Hi everyone,
I want to use PWM to control a vibration pump. I read on an old thread that someone had done something like this using phototriacs to change the phase angle, but I did not want to revive a dead thread. I understand that a phototriac (non-zero crossing) will enable the
I obtained some VO2223A phototriacs, but I'm not sure how to connect the AC side as the vibration pump has only 2 terminals and the phototriac AC side has 3 pins. Unfortunately Im not very familiar with triacs. I had assumed they would work in a similar way to a DC optocoupler, however I don't know what to do with the extra output pin.
Here is the datasheet - http://www.vishay.com/docs/81166/vo2223.pdf
The phototriac can switch 0.9A, which is more than enough for the 40W pump pulling 330mA at 120V.
My research has led me to believe I may need to use some sort of snubbing circuit, but am unsure how to proceed.
Any advice is most welcome, many thanks in advance!
When I connect the pump across pins 6 and 8 (ignoring the gate) and apply power to the AC side, the pump begins to hum. When the microcontroller attempts to drive the pump, nothing happens (except for the hum).
I have tried connecting the pump across pins 5 and 8 as well (as my knowledge of triacs is currently very limited) with the same results.
What would be causing the humming when the optotriac is not being driven by the microcontroller? :~
I have tested the microcontroller PWM output on a LED and can confirm that it is working as expected.
Sorry, I didn't explain myself very well.
The hot wire goes to pin 6, pin 8 goes to pump. Neutral of pump stays connected to pump. So I am switching the hot wire
Edit: I have also tried hot wire goes to pin 8, pin 6 goes to pump.
In both cases the pump hums when AC power is applied, even when the mcu is powered off.
A hum would imply that there is excessive leakage current going through the motor. Have you measured it?
The data sheet shows it should be small. Compair what you measure with this value. It could be a damages opto.
I am getting about 0.9V across the LED when it is switched high. According to the datasheet it should be between 0.9 - 1.3V, so it matches with the datasheet.
A random fire phototriac is the correct sort for driving an inductive load such as your pump.
Check with a multimeter that the series resistor you are using really is 500 ohms and not some higher value.
Use a lower value resistor. The minimum current guaranteed to trigger the optotriac is 10mA. The maximum rated current is 50mA. So try about 220 ohms, which should give about 18mA, or 330 ohms to get about 14mA.
Here is the connections I am using,I didn't have the correct part on Eagle, so I used this Eagle part, however I am using the VO2223A phototriac. DC connected across pins 1 and 4, AC connected across pins 6 and 8 lt
I have checked and confirmed that the series resistor I am using is in fact 500 ohms. I have also tried 390 ohms with the same result.
Grumpy_Mike:
If you short out the pins 6 and 8 does the motor start?
If you apply 5V across pins 1and 4 does it start?
Shorting pins 6 and 8 is a good test, but according to the datasheet, pins 1 and 4 are connected together, so applying 5V across them makes no sense. Perhaps Mike meant something else?
Some further thoughts:
Connecting the load between pins 5 and 8 may well have damaged the device. I think you should get another one.
Connecting a 1k resistor between pins 5 and 6 may possibly help, if leakage in the opto triac is turning the main triac on.
Check with your dmm what the current consumption of the pump is, under various conditions, e.g. without any water (if that is allowable for the pump) and when pumping water. The triac has a holding current of 25mA max, so under some conditions, the pump might be too light a load. If so then you could connect a 3.3k 5W resistor in parallel with it.
You should use a snubber. Something like 0.1uF metallised film rated 120VAC or greater, in series with 220 ohms.
Sorry, typo, resistor is 510 ohms. I metered it & got 500 ohms.
Shorting out pins 6 and 8, the pump runs as it should.
5V across pins 1 and 4, the pump does not run.
I have tried a new VO2223A in case I damaged the first one, the pump does not run.
I tried a 1K between pins 5 and 6, the pump does not run.
I measured the current draw when the pump is running with water. It pulls 1.5A. Considering its rated at 41W, its only supposed to pull 340mA.
I guess I have found the problem, I need a bigger optotriac
It is entirely possible for the pump to draw 1.5A and only consume 41W. What this suggests is that the pump is a highly inductive load and the current is close to 90 degrees out of phase with the voltage. I'm still surprised that it didn't run for a while. Anyway, random fire SSRs rated at 2A or 2.5A are readily available.
I tried a 1K between pins 5 and 6, the pump does not run.
I hope that included the resistor otherwise you could have blown up the LED.
Yes when the current and voltage is so out of phase the power and current calclulaltions are not straight forward. It is a vector multiplication you have to do.
Considering its rated at 41W, its only supposed to pull 340mA.