Need advice on Micrologix 1200 purchase

This is my first post, and I am contemplating the purchase of a ML1200, more specifically 1762-L24BXBR. I think it's a pretty good deal ~ $100 and it's never been used. I'm basically buying this thing to learn more about the hardware aspect at home, in my spare time. I'm probably just going to construct some basic circuits to control fans, lights, small DC voltages from thermostats or other transducers and the such. I have read all of the AB docs on this unit, and have done many searches trying to find an answer to a pretty..a very basic question. According to the specs, this units input power is 24VDC. What I need to know is do I still have to run 120VAC to power the unit also? Do I also need a separate 24VDC power supply to power the unit, and then just use the on-board 24VDC to power the inputs? I cant really afford to buy anything in addition to the PLC, this may be a deal breaker. Any insight is GREATLY appreciated!

It's a good question: A-B sells a variety of power and input/output voltage models.

The first "B" in the 1762-L24BXBR means you need to provide +24V DC to power up the controller, and the second "B" indicates that the inputs are also 24V DC.

For this controller, you need to buy a 24V DC power supply as well. It doesn't need to be special; any bulk 24V power supply will do.

Since your budget is very tight it probably doesn't have room even for the RSLogix 500 Micro Starter software, which is required for the MicroLogix 1200.

If I were you, I would try to get a MicroLogix 1000 or 1100 model controller, because RA provides a software edition called RSLogix 500 Micro Starter Lite that is free of charge, for those two models of controller. The instruction set and hardware are very similar to their cousin controllers, the MicroLogix 1200, 1400, and 1500, and to the modular SLC-500 controller family.

If you're hitched to Allen-Bradley, the little Micro 800 controllers program with free software as well. And of course a dozen small controller makers also provide their software at no charge.

First, thank you for the reply Ken. This is exactly the answer that I was searching for..

"..you need to buy a 24V DC power supply as well."

I'm wondering why AB makes a controller with this spec..? There must be an advantage/application for this, but that answer eludes me at this point.

Does anyone know the advantages/disadvantages of this?

If you don't mind Ken, I have a follow-up question. Rather than buy a 24VDC power supply for this unit, could I just build a bridge rectifier using 120VAC from the standard wall outlet to achieve the necessary DC voltage?

A former employer provided me with RSLogix 500, so my machine is fully equipped (including RSLinx) to program the ML1200. I would just rather designate any additional expenditures on my part to adding other functionality (i.e. analog IO capability) to this unit.

Once again, thanks for the reply, and I would like to thank anyone in advance for any additional input.

AB sells a 24VDC power model because it is pretty common in small machinery to have 24VDC power everything. All the machinery we receive from Europe has 400V 3 Phase to 24VDC power supplies, so there is no 120VAC available. 400V 3 Phase for motors, 24VDC for everything else.

You could build a rectifying circuit (a power supply) yourself, but wouldn't it be easier to get a cheap 2 amp 24VDC power supply? Like this one:
http://www.automationdirect.com/adc...INO_PS,_PSB,_PSC,_PSM,_PSP_Series)/PSP24-060S

some companies strictly enforce NFPA70E - arc flash requirements. basically, anything over 50 volts ac requires PPE. the higher the voltage and calorie count, the more PPE is required.

other companies require everything be 24 volts dc.

regards,
james

Different markets dictate different voltages.
In the USA 115VAC is a common control voltage, but it is not in europe where 24VDC is more common. PLC manufacturers make I/O positive an negative logic too depending on the market. Negative logic where NPN sensors are used is not the norm in Europe, but common In USA and Japan.
Manufacturers like Rockwell have a global marketplace, so must cater for all voltages while also minimising the number of versions required.

You could use a power supply like this, just cut the plug off the end or buy a connecter to fit. Try the 760 version.


http://www.ebay.com/itm/Elpac-Power...aultDomain_0&hash=item19c8df4456#ht_909wt_890

James Mcquade said:

some companies strictly enforce NFPA70E - arc flash requirements. basically, anything over 50 volts ac requires PPE. the higher the voltage and calorie count, the more PPE is required.

other companies require everything be 24 volts dc.

regards,
james

Click to expand...

Well.... technically according to the arc flash training I received, regardless of what the arc flash calcs say, anything under 240VAC doesn't have enough energy to sustain an arc. IEEE rules (can't tell you which code right now...) says that anything under 240 is Category 0 - therefore requiring no arc flash ppe. You might get a spark, but not an arc.

HOWEVER - that does NOT negate the requirement for gloves or "touch proofing". But a typical 120VAC control panel does NOT require arc flash PPE.

Thank you all again for all of your input/answers/suggestions, you have all been a big help. Thanks to Tharon and Liam for the links. I have been doing some looking after reading your replies, and I'm leaning towards this..

http://www.ebay.com/itm/ENTRELEC-SC...855?pt=LH_DefaultDomain_0&hash=item5197dbe9e7

Its pretty cheap, and I think it should suffice. Plus, I can mount it alongside the ML1200 quite nicely.

I will continue checking back to this thread throughout the next couple of days for any additional insights that anyone may be able to lend about the 1762-L24BXBR (and any associated hardware). If anyone has experience with this particular unit, and has any beneficial tips, precautions, etc. to share, please do.

Thanks again.

The biggest drawback with the Micrologix 1200 (and the 1000 and the 1500) is the lack of ability to do online changes in run mode. This is surprising from a company like Rockwell this day and age selling hardware with 1980's features. This is the main reason I would not specify one of these PLC's for a project. It is ridiculous to have to stop a process to do a small change in the logic.
However as a learning platform it would be ideal to learn on.

Have to agree with Liam we had a supplier of a piece of equipment persuade our purchasing department to downgrade to a 1500 as cheaper great for them pain for us because as liam says have to go off line to make program changes which means shutting down process which nobody likes