looking for a delay off circuit

[izzi4]

Hello, i'm looking for a simple delay off circuit. I have a switch which
controls the 120vac via a relay which turns on a computer power supply. I
am looking for something to be able to turn off the switch and then have the
120v be turned off about 3-5 minutes later (cooling purposes) the relay
would still have the 120 going to it, when switched off (aka no battery
system or anything). I was planning on paralleling a second relay with the
first, one controled by the switch and the second controlled by the timer
circuit powered from the power supply. any suggestoins are welcome, i'm
looking for a simple design that wouldn't be to cost prohibitive. Thanks
for any input.
-krem

 

[John Fields]

Hello, i'm looking for a simple delay off circuit. I have a switch which
controls the 120vac via a relay which turns on a computer power supply. I
am looking for something to be able to turn off the switch and then have the
120v be turned off about 3-5 minutes later (cooling purposes) the relay
would still have the 120 going to it, when switched off (aka no battery
system or anything). I was planning on paralleling a second relay with the
first, one controled by the switch and the second controlled by the timer
circuit powered from the power supply. any suggestoins are welcome, i'm
looking for a simple design that wouldn't be to cost prohibitive.

 

[John Fields]

---
Oops...

Here's one with a 5 minute timeout:

http://www.grainger.com/Grainger/productdetail.jsp?xi=xi&ItemId=1611716878

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Hello, i'm looking for a simple delay off circuit. I have a switch which
controls the 120vac via a relay which turns on a computer power supply. I
am looking for something to be able to turn off the switch and then have the
120v be turned off about 3-5 minutes later (cooling purposes) the relay
would still have the 120 going to it, when switched off (aka no battery
system or anything). I was planning on paralleling a second relay with the
first, one controled by the switch and the second controlled by the timer
circuit powered from the power supply. any suggestoins are welcome, i'm
looking for a simple design that wouldn't be to cost prohibitive. Thanks
for any input.
-krem

One really simple, really cheap way to do this is to get the mechanical
timer out of a scrapped microwave oven. This is the kind you have to
physically turn the knob to so many minutes, and it usually goes ding at
the end of the cycle. These should be easily obtainable from a thrift
store. But this has the disadvantage of having to be set manually.

I would also consider connecting power to the fans just by themselves.
To keep the external power out of the PS, you can put a diode in series
with the power lead from both the power supply and the external power
supply, probably a wall wart. This is what's called a diode OR.

Here's one simple time delay. You can make the delay much longer by
using another transistor as an emitter follower to the first one. With
two transistors I've had no problem getting 2 or more minutes delay.
http://ourworld.compuserve.com/homepages/Bill_Bowden/page2.htm#relay_i.g
if

 

[quietguy]

Perhaps one of the turbo timer circuits would be suitable - the gizmos that
keep the car engine running for a short time after the ignition is switched off



David

 

[Dingus]

message

Perhaps one of the turbo timer circuits would be suitable - the gizmos that
keep the car engine running for a short time after the ignition is

switched off

.... pre-ignition?

 

[DBLEXPOSURE]

These guys have all kinds of timers with differnt time settings. Perhaps
it's worth checking into


http://www.weisd.com/store2/45201.html




message

 

[DBLEXPOSURE]

Here are some timers from National Controls

http://www.weisd.com/store2/45201.html





message

 

[quietguy]

I don't think that can happen with a diesel, but....

David

 

[Jasen Betts]

Perhaps one of the turbo timer circuits would be suitable - the gizmos

I don't think that can happen with a diesel, but....

I don't think a diesel engine can run without it (or something similar) happening.

Turbo timers run the engine at idle for a few minutes to allow the
turbocharger to cool, this allows the rotor to cool from orange-hot
in the relatively cool idle exhaust gasses rather than cooling by
conducttion up the shaft and cooking the bearings.

Bye.
Jasen