12 volt relay driver curcuit

Thread Starter

Thatnewguy

Joined Sep 30, 2021
3
Hi, all I am very much a newbie and only just starting to learn the basics of electronics and I need a circuit to drive a relay and wondered if someone on here might be able to assist. I need to switch a 12 volt relay that has 80 ohms resistance and requiring 150mA draw to hold the coil, the electronic pressure switch that will trigger it provides an analogue 12 volt negative output but is only capable of 4-20mA draw. My first thought was to use a transistor but I don't know enough about them yet to select the appropriate transistor or what resistors would be required to make this operate. Any help would be greatly appreciated.
 

crutschow

Joined Mar 14, 2008
28,204
What voltage/current from the pressure switch do want for the relay to turn on?
Is the switch output a 4-20mA current loop?
 

Thread Starter

Thatnewguy

Joined Sep 30, 2021
3
I have tested the pressure switch and it has 0 volts when off and 12 volts when on and it switches the negative. The 4-20mA is what the data sheet for the pressure switch stated which I didn't really understand but it is not capable of switching the relay on it's own. It does say it can be reconfigured to a digital 1.5v as well but I thought that the way it is set up is easier. I have attached a copy of the data sheet.
 

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LowQCab

Joined Nov 6, 2012
1,343
Why are You using such an expensive Sensor if all You want
is to control a Relay ?

What does the Relay control ?

What Voltages do You have available,
and what Voltages do You prefer to use and why ?
.
.
.
 
Why are You using such an expensive Sensor if all You want
is to control a Relay ?

What does the Relay control ?

What Voltages do You have available,
and what Voltages do You prefer to use and why ?
.
.
.
The switch is just what I had, I bought it cheap in a mixed bag of bits and pieces. The relay will control a compressor. The supply voltage for both the switch and compressor are both 12 volt dc and is the only source available.
 

LowQCab

Joined Nov 6, 2012
1,343
Are You referring to an Automotive "Emergency-Compressor" ?
If so, your project probably won't work because of severe vibration problems
and Motor over-heating issues.

If You are using a high-quality Automotive-Compressor designed for
"Air-Bags" or huge "Air-Horns", it probably already comes complete with
an Air-Pressure-Reservoir and an automatic Pressure-Switch.

Is there some other type of Compressor arrangement that You are using ?
A proper Pressure-Switch specifically designed for the job at hand
would be a much better choice.
.
.
.
 

Lo_volt

Joined Apr 3, 2014
233
It will help to find the operation manual. I took a few minutes to search for it and couldn't find anything. You should contact IMI Norgren's applications department or field applications engineer to see if they can help.

The sensor is very versatile, but that makes it a little less simple. From what I read in the spec sheet, it looks like Output 2 is the 4-20 mA output and Output 1 is a programmable set point. If the set point for Output 1 is programmable, you should be able to use that to control your relay. Again, without more info I'm only guessing.
 
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