Snap-in Module Power Supply

[russedwards]

Hi

 

Has anyone had any experience of running a snap-in module (E3XB) from a 12 VDC power supply?  Is this possible?

 

I am looking at a new application and it would require a 12 VDC power supply to all the electrical items - PLC is being mounted on a vehicle.

 

Thanks

[Eyal Koren]

In general, it is not recommended to use 24V expansion modules in a 12V system. 

I do not know what PLC's you were using so far for your projects, but to avoid using I/O expansions at all, you can consider working with the Vision V120. There are several models (with built in I/O) that require 12V.

See attached PDF

V120 comparison.pdf

[Simon]

The snap-in I/O modules are strict about supply voltage, and it needs to be 24V.  For example, with digital inputs the switching thresholds are based on 24V, so 12V applied to a 24V input will not be enough to switch it on.  The threshold is usually around 17V (this is specified in the datasheets for each module).  There are issues with digital outputs as well, but I won't blabber on and on.

 

As Eyal mentioned you can use the V120 and select a model that has 12V capability (usually controlled by jumper settings inside the unit).

 

Alternatively, if you want to stay with the larger PLC then you can use expansion I/O on 12V.  You need the special "-L" versions, look at the listing of I/O modules on the Unitronics website for those.

 

The only issue I have had with the 12V operation is the lack of analogue outputs.  In the M91/V120 families, none of the models with analogue outputs have a 12V option, they are 24V only.  When looking at the "-L" I/O modules, there is also an absence of analogue output models.

 

The final option is to use a 12V-24V step-up convertor and run your automation logic on 24V.  Note if you have relay outputs on a 24V module, you can still use them to switch 12V directly, but you would need 24V power for the relay coils.