Using OptoTriac without external triac - Page 1
Forum section: electronics / beginners

author: TopGun
author_rank: Contributor
timestamp: July 18, 2021, 04:56:37 pm
content: Hello.I'm trying to build a circuit to control some solenoid valves (@220VAC). The valves require a nominal current of around 45mA.I want to use an OptoTriac instead of a relays. The MOC3041 (Datasheet linked below) seems to kind of fit the bill, but for one problem. The datasheet says that the Triac can handle pulsed loads of upto 1A, and to not use it directly without an external triac/SCR. Can I use it directly to control the valve considering that the current is so low?Also, are there any other OptoTriacs that can handle mu 50mA, 220VAC load directly without needing any external Triac/SCR?MOC3041 Datasheet:https://cdn.sos.sk/productdata/61/2a/8c2cd9a7/moc-3041.pdf

author: WattsThat
author_rank: Frequent Contributor
timestamp: July 18, 2021, 05:25:56 pm
content: The MOC3041 is not a triac, it’s a triac driver. Big difference.You’re looking for an SSR, AKA a solid state relay. Something like this:https://www.mouser.com/ProductDetail/Omron-Automation-and-Safety/G3MC-202P-DC5?qs=FGnoE8EzQws5coPBVpGY3Q%3D%3D

author: TopGun
author_rank: Contributor
timestamp: July 18, 2021, 05:52:50 pm
content: That component is too expensive, and overrated for my application. It does not make much sense to use a 10 units of a $6 part that can do 2A, while I need only upto 50mA.

author: emece67
author_rank: Frequent Contributor
timestamp: July 18, 2021, 06:12:36 pm
content: .

author: Benta
author_rank: Super Contributor
timestamp: July 18, 2021, 06:24:44 pm
content: Just add a cheap triac and a resistor, eg, BT131. Costs a few cents.

author: floobydust
author_rank: Super Contributor
timestamp: July 18, 2021, 06:40:13 pm
content: Real world solenoids have high inrush currents, due to residual magnetism and the armature moving. Design for 50mA and you will have smoke.For lowest cost, use SOT-223 triacs with MCU on the AC mains side, which is what appliance manufacturers do.

author: TopGun
author_rank: Contributor
timestamp: July 19, 2021, 02:52:18 am
content: My solenoid valves have inrush snubbing. Measuring with an oscilloscope shows current never exceeds 65mA.

author: floobydust
author_rank: Super Contributor
timestamp: July 19, 2021, 03:44:03 am
content: What is "inrush snubbing"? My point is the solenoid impedance is not constant. You don't get much force for 65mA, to push a pintle against water pressure for example, which kicks back on return. These must be very tiny.I also see winding shorts on solenoids running high duty cycle. For low current AC switching, you can use an opto-triac but a bit expensive and it has to be able to clear that fuse if there's a fault with the load.Vishay BRT21 family"...to control resistive, inductive, or capacitive AC loads like motors, solenoids, high power thyristors, or TRIACs and solid-state relays." They appear not only for triac driving.Bolting on a low cost Z01 triac to theMOC3041MOC3021 for example, may end up cheaper and tougher than the opto-triac ssr. Check the SOT-223 doesn't have the spacings requirements so they offer the SMBflat-3L package.edit: zero-cross switching of inductive loads is proven to have the highest inrush currents, due to dV/dt being highest at zero-cross for a sine-wave.

author: Zero999
author_rank: Super Contributor
timestamp: July 19, 2021, 10:53:40 am
content: I have heard of a TRIAC output opto-coupler being used to switch a small motor, in a Dyson fan. Check out the thread linked below. I questioned it at the time, but don't think the original poster was lying.https://www.eevblog.com/forum/repair/triac-failure-mode/msg3586482/#msg3586482Even though I wouldn't recommend it, try it yourself, but be prepared for it to not work and emit magic smoke.

author: perieanuo
author_rank: Frequent Contributor
timestamp: July 19, 2021, 12:03:11 pm
content: exactly, a real triac + gate resistance costs nothing.moc3xxx, i'm not sure why you want this. at limit, a moc can help with zero-cross to minimise emi/maximise life of triac

author: TopGun
author_rank: Contributor
timestamp: July 19, 2021, 05:11:47 pm
content: "Inrush snubbing" = Doesn't act like a pure inductance coil would. It has a hard current limit, Idk how they accomplish it.The valves are pretty big and control high pressure air (15-20Bar), but they are pilot air operated. So, the solenoid doesn't need to be very big.

author: langwadt
author_rank: Super Contributor
timestamp: July 19, 2021, 05:20:42 pm
content: VO2223 or similar ?

author: Zero999
author_rank: Super Contributor
timestamp: July 19, 2021, 06:45:07 pm
content: Quote from: langwadt on July 19, 2021, 05:20:42 pmGood suggestion. The fan discussed in thethreadI mentioned used the MOC3083M, to switch a motor which caused the fan to swing from side to side.

author: David Hess
author_rank: Super Contributor
timestamp: July 19, 2021, 06:46:39 pm
content: Test it and find out. Then test it with double the load just to make sure.