Query about a Flex Modual 1794-OB16


Thread Starter

Graham Steele

I have been told that Flex modual 1794-OB16 channels can not pull in a 24V DC Telemecanique LCD1 contactor and a seperate relay has to be used. The reason given is that the transisterised switching will not take the inrush current. I would be grateful if somebody could clarify this matter.

G Steele

Curt Wuollet

That's a really interesting theory since inductive loads actually delay the rise of current. I would suspect the problem is really either the steady state current or over voltage on turn off (inductive kick).


Just some facts about the output module:

Continous output current per channel: 500mA
Inrush current: 2A for 50ms, repeatable every 2s
(page 6 in the manual 1794-in094_-en-p.pdf, which you can download from www.theautomationbookstore.com

Assuming that the contactor is a LC1D, the coil "burns" 2.4W (100mA at 24VDC). Therefore, there is no problem at all. For further details see www.schneiderelectric.com.

You need an interface relay if you use the contactors with the AC-coil!

Feel free to contact me at
stephan at marelec dot ch

Greetings from Switzerland
If the DC outputs are not up to the job, why not just replace the Flex module with a relay version? Tele also has (or used to have) a little interposing relay, available in solid state and electromechanical versions, that would screw directly onto the contactor coil terminals. Very convenient, but a bit spendy if I recall.
Steve Myres, PE
Automation Solutions
(480) 813-1145
The Low Consumption 24VDC version (BL) coil works very well with the OB16. No interposing relay is required; I have had some in severe duty applications for over 12 months with no problems.
Hi Steve

The panel already has a relay output modual with seven of the eight channels used and we need to add another two outputs and the panel has not enough room for another modual.