12vdc relay triggered by 5v

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drsnoze

Copper - Posts: 66

Joined: May 06, 2004

Posted: September 20, 2008 at 7:46 PM / IP Logged

Im trying to find a way to trigger a 12vdc relay by 5v. All of the relays i have and have tried will not work with the 5v wire. What i have is a mobile camera system for a local police department and im trying use this one wire that we currently have connected to a small led in the headliner. Bu we want to add another light in the grill but the problem is that the wire we have for the headliner wont power the grill light and the headliner light. Any imput would help

i am an idiot

Platinum - Posts: 13,670

This member consistently provides reliable information

Joined: September 21, 2006

Location: Louisiana, United States

Posted: September 20, 2008 at 8:02 PM / IP Logged

Use a 5 volt relay to trigger a 12 volt relay.

http://www.radioshack.com/product/index.jsp?productid=2062480&cp=&sr=1&kw=relay&origkw=relay&parentPage=search

drsnoze

Copper - Posts: 66

Joined: May 06, 2004

Posted: September 20, 2008 at 10:31 PM / IP Logged

what do i need to get this relay to work?

i am an idiot

Platinum - Posts: 13,670

Joined: September 21, 2006

Location: Louisiana, United States

Posted: September 20, 2008 at 10:50 PM / IP Logged

Where is the 5 volts coming from? How much current is available on that wire?

drsnoze

Copper - Posts: 66

Joined: May 06, 2004

Posted: September 21, 2008 at 7:39 AM / IP Logged

its coming off a panisonic arbitrator camera system. not sure how much is available but it has just enough to barely liight up 4 5mm leds

KPierson

Platinum - Posts: 3,527

Joined: April 14, 2005

Location: Ohio, United States

Posted: September 21, 2008 at 9:02 AM / IP Logged

You can use a 2N2904 transistor to amplify the current of the 5vdc output and switch a 12vdc load.

The transistor has 3 leads on it - a collector, an emitter, and a base. Wire the base through a 470 ohm resistor to the 5vdc output. Wire the emitter directly to ground. Wire the emitter to the (-) side of the relay coil. Make sure you use a relay with a diode across the coil - the stripe of the diode should face the 12vdc side of the relay coil.

Whenever the 5vdc output is active it saturate the base of the transistor causing the transistor to switch on. The ground at the emitter will pass through the transistor and output on the collector, causing the relay to turn on.

Should only be $2 in parts at Radioshack and only $0.25 worth of parts if you have a real electronics store close by.

Kevin Pierson

drsnoze

Copper - Posts: 66

Joined: May 06, 2004

Posted: September 21, 2008 at 10:28 AM / IP Logged

thanks i couldnt find any on radioshacks website. i did a google search and found these http://www.google.com/products?hl=en&q=2N2904%20transistor&um=1&ie=UTF-8&sa=N&tab=wf any recommendations?

i am an idiot

Platinum - Posts: 13,670

Joined: September 21, 2006

Location: Louisiana, United States

Posted: September 21, 2008 at 10:33 AM / IP Logged

Do you have the LEDs wired in series or parallel?

drsnoze

Copper - Posts: 66

Joined: May 06, 2004

Posted: September 21, 2008 at 10:35 AM / IP Logged

not sure the the 4 leds are part of a lighthead that i have no idea who the mfg is it was supplied by the customer

drsnoze

Copper - Posts: 66

Joined: May 06, 2004

Posted: September 21, 2008 at 11:39 AM / IP Logged

http://www.1075lighting.com/2008FordCrownVictoriaRidgefieldNJa.html bottom left hand corner

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