Instructables

220 VAC to 12 VDC with minimum no-load wastage?

Hi,I want to convert 220 VAC to 12 VDC without using a transformer since they consume power even when a load isn't connected to the secondary output.So this is how its to be-A 12 volt dc supply should be available,which will be fed to a relay once a switch is set 'ON'.I could easily depend on a transformer but this 12 VDC supply is to be available always and can't afford the wastage.pls suggest an alternative(and FYI a battery is not applicable in this situation).

You don't say how much power you need.

Cheap transformers waste power. Buy a decent one and the power losses are truly negligible.

If there is no load, why leave it switched on ?
Adarsh_tronix (author)  steveastrouk1 year ago
That's the tricky part.Actually this is a part of a doorbell project and a doorbell needs to be working at all time and is not something you could disable like that.That's why I have to provide the desired 12 VDC all the time.
Then use a 220VAC rated switch/button for the door bell so the door bell controls the 220VAC input. Then it won't matter what transformer your using since no power will be going to it till the button is pressed. Just make sure the area is well shielded and insulated so there are no foul weather mishaps.
Adarsh_tronix (author)  mpilchfamily1 year ago
mpilchfamily!the foul weather mishaps do cast their evil here in my town,frequently.The whole thing's serialistic.I bought a pet pug(whic is BTW very cute!).Now,no one dares enter my compound because of the ferocious beast!(atleast thats what they think!).I decided to add a secondary switch on my compound wall so that someone could alert my by ringing my doorbell and won't have to enter my compound.A direct extension from 220 vac is easy but not preferred since-1)Rain water,water from the garden etc leads to a high risk factor of short circuiting.2)The cost of wire rated for 220 VAC to cover the whole length is more expensive than a 12 volt relay and 12 volts rated wires put together and also I have plenty of transformers with me which is why I thought of going this way. But if there's 'no other way'I'll be confined to spend the big bucks,use 220 VAC and extra expenditure on insulation(since the switch and the wires are in the open).Atleast the purpose is served.....
Have you considered a wireless doorbell system that runs off batteries? They have a range of about 100 feet under ideal conditions. If that isn't enough you can always mount the receiver in range and use a length of wire to place the speaker where you need it. You shouldn't have to spend more then $30 US for one (about 1600 rupees)
Adarsh_tronix (author)  mpilchfamily1 year ago
Woah!Thats something I haven't thought of....but My doorbell is brandnew and my family seem to like the jingle,I can't propose a change in that for a while.I've always wanted to own one of those wireless bells and one day,YES I will.
Then stick with the door bell for your front door but use a wireless one to indicate when someone is at the front gate.
How much power do you anticipate wasting here??
Adarsh_tronix (author)  steveastrouk1 year ago
well,I don't know exactly.....I did a bit of research and came to know that a real world transformer(not to confuse it with an ideal one) wastes as much as 1W of energy every hour and 24*30=720 Watts of energy per month!OH MY GOSH!.....They haven't mentioned if its the transformers dealing with smaller voltages or the bigger ones.Atleast all I know is any Kind of wastage of electricity should be minimised for the sake of providing equitable resources for all.
Not it, for example, the amount of energy required to make the alternative can never be recovered.

Energy is measured in Watt-hours incidentally, so you're wasting 0.024 kWh/day, or 0.72 units/month.

Use a solar cell powered ultracap.

Steve