Ac Power Off Delay Circuit

[jaspreet]

hi
i need a help , i need a circuit that should delay(probably after 2 minutes) shut off after the ac-power is turned off.So plz help me

 

[Hayato]

I really did not understand what you tried to say there.

 

[Hero999]

Oh no not another fague request.

What do you want to power your circuit from when the mains power goes off, batteries or a small neuclear power plant?

 

[Hayato]

Oh no not another fague request.

What do you want to power your circuit from when the mains power goes off, batteries or a small neuclear power plant?

Maybe he wants a small nuclear power plant.

 

[jaspreet]

the better way

hi
"""""""""""""Originally Posted by Hero999
Oh no not another fague request.

What do you want to power your circuit from when the mains power goes off, batteries or a small neuclear power plant?
Maybe he wants a small nuclear power plant.""""""


that was funny now getting to the business
i need delay power off circuit
i m using a fan for my amp circuit,it is placed on to the heatsink
i just wanted that the fan should remain on for 2 minutes after the amp power is shutt off to sink the heat on the heatsink
Jaspreet

 

[Dr.EM]

So long as power is still available after the amp is shutoff, you just use a simple timer and transistor/mosfet to operate the fan. If power is removed completely from the unit, the only real solution is a set of small rechargeable batteries that recharge while it is on and power the fan at shutoff.

 

[jaspreet]

i need the circuit

hi
thanks for the advice but i need the circuit plz if u have then post it
i need it urgent , i'll b thank full 2 u

 

[Hero999]

No.

We don't mind helping you but we won't do all the work.

The 555 timer will do what you want, you need to connect it to the fan using a suitable relay and connect the trigger to the power off switch using a suitable circuit.

**broken link removed**


You still haven't provided enough information, what type of fan are you using? AC/DC current & voltage?

How about the power off switch, does it turn the whole amp off?

You might need to build a separate power supply for the timer and fan?

Have you actually considered whether you really need this circuit?

You might not even require it?

Surely if the power is disconnected then it doesn't matter if the fan is off as it won't be generating anymore heat.

 

[GJS]

I'm trying to control the turning off of a small submersible pump (120V AC, 10W) in a water tank. I'm using a float switch at the bottom of the tank to turn off the pump to ensure it doesn't run dry. Initially I was using the switch to directly pass AC to the pump but when the switch opens and the pump turns off a small wave is created in the tank which bobs the float, momentarily closing the switch, turning on the pump. This creates another little wave and an oscillation of float-switch-bob/pump-cycle-creating-wave results. If I could get the pump to turn off 1 second after the switch is opened enough water would still be in the tank to make sure the pump wouldn't run dry but the water level would be below where a wave could re-close the switch.
From reading this thread it sounds like the LM555 will do the timing part of the task. One of the links in this thread has a circuit called "TIMER RECOVERY DELAY CIRCUITS - NEGATIVE RECOVERY" which seems perfect but I'm not sure what other circuit would be controlled and pass the AC to the pump.
I already have a 12V DC power supply I can use to power the circuit(s).
Thanks for any help.

 

[stallione]

Hi, I am trying to solve a similar problem.
Want to turn off a 110V regular switch which would in turn start a delay of 30 minutes and then shut off power to my projector. The projector needs power for a few minutes to cool off when you turn it off using the remote. On the flip side, I need the power to be restored to the projector instantly when I flip the switch to on.
Any ideas?
Thanks!

 

[gary350]

This is probably much easier than you think. Some of this heat sink fans don't use much power I have done some experements with this stuff already. You solder a very large capacitor in parallel with the heat sink fan you already have. You MUST use a current limiting resistor to keep the capacitor from acting like a dead short on the circuit. When you are using your amp the fan on the heat sink runs and the capacitor charges up over a period of, lets say maybe 15 minutes. When the amp is turned off the capacitor discharged through the fan so the fan continues to run until the cap has discharged. You have to size the cap large enough to run the length of time you want. You also have to put diodes in the circuit so the cap discharges through the fan and not the amp circuit.

 

[mbarazeen]

GJS,

you can try a complete electronic controller eleminating the float switch, use the conductivity of water to stop your motor when its lower and again to enable its start when water level reches up a bit. no need for timer or complications.