12v Digital Inputs - plc

mad4x4

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mad4x4
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Mar 2009
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Most PLCs are 24v for digital logic, will a Digital input card detect a 12v (automotive) signal as a 1

Looking to do some work on a Kitcar and thinking about doing some of it on a s7 1200 don't want to have to fit relays to step up the voltage for each digital input. I could run a lot of input at 24v I suppose but that a bit unusual for a CAR
 
I think B&R has a PLC that rated for mobile use 12VDc Power and 12VDc in / out
if its not them then do and internet search i know ther eis a lot of mobile equipment using 12V PLC's
 
Try it, or look at the specs, a 24v digital input card will have specs on the hysteresis switching points, I do remember some years ago an Omron I tried reliably switched on 12v, I seem to remember that the on voltage was about 6-8 volts so it may be possible to use 24v inputs on 12v although not recommended for reliability.
 
The Automation Direct Productivity 1000 has both input and output modules rated 12 - 24 vdc as well as a power supply to power the PLC with 12 - 24 vdc input.
 
Automation Direct Click and Allen Bradley Micrologix 1400 inputs are rated for 10 to 12 volts. Worked on a lighting re-control for a SUV and all I had to do was get 24V DC to DC power converter to power the CPU. I think the Click has one in it's line.


Also, DC transistor outputs on ML & SLC will control 12V
 
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When I put a SLC in my race car I used the 1746-IB16. They switch on at 10vdc. Had a IB32 but they don't switch on until 15vdc.
So really I would check the specs, or just give it a try.
 
mad4x4 said:
Most PLCs are 24v for digital logic, will a Digital input card detect a 12v (automotive) signal as a 1

Looking to do some work on a Kitcar and thinking about doing some of it on a s7 1200 don't want to have to fit relays to step up the voltage for each digital input. I could run a lot of input at 24v I suppose but that a bit unusual for a CAR
Click to expand...

Look at the data sheet of the digital input card. It should specify somewhere on it at what voltage level it will transition to logic high and logic low.

Beckhoff EL1008 digital inputs transition to logic high at 11-30VDC. Or, simply go with an EL1144, which is a 12V digital input card. It's inputs transition to logic high at >8.5VDC.
 
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One other thought, you won't be dealing with 12V. If the engine is off you will be getting about 12.6V, if the alternator is working you will be at about 14.4V, maybe up to 14.7 volts. When the engine starts the voltage can easily drop below 9V. Also make sure you isolate the PLC from the battery when not in use or you will flatten the battery. Which is again why I mention the Barth controller, it takes 10mA, an S7-1211 takes 10watts meaning over 800mA.
 

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