Hot answers tagged

6

Flyback diode is there to avoid voltage spikes when an inductive load is turned off. In your case, only the one on the left side is necessary as you want to protect the arduino against the coil spikes of the relay. The one on the right side should not be there as it's AC, you will have a short. You may want to check the Arduino pin can provide enough current ...


6

For reasons that have little to do with the static calculations in the other answers, I would use a beefier transistor such as the 600mA 2N4401 or a MOSFET. Switching an inductive load is harder on the transistor than switching a resistive load, even with the diode. At some point the full relay coil current is flowing through the transistor for a short ...


5

simulate this circuit – Schematic created using CircuitLab Figure 1. Eavesdropping with an opto-isolator. Inserting an opto-isolator into the original LED circuit provides the best means of doing this as it provides complete electrical isolation between the two devices. It does require minor modification of the source but it should be a trivial ...


5

simulate this circuit – Schematic created using CircuitLab Figure 1. Mains XOR using relays. It seems unnecessarily complicated to change voltage levels. An XOR can be created using two relays. Mains powered relays can be obtained in small form-factor. Look for "ice-cube" relays, for example. Figure 2. A selection of ice-cube relays. Double-...


4

Theoretically, it would be ideal, but you want to do it for zero CURRENT, not zero voltage. But the zero-crossing on 50-60Hz AC is far too fast to worry about that on an electromechanical relay which has inconsistent opening/closing times, takes tens of ms to open and bounces for ms, sometimes tens of ms when closing. It can't be achieved in practice. You ...


4

Relays are electro-mechanical and dropout time will be in the order of tens of milliseconds or more. If a snubber diode or resistor is use the drop-out time will be longer. In addition, mechanical differences between the contacts of several poles of the relay will mean that the contacts open at different times. It will not be possible to control the relay to ...


3

The diode on the left is appropriate. The one on the right isn’t -it will half-wave rectify when the contact is open, which probably isn’t what you want, and will do nothing when it’s closed.


3

Your calculations make sense. You should also calculate the transistor's power dissipation to make sure it doesn't overheat. Note that when the relay is on, the voltage across the transistor is only about 0.2V (this is a typical number for silicon transistors), not the full 12V - the remainder is across the relay. The power dissipation should be about 0.2V x ...


3

D6 is backwards on the schematic. It is not clear from the PCB decal which end is the cathode. Consider adding a 10K resistor from Q3 base to GND to assure a rapid and complete turn-off. Based on typical values for the Vf of an LED and an optocoupler, it looks like there is only 1.5 mA of current through the opto primary side. Depending on the minim coil ...


2

It's very difficult to tell from the poor quality images posted but it appears that you may have connected the wires on the left side of the board one pin out of position. Figure 1. The relay module requires 5 V so it should be powered from the 5V pin on the WEMOS board. The relay module GND should be connected to any GND pin on the WEMOS. Figure 2. ...


2

When switching the mains (230 VAC) to a load your most important concern is: How long will the relay's contact last? Each time you switch the mains, the energized contact of the relay will create a small electric arc in the air that goes to the non-energized contact. That arc shortens contacts' life. To prolong relay life you might want to buy relays with ...


2

and i guess solid state may harm the quality Overcome your fixations here. I'm (also) a guitarist (and music producer) and have recorded probably about 100 of my own songs and, it wouldn't bother me one bit to use solid state switching and dump mechanical relays straight into the garbage. I've also mastered about 500 other songs hence, I have some knowledge ...


2

You MUST add a current limiting resistor as shown below: - The value depends on the type of isolator you are using but, from 24 volts, 2k2 is probably going to be OK. It can be fitted in series with pin 1 or pin 2.


2

See Phoenix Contact FBST, it's a bar that goes in the slots under the wire connector you see on the blue relay module. Finder will have similar. 093.16 for example. See their catalog. Keep an eye on the total current running in this bar. Tip: when looking at this kind of industrial products. Find the catalog PDF! It has more seachable info than the websites....


2

If the current stays below the specified limit for the relay at all times, there's no reason to do anything: the relay is supposed to perform its rated number of cycles in these conditions. Making sure you switch at a lower current may increase the possible number of cycles beyond the spec, but you shouldn't count on that anyway. If you're afraid you might ...


1

Generally you ought ought to draw schematics with logic symbols not photos, but I understand your concept. But if you do not specify currents for each, you can run into problems like NPN Ib, coil current and power relay contact derating for a large AC motor. You show a phone trigger for a relay to drive a Johnson counter after so many pulses to drive motor ...


1

Nothing happens when there is 24V on pins 1 and 2, as there will be 0V over the LED. However, without a resistor, setting pin 2 to 0V will damage the LED immediately.


1

Fail safes usually include redundant devices configured properly. For instance if you absolutely have to shut off something, this would be two switches in series, so that if one failed to open, the other could have a chance. Welding shut can happen if a relay is used outside its specification. For AC applications there are some circuits that only open the ...


1

If everything is OK until you close or open relay contact applied to the motor, it means it is an electromagnetic compatibility problem. Use a snubber circuit which can be simply a freewheeling diode for DC motors at the motor terminals to avoid electromagnetic interference. Add diodes on both motors.


1

There are many 4:1 analog mux parts that will meet your requirement, in both the CD4xxx series and DGxxx series. Analog Devices, Vishay, TI, etc. There are two addressing options: The CD4066 has multiple, independent switches, and any of them can be on/off in any combination because there is one enable input per switch with no internal decoding. Three ...


1

I don't think three position relays exist - you'll probably have to use two SPNO or SPDT relays where you are thinking of using a three-position one. Latching relay do exist. You will probably want the two-coil type - pulse one coil to operate, pulse the other coil to release. With a single-coil latching relay, you apply power in one polarity to latch, ...


1

I would say yes to your last thought. Just keep those two separated from the whole circuit and hook your arduino and mosfet there. Keep the connections from the rest of the circuitry as little as possible. For example you can take the output from this "LIGHNING SWITCH" and use it as an input to your arduino. When you press the switch, the arduino ...


1

D6 is backwards in the schematic - mentioned in comments and other answers. With it backwards, trying to activate the relay will cause a short circuit across the 5Vgreen_o line, probably short circuiting the power to everything (including the microprocessor.) The optoisolator isn't needed here. You have both sides tied to the same power source - there's ...


1

The easiest way is to buy a commercially available alternating relay from an electrical distributor.


1

Imagine what would happen if the transformer was reconnected while the loads on the secondary were still spinning down and no longer in phase with the grid supply. Reconnection out of phase would be a Bad Thing : I hope you already understand (or the book explains) why. So it would make sense for there to be a secondary means of disconnection to prevent that....


1

@Ben G here is my final product which is working like a champ with your help. Bottom right corner is a 120v coil contactor connecting to a bus bar. Out of the bus bars 120v goes to the relay. On either side of the relay are 120vac to 12vdc transformer, 1 per motor/blast gate. I have 1 blast gate open when a machine comes on and one close when the same ...


Only top voted, non community-wiki answers of a minimum length are eligible