plc help

i am trying to build a plc controller. i have to control 24vac actuators. should i send a signal to an outside power source relay to power these or is there a multi output card that can handle that?

I have to control 24vac actuators. should I send a signal to an outside power source relay to power these, or is there a multi output card that can handle that?

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Yes, there are PLC output modules that can handle AC voltages from 0 to about 264 VAC. Some have relays, some use AC transistors ("triacs").

But you do not have to build the PLC controller from scratch. You can order it already built (saves a lot of wear-and-tear on the old noggin), then customize the PLC rack with the Input and Output modules that you need for your particular job.

What brand and model of PLC that you might need depends on the whole job, whether you already have some PLC programming software, what specs your company might have on PLCS, what voltage level, and what type of inputs and outputs.

The first step is to list all of the known requirements: power supply voltage level, a list of all the outputs and all the inputs. Then you have only the place to start the PLC selection process.

PS: Just a tip on site etiquette: It is best not to start a new thread with every question. Many of the old-timers will get frustrated with having to look at different threads to try to help you. Instead, add your questions and comments on to this one thread.

thanks for replying lancie1 ! and sure all replies can be right here. here's the basics of what i have and what i'm trying to achieve. i have two pumps and several solenoid water valves which have to come on at particular times for particular time periods and i have 2 level switches. i don't yet have relays yet for the pumps or anything powering the actuators yet either. to simplify i'll call pump 1 the primary and pump 2 the secondary. and, i can explain all functions of this equipment and how it is supposed to function. interested?

pumps are 115 vac. solenoids(10)are all 24vac 1.1 to about 2.4 amp coils and float switches.. are just switches... which would control the starting and stopping of the secondary pump with one of the solenoids.

danl said:

pumps are 115 vac. solenoids(10)are all 24vac 1.1 to about 2.4 amp coils and float switches.. are just switches... which would control the starting and stopping of the secondary pump with one of the solenoids.

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I would start by drawing the schematics for the inputs and outputs - if they do not already exist? (even a rough hand drawn schematic), followed by a "flow" diagram of the layout. This will help determine the number of i/o required as well as the type.
Also if any relays/contactors/overloads/circuit breakers are required and if theses feed back into the PLC.

is this a personal use system? or is it for sale or public use? there are many plc that meet your requirements. If it is for your own use cool! for resale or public use you need an electrical license in the state of Texas. explain your project in a bit more detail IE: do you want to store water and water your lawn with several different zones at different times ect....

i started the ladder diagram, it's not all that hard to figure. helps quite a bit actually. and yes this system is for my back yard. i have two ponds which circulate water, an underground tank to replenish the ponds and a sprinkler system which w/ city water use pond water to distribute in 6 controlled zones.

one pump circulates the ponds and also drives the sprinkling. the other pump repaces pond water from the underground tank. that one uses level switches. one in the pond sump and one in the underground tank.

the underground tank captures rain water and also has a city water which can only be added if opening a manual ball valve.

be careful to use a back flow preventer at the city water unless it free flows (through open air) to prevent your drinking water from being contaminated

What brand of plc do you intent to use?

ok,so it sounds like a 16 output card would be what you are after, not many inputs in your list tho. what are you controlling the 6 controlled sprinkler zones with?

also, since this is just for your backyard, i would suggest a micro plc of sorts, as they will be nicer on the wallet lol. also more compact, unless you already have one in your hands? if so, what brand.

also, on your duplicate thread, u asked for a continuous time clock, is this the control method you are gonna use to turn it all on or off? the more details the better

I started the ladder diagram, it's not all that hard to figure. helps quite a bit actually.

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That is a good start.

Now how did you do the ladder diagram? Draw it by hand, or use some PLC software that you already have, or what? That will help us to set where you are in the PLC selection process.

Yes, this system is for my back yard.

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That is a pretty good indicator that you need to power it from your 120 volts AC utility power. But it would be safer for home use if you could limit your PLC Inputs and Outputs to 24 volts AC. Also, you will find much more PLC equipment rated for 24 volts DC, so is it possible to switch your solenoids to DC versions?

If you can run everthing with 24 VDC, then you can buy a 120 VAC to 24 VDC power supply, and then buy a PLC that runs from 24 VDC and also has 24 VDC Inputs and Outputs. If the Outputs must be 24 VAC, then you will probably need PLC relay outputs (for a 24 VDC PLC) and a 120-to-24 VAC power supply.

EDIT: Reading back, I think you probably already have the 120 VAC pumps and the 24 VAC solenoids. So you need a PLC that can handle both of those voltage levels. The best fit is probably going to be one that has relay outputs. For the two pumps and the 2.4 Amp solenoids, you may need large external 10-Amp relays to handle the in-rush currents. Your PLC internal relay outputs would control the external relays (which in turn switch the larger motor and solenoid currents). Generally a PLC relay will handle about 1 amp, although there are some that go up to 7 Amps, but your pump starting current may easily exceed 3 Amps even if the running current is much less.

Look at the Automation Direct CLICK PLC. It is cheap, comes in 120 VAC or 24 VDC models, the three "standard" Click models have internal real-time clocks that can be used for control, and there are many Input and Output modules available. One of the output modules is the CO-04 TRS Isolated Relay module ($44) that has four 7-Amp relays. That might be just what you need to avoid using external interposing relays. You can use up to 8 Input and Output modules on the CLICK (in addition to the built-in I/O points).

http://www.automationdirect.com/adc...kable_Micro_Brick)/AC_I-z-O_-a-_Relay_Outputs

Probably the model CO-01AR-D is going to be your best CLICK PLC fit. It has 8 AC Inputs and six 1-Amp relay outputs ($109). Buy a CO-01AR-D PLC, 3 or 4 of the CO-04 TRS output modules, a 24 VDC power supply, the programming cable, download the free software and free manuals, then you are in business!

vs. Relay logic

What is your rationale for going to a PLC ? If you just want to control the pumps with switches, hard-wired relays may be cheaper. Once built, the PLC system would be easier to modify or adjuat by editing the program.