We are creating a novelty drink dispenser that controls a set of 8 pumps with a Siemens Simatic Step7 1200 PLC. The decision to use this PLC was based on our need to have a very stable prototype.

Now we are nearing a stage where we are going into mass production, and the PLC feels like overkill. It has many features that we don't use and it costs a lot. We would like to replace this with a simple relay-card.

We have limited experience with making electronics and we will most likely use a professional service for the development and production of this card. However given the importance of this card for our business, I would like to ask some general advice here first.

For example, what are the most important things to think about when selecting a relay for controlling small valves, and what features should we know about in a valve that can make our product better?

Of course, we want them to be able to open/close as many times as possible without failing, and when failing, never failing in an open state. Also if there is any way to detect wear/failure that would be awesome.

For reference, our valves are 24VDC 5W solenoids.

For this application?

1. How much does it cost
2. How much does it cost
3. what voltage and current are the contacts rated for?
4. Hoe much does it cost
5. What is the MBTF
6. How much does it cost
7. How mush does it cost to install
8. How much does it cost
9. What is the switching frequency
10. How much does it cost

However, the outputs are rated for 0.5A, so I would not be using any relay and just use a diode around the solenoid coil.  It took me a long time to wean my guys away from the *** Mitsubishi 0.1A outputs with relays and say you just don't need them.

I've had 200W solenoid systems running for many years like this.