5V-220V Relay

[sirwoggle]

Hi Folks, i am a relative newbi to electronics so bear with me here

i live in the middle of nowhere and there is only one small electronics suplier store, and they dont have relays with a 5v trigger that can switch 220v

(i built a parellel port interface (5V and a couple Milliamps) and want to switch mains power with it)

Can anyone help with methods of building them out of common components?

 

[OperaHouse]

Use a solid state relay block like Crydom. You can probably get them for about $5 on ebay or

http://www.mpja.com

You can even get a complete relay board that plugs into the printer port with 8 relays from

http://www.electronics123.com

This may need a boster relay if you have a large current requirement.

 

[felixc]

You have no much choice because you need electrical isolation. So either a relay or an opto-relay.

If you need more drive from your parallel port you can parallel logic lines, provided of course that you drive them with the same polarity.

If you need a special part you have to use the mail-order places. Where are you located? Is there a Mouser or a Digikey in your country?

 

[ScottyUK]

If you are looking at building, rather than buying, have a look at opto-couplers and triacs. There are plenty simple circuits to switch mains voltage. What current are you looking to switch, and what is the load (heater, motor, tungsten lighting, etc)? The load can make a lot of difference to a semiconductor switch.

Operahouse's idea of buying a ready made SSR may work out cheaper than building the functional equivalent out of discrete components. If you factor in your time to develop the circuit, it willdefinitely be cheaper to buy a ready-made item.



----------------------------------

If we learn from our mistakes,
I'm getting a great education!

 

[Paulusgnome]

Suggestions :

1) You could use logic-level relays, these do switch at 5V but sourcing them may be a problem. (Large mail-order companies like Farnell and RS components are very good if you live out-of-the-way.)

2) Use a higher-voltage (say 12V) relay in conjunction with the usual transistor and diode arrangement. Assuming that you have 12V available. The choice of relays is probably better this way. Make sure that the transistor is sufficiently rated for the relay coil current.

Do take care with clearances and good wiring practices around 220V - it is unforgiving of mistakes!

 

[sirwoggle]

Wow, this site works realy well, i wasn't expecting a reply so soon Thanks guys

I found some 12V trigger, 240V 10A relays in a copuple old UPS's i had lying around and mannaged to find a nice safe NPN based low voltage switch to pump 12v through to powwer the relays

Vcc
|
+------+
| __|__
Relay /^\ Diode 1N4002
Coil /---\
| |
+------+
|
Diode | /
1N4148 4.7K B |/ C
parallel >-|>|-+--\/\/\/--| BC547A or 2N2222A
port data | |\ E
pin +-|<|-+ | V
1N4148 | |
parallel >-----------+------+
port ground |
Ground


I think this is what paul was saying

Felix, i found some diagrams on a opto-circuit but im not too paranoid about the comp im using, it an old piece of junk so if it blows, meh no big loss

Does anyone know of a resorce where i can check the ratings or the NPN's? i need to find one to use 12v and low amps

Anyways thanks a lot folks

 

[Paulusgnome]

You got it, Sirwoggle.

Your BC547 is probably OK for the job but has a maximim Ic of 100mA which may prove inadequate. The 2N2222A has Icmax of 800mA, and this should be more than adequate.
You can also use the ubiquitous BD139 (Icmax=1A) which even an out-of-the-way electronics shop should have, and this would probably be my personal pick.