Small PLC recommendation wanted

I've got a small hydronics (hot water circulating) heating system that includes five pumps and 3 thermostats. I'm interested in converting from relays to a small PLC and have been looking on e-bay for an older used PLC for this application. I really would like to get the whole system for less than $200 (inc. software).

My main considerations are cost, software cost/availability and size. I would like around the size of a DL 305 series or smaller. I like the older racks like this because of cost and flexibility. I figure if I have some extra slots I'll purchase some additional cards later just to play around with.

Currently I really only need a couple digital inputs and some relay outputs.

The main reason I really want this system is to build in some counters to determine how long each zone is calling for heat and how long the boiler is firing so I can determine fuel consumption per zone. An internal clock might be helpful in the future if I decide to get make the logic more complicated by varying temperatures based on time of day. I think one consideration also might be programming capabilities as I will need some timers and the simpler, the better for me.

I would also like to be able to connect and either track the timer/counter values or logging them would even be better.

It seems the GE Series One PLC's might fit the bill but the software seems a bit older.

From my research, the 250,350 and 450 CPU's from Automation Direct seem to be much more advanced as far as programming but I'm wondering if there are other similar products.

Thanks for any input!

I'm not sure on any other products other than AB. And, as we all know AB is high dollar. But, they do have a PICO controller that might be sufficient for your control.

As for the logging capabilities I'm not sure on the PICO. I do all of my logging via OPC clients into a SQL database.

The software for the PICO is free as well. The PICO is around $100.

Hmm... AD's DL05 (8DC In/ 6Relay Out) is going to cost you $99, programming software is $99, programming cable $30, plus shipping. That'll put you over $200.

Really, I don't think you'll find anything cheaper (in price) than AutomationDirect. Depending on what you want to do in the future, go with a DL05 or a DL06.

Thanks Hardwerk. I will look into the PICO controllers. I don't have a very broad background in PLCs so I am grateful for any input. I did consider the Micrologix controllers from AB but I think the software will be expensive. I'm also don't know anything about their capabilities as far as programming commands and expandability of the system. That's why I've been leaning towards a rack system.

I've read in other posts that you can get a stripped down version of RSLogix for free that only works with a Micrologix controller when you purchase a particular model controller. The micrologix is very capable and can do as much logging as memory allows. The only major drawback in industrial use is lack of online editing. Every little change requires you to stop the controller (put it in program mode) and download.

billybob said:

Thanks Hardwerk. I will look into the PICO controllers. I don't have a very broad background in PLCs so I am grateful for any input. I did consider the Micrologix controllers from AB but I think the software will be expensive. I'm also don't know anything about their capabilities as far as programming commands and expandability of the system. That's why I've been leaning towards a rack system.

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Several companies make PLC's comparable to the PICO controllers that are very inexpensive. Most also provide free programming software. Moeller and EasySoft(?)are two that come to mind. However, if you plan to use PLC's for future projects, I would recommend purchasing the DL05 and software. It provides much more flexibility.

I am going to give Stephen a plug here, look at Entertron www.entertron.com. They have plcs and accessories at a reasonable price plus the software is free. The cost for a starter unit is $195 that includes a Smart-Pak, cable and software.

In most cases you can "network" small plcs together to expand the system.

As mentioned DirectSoft for the DL05/105 is $99 but for the DL205 it is $199, the full package is $495. Obtaining used parts with capability of getting new if needed then the DL205 may be a good choice. http://web3.automationdirect.com/adc/Shopping/Catalog/Software_Products/Directsoft_PLC_Programming_Software/Directsoft_Software

Also mentioned was the Micrologix 1000 which has a free version of RSLogix500 http://www.ab.com/plclogic/micrologix/1000/

I concur with Ron that Entertron's unit will be a good choice for you. It has relay outputs, so you can use AC or DC, (or 3 of each).

And you will find their staff friendly and very willing to help you in any way.

The little Allen Bradley unit is okay, but has fewer outputs, and last time I had one, was AC/AC only.

regards.....casey