Need some help choosing components for a relay circuit and building it - Page 1
Forum section: electronics / beginners

author: Shaydzmi
author_rank: Regular Contributor
timestamp: December 29, 2021, 07:45:06 am
content: In this VFD, I have an open collector transistor output, I want to use it to build a relay circuit, so when the VFD runs, the relay operates after a 5 to 10 seconds delay.What I have in hand is:- 24VAC supply.- MY4N-J 24vac Relay.https://www.tme.eu/en/details/my4n-24ac/industrial-electromagnetic-relays/omron/my4n-24vac-s/- BTA16 Triac.https://www.st.com/resource/en/datasheet/bta16.pdf- 555 Timer.- PC817 Optocoupler.https://www.farnell.com/datasheets/73758.pdfI have no information about the transistor in the VFD except what is in the attachmentsWhat are your suggestions?Thank you!

author: Zero999
author_rank: Super Contributor
timestamp: December 29, 2021, 11:07:53 am
content: The VFD has an open collector output, which can't switch AC. You need to use a 24VDC power supply. It's possible to use a 555 timer, to delay the switching of a relay, but it's easier to buy a timer relay.

author: BeBuLamar
author_rank: Super Contributor
timestamp: December 31, 2021, 05:58:18 pm
content: As in the above post you can't operate the relay with the NPN open collector output. You need DC and I am sure most drives were designed for 24VDC. What do you want the relay to turn on? Can you buy some components?

author: james_s
author_rank: Super Contributor
timestamp: December 31, 2021, 06:04:46 pm
content: It will probably work to simply put a diode in series with the 24VAC supply to get pulsating DC and use that with a DC relay and the open collector transistor pulling the other end of the coil to ground. A relay is typically much too slow to chatter on the pulsating DC.

author: BeBuLamar
author_rank: Super Contributor
timestamp: December 31, 2021, 06:27:52 pm
content: The relay won't chatter but perhaps run hot because the OP has an AC relay. By mistakes I have operated 24VAC relays with 24VDC power. They work but very hot.

author: james_s
author_rank: Super Contributor
timestamp: December 31, 2021, 09:45:21 pm
content: That's why I said use that with a DC relay. If you have to use the AC relay then you could use a smaller DC relay to control the AC relay.

author: wizard69
author_rank: Super Contributor
timestamp: December 31, 2021, 10:17:33 pm
content: Look into time delay relays as they are designed for this sort of use case. Having 24 VAC may make the search a bit harder. The problem is that an open collector output is not compatible with AC components. So what you might need is a device to isolate between the two systems and what that might be depends a great deal on the motor drive. Some drives will supply power (often far less than 1 amp) for limited I/O so that you can drive a small relay, optical isolator or other circuit. Other drives will require you to provide a DC power supply. Which you have only you know.In any event coming from an industrial environment I would not try to fabricate anything, instead I'd buy the required components. You may even find a time delay relay that can be driven directly from the output, so you are down to one component.