RELAY HELP - Page 1
Forum section: electronics / beginners

author: robertlopez925
author_rank: Contributor
timestamp: August 25, 2014, 01:29:52 am
content: Alright i have a project and i need help trying to figure out how to pull it off. I belong to a non profit train club as of right now we have a gate alarm that activates when the electrical breaker is turned on and if the cherry switch is not depressed. This sounds the alarm until the gate is closed. It has worked a little to well...Now i have been tasked to figure out a circuit where the alarm will only sound if the track power is on. The difficult issues am having as follows 1.The Horn Strobe is a wheelock MT-12/24W it runs on a 12v DC Driver the amps the horn and strobe does not pull a lot of power maybe 2A MAX. 2.There is two separated powered tracks they run on 5-24VAC about 1-15A MAX now NONE of the power from the tracks can NOT intermingle with each other they are on two separate transformers and are two separate isolated loops.The Goal: The goal is to have it setup when the gate is open and no power to the track nothing happens... But the second any of the two tracks receives power the horn will sound until the gate is closed. I was thinking of using a magnetic switch for the door portion the cherry contact switches are not holding up well through a high traffic area. I was thinking of some thing like this "http://www.amazon.com/gp/product/B0009SUF08/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=ATVPDKIKX0DER" and i know i will need some sort of Relay to accomplish the task that is where your help comes in. I don't really know a lot about circuit's. I know enough that it has gotten me this far. Now i am stuck.HELP!!!!Thanks , Robert Lopez

author: IanB
author_rank: Super Contributor
timestamp: August 25, 2014, 01:35:38 am
content: Put two relay switches in parallel on the horn strobe circuit. The alarm will sound if either or both of the relays are closed but will be silent if both of the relays are open. Energize each of the relays independently from each of the track power supplies.

author: robertlopez925
author_rank: Contributor
timestamp: August 25, 2014, 01:44:36 am
content: But wont the horn which is DC powered and the track is AC powered. Wont there be a issue between that

author: IanB
author_rank: Super Contributor
timestamp: August 25, 2014, 01:54:30 am
content: Relays have complete isolation between the energizing coil and the contact switches. The track power goes to the energizing coil to turn the relay on and off and the contact switch goes in the horn circuit. You would wire the relay so the switch is closed when the track power is on.

author: robertlopez925
author_rank: Contributor
timestamp: August 25, 2014, 01:57:08 am
content: AHH That does now make sense.. DO you have a relay you would suggest there are a lot to chose form form SPDT To DPDT AC, DC or AC/DC

author: DanielS
author_rank: Frequent Contributor
timestamp: August 25, 2014, 02:01:27 am
content: Quote from: robertlopez925 on August 25, 2014, 01:44:36 amIf you use relays as suggested, the coil that closes the relay and the relay's switching contacts are electrically isolated. This is an electromechanical equivalent of optocouplers.

author: IanB
author_rank: Super Contributor
timestamp: August 25, 2014, 02:13:15 am
content: You might consider something like this:http://www.amazon.com/Packard-C230B-Pole-Contactor-Volt/dp/B001KGSJ74The coil is energized by 120 V mains and it can switch 120 V mains. So you would power it from the switched input side of the mains supply to the track power supplies, and you could perhaps have it supply mains power to the alarm system. I suggest this because the 5 - 24 V on the low voltage side of the track power supply is quite a wide range for a relay to handle. The disadvantage is that you would need to work with mains wiring and that would be a bad idea if you have no experience of that.

author: robertlopez925
author_rank: Contributor
timestamp: August 25, 2014, 05:11:13 am
content: Yea i think i want to stay from the main 120v...

author: IanB
author_rank: Super Contributor
timestamp: August 25, 2014, 05:45:44 am
content: On thinking about it some more, why can't you just put the track power transformers and the alarm system on the same master switch? That way the alarm will only be on if the track power is on.

author: robertlopez925
author_rank: Contributor
timestamp: August 25, 2014, 06:07:07 am
content: they are currently in a way.... The issue is when we work on the layout though we have to turn on that fuse to run some tools. Most of the time we would like to walk in and out of the gate/lift bridge with out the alarm beeping. It is really Loud it was designed to chase people out of buildings during a fire. It is set on its maximum setting which is ok when trains are running it does get loud in there when there are 50+ people and 14 trains running.Now i am thinking of taking a different route and you can tell me if it is doable. The goal is to silence the alarm when we are working on the layout. NOT to be confused with running on the layout. What my thought is using a two magnetic reed switches and set them to when a magnet is placed on them the circuit is open. Now i was thinking of placing them in two separate locations and making it so the alarm will only silence if both reed switches have magnets on them. Any thoughts if this is doable

author: IanB
author_rank: Super Contributor
timestamp: August 25, 2014, 06:38:31 am
content: I think it would be easier and more conventional to have a key switch to override the alarm and disable it when you are working on the system. Then only someone with the key can turn the switch off and disable the alarm. It is very common to have a special override like this for maintenance work.

author: robertlopez925
author_rank: Contributor
timestamp: August 25, 2014, 06:40:09 am
content: I did not think of that that would life much easier