A Small circuit for use in Ghana

[partyjups]

Hi Im new on the list. my name is jeppe cohrt 25 years old music student from Denmark.

When studying music in Ghana West Africa. I find Out that
there is a lot of electronik stuff that they need down there. My friend is running a small company building speakers and amp's, and we are now working together to make some direckt import of transistors and ic's and much more.

Im now planing to make up a new small circuit and i need some help.

The circuit have to Delay the main voltage 220 some secounds (5) the reason for making up this circuit is that they offen have lightoff, and when the electricity is turned on again, they are told from the goverment that it's is best if they have turned the freazer(collers air condition m.m.) off. I think that it's because when all these devises are turned on at the same time they need more curent (A) than the eletricity company can provide.
People belive that. it's is can damage there things if they are not turned off, when the electricity it turned on again.

I know how to make up this small circuit with use of an small power supply to drive the relay to be turned on
like a speaker protection delay.

But the circuit need to be very small and very low cost
SO MY QUESTION IS can i make the up without use of power supply. can a power resistor run the relay and the driver transistor ???? and how

If any can tell me how or make up a circuit for this
I'll be happy to hear about it.

jeppe c.

 

[promitheus]

the best is to make a delay on circuit direkt to the mains voltage using a relay to connect power. So in this case when the power is off the relay will turn off fast and when it gets power it will turn on after as much time as you want. Simple.

 

[partyjups]

Yes that was what I plan to build, but My Question is how to make up the circuit without power supply?
I don't know how to use the relay and the transistor from 220 volt AC.

hope to get some help jeppe c. thanks.

 

[arnach]

Hmm..

A small company eh?

Well Well..

Switch the AC coming in on and off with a relay. After this I hope you know how to build a power supply directkly after this.

You will control the 220V AC input with say, a 5-12VDC trigger.

Thus you need a small 12VDC supply to run the relay. You will need a step-down transformer, that steps down the 220VDC to 5VDC (i am describing a simple supply, skip). Then a rectifier to produce 5VDC. Then build a simple timer circuit to calculate to five seconds then provide power to the relay. The simplest way I see of doing this, rather than using a transformer, is to use another relay, to switch 12VDC to the other relay. So build a 5VDC supply for the logic and a 12VDC for the trigger if you want to go this way. Or you could just use a transistor. Pick up a circuit encylopedia or look at many sites on the net if you want a circuit for either of these.

-- Finley

 

[promitheus]

There is a small circuit in the Elektor magazine that protects amplifiers from the big inrush current of toroids. I don´t know the code of the circuit. You can check at http://www.elektor.de or link from there to the english web site. It doesn´t use a transformer. But you will have to make the delay time higher for your case.
Ok I found the code of the project it´s 974078-11 There is even a ready PCB for this. The code for that is 974078-1.
It´s from 1997 but you can see the circuit in the April 2001 magazine. Good luck !!!

 

[Remco]

I wonder if it can be done with only a an resisor a cap and a diode and a relais. If you know the resistance of the relais coil you can figure the resistance you need to get a nice voltage across the relais coil. You need the diode to get some dc and the the cap acros the relais coil so it need's to be loaded first before the reais goes open. when there is no more main's it wil shut off fast because the resistance of the relais coil is a lot smaller then the resitor that loads the cap and maybe fast enough for this aplication Try and experiment but i do not know how safe it is..

 

[partyjups]

Thanks for these advise

I think I will try to use your idear REMCO Im not shure if the resistor can drive the relay, of cause it depends on the relay but. im not use to work with high voltage these way
so if any one can make up a small circuit eksample it will help me .

Let say I use 24v or 12 relay

I have an Idear thet the cap need to be very big with these type of sulution ?

jeppe c.

 

[hifi]

why not use thermistors they will limit the inrush current....? otherwise u can use a zener to lover the voltage for the relay.....


/micke

 

[Helix]

I can be done useing the design from elector, all use need is a little juggling around with the resistor and the cap. The best way to find the values is on a circuit simulator.

The only problem i can see with this extendid delay is that the soft start balast resistor wil get very hot. Though if this is a small pwer supply with a toroid smaller then say 200va, you probably do not need this.

 

[Thoth]

The simplest thing you can get to do the job is called a time delay relay. The version you need is called 'delay on'. These are a little hard to find for 240V (they have to be DPDT also, to switch both 'hot' legs), but I did find one. Allied Electronics has one that should work at 'http://www.alliedelec.com/catalog/pf.asp?FN=123.pdf'. The manufacturers type is 'GT3-4AF20', and the Allied stock number is 814-3144. The relay portion is solid-state for reliability.

I think that this can be just plugged into the line (use a socket), and configured (set knob, set switches). No external components needed. The downside is that it costs ~$50. You might be able to find something similar at a surplus shop for less.

Good luck