Money can be pretty tight if you are on your own and wanting to learn PLCs for the first time or maybe you are just starting out in a business.  One of the most common reactions to buying a PLC for the first time is sticker shock.   Just to purchase one of the most popular PLCs like Allen Bradley can run into the thousands of dollars that you don't have.  Well nothing is for free but if you're willing to cut some corners let's discuss the options for getting a PLC for education or testing that will not break the bank.

Buying New

Let's start with what you think would be your last option but not necessarily your worst choice.  There are smaller units out there that can get you started on learning the basics of PLCs.  If you're intent on learning one type of PLC just consider that all PLCs have the same basic principles and once you've learned those it's easy to apply them to other platforms.  If you are worried about prospective employers asking about your knowledge of a certain type of PLC then be honest and say you just know this one type of PLC but given a few weeks you would have no problem learning the additional features of their preferred PLC.  I've found this approach has worked personally and any smart employer will be impressed with someone who's taken such self initiative to learning.

Automation Direct 

The biggest bang for the buck I've found when buying new is AutomationDirect's 05 or 06 platform.  Their manuals (download for free) are also very well laid out, instructive and complete.

First consider the D0-05DD which is only $99 out of your pocket and an additional $99 for the programming software.  The cool thing about this PLC is for the price you get digital inputs/outputs, built in PID control, two communication ports with History | Specifications | Modbus Organization">Modbus capability, high-speed counter inputs, and a spare slot for option cards like 4-20mA current inputs.

For a few extra dinero the D0-06DD1 is well worth it.  It adds some extra punch like the ability to handle real numbers, built-in real-time clock/calendar, and four slots for option cards (that are the same as the 05 platform).  The CPU on this one is just like the DL250 so it has a lot of functionality.  There's also an option for an LCD display ($69) that snaps into the front of the model.

Allen Bradley
Allen Bradley has a good deal for learning the RSLogix software.  Basically you can get the RSLogix 500 software for free but it's only good for programming the MicroLogix 1000 10-point controllers (6 inputs / 4 outputs).  Not a bad deal though considering you can get a new 1761-L10BXB for $99 which is not that much more expensive then the $59 programming cable you'll also need (1761-CBL-PM02).  Unfortunately to add analog capabilities is not that cheap compared to the AutomationDirect PLCs.

You can download the free RSLogix 500 software here.  Beware it's a 20MB download and requires registration.  Just follow the instructions on the screen.

Buying Surplus or Refurbished 

If you're still bent on buying a certain manufacturer's PLC another option is to buy surplus or refurbished equipment from a third party.  Surplus is old inventory that has never been used so it usually comes in the original packaging.  Refurbished is used equipment which has been repaired (if needed) and tested to make sure it works right.  You can expect to save from 30 to 50%.

Some traps to look out for when taking this route:

• On older equipment the original manufacturer's warranty will be outdated or void.  Make sure the vendor supplies a warranty in case there are any problems.
• PLCs with processors may have older firmware versions.  Sometimes different firmware versions can create conflicts with newer versions.  Older firmware versions may be missing features or have bugs.
• Depending on how the equipment was used or stored the electronics may be affected and while they work fine on test benches they may fail sooner then newer components.

So with that in mind visit companies that specialize in surplus and refurbished PLC repair and supply. 

Buying Used

If you have the patience and knowledge there's no better place then eBay to shop for a used PLC.  The category is under Home > Buy > Business & Industrial > Industrial Electrical & Test > Industrial Automation, Control > Control Systems and PLCs (whew, that's long winded).  Make sure to create an account and sign up for your favorite searches to be emailed to you when they come up for bid.

I mentioned patience because it takes some time to figure out the usual selling price for components.  Once you get experienced there's good deals to be had, but you have to stick with what you think is a reasonable bid and if you lose move on to the next one.  With most of the popular components there's always something coming through even though it can be very frustrating when someone out bids you by one dollar at the last minute!

So here's how my hunting trip for an Allen Bradley SLC500 went on eBay. 

1. Initial Research --- I scope out part numbers and list prices of what I want on the Allen Bradley site.  They have a good overview of the SLC 500 system on their website and you can look up the pricing in the Rockwell Automation Webstore.  Keep a list of the part numbers and any slight variations as it makes for easy searching on eBay.    So I decide that I need a 4-slot rack since this is only for testing (part number 1746-A4) but I should look out for a 7 or even 10 slot rack as well.  For my minimal purposes a power supply like the1746-P1 is fine but I'd also buy a 1746-P2 for a good price.  Next is the CPU like the SLC 5/02 (1747-L524) which should do fine for the essentials.  I also picked this as a minimum because the 5/01 isn't supported with the hand held programmer (more on this later).  For cards I'd like some digital inputs to play with and there are a lot of choices but a 1746-IB16 will work but I'll keep a look out for any others like it.  As an added bonus some analog inputs (1746-NI4) and a thermocouple card (1746-NT4) would round out the set. 

   So here's what all that would cost me if I bought it off the Rockwell website:

   Part	Price
   1746-A4	$245.00
   1746-P1	$346.00
   1747-L524	$857.00
   1746-IB16	$250.00
   1746-NI4	$646.00
   1746-NT4	$964.00
   Total	$3,308.00

   That's a lot of dough even if you knew the right people and could get a good discount.

2. eBay Setup --- What's neat about eBay is that some people are selling complete PLC systems with all these components included, but on our tight budget I can't afford to buy it all at once.  So the best I can do is buy one piece each month.  The disadvantage here is that I can't test these initial purchases to see if they work right until I get at least a rack, power supply and CPU!  So I sign up with eBay and do a search for each part number and save it to my watch list and favorites so that they can email a notification when new ones come up for bid.
3. Racking it up with Power --- I start targeting racks first as it seems a good place to start and not much can go wrong with this simple part.  Just in case I was also looking out for power supplies.  I test out the waters with a 10-slot rack that's coming due soon and if I can get it for a steal.  I'm outbid right away though and it closes at $77.25.
   
   

   Item Title	Max Bid	Outbid
   ALLEN BRADLEY SLC 500 10-SLOT RACK	$30.00	$77.25
   Final price		$77.25

   Undeterred I set my sites on a power supply that I'd like to get for around $30.  I'm outbid right away so I try to up it another five bucks but I'm outbid again and it finally sells for $43.36.
   
   

   Item Title	Max Bid	Outbid
   ALLEN-BRADLEY SLC 500 POWER SUPPLY 1746-P1	$30.00	$31.00
   	$35.50	$36.00
   Final price		$43.36

   So this is not going to be easy.  There are not a lot of 4 slot racks showing up.  I find another 10-slot rack that might be a good price.  Might as well up my max bid a bit but I still lose.
   
   

   Item Title	Max Bid	Outbid
   ALLEN BRADLEY SLC 500 10-SLOT RACK	$50.65	$51.65
   Final price		$66.00

   Suddenly I spot a 4 slot rack and pounce on it and I'm the current high bidder at $9.99.  A couple days later though I'm outbid and I wonder about their max bid might be.  I really want to stay under $40 bucks so I let it go and it goes for $41.55.  Hmmm....
   
   

   Item Title	Max Bid	Outbid
   Allen Bradley SLC-500 Modular Chassis 4 Slot Rack	$40.55	$41.55
   Final price		$41.55

   A new power supply that's more then I need comes on so I bid just to see if I can get lucky.  I'm like the high bidder for 1 second so I let this one pass.  It still shows you can get some great prices on even new parts.  The 1746-P2 has a list price of $506.
   
   

   Item Title	Max Bid	Outbid
   ALLEN BRADLEY SLC500 POWER SUPPLY 1746-P2 (NEW)	$20.50	$21.00
   Final price		$121.50

   I still stalk my prey patiently.  I new 4 slot rack comes up for bid but I'm outbid and it goes for a great price.
   
   

   Item Title	Max Bid	Outbid
   Allen Bradley SLC 500 4 Slot Rack New In Box	$50.00	$51.00
   Final price		$68.88

   One of those combo packs come up with a 7 slot rack, power supply and CPU.  Boy, if I can get that for $100 I'd be way ahead.  I'm the high bidder at $51.00 but I'm outbid the next day.  It finally goes for $181.38 which is just remarkable for all those components in one.
   
   

   Item Title	Max Bid	Outbid
   Allen Bradley 1746-A7 Rack & 1746-P2 & 1747-L532	$100.00	$102.50
   Final price		$181.38

   Here comes another combo pack that I lose out on by $2.50, ouch!
   
   

   Item Title	Max Bid	Outbid
   Allen Bradley 1746-A4 with 1746-P2 excellent	$100.00	$102.50
   Final price		$102.50

   By this time I'm running out of patience so I get serious on a power supply.  Again, I'm a loser by $2.50!
   
   

   Item Title	Max Bid	Outbid
   Allen Bradley SLC 500 Power Supply 1746-P2 NO RESERVE	$104.00	$106.50
   Final price		$106.50

   This time I go after another rack and this time I'm way out of there.  Somebody wanted that one real bad.
   
   

   Item Title	Max Bid	Outbid
   ALLEN BRADLEY PLC500 SLC 5/02, 7 SLOT	$165.00	$167.50
   Final price		$405.00

   After all this mileage I'm beginning to think I'm really going to have to up my bids.  Then an amazing thing happened.  A 7 slot rack with a P1 power supply came up for bid with a "Buy It Now" option at $100.  I couldn't believe my eyes after seeing a rack just go for $405!  No time to fool around if it's real so I make the purchase.
   
   

   Item Title	Max Bid	Outbid
   ALLEN-BRADLEY SLC 500 1746-A7 Rack 1746-P1 Power Supply
   Final price --- BUY IT NOW!!!		$100.00

   I'm happy to say that it's worked great ever since I bought it.  In this case the patience really paid off.  I get a rack and power supply at an unbelievable price.

4. If I only had a Brain --- The CPU is going to be the brains of the whole outfit so I'm expecting to shell out a few more bucks for this item.  First I watch a couple of SLC 5/02 CPUs go through and finally sell for $197.51 and $179.01.  My first meager attempt starts with a max bid of $30.00.  I think I fell asleep or something because this one because I get outbid and it actually goes for $31.00 (which is $857 brand new).  Somebody got a steal but at least there's consolation that I might be the next lucky winner.
   
   

   Item Title	Max Bid	Outbid
   ALLEN BRADLEY SLC500 PROCESSOR 1747-L542	$30.00	$31.00
   Final price		$31.00

   When the next one comes up a set a max bid of $40.00 and I end up winning it for $33.00!
   
   

   Item Title	Max Bid	Outbid
   Allen Bradley 1747-L524/B SLC500 5/02 PLC	$40.00
   Final price		$33.00

5. Inputs Scored --- I spot a good looking input card that's all ready been bid on and place a max bid of $34.50 but it doesn't take.  I'm automatically outbid.  So I go back and try again with a max bid of $37 and this time it works and I get my input card on the first try!  Funny how that cost more then my CPU.
   
   

   Item Title	Max Bid	Outbid
   Allen-Bradley 1746-IB16 SLC 500 DC Input Card	$34.50	$35.50
   Bid again and WON!!!	$37.00	$37.00

6. Give me some Analog --- I now have a functional system but I'm looking to add a little more to it by getting an analog card.  I don't need anything fancy so the 1746-NI4 looks like a good prospect.  I'm looking good at first with my bid at $25.00 but I'm outbid in a flurry just before it ends.
   
   

   Item Title	Max Bid	Outbid
   Allen Bradley 1746-NI4 Analog Input Board	$50.00	$51.00
   Final price		$78.00

   Try, try again.
   
   

   Item Title	Max Bid	Outbid
   1746-NI4 4-chan Analog Input Card	$62.00	$63.00
   Final price		$63.00

   and again.
   
   

   Item Title	Max Bid	Outbid
   Allen Bradley SLC 500 1746-NI4 Analog Input Module	$55.00	$56.00
   Final price		$158.00

   and again.
   
   

   Item Title	Max Bid	Outbid
   Allen Bradley AB SLC 500 Analog Input Module	$70.00	$71.00
   Up the bid	$80.00	$81.00
   Final price		$81.00

   I'm getting tired of losing so I up the max bid.
   
   

   Item Title	Max Bid	Outbid
   ALLEN BRADLEY 1746-NI4 MODULE SLC 500 SER A	$91.00	$92.00
   Final price		$92.00

   and again... I'm the highest bidder this time for $69.00 and it holds.  Finally!
   
   

   Item Title	Max Bid	Outbid
   1746-NI4 4-chan Analog Input Card	$95.00
   Final price		$69.00

7. The Heat is On --- Now all I need it someway to measure temperature.  All I need is four channels so I start stalking the 1746-NT4 part number.  I've all ready been watching some go through and there are not as many of them.  So I'm expecting to pay a high price but I don't want to go over $200.00.
   
   

   Item Title	Max Bid	Outbid
   Allen Bradley 1746-NT4 Thermocouple / mV Input	$191.50	$194.00
   Final price		$202.50

   I get outbid but there's another one just like it that I go for with the same strategy.
   
   

   Item Title	Max Bid	Outbid
   Allen Bradley 1746-NT4 Thermocouple / mV Input	$195.00	$197.50
   Final price		$197.50

   So I lose that one too but it seems sometimes waiting out the competition is the name of the game because I score the next one.  I put a max bid of $190.00 and my bid starts at $76.00 but when it's said and done it's only gone up to $109.39.  So I'm glad I didn't win the others after all.
   
   

   Item Title	Max Bid	Outbid
   1746-NT4 THERMOCOUPLE INPUT MODULE ALLEN BRADLEY	$190.00
   Final price		$109.39

Counting the Cost

I'm sorry if that seemed long and drawn out but I hope it gives the important lesson that patience pays off when bidding on eBay.  Let's do a summary of what we saved when buying used instead of new.

The savings are just under $3000 or 10% of a new system.  While some may worry about problems with eBay I can honestly say all my transactions went very smoothly and I have a functioning test system for a fraction of the cost.  I haven't found anything to compare with eBay's selection and volume.

Software Programming 

Now comes the bad news.  There are not many options for finding cheap software to program the PLC.  The cheapest option by far is to buy a handheld programmer.  The reason they are so inexpensive is because they’re such a pain to use but you can learn and program your PLC.  The Allen Bradley part number is 1747-PT1 and they come up in eBay every once and awhile.  I ended up buying one for $99 and downloading the instructions manuals from the Allen Bradley website. I ended up writing a small 1747-PT1 tutorial.

With any software on eBay you want to make sure it legit and that you can get a proper license.  Make sure there’s a picture of the software and that you’re not the only one bidding on it.  It get’s competitive for legitimate software so usually if it’s not legal then nobody is bidding on it.  Some items will look like programming software when in all actuality they are just training disks so read the fine print.

But, hey, with all the money saved on the hardware you can at least buy the RSLogix 500 Starter software.