Trying to figure out motor timing for starts

[jd2325]

I am tasked to make a motor starter only operate 3 times in one hour. If the start button is hit the fourth time there can be no engagement of the motor starter. As soon as 1 of my timers drops off then the motor starter can operate once until another timer drops off or reset to two or three starts if all three motor starts are over 1 hour. I am having a difficult time figuring out how to reset when one timer ends.

Thanks Jim

 

[bernie_carlton]

Here's one try but somehow I feel there's a more elegant way.

 

[Gil47]

When I read motor specs that say 3 starts an hour, I see that as 20 mins between starts,
and set up a start block that times for 20 mins at a motor start up, calling it start not available.
Only uses one timer, and prevents automatic equipment suffering controls contact bounce, which eventually destroys switch gear first, then the motor.

 

[leitmotif]

I am tasked to make a motor starter only operate 3 times in one hour. If the start button is hit the fourth time there can be no engagement of the motor starter. As soon as 1 of my timers drops off then the motor starter can operate once until another timer drops off or reset to two or three starts if all three motor starts are over 1 hour. I am having a difficult time figuring out how to reset when one timer ends. Thanks Jim

Jim What size is motor?
How do you intend to do this hardwire or PLC?
Uhhhh do you really NEED to do this?

the first thing to decide is what you are doing ie
A 20 minutes between motor starts MINIMUM
OR
B motor can restart 20 minutes after stopping.

If you go with B and you are hard wiring it then the refrigeration types have a short cycle control that will not allow restart for XX time after stop. Somewhat the same if you do in PLC but you have not clearly stated what you are using to accopmplish this.

If you are doing A and hard wire a simple timer that is actuated with the start should work OK. The first start would start timer a timer contact between timer input and START would allow timer to run out and not have subsequent START pushes reset teh timer. Basically the same in PLC.

Dan Bentler

 

[jd2325]

Thank You for your reply We are using RSLogic 500 on a 1000 processor with a trainer (I am a student in college). Will the program you sent me work with that software and hardware package.

Thank You
Jim

 

[jd2325]

Dan this is a college course and we are using RSlogic 500 with a 1000 processor and a trainer with start stop estop and motor starters on the trainer. This is a programming exercise to learn how to write a program that allows only three starts in a cumulative hour of the motor starter.
Thanks for your Reply
Jim Dalton

 

[jd2325]

The motor starters can engage in any intervals but when 1 hour from the first engagement it needs to let us start the motor again even if starts 2 and 3 were a few minutes before should we do another start then we would not be able to engage starter until 1 hour had passed from the oldest start time.

 

[TConnolly]

Bernie's basic method is pretty much how I thought I would do it from the initial post. Except for one thing: The timer preset needs to be 3600 seconds to get a full hour.


Edit to add:
We are more than happy to help students with their homework - but we ask that you make an effort to understand the problem and really understand the solution and how it works. Remember, some day you will be our coworker, and we want you to be competent. Most of us have dealt with too many people who obviously coasted through their coursework relying on others for their answers, they rarely get along with their coworkers and the employment experience is an unhappy one and unrewarding. So before you apply the solution given, please understand it, and maybe even improve upon it at bit. Welcome to the field, its an exciting and rewarding career for those who will make the effort to become really good at it.

 

[Steve Etter]

Looks to me like Bernie almost nailed it. The one problem I see is that it appears all three timers will start on the first press of the button. This is fixed by adding a XIC T4:0/TT bit on line 4 and another XIC T4:1/TT bit on line 7.

As Bernie must have noted, Jim said nothing about when the motor stopped, only the start. Consequently each "start" can only be allowed again an hour after its own previous start - this means the first start is timed separately from the second, and so on. Doing it Bernie's way, you could start the motor three different times with no time limitation between starts, but not again until an hour past from the first of the three starts.

Steve

 

[leitmotif]

OK that clarifies
1. You can start the motor at any time interval
2. Up to 3 starts maximum
3. In one hour starting from first start.
4. After an hour you can start for 4th time.

I was thinking real world - I guess - where you do not want to start larger motors too frequently ie let em run and cool or shutdown and cool. Starting is a large current draw and heating so you cannot start too often without damaging insulation.

OK so much for reality - back to school.

I do not see how you can do this with just timers. You are going to have to measure both number of motor starts and measure time.

The ball is now in your court - you are the student - and you need to learn.
Reply with your logic stated in just words.

Dan Bentler

 

[bernie_carlton]

Steve - the Unlatch of B3:0/1 in a sucessful test of a timer's OFF state prevents the next from being triggered by this one shsot.

Alaric - thanks for the catch - somehow my aged mind was thinking a 1 minute time base.

I should have thought 'homework' but as I though about it it became a challenge. Is there an easier way? We'll let JD2325 let us know.

 

[jrwb4gbm]

I know its just homework but as Bernie said, "It's a challenge". Based on post seven attached is my attempt. Probably some errors in it.

 

[TurpoUrpo]

For you who do it just as a challenge, do it so that the time is "dynamic". I mean that it is counted starts in time interval instead of starts in time after first start. Lets make it more demanding and have time and start count as parameters that can be changed.

 

[jd2325]

I appreciate your concern I wrote a program trying to use an equal to instruction with and logic of timers 1-3 but could not figure out how to get them to drop off. My class got cancelled tonight so I cant try my methods on the trainer while looking at Bernie's solution I am going to have to install an estop and stop pushbutton. I am not sure that the program he sent will do all of what I need but it did give me a direction to try and make the problem work. I wish there was a way that I could try different methods and see if they work but with 1 four hour class a week it is difficult to do as much playing around with the logic as I would like. Not to worry though I am dedicated to learning PLC programming and becoming proficient in PLC's I will not use you guys to do my homework I just look for other ideas that I may not have thought of. Thanks for your help and concern

Sincerely,
Jim Dalton

 

[jd2325]

Hey Bernie class got cancelled tonight so I didn't get to try my program. Just want to let you know I write a program and try to do it on my own first but with only 1 four hour class a week and no ability to get trainer time other than then I come up with an idea and then ask you guys a question so that I can look at other ways to solve my problem. I have to have a stop and e-stop in my program, I originally used AND logic for timers 1-3 with an equal to instruction to stop the fourth motor start but got stuck on how to make them reset and drop off when 1 hour was up to allow one more motor start when the first start had been an hour old. Not sure if what you sent me will work but I am studying the logic to see if I can incorporate it or ammend my program to make it work. I won't get to put it on the trainer until next Tuesday now but will send you a copy of my work once I get done. Just didn't want you to think I was having you do my homework for me, just trying to get another viewpoint to explore other options.

Thanks for your help
Jim Dalton