hi jorgenbg,

I would also say there is a problem with your Power supply.

You can also try to change the PLC if you have an other. So you can exclude that the current PLC is defekt.

hope this helps,

regards,

I had this very same type of thing happen to me when attempting to close (using a relay contact) a circuit breaker powering a large motor drive.  The circuit breaker required more current to pull in than the power supply could provide.

After finding out the root cause was me not seeing the required in-rush current requirement, I spec'd and ordered a replacement power supply (and related power distribution device changes), I scrounged on-hand power supply options.  Found a couple P/S's that were designed to operate in parallel so they could together handle the large in-rush requirements.  That proved the concept was correct, and allowed continued project commissioning while waiting on parts.

If I had not found P/S's designed for parallel operation, the project would have been stuck with anything related to having that large circuit breaker closed - at least for another day or 2 waiting on parts.

jorgenbg

Hi

I have a problem when starting x number of electrical motors. The PLC just shuts down. I suspect it might be a power supply issue.

The thing is, the PLC is behind av 24V DC power supply and when the PLC shuts down I cant measure any drop in voltage to the PLC from the power supply. Its steady on 24V.  

Its not just one process, but it happens with different motors. It only happens at certian load on the system. Im already in contact with the electrical company, but I want to make sure everything are corrrect at my end. 

Im a total newbie and dont know about logging and if I could find the cause that way?

Thanks in advance.  

I am glad you got it worked out and things work now.

Siemens does not require the use of their P/S.  In the past, I rarely used a Siemens supply. Everything would work fine.

Lately our group decided to standardize on Siemens supplies, so most projects get a Siemens supply.  If it's a small project, we try to use non Siemens supplies we have on-hand to get them in use and stop collecting dust.

Now that you know you have several contactors with large in-rush, the PLC can time their closing so they are not all hammering the supply at the same time.  Even a 1/4 sec of stagger helps, provided the process allows that.

jorgenbg

Hi

Thanks for the tips. This was really helpful. 

I have an AC/DC/RLY model with two additional modules 1221 and 1222. The power supply was the problem. I have too many large contactors.

I have now dropped the siemens PS and connected to another stand alone PS in my panel. This was only powering the HMI. 

Now, everything works. I hope this wont cause any problems in the future. The panel builder told me siemens specify that you should only use their PS. 

Im a total newbie and I knew what kind of PLC I had, but in the stress of it all I forgot it had an internal PS. 

Regards

Jørgen