PLC Controlled greenhouse

[Clay B.]

Hey all should I use C Curve or D Curve circuit breaker? What does that mean?
Thanks

The curve defines the delay in time before the breaker tripps. The general rule I use is Motors= D curve, Electronics = B curve.

Can the Breakers be installed right next to each other? And can they be right next to the power distribution block? Like less then an inch apart?
Can the DIN mounted Double-level terminal block be mounted next to the relays? I did order separators for the terminal blocks. I think I have plenty room if I need to have space. I am going to place an order tomorrow, should I post a list of what I am ordering? I am buying stuff for the greenhouse relay box. I will be buying enough relays and terminal blocks for the whole system, but am just building one relay box.

Relays Can be mounted side by side no gap needed. Generally anything DIN rail mounted does not need a Gap. The exceeption to this rule is PLC's and DC Power supplies. Unless you see a vent on the side of the device and it is DIn rail mountable then no spacing needed.

Posting your list would help. Since you have been ao the Automatiin Direct web sight, take a look at the 22mm switches. These are NEMA4X rated. Since you want to start this project basically as 'relay logic" then these switch will be handy. Also they are pretty cheap.

 

[Lancie1]

The curve defines the delay in time before the breaker trips. The general rule I use is Motors= D curve, Electronics = B curve.

The B and C-curve breakers are okay for lighting cirucuits also. Unfortunately, Northpad has a pump and a lighting circuit on the same breaker. What curve would you recommend for that one? How about F for Failure!

Northpad,

You might want to back-track and make a panelschedule and figure out what size breaker you SHOULD have for each of your greenhouse circuits. Here is a spreadsheet that I use to make homeowner panelschedules. I buy a clear-plastic notebook insert, print out the one-page schedule, insert it into the plastic cover, and tape it to the back of the panel door. Now I know WHAT is on each circuit.

 

[Lancie1]

Relays Can be mounted side by side no gap needed.

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!

If you have wireways to separate 240/120 volts from 24 VDC (desirable for a beginner), then it takes even more room. Then you need your vertical wireways, sometimes one on each side, to connect it all together. Box design is an art learned from experience, and hard to explain in a few sentences.

Consider using different wire colors for your 24 VDC wiring. Many use blue and white/blue.

 

[northpad]

Ba Ba Booey

You have a ballast and a water pump on the same circuit? I don't think I have ever seen that done before - mixing motors and light circuits. If this breaker trips, how you going to know what caused it, the pump or the ballast? I doubt that the 30 amp breakers are sized correctly for either of these circuits.

I know what you're saying, and when I build the relay enclosure for the utility room I'll tackle those problems. Luckily I have not had any troubles with currents setup, well nothing major. One reason I am building this system is for trouble shooting, so IF i ever have problems I can fix it, and don't have to call for help.

Do you have a CB panel schedule showing the circuits and breaker sizes, and wire sizes?

I will soon, thanks for the file. I'll start working on this too. LOL


Here is a JPG of the wiring for the greenhouse relay enclouser. This is my FIRST attemped at ANYTHING like this so be nice. Any thought? Hope this one works. Thanks
http://sdnclan.net/images/relaywiring.jpg

 

[Lancie1]

Luckily I have not had any troubles with currents setup, well nothing major.

Maybe I am being overly conservative, but I know it can be dangerous to give advice long-distance like this, not knowing the complete picture.

I used to buy and remodel old houses for an investment hobby. I have seen some realy dangerous wiring done by homeowners who thought they knew what they were doing. Things like installing a 30 Amp 2-pole breaker for a 15 amp 1-pole receptacle, and using #14 wire to connect between one pole of the breaker and the receptacle. Of course it worked just fine, and the homeowner was happy. I would not have wanted to be his fire insurance company though. Other problems I have seen were much worse. It is really amazing that more homes don't burn down.

Newer electrical codes highly encourage sizing the circuit breaker and the wiring for the actual connected loads, not installing a large breaker then wiring it to whatever is handy. It is good to add up the total watts on each pole of each circuit, and compare that to the minimum size circuit breaker or fuse that could be used to serve the load.

Your drawing looks pretty good. If you have the option, you could use the arrows on the ends of the wires to show direction of power flow. Most drawing programs allow you to click on the arrows and select direction of rotation.

Power entering a device would always have an arrow, pointing toward the device. That makes it easier to trace through from "upstream" to "downstream" on each circuit (power leaving a device would not have an arrow, or it it does it would be turned outward in the direction of power flow).

 

[Lancie1]

I like your different colors for different types of wires. I don't mean to jump on you or be overly critical, but critisism is what you asked for, right? I will try to make it constructive and helpful!

The next drawing step might be (after you select your actual devices such as plug-in relays) to expand each block into a Connection Drawing, showing the physical location of each wiring terminal, the wires, and routing of the wires. Some relay brands will have coil terminals on the top of the base, others on the bottom, with the contacts at different places on the base. It helps to get a physical layout for the actual relay base (or if unavailable, draw your own by copying the relay base) and use that to make your connection drawing.

You have one switch with an upside-down label "Dehum" best I can make out by twisting my neck. Oh, Dehumidifer! It looks more professional if you adopt labeling standards. Basically you make your drawings to be easy to read by the user. Labels and text should be readable from bottom looking up, or from the right side, but not from the top looking down and not from left side.

It appears that your power goes: from rotary disconnect switch to distribution block to switches to relays? And your PLC outputs go to relay coils, but also to switches? So you want your switches to have 24 VDC inputs? I am confused. I am not sure what the two sets of boxes are that are both labeled "Fan", "AC", CO2", and "Dehum". I ASSUME one set is the actual load devices, and the other set is switches, but you know what AssUMe makes out of U and Me. Which is which?

 

[Lancie1]

I guess the long skinny rectangles on the center-right are not actually your PLC outputs, but terminal blocks. It is okay to put device labels near equipment, or to put a legend with symbols somewhere on the drawing. It is better to over-identify stuff than to leave everyone that sees your drawing guessing what each "thing" represents.

 

[northpad]

I like your different colors for different types of wires. I don't mean to jump on you or be overly critical, but critisism is what you asked for, right? I will try to make it constructive and helpful!

It is all good, any information good. I am loving all the help.

Maybe I am being overly conservative, but I know it can be dangerous to give advice long-distance like this, not knowing the complete picture.

I hear you Lanciel, I know where my weakneeses are when it come to this project, I want to make this system as safe as possible, even if I have to run new wire from the sub-panel. But I am not there yet. And sense the system is running I will only be worring about the greenhouse. I may end up running a new circuit to the greenhouse relay enclose. I'll have to see.



I know the drawing needs a lot of work, I just want to see if I was on the right track. I will start labing it and fix the arrows. Lanciel1, I was going to run the power from the circuit breaker to the switch, If the switch is in postion A power will flow to the relays, if the switch is in postion B power would flow to a sencond set of the termination block, then to the solenoid. (I am working on my terminology hope I'm right) Well back to the drawing board....


Thanks

 

[BobB]

I hope this does not cause confusion but perhaps a different way of doing things and may help. This is basically how I do all my designs.
Power and control circuit attached and PLC control circuit attached for a swimming pool job just completed.
PLC has inputs on left, outputs on right, desription above line, wire numbers below line and close to PLC and numbers in the PLC block are the actual program input and output numbers.
terminals are numbered too.
Hope it helps.

 

[northpad]

Bob A thanks for the examples, I hope to be able to draw something like that but the end of this project. I still have a lot to learn. Learning the symbols is a pain. ha ha I am using a demo software right now, and it's hard to find the right symbols. In time tho I will get it down, with your drawing and Lancie1s I should make some head way.

This is starting to feel like a second job, but I love it. Thanks again

 

[northpad]

Ok I must be missing something. How do you circuit protect the 24VDC coming in for the relays? Would you have the circuit protect in the PLC module? I'm sure I want to have something in the relay enclosure. I was going to use - FUSE HOLDER, CC CLASS, 1 POLE, DIN MT, W / INDICATOR,30A

Can I buy a fuses small enough to protect the 24VDC?

 

[northpad]

http://sdnclan.net/images/relay1.pdf

Here is my second attempt at a wire diagram. I think I fix it. Relabeled everything, fixed the arrows, and made a legend. I still don't know about the 24VDC circuit protect, so I am sure I'll need add more. What else should I have in the drawing? Oh I make the boxes close to scale, and it should all fit in a 11.5X11.5 enclosure. I think....

 

[OkiePC]

Ok I must be missing something. How do you circuit protect the 24VDC coming in for the relays? Would you have the circuit protect in the PLC module? I'm sure I want to have something in the relay enclosure. I was going to use - FUSE HOLDER, CC CLASS, 1 POLE, DIN MT, W / INDICATOR,30A

Can I buy a fuses small enough to protect the 24VDC?

Sure. I normally use a fast acting fuse rated the same as the power supply output, and put the fuse right after the power supply. If you are running DC output wires out into the field, then you can fuse those wires too, but if they're local to the panel (power supply, PLC and relays in one box), then you can proabably skip fusing each output.

If you buy a holder with an indicator, make sure the indicator is for 24VDC. You can get din rail mount fuse holders that hold miniature glass fuses. They'll be less money and readily available and take less space.

 

[Lancie1]

What Okie said!

Now may be the time to make some schematic diagrams, at least some scribbles on paper, to show the logic of your system. You may have enough of the equipment pinned down so that you can draw most of the schematic. Bob provided some great examples to shoot for.

Different types of drawings reveal different aspects and different problems for any design. Each type - block diagrams, schematic, ladder logic diagrams, wiring connection diagrams, - are different ways to look at same electrical system, but show it in different ways.

A schematic is usually a one-line diagram, representing each device with a symbol, and the main thing it shows is the electrical logic of the system. A wiring connection diagram attempts to show the physical relationship between devices and the wiring that connects them together.

 

[Lancie1]

Northpad,

Are you planning to use the PLC internal 24 VDC power supply to handle all your 24 volt stuff? That may...or may not work because you probably will have fairly long runs of 24 VDC wire from PLC out to greenhouse sensors, and from PLC to relay cabinets, not to speak of the large inrush currents required by the relay coils.

The 24 VDC PLC power is usually very limited (DL-205 and DL-06 have about 300 mA (0.3 Amps) of spare 24 VDC). You may need to add up your 24 VDC loads (including voltage drop due to relay inrush current and also the long runs of wire) and try to calculate how many miliamps of DC power needed, and compare that to what is available in your selected PLC.

24 VDC Required:
internal current for PLC modules, and
current for all PLC input sensors, and
inrush (short-term starting) current for the 24 VDC relays, and
current due to losses in wiring.
Add above for total DC current required

If not enough 24 VDC current is available from the PLC, then you will need an external 120VAC-to-24VDC power supply. I would get about a 5 Amp (5000 Miliamps) external power supply, something like a Sola Hevi-Duty SDN5-24-100C.

http://www.solahd.com/psselect/index.cfm

I have a voltage-drop spreadsheet calcualtor somewhere, and it works for DC circuits if you set the Power Factor = 1, down to #14 wire I think. Yes, I found it and will attach.

For example, if it is 100 feet from your PLC cabinet to your relays, and you have a 1.16 Amp inrush current, then it will take a #14 wire to reduce your voltage drop to 3% (23.28 VDC at the load out of 24 VDC originally). Whether or not 3% is the goal to shoot for is another question with DC circuits, but for AC circuits it is fixed fairly rigidly by the National Electrical Code.

The voltage drop is one reason I suggested putting your relay cabinets near the PLC cabinet. However you can make it work with the relays remotely located, but please do consider the amount of 24 VDC power you will need. From experience, it is embarassing to get everything installed, wired, programmed, then find that your relays won't pull in due to low voltage. Low voltage at the loads is caused by not having enough power - same thing as not having "enough lead in your pencil".