak.

Voltage and current are essentially in phase.



........ Phil