Love your videos

Hey, I’m back… I hope you’re doing well. I have a new question for you for a different project. Is the MOSFET between the microcontroller and the optocoupler necessary? Can the MCU provide the 3.3V/5V to the Anode with a limiting resistor and then just have the Cathode connected to ground? From the datasheet, if I’m reading it correctly, it looks like the MOC3041 has a max LED trigger current of 15 mA. The limiting resistor value would be key for the optocoupler and the MCU, I presume. Vf (1.25v) is the drop across the LED, correct? The datasheet also says that value is at 30mA typical. That’s confusing if the max current is 15mA. Ugh, me and datasheet 😁. (3.3V-1.25V)/300 ohms approximately 7mA. Is that saying I can successfully turn ON the optocoupler LED with 7mA? If so, my MCU can handle that. SORRY, that’s more than “a” question. I have used optocouplers in the past with a MCU to switch higher DC voltages. This application with AC voltages has been an interest but now I have projects on the bench. I’d like to get this first part nailed down before I start smoking some TRIACS 😁. Oh, and I well. I have watched this video several times and find it very helpful in jump starting those projects. Also watching your other videos 👍.

@ForceTronics

5 ай бұрын

Yeah if the microcontroller pin can source enough current then that should work. You can either use a logic high to source current or you could connect the negative side to a pin and use an active low to sink current. I went with the MOSFET so the video showed how to do it independent of the logic control source they were using. I don't remember the current values off hand but I do remember that datasheet covers multiple opto-coupler part numbers so just make sure you are looking at the same part number for current values for the internal LED

Great video, thank you! I do have a basic question though. It's always been my understanding that for any sort of isolation device such as an optocoupler to be effective, the grounds on both sides of the circuit should NOT be shared. However, what if my microcontroller power adapter (wall wart) and the AC device (Edison bulb) are both plugged into the AC mains outlets within the same house/building? Wouldn't they share grounds in that case? Thanks.

@ForceTronics

Жыл бұрын

Great question. Wall warts are isolated from the AC hot and neutral lines because they have a transformer inside. If it is a two prong wall wart then it has a floating chassis ground (that is why it has a plastic case) that is totally isolated from the AC lines. It is possible that a DC circuit could be tied to AC line power earth ground without any issues. Earth ground in your home AC wiring is there for safety purposes and not actually tied to the AC's current path. You just want to avoid connecting DC potentials to AC line power neutral or hot lines. Sometimes folks will tie DC ground to AC neutral thinking they are the same thing and they are not.

@douglasosborn3378

6 ай бұрын

Great question followed by a great answer

Question… How can this be applied to a 240V split-phase (3 wire single-phase) system? There’s L1 and L2 with 180° phase difference. Ugh, I feel like I’m not being clear enough on what I’m asking. It’s something I’ve been trying to get my head around for a while now. Google, as clever as she is, hasn’t been able to direct me in the correct direction. All I get are 120V single-phase responses. Out of the responses on single-phase and TRIACs, this video is absolutely the best I’ve come across to date. I’ll check back to see if you respond. I feel if there’s anyone out there that can help me or point me in the right direction it’s you.

@ForceTronics

6 ай бұрын

Unfortunately I am not familiar with a split phase system. If you are working with a 240v line I believe the video tells you how to adjust the resistor values for the higher voltage. You can also refer to the datasheet of the optocoupler for guidance or refer to their support such as forum.

@douglasosborn3378

6 ай бұрын

I’m almost positive all that is needed is to switch one leg of 120v. For example, when using a 1-1/2 pole contactor on say a HVAC compressor, one 120v leg is switched and the other 120v leg goes through the shunt. It would be the same thing, correct?

@ForceTronics

6 ай бұрын

It sounds like you just have a standard single phase setup with a "Hot" path and a "Neutral" path. The hot path can be seen as the source of the positive portion of the AC waveform and the neutral is the return path. And just the opposite for the negative portion of the waveform. In that case you could just switch one of those paths so that there is not a completed circuit and current does not flow in either direction. But if you are working with a generator or any inductive load sometimes the coil in the load can hum if it has a voltage on it so you may want to switch off both to prevent the coils in the compressor from humming. But the compressor may also protect against that so it maybe best to just try both approaches and decide what is best for your needs and setup.@@douglasosborn3378

@douglasosborn3378

6 ай бұрын

Thank you for your response. I’m doing a poor job asking the appropriate questions. I probably also confused things worse by using the HVAC compressor as an example. I’ll try to elaborate. Say for instance, I’m trying to switch a 240v single phase HVAC strip heater or a 240v hot water heating element… 240v in the USA. There’s two hot 120v legs with 180° phase difference, L1 and L2. The potential difference gives 240v. Please know, I'm not trying to educate; I’m just trying not to repeat a mishap I had in the past by me trying to be too clever. At the time, I thought I was, but NOT. 🤫 In my defense, I did have tech support on the phone. After the huge bang, sparks, and smoke, I thought, “I really need to understand this (TRIACs) more.” The TRIACs gave up the ghosts! BTW, thank you again for your response and patience. To continue… I recently had the opportunity to have my head in HVAC package unit with 3x 240v strip heaters switched with relays. L1 was switched through a relay to one side of the element. L2 went through a sequencer to the other side. The sequences are there so all elements don’t come ON all at once and draw huge current. The order of operation is all relays CLOSE then the sequencers CLOSE one after the other. Sequencers, bi-metal switches do their magic after the circuit is complete. They are there to keep from over current tripping breakers. Take the sequencers out of the equation and instead have a microcontroller control the TRIACs through a driver. For the on-demand water heaters, there are no sequencers. A microcontroller receives input from a flow-sensor and turns ON each element depending on demand. Oh gosh, TMI! Anyway… not 120v single phase with a hot 120v hot and a neutral… nor, 240v single phase as in Europe…. 2 phase? No, people will look at you like you’ve lost your mind. 😁 240v single phase USA. Split phase, i think is the correct terminology… but, 🤷🏼‍♂️. I wish I knew how to send a circuit diagram. Ugh, if I could even find one, so far, I haven’t been able. Best regards and kind wishes. Cheers.

@ForceTronics

6 ай бұрын

If inrush current is the issue you are trying to solve you can always turn to a NTC Thermistor based inrush current limiter. When they are "cold" the present a resistance that prevents a large current rush, but as they warm up they act like a short. Here is a link to an example one: www.digikey.com/en/products/detail/ametherm/SL12-10006/1873481@@douglasosborn3378

R11 resistor provides 11mA given there is 0 voltage drop through the LED and the MOSFET. I am either missing something or there is no way you are getting more than 10mA through that LED. It's probably more like 6-8mA.