×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

slow switching relay

slow switching relay

slow switching relay

(OP)
I am setting up a circuit where I need to have a timer drop out when a relay switches.  Is there a relay I can use that will have a deadband time of approx .5 sec?

RE: slow switching relay

such relay dose not exist.but you can creat a delay time before applying signal to relay by adding 1 resistor(seri) and 1 capacitor (parallel) to the circute.(for .5 sec, 1 uF and 470k are suitable).

RE: slow switching relay

If you use a relay with more poles, you can use a set of contacts to control your timer. If you need a longer dropout in the relay itself, you will need 2 relays with a sequencing circuit to control the delay. More application information would help.

RE: slow switching relay

(OP)
Each time a set point is reached a relay is switched.  At this time we need to reset a delay timer to complete another circuit function.

RE: slow switching relay

vj:
The pull-in voltage of a relay is not well defined - it changes from unit to unit etc.
What are you trying to do ?

<nbucska@pcperipherals.com>

RE: slow switching relay

(OP)
We are controlling an existing cooling unit which has to be energized or de-energized by closing a circuit for approx 2 secs (momentary contact).  The thermostat controlling the units operation energizes/de-energizes a relay.  To provide a momentary closure to the cooling unit we are using a timer to provide a closed circuit for a short period.  Problem is that each time the thermostat controlled relay is cycled we need to reset the timer so it goes through its cycle again.  That is why I wanted to delay the switching deadband time to permit the timer to reset.

RE: slow switching relay

Can you use a programmable relay?

RE: slow switching relay

Your description is not very clear, but here is what I think you are doing.  When your thermostat reaches its threshold it makes a contact closure or energises its internal relay.  AT that time you need to provide a 2-second pulse to the cooling unit to start it.  At the end of the two seconds, the start pulse ends and the cooling unit continues to run until it brings the temperature of the thermostat back down and turns off.  You now are waiting for the thermostat to warm up and start the cycle again.  So basically you need a motor start-up pulse.

If this is correct, you just need to control the relay from a one-shot.  You will need a relay to provide the power to the cooling unit.  You will need a one-shot such as the LM555 to provide the timing. You will need a power supply of 5-15 volts.
You will need a reverse diode across the relay coil. (1N4002).  You will need a transistor from the output of the LM555 to use for turning on the relay.  You will need a decoupling capacitor, an input noise resistor-capacitor, and a timing resistor-capacitor.

Search application notes for the LM555, MC1455, UA555, LMC555, and I think you will find a suitable application note.

RE: slow switching relay

Hello,

Melone is correct. You can use a programmable relay. SSAC makes one that can be configured as a 1-shot. Is is rated to run off of 24 to 120 Volts ac/dc.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources