12vdc relay triggered by 5v

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Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=107579
Printed Date: May 27, 2024 at 7:43 PM

Topic: 12vdc relay triggered by 5v

Posted By: drsnoze
Subject: 12vdc relay triggered by 5v
Date Posted: September 20, 2008 at 7:46 PM

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

Replies:

Posted By: i am an idiot
Date Posted: September 20, 2008 at 8:02 PM

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

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

Posted By: drsnoze
Date Posted: September 20, 2008 at 10:31 PM

what do i need to get this relay to work?

Posted By: i am an idiot
Date Posted: September 20, 2008 at 10:50 PM

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

Posted By: drsnoze
Date Posted: September 21, 2008 at 7:39 AM

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

Posted By: KPierson
Date Posted: September 21, 2008 at 9:02 AM

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.

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Kevin Pierson

Posted By: drsnoze
Date Posted: September 21, 2008 at 10:28 AM

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

Posted By: i am an idiot
Date Posted: September 21, 2008 at 10:33 AM

Do you have the LEDs wired in series or parallel?

Posted By: drsnoze
Date Posted: September 21, 2008 at 10:35 AM

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

Posted By: drsnoze
Date Posted: September 21, 2008 at 11:39 AM

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

Posted By: KPierson
Date Posted: September 21, 2008 at 11:44 AM

https://www.radioshack.com/product/index.jsp?productid=2062609&cp=&sr=1&kw=npn+transistor&origkw=NPN+transistor&parentPage=search

That is the part - you can use any general purpose NPN transistor though (2n2222, 2n4401)

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Kevin Pierson

Posted By: drsnoze
Date Posted: September 21, 2008 at 3:09 PM

KPierson wrote:

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.

2 things

which resistor should i use

https://www.radioshack.com/search/index.jsp?kwCatid=&kw=470%20ohm%20resistor&origkw=470%20ohm%20resistor&sr=1

and second you said emitter twice, is one supposed to be collector if not where should the collector go?

Posted By: KPierson
Date Posted: September 21, 2008 at 7:02 PM

Sorry, Emitter goes to ground, Collector goes to (-) side of relay.

I would use this one:

Model: 271-1317 | Catalog #: 271-1317

But, any one will work, you don't need it to be big - an 1/8th watt would do the trick, but they don't stock them. So, go with the 1/4 watt

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Kevin Pierson

Posted By: drsnoze
Date Posted: September 21, 2008 at 7:26 PM

is this correct?

[IMG]https://i2.photobucket.com/albums/y17/drsnoze/rfpd.jpg[/IMG]

Posted By: KPierson
Date Posted: September 21, 2008 at 8:01 PM

yeah, looks good

posted_image

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Kevin Pierson

Posted By: drsnoze
Date Posted: September 21, 2008 at 8:43 PM

thanks appreciate all your help im going to try it withing the next few days

Posted By: fsmyth
Date Posted: September 25, 2008 at 10:02 PM

https://hmin.tripod.com/als/fsmyth/pages/drivers4.html#RMD44

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https://hmin.tripod.com/als/