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Old 10-15-2011, 07:48 PM   #1
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Default Please help with alternating pumps

I am currently taking a motor controls class and I am working on a project that I need help with.

senario: 2 pump with flow switches. when water level comes up to 1st switch pump 1 comes on, when water lowers in goes off, when water rises the second time and hits the first switch pump 2 will come on, when level goes down pump 2 will go off. If the water level gets up to the second switch at a higher level both pumps will come .

I have 208v coming thru a transformer down to 110 which goes to my E stop, I have 208v 3 phase going to a square D contactor/overload. I have 2 208v motors (simulating the pumps) Im using 2 micro switches (simulating the flow switches) and I have 2 allen bradley 120v control relays.

I have the hot coming from the E stop to the first switch and then to A1 on the relay A2 going to the nuetral bar, from there I have A1 jumpered to #9 N.O. and then out #6 going to the the contactor/overload and then to the 1st motor. Works perfect, if water came up hit the switch and motor started

The part I cant understand is when the level comes up the second time how does it start the 2nd pump without starting the first pump?????

comes someone please help me understand this. I do have a drawing of the circuit

Thank You greatly to anyone that can help me
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Old 10-15-2011, 09:30 PM   #2
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you need an alternating relay.

Also they are float switches not flow switches. Two very different animals.
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Old 10-15-2011, 09:31 PM   #3
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Old 10-16-2011, 09:35 AM   #4
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I dont have acess to an alternating relay. I have to make it work with the 2 relays i have




Quote:
Originally Posted by kondia View Post
I am currently taking a motor controls class and I am working on a project that I need help with.

senario: 2 pump with flow switches. when water level comes up to 1st switch pump 1 comes on, when water lowers in goes off, when water rises the second time and hits the first switch pump 2 will come on, when level goes down pump 2 will go off. If the water level gets up to the second switch at a higher level both pumps will come .

I have 208v coming thru a transformer down to 110 which goes to my E stop, I have 208v 3 phase going to a square D contactor/overload. I have 2 208v motors (simulating the pumps) Im using 2 micro switches (simulating the flow switches) and I have 2 allen bradley 120v control relays.

I have the hot coming from the E stop to the first switch and then to A1 on the relay A2 going to the nuetral bar, from there I have A1 jumpered to #9 N.O. and then out #6 going to the the contactor/overload and then to the 1st motor. Works perfect, if water came up hit the switch and motor started

The part I cant understand is when the level comes up the second time how does it start the 2nd pump without starting the first pump?????

comes someone please help me understand this. I do have a drawing of the circuit

Thank You greatly to anyone that can help me
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Old 10-16-2011, 09:49 AM   #5
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When i get home today i will scan in my drawing of the circuit and post it
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Old 10-16-2011, 07:31 PM   #6
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Maybe I should read the OP before I comment. I was going to say a alternating relay is not required.

Last edited by John Valdes; 10-16-2011 at 07:33 PM.
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Old 10-16-2011, 07:41 PM   #7
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Quote:
Originally Posted by kondia View Post
I am currently taking a motor controls class and I am working on a project that I need help with.

Scenario: 2 pumps with two float switches.
When the water level comes up to 1st switch, pump #1 comes on, when the water lowers it goes off.
When the water rises the second time and hits the first switch, pump #2 will come on.
When the water level goes down pump 2 will go off. If the water level gets up to the second switch at a higher level both pumps will come.
Check this, the way I worded it. Is this what you mean? I am not sure what your instructor is getting at here. Because we would not connect two pumps this way. We would use the second pump to help the first pump. So please show us what you have.

I wish I new how to make this scanner work. The drawing I made is impossible to read.

Last edited by John Valdes; 10-16-2011 at 07:47 PM.
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Old 10-16-2011, 07:47 PM   #8
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Quote:
Originally Posted by John Valdes View Post
Check this, the way I worded it. Is this what you mean? I am not sure what your instructor is getting at here. Because we would not connect two pumps this way. We would use the second pump to help the first pump. So please show us what you have.
I can see how you could have one pump or the other come on every time with the first "on" float, and then have the other pump come on to help it if the next float was activated, but I can't see how to alternate between pump 1 and pump 2 in any scenario with only a couple of ice cube relays.
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Old 10-16-2011, 08:03 PM   #9
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Quote:
Originally Posted by erics37 View Post
I can see how you could have one pump or the other come on every time with the first "on" float, and then have the other pump come on to help it if the next float was activated, but I can't see how to alternate between pump 1 and pump 2 in any scenario with only a couple of ice cube relays.
Thats what I was getting at. No need for the alternating relay. It can be done without one.
His description does not sound right. It would never work that way in the real world. But instructors sometimes try and make it hard, even though it would never be wired this way.
I hope he makes it clear as to exactly what the two pumps are supposed to do.
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Old 10-16-2011, 08:36 PM   #10
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Google - Square D class 9038 Mechanical alternating float switches
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Old 10-17-2011, 12:58 AM   #11
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2 relays, easy as long as one is a double throw, that will be your primary.
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Old 10-17-2011, 01:00 PM   #12
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Quote:
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2 relays, easy as long as one is a double throw, that will be your primary.
Nope. Regular relay is what he said. Instructors tell you what is allowed in the circuit. The OP still has not returned and told us exactly what he is allowed to use. He said he had a print, but I thought he was to draw one for his class. So, we cannot answer his question yet. We need to be certain that the operation is correct. And we must know exactly what materials (devices) he is allowed to use.

The answer from the forum can only come from a schematic drawn by a member or a stock drawing that I doubt exists.
Just throwing out relays does not satisfy this question. Only your drawing will. The proof is in the drawing.
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Old 10-18-2011, 06:01 PM   #13
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ok I scanned in my diagram but I can't get it to post here. If you guys want to email me I will send it direct to you



Thanks
Bill

Last edited by guest; 03-12-2014 at 02:05 PM. Reason: removed email addy
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Old 03-11-2014, 11:33 PM   #14
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I have a very similar situation, so stumped on my homework
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Old 03-12-2014, 12:16 AM   #15
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You can do it with like 6 relays, or an alternating relay. Designed something similar for my sump pump at home.
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Old 03-12-2014, 12:37 AM   #16
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We did this in college. We did it four different ways; relays, alternating relay, and 2 different PLCs.

I don't recall off the top of my head, but I think doing it with regular relays involved late break contacts on the contactor.
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Old 03-12-2014, 07:05 AM   #17
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Welcome back, thread from 3yrs ago
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Old 03-12-2014, 01:08 PM   #18
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Zombie thread...
But yes, it can only be done with non-alternating relays if one of them has a late-break contact.
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Old 03-12-2014, 01:31 PM   #19
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This one has 2 pumps. Alternate.
If the pump called for fails. The other pump comes on with it
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Old 03-12-2014, 02:07 PM   #20
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Since OP is long gone...thread closed. If anyone has the answer and can post a diagram making the pumps alternate using the two standard relays and not the alternating relay, please start a new thread.

Otherwise this is just beating a dead horse.
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