switch a 12v device from 3v source

Other Hardware General Electronics
1

G'day, I'm hoping for some help with my project. I'm not electrically versed, just a handy man.

My project is to switch a 12v power source on and off with a 3v current from a computer.
I was going to use a relay until I found the ones I have are 12v coil only. These where sourced from an old dis functional UPS.

Whilst searching on the internet I found there are other ways I could achieve my switching device. ie; Power MOSFETs, or maybe transistors, diodes.

Could I utilise a IRFZ24N in this situation?
I'm not sure if a IRFZ24N will work on 3v's or if I need more component in circuit to achieve a reliable switch.

Reading some post here I see I need to provide more info.

The 12v source is automotive. This is fused at 10A. Then there are two switchers that activate two separate air-conditioner type clutches.

The 3v source comes from a GPS Guidance computer. This uses a old automotive type dipper switch to activate the Run - Hold for swath marking. (This is probably useless info).

What I'm tiring to achieve is when the dipper switch is activated the start - end of a swath it also turn the clutches in and out of gear.

A simple relay to cut the power or earth feed is likely to be the easiest answer.
Cheers

2

What you want is a small transistor to amplify the 3v signal into a 12v signal to switch a relay that can handle the heavier load.

Any small NPN transistor should do the trick, like a BC337, a PN2222, etc.

Replace the "To Arduino +5V" with "To +12V power supply" and the "To Arduino Ground" with "To Common Ground".

3

Thanks Majenko,

This looks interesting, though there are a couple of things I omitted.

  • I dont use Arduino...
  • The 3v power must not drop after-during switching. What I mean by this is that the 3v is a loop circuit. If it was to be grounded or had voltage drop, it may not complete its operation (swath)

TRY TO POST A DRAWING SOON
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4

I dont use Arduino...

So why are you here then?

The 3v power must not drop after-during switching

With this switch arrangement in parallel to the existing ciruitry there will be a slight increase in current draw on the 3V signal, but no (or no noticable) voltage drop. The 1K? resistor limits the base current to the transistor which will be in the order of microamps, or even nanoamps. If you want even less current draw, then increase the 1K? resistor. I usually use a 10K? myself.

5

Majenko,

The reason I'm here?
Well I was searching for information on how to go about this project. Came across this site as a forum, so I asked the question. In further reading I noticed "Arduino" being used, and of coarse in your comments.

Just trying to recycle the old dis-func. UPS

Thanks again