# DC Relay

Discussion in 'Electronic Basics' started by Joe Webster, Mar 10, 2005.

1. ### Joe WebsterGuest

Hello,

I'm just a complete novice when it comes to building circuitry. The
current project I'm working on involves a electronic door strike. The strike
requires at least 6vdc to unlock, I'm not sure how many amps right now and I
don't have it with me. Given things I can't change, when the door is to be
opened I'll have 3.3vdc to trigger the lock. My first thought was just to
get a simple relay that will switch the 6vdc when I supply 3.3vdc to the
coil of the relay.

So I need a relay w/ a nominal voltage of 6vdc w/ a minimum coil voltage
of 3.3vdc. Searching online at RadioHack and Mouser, this seems easier said
than found. I've found some that come close. RadioShack part# 275-232 which
has a min. switching voltage of 3.5vdc.Same goes for mouser.

So my question is "is there a better way to solve my problem" -- or
"could I somehow step up the 3.3v to say 6v and maintain that for at least
5-10 seconds?"

Thanks everyone,
Joe

2. ### Rheilly PhoullGuest

It's a bit hard to understand what you are asking but if I have it right,
you want a relay with a coil that operates on 3.3vdc to switch a 6vdc supply
to the door strike ?
Is the "min switching voltage" of the relays mentioned the actual voltage
required for the coil ? since a "min switching voltage" sounds a little
strange to me.
I would be inclined to try one, and mebbe increase the supply volts for the
strike too

3. ### petrus bitbyterGuest

Sounds you have a 6V power supply already and I assume it to be powerfull
enough to activate the door strike. All you need is a resistor, a transistor
and a diode. The transistor needs to be able to handle the current the door
strike needs. Use a TIP41 for instance.

+---+--------6V
| |
| |_
1N4003 - )|
^ )| door strike
| _)|
| |
+-+-+
|
100_Ohm |/
3.3V-----|___|-----| TIP41
|>
|
|
|
-----------------+-----------
(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)

petrus bitbyter

4. ### ChrisGuest

Hi, Joe. Not quite enough information to work on, but I'm going to
assume you're working with a 3.3V logic signal. 3V relays are made,
but they usually require more current to drive the coil than a logic
signal can provide, and they're not that common. Also assuming the
3.3VDC control signal and the 6VDC-plus power source have the same
common, it might be better to use a transistor to turn the lock
solenoid on and off (view in fixed font or M\$ Notepad):

6VDC Plus
o------------o--.
1N5402| | Solenoid
- C|
^ C|
| C|
| |
3.3VDC '--o
Control Signal |
(1 = ON) ___ |/
o-----|___|-o-| TIP120
4.7K | |>
.-. |
| | |
4.7K| | |
'-' |
GND | |
o-----------o---'
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

You can get the specified darlington transistor as well as the diode
and the rest at Radio Shack or Mouser. This circuit is good for
switching up to 1 amp, and 3 amps with a heat sink on the transistor.
If you need to switch up to 6 amps, you'll have to replace the diode
with a 6 amp diode.

Good luck
Chris

6. ### Lawrence OravetzGuest

Joe Webster was thinking very hard :