Dear all,

I am facing an annoying problem:

A number of outputs from a DM16 24 expansion module seem to have failed and I cannot find the reason for this. 

Observations:

- Measured output voltage of a failed output:  high state or low state: 0.0V
- Measured output voltage of non-failed output : low state = 0,4 V, high state = 23,7V
- in one expansion module, 5 outputs have failed, in the other 6 outputs. 

Circuit configuration:

- Power supply 24V, 4A
- Controller 24CE: 24VDC with transistor outputs
- 2 expansion modules DM12 24: 8 idigital inputs, 8 dgital transistor outputs each
- Load to expansion modules: 1 relay WAGO 788-304 per output.
  This relay has in input coil of 24V DC, 22 mA with protection diode against back-EMF.
  Output: 250V AC, 16A

What could have caused this failure?

Thank you for your quick answer.

As a test I removed all external wiring and programmed a hard "high" on all ouputs.
As mentioned before only a few outputs produce the 24V, the others remain at 0V.

I will try Siemens support as you suggested.
I will keep you posted.

All the best.

Thank you for your suppport.

You are right about the power consumption but I did a test by removing all external wiring and programming a hard " high" on all outputs.  Only a few outputs showed 24V, most of them were at 0V.

So probably both modules are broken.

What is the chance that 2 so called new modules are defect?
I noticed though that, at delivery from my supplier, the seals on the boxes were broken. The supplier claims that the modules were new and refuses to take them back. 

What worries me is that there is something fundamentally wrong with my circuit and that placing new modules will result in defetcs again.  As mentioned each output is loaded with one relay type WAGO 788-304.

The documentation states that the outputs are protecetd against short circuit and overload.  What can be the reason to destroy them anyway?

In order to rule out misunderstandings with the output circuit for the Logo controller, a detailed circuit diagram would be good for inspection.

Normally the outputs can only break if an external voltage is applied. This can also happen when an induction voltage is generated. If you are sure that the relays have a protection circuit to avoid induction voltage and everything is wired correctly, then i also have no further ideas, where to search a fault.

Regards, Scorp

Scorp

This can also happen when an induction voltage is generated. If you are sure that the relays have a protection circuit to avoid induction voltage and everything is wired correctly, then i also have no further ideas, where to

 IIRC LOGO BM-s and extensions with transistor outputs used Infineon ITS4140N drivers at output.

From datasheet:

• Clamp of negative voltage at output with inductive loads

which means external clamping diode won't hurt, but in reality is not neccessary.