Relay Confi.

Just about the only way would be to used a 5V/12V DC-DC converter (which would probably cost 5 or 10 times as much as your relay).

Sorry.

[ Oh, by the way,

From CR4 FAQ - rules for posting:

Do not post the same thread multiple times. The CR4 Admin will delete all but the most appropriate instance, or we may delete them all if we get sufficiently ticked. ]

It is possible to use a DC/DC converter to step up 5V to 12V. It will be cheaper to just buy a 5V coil relay. If you have 12V available then you could just use that voltage to power the coil and use a MOSFET with a gate threshold voltage (V_gs) of less than 3.5V to turn on the coil.

Whats the point of using MOSFET here if i got 12V i would have used it directly. Instead of buying a dc/dc converter why can't i design a voltage of 12VDC from 5VDC. Is it a foolish approach? Or should i make a converter here?

Well I assumed that the reason you are using a relay is that you want to turn something ON and also OFF with some logic. I also assumed that your control logic operated on 5VDC. I see now that I made some foolish assumptions.

You most certainly can try to design a 5V to 12V step-up or boost converter. I've used the MC34063A without a problem. I recommend studying the application note that explains how to design a converter using this part.

I think that you'll find that using a 5V relay will be more cost effective.

If you're not intending to turn the relay OFF, why use a relay at all?

Your assumptions where right but if i use MOSFET than i need 12V supply for that separatly thats the reason i said so.

Googling "5vdc relay" turned up 153,000 hits, with lots of suppliers. Electronics stores are perhaps more likely than automotive sources to have them. Rather than buying or making a converter, it will almost surely cost much less to get a relay of the correct voltage.

The following circuit shows a principle for turning on a 12 volt DC relay with a 5V DC supply. With switch S as drawn, the capacitor charges to near 5V. When S is switched over, the capacitor voltage is added to the supply voltage. To work, the 12v relay must actually pull-in at 9V which is often possible. The relay gets 4.5V always, which is probably above its release point! To overcome this, you could have another switch in the relay coil negative - which is only closed while the relay must be on.

There are variations, like connecting C to R permanently and making S single pole to positive.

So 67model connecting a capacitor as you said solves the problem but i want switch S working itself.

You could use a vibration switch and sit back and wait for a passing truck or earthquake!

If you only need to energise relay a few times, following circuit is OK since only a pulse of current is drawn from the battery.

Who are you..! You are designing circuits in seconds.how talented...!

Clever idea, but to not use a relay to turn on a relay to charge the capacitor will require a transistor (MOSFET) bridge for a switch. I still believe that getting a 5V relay will be much easier.

So the simplest way to get 12V from a 5V supply is to use a converter. I have seen cellphone charging from a 1.5V cell in a pen type device i hope thats a converter.

No. The simplest way is not to use a converter; it is to get the right voltage of relay in the first place.

How many box tops do you have to send in to be an electronics engineer?

Here ends the topic. 12V relay coil worked for 5V also.

The simplest way to get anything done is to hire people to do your work. A cheap simple method is to ask for free advice, but you have to listen and you often get what you pay for. A monetarily cheap but valuable method because you add the value is to independently study a method described by the free advice. Particularly if the free advice includes some references.