PLC Controlled greenhouse

[BobB]

In the circumstances shown in my drawings, I do not use fuses or circuit breakers at all as the switch mode power supply turns itself off if something goes wrong.
I also do not ground the negative output from the switch mode as this destroys the isolation properties of the power supply.
If feeding from batteries with potentially high currents I use Schneider circuit breakers for input and output supplies, despite the fact that I also use 24VDC/24VDC switch mode power supplies between the batteries and the PLC. A lot depends on what the customer is prepared to pay. Once again no grounding of the negative output from the switch mode. Let it float - no problems as there is no ground reference.

 

[Lancie1]

Once again no grounding of the negative output from the switch mode. Let it float - no problems as there is no ground reference.

Bob, I think he has that part - no ground shown on Northpad's drawing for 24 VDC. However the part that bothers me is that there is no switch-mode power supply shown either - only 24 VDC from the PLC internal power supply. I haven't added up the 24 VDC load, but I doubt if the PLC power supply will be adequate (if he uses an Automation Direct DL-205 or Dl-06 as stated previously). If more than two or three of those relays are on at a time, the 24 VDC may drop off sharply, down so low that things will not operate properly, including the PLC analog input sensors.

 

[northpad]

Lancie1 I'm not sure what you mean by "switch-mode power supply" is that a auxiliary power supply wired inline with the internal power supply or is that something that is installed in the relay enclosure and is powered by the 120VAC inside the enclosure? I know you brought this up before, I just haven't gotten my head wrapped around it all, just yet. I will have it all figuared out before anything is installed. Well off to bed, still on nights. Thanks for blowing my mind.... ha ha

 

[Lancie1]

I think you will need an auxiliary power supply for your 24 VDC equipment. PLC will allow you to use the auxiliary supply instead of the built-in internal supply, which has limited power and probably will not have enough power for your application. "Switch-Mode" just refers to a type of power supply that uses rapid transistor-switching to transform the AC to lower voltage, instead of the older, larger, more expensive, transformer-and-rectifier type.

Because you are splitting up your relays into two different locations, you can install one large 24 VDC power supply, fed from 120 VAC, and then run wires from it to the PLC modules, and to the relay cabinets, being careful to use larger wires to offset the voltage drop caused by long rungs of low-voltage wiring.

I think I showed a power supply on my block diagram drawing for the PLC Cabinet that I did earlier. I thought then, from past experience, that you would need an auxiliary power supply, as that is the usual case.

 

[Lancie1]

Northpad,

You might want to read through these posts on MrPLC.com, that Mickey recently referenced. It is a good overview of Control Panel Design.

http://forums.mrplc.com/index.php?showforum=35

 

[Clay B.]

Layout tip

But you need a gap both above and below the DIN-rail for wiring the terminals on the relays. This applies to most other DIN-rail mounted equipment also. Going vertically down the box, when you add up the space required for: Wireway, Wiring space, space for widest DIN-rail equipment (not just space for the rail itself), Wiring space, Wireway, then repeat for each DIN-Rail row in the box, the box can become large in a hurry. I make each wiring space at least 3 inches for my fat hands. Others use 2 inches, it depends on how easy you want to make the wiring job, and whether or not YOU are going to be the one working on it!

As Lancie stated you need a gap between the top and the bottom of most devices. The place where most people get caught is here. If you have say a power supply and a relay on the same din rail then the gap is set by the power supply. THe point is make sure you have all of your componets that you are going to put on a rail to get it sized properly. Since this is your fist project I would buy my componets first then my Enclosure. You can lay out your parts on a table and figure out your panel size that way.

Sizing your wire way (also known as panduit) can be tricky. These tend to fill up faster than you expect. One trick I use is my wire way is always taller than it is long. This saves on panel room while giving me the same area for my wires.

Keeping your high voltage away from you low voltage can be done alot of different ways. I tend to use the left right top bottom method. I try and put my low voltage bottom left and my high top right. My reason for this is mainly the door. The panels I build tend to open from the right hand side. A thru the door disconnect will need to be to the right of center in this case. Most items on my dsoor are low voltage so by making my low voltage items bottom left I reduce the wire I run and segragation is easier.

Also, I have not seen anything your working with other than a power supply that generates much heat but this must be considered. If you look at the spec sheet for most of your devices it will tell you how much room they will need for heat disapation. Remeber this is adding. If you have 2 drives that need 5 inches around them then you will have 10 inches of cooling area required in your panel. This does not have to be wasted space (good place for wire ways).

No such thing as to many terminals. Every field device should have it's own terminals. Never run a field device directly back to a PLC.

Anyway, like everything else just a few things to consider.

 

[northpad]

OK, I can't find the symbols needed to draw a wiring schematic. There are so many different symbols in the software I am using, Smart-draw 2010, I don't know which ones to use. Could someone point me to a good reference site? Or maybe just post pictures of the symbols I need? I don't think I need many, just symbols for: 24vdc relay, a 3 position switch. How do I show the termination blocks? I found the symbols for circuit breaker/fuses. Thanks

 

[TheStarr]

http://lmgtfy.com/?q=electrical+symbol+reference

 

[BobB]

I drew my own and modify them to suit changes in the standards.

 

[Lancie1]

Typical schematic symbols

|    stop pb   start pb        relay     |

|        |        __|__         coil     |

+-----o__|__o--+--o   o--+-----( r1 )----+

|              |         |               |

|              |  open   |               |

|              | contact |               |

|              +---| |---+               |

|  closed           r1          relay    |

|  contact                      coil     |

+---|/|------------------------( r2 )----|

|    r1                                  |

 

[Lancie1]

+24 VDC                            -24 VDC

|             3-POS. SELECTOR            |

|             HAND OFF AUTO     RELAY    |

|               H   \           COIL     |

|-----------------o | o--+-----( R1 )----|

|                   |    |               |

|     PLC           |    |               |

|    OUTPUT     A __|__  |               |

|-----| |---------o   o--+               |

|                                        |

 

[Lancie1]

+24 VDC                            -24 VDC

|             2-POS. SELECTOR            |

|                OFF ON         RELAY    |

|                 __\__         COIL     |

|-----------------o   o--+-----( R1 )----|

|                        |               |

|      PLC               |               |

|    OUTPUT              |               |

|-----| |----------------+               |

|                                        |

 

 

L1-------------120 VAC-------------------N

|    RELAY                               |

|   CONTACT                     EQUIP.   |

|-----| |----------------------( M1 )----|

|     R1-1                               |

 

[Lancie1]

A SIMPLER METHOD - ALLOWS OPERATION BEFORE INSTALLING PLC AND 24 DC POWER SUPPLY. 2-POSITION SELECTOR SWITCHES MUST BE RATED TO HANDLE FULL STARTING CURRENT OF GREENHOUSE MOTORS.

 

L1-------------120 VAC-------------------N

|                                        |

|            2-POS. SELECTOR             |

|                OFF ON      GREENHOUSE  |

|                 __\__        EQUIP.    |

|-----------------o   o--+-----( M1 )----|

|                        |               |

| PLC-CONTROLLED         |               |

| RELAY CONTACT          |               |

|-----| |----------------+               |

|     R1-1                               |

 

 

+24 VDC   --- DC POWER SUPPLY ---  -24 VDC

|                                        |

|  PLC OUTPUT                RELAY COIL  |

|-----| |----------------------( R1 )----|

|                                        |

 

[Lancie1]

SIMPLE SCHEMATIC FOR CONTROL OF 240 VAC EQUIPMENT

L1--L2-----------240 VAC---------------------N

|   |                                        |

|   |           2-POLE SELECTOR              | 

|   |             OFF ON       GREENHOUSE    |

|   |              __\__         EQUIP.      |

|------------------o | o----+----( M1 )--+   |

|   |                |      |            |   |

|   |              __|__    |            |   |

|   +--------------o   o-----------------+   |

|   |                       |            |   |

|   | PLC-CONTROLLED        |            |   |

|   | RELAY CONTACT         |            |   |

|-----------| |-------------+            |   |

|   |       R1-1                         |   |

|   |                                    |   |

|   | PLC-CONTROLLED                     |   |

|   | RELAY CONTACT                      |   |

|   +------| |---------------------------+   |

|          R1-2                              |

 

+24 VDC  ------  DC POWER SUPPLY  ---- -24 VDC

|                                            |

|    PLC OUTPUT                  RELAY COIL  |

|------| |-----------------------( R1 )------|

|                                            |

 

[Lancie1]

So, how is the greenhous coming along? Up to your bottom in aligators?