Gate bleeder+RC snubber for triac+optocoupler - Page 1
Forum section: electronics / projects

author: okw
author_rank: Frequent Contributor
timestamp: June 01, 2025, 07:09:20 pm
content: I am trying to find out why my vibratory pump sometimes doesn't turn off.It's for 48-52W Ulka pumps, driven by the circuit below (PUMP_ENGAGE is controlled by a larger circuit, and I know it turns on and off as it should, so I expect to find the answer in the triac/opto).It happens randomly, and when it does, powering down everything usually releases the triac.I've tried with both R4=39R and R4=360R (as per the MOC3083 datasheet, resistive and inductive loads).I'm not sure how to size the snubber and gate bleeder components, except hooking the pump (mains!) up to an oscilloscope, and I'm not quite ready for that.

author: Zero999
author_rank: Super Contributor
timestamp: June 01, 2025, 07:58:01 pm
content: What's the inductance and resistance of the load?The snubber should ideally made the circuit critically damped.I would just use a MOV: it's much easier.

author: Benta
author_rank: Super Contributor
timestamp: June 01, 2025, 08:14:59 pm
content: If it's really a MOC3083, both the symbol and the pinout is wrong. Pin 5 is NC and is not allowed to be connected to anything.https://www.onsemi.com/download/data-sheet/pdf/moc3083m-d.pdf

author: okw
author_rank: Frequent Contributor
timestamp: June 01, 2025, 08:20:23 pm
content: Quote from: Zero999 on June 01, 2025, 07:58:01 pm4.35M and 4.85M (measured two pumps). It's a vibratory pump which should be like a standard solenoid/coil thing... 48W and 240V = 1.2k so I'm not sure why it's measuring so high.Regarding inductance, I'm not sure how to measure. I just got a ZT-MD1, but haven't used it yet. With it I measure:0.1V: nothing.0.3@1kHz: 5.947 H. Rs 528.5 kOhms, Q: 0.0707.0.6@100 Hz: 96.30 H. Rs 734.6 kOhms, Q: 0.0824.0.6@1kHz: 2.712 H. Rs 38.49 kOhms, Q: 0.4428.0.6@10 kHz: 26.19 H. Rs 56.66 kOhms, Q: 0.0290.I'm not sure how to interpret the readings, or if the ZT-MD1 is at all capable to measure a pump.

author: okw
author_rank: Frequent Contributor
timestamp: June 01, 2025, 08:24:18 pm
content: Quote from: Benta on June 01, 2025, 08:14:59 pmMy bad, wrong symbol, but pinout is correct (MOS3083 pin 5 is cut). I just used this symbol as I was accommodating different kinds of optos).

author: okw
author_rank: Frequent Contributor
timestamp: June 01, 2025, 08:24:50 pm
content: Updated symbol

author: floobydust
author_rank: Super Contributor
timestamp: June 01, 2025, 08:54:43 pm
content: Ulka vibration pumps (i.e. model E) have an integral rectifier diode (1N4007) inside. I would check for that.edit:datasheet url

author: okw
author_rank: Frequent Contributor
timestamp: June 01, 2025, 09:12:10 pm
content: Quote from: floobydust on June 01, 2025, 08:54:43 pmOh that's right. Does it mean I can't reliably use a triac for this kind of pump? Could it be that every time it cuts power in the "wrong" quadrant, it's stuck on forever, unless I break power completely?That certainly would explain the random behaviour of failed "off" attempts.

author: floobydust
author_rank: Super Contributor
timestamp: June 01, 2025, 10:52:32 pm
content: Should work, you'd only be using half the triac if it was a true 1/2 wave load.But the pump solenoid armature is a moving magnet, and 1N4007 is a slow recovery diode, so this is a bit complicated.The snubber might be resonating as well. I can't speculate on why the opto (zero-cross) seems to keep retriggering sometimes, without poking around with a scope which is dangerous with mains present.Things to try - disconnect the snubber or add a load resistor say 100k across the solenoid, but this makes heat and takes up room.Pic related - some circuits I see a small cap and resistor across the opto output but not sure why. The dV/dt rating is plenty high for these parts

author: okw
author_rank: Frequent Contributor
timestamp: June 02, 2025, 12:03:09 am
content: Quote from: floobydust on June 01, 2025, 10:52:32 pmI'll try both suggestions. Regarding the 100k. Can I do this on the PCB, or will the return path for the neutral be "too long"? The neutral potential is the same, but the pump neutral is 30-40 cm "away".One thing I noticed, if I swap the wires on my pump, it's on all the time. Would the internal diode be the cause of this?I just saw this guy driving the same Ulka pump with an IGBT (his focus is PWM for flow control - but it shouldn't make a difference?). He uses two diodes, one in series (to prevent AC passing - but the internal diode would do the same?) and one across (flyback protection). I wouldn't think this makes any difference?First image is his first version. Second is second

author: floobydust
author_rank: Super Contributor
timestamp: June 02, 2025, 01:45:21 am
content: The (pump internal) series diode does not block the back-EMF from the solenoid, so you need that extra diode and then that means you need another series diode. Makes sense to me to do it that way. You should try it.I don't get why the solenoid's connections make a difference to your circuit, if they are flipped it's still supposed to be an AC feed to itunless your triac or opto are damaged.I'd have to measure the inductance of a pump to see how much energy is there, to give you a solid solution.Take a look at other espresso machine schematics, they just seem to use a relay for the pump power.

author: okw
author_rank: Frequent Contributor
timestamp: June 02, 2025, 03:36:21 pm
content: I just added the two diodes, and the turned on the machine. At first the pump ran a few seconds to maintain water level, and stopped.Since the pump is also for coffee brewing, I tried the brew switch to activate the pump. The circuit breaker flew and the triac died (shorted).

author: floobydust
author_rank: Super Contributor
timestamp: June 02, 2025, 07:49:40 pm
content: That's unfortunate - but you have the circuit wired wrong? The Brew switch puts mains across D2.I would redraw the schematic for clarity, usually Line is up top and Neutral at the bottom and only one netlabel for dangerous (mains) nodes keeps it easy to spot mistakes.

author: okw
author_rank: Frequent Contributor
timestamp: June 02, 2025, 08:22:58 pm
content: Quote from: floobydust on June 02, 2025, 07:49:40 pmOh, yes of course. D2 can't be there. It was the suggestion from the other blog post, but that guy is controlling the pump differently. He is actually replacing the brew switch with an IGBT, and his machine doesn't have a tank reservoir.My machine has a dual use of the pump. It is either (1) maintaining water level in the tank (along with engaging a solenoid valve to direct the water in the tank, not through the brew group), and (2) brewing coffee.So the dual diodes won't apply for my circuit.I guess a 100k resistor across the pump solenoid or removing the RC snubber is my next attempt?