slow switching relay

[wj33]

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?

 

[amidabadi]

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).

 

[nbucska]

You need electronics -- no relay will work with 470kOhm
in series.




<nbucska@pcperipherals.com>

 

[Heydave]

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.

 

[wj33]

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.

 

[nbucska]

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>

 

[wj33]

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.

 

[melone]

Can you use a programmable relay?

 

[lcsjk]

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.

 

[fangas]

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.