S7-200's - Relay output contact

[mjamil]

Thanks Eric,

We mostly use LG contactors/overloads here. I havent seen them coming suppression or otherwise, but'ill check that possibilty too.


But what about the life of the RELAY contact within the PLC????



Now, if you look at the technical specs. for S7-200 (relay types) it mentions that;

RELAY
Lifetime - Mechanical (no load) 10,000,000 open/close cycles
Lifetime contacts at rated load 100,000 open/close cycles


Assuming the above is expected life span of the contact, I calculate that

@ 1 click of relay contact per minute

= 60 open/close per hour,
= 960 per day (in two 8 hour shifts)
= 24,000 per month
= in four months, I can use the Relay unit with peace of mind!!! after that .........

am I going wrong somewhere??

I first tried attaching a JPEG image @ 150dpi, now lets try a BMP file.

Thanks again.

 

[Nomanjamil]

still waiting for your replies, guys!

adios

 

[Eric Nelson]

The 100,000 operations is AT RATED LOAD. You stated earlier that the relay was rated for 2A. If you are switching a 2A load, they yes, it MAY fail after 4 months of operation. At a lower load, it will most likely last longer. Probably quite a LOT longer... :nodi:

Fail to put a supressor on your contactor coil, and expect it to **** out sooner...

If longevity is going to be an issue, then consider using transistor outputs instead of relay outputs.

By the way, your picture made it this time. Here it is in a format that will display here automatically:

[attachment]

You have it wired as we all suspected.

There is 220V from each phase TO NEUTRAL. The relay coil is NOT referenced to the neutral. The relay coil is connected across two phases, so you would have 440V passing through your relay, which you now know NOT to do!...

beerchug

-Eric

 

[jvdcande]

BTW Eric, if the voltage from neutral to phase is 220V, then the voltage from phase to phase is NOT 440V, but about 380V. Don't forget the phases are rotated by 120° and not 180° (basic knowledge from electrics 101).

Kind regards,

 

[Eric Nelson]

You're right, Jean Pierre. Mjamil's "440V coil" statement got it stuck in my head...

In any case, 440V sounds 'scarier' than 380V, which will hopefully reinforce the main point of this thread, which is that he shouldn't be running it through the PLC's relay!...

I wonder if his contactors really have 440V coils?...

beerchug

-Eric

 

[Rube]

I wonder if his contactors really have 440V coils?...

If so he should try to never let that happen again.

In all the systems I've ever designed, I have only used one coil that needed more than 120VAC (it couldn't be helped). I labelled it on every side and splattered labels inside the 12" square box.

I still think about it every once in a while. I shouldn't have to.