How to protect circuit? Turn one line on another line off with two pole DPDT Rel - Page 1
Forum section: electronics / projects

author: nardev
author_rank: Unknown
timestamp: August 29, 2019, 12:54:20 pm
content: I have a situation where i'm supposed to turn of one line and turn on another line at the same time. Actually, it would be great if there is slight delay between those switching to let the device be protective and to do it bit more safe. (Avoid sparks etc)If i use two relays, i would not have that problem, i would simply make 0.5s delay between on/off of the relays and everything ok. But for the sake of using only one two pole DPDT relay, i need this.The power lines that are used for switching could be 12VAC or 12VDC, max 1A current.Any idea? Any suggestion? How to protect the circuit? Etc?

author: Psi
author_rank: Super Contributor
timestamp: August 29, 2019, 01:24:48 pm
content: You will be fine using a relay.A relay is already a mechanical switch with delay.When the movable contact breaks one connection it has to physically move before it makes contact with the other side. During this time neither side is connected to the movable contact.99.99% of all relays and switches are of the "Break-Before-Make" type.(I don't think i've ever seen a "Make-Before-Break" type relay, although i'm sure they exist. And Make-Before-Break switches do exist but are very specialized)If you want to add extra delay use a bigger relay with bigger contacts, they will take longer to move between states.Or you could drive it with a lower voltage.

author: nardev
author_rank: Unknown
timestamp: September 11, 2019, 12:41:37 pm
content: I think this picture is bit more descriptive ?This is what i'm wondering about?

author: wraper
author_rank: Unknown
timestamp: September 11, 2019, 12:47:14 pm
content: Quote from: nardev on September 11, 2019, 12:41:37 pmContact group on bottom does nothing. It always stays open.

author: nardev
author_rank: Unknown
timestamp: September 11, 2019, 12:49:14 pm
content: Quote from: wraper on September 11, 2019, 12:47:14 pmYes, that line is common for everything there.I have specific reason why i would do this. Nothing out of the text book IMHO that's why i'm asking.And, this is only for DC.For AC i think i have another option.

author: wraper
author_rank: Unknown
timestamp: September 11, 2019, 12:57:09 pm
content: Quote from: nardev on September 11, 2019, 12:49:14 pmI don't get it. You can not connect it to relay at all just as well. Because it does nothing.

author: ledtester
author_rank: Super Contributor
timestamp: September 11, 2019, 01:02:19 pm
content: What wraper is saying is that the way you have it wired the green circuit will always be open - the relay will never complete it.WHen you talk about the "common for everything" which color circuit are you referring to? It seems to me you mean the blue circuit.The joining of the red and green circuits at the black area is confusing. Are they electrically connected there? What does the black area represent? A power supply?

author: nardev
author_rank: Unknown
timestamp: September 11, 2019, 01:05:57 pm
content: Quote from: ledtester on September 11, 2019, 01:02:19 pmI'm sorry, you are right. I didn't describe it well.The black area is "a device".Only thing that i want to do int hat particular case is when i activate the relay to disconnect the red and connect the green one. That is all.Everything else should not make any problems.The green and red are actually both 12VDC but from different sources that are grounded together.

author: nardev
author_rank: Unknown
timestamp: September 11, 2019, 01:09:23 pm
content: Anyway, i think that i have solution from another source. I just forgot about it. Looks like much safer option. In case the relay fails.But again, would this be safe for switching? Safe as that it would not make any short circuits between power sources?

author: ledtester
author_rank: Super Contributor
timestamp: September 11, 2019, 01:12:45 pm
content: What are the power supplies? Are they isolated from each other?

author: nardev
author_rank: Unknown
timestamp: September 11, 2019, 01:14:07 pm
content: In the first case yes however, i also have an option where is use rectifier and some caps and convert 12VAC to DC on the same board and i want to use that one.p.s. the device can tolerate current/voltage "jumps" and doesn't need to have very stable power supply.

author: ledtester
author_rank: Super Contributor
timestamp: September 11, 2019, 01:26:29 pm
content: Quote from: nardev on September 11, 2019, 01:05:57 pmHow about just using a SPDT relay?

author: nardev
author_rank: Unknown
timestamp: September 11, 2019, 01:33:01 pm
content: Well, yea, the way of switching is not a problem. It's rather if that would be safe for the circuit and power supply.