# help with a circuit to control a 5HP Motor

Discussion in 'Homework Help' started by Tellwisdom, Jan 1, 2017.

1. ### Tellwisdom Thread Starter New Member

Jan 1, 2017
23
0
Hello,
i personally would want to appreciate everyone for the contributions,suggestions and advice here.
i am stucked with an assignment which i have tried to figure out the solution but to no avail,several attempts searching over the internet proves abortive.
just like the forum says: post your questions and attempts here before any help could be given if i understand correctly.
Now,i was given an assignment to design a circuit to control a 5HP MOTOR which i don`t know where to begin from as i am new to electronics/electrical.
any help would be appreciated,i am ready to learn to enable me succeed in this course.

best regards

2. ### AlbertHall AAC Fanatic!

Jun 4, 2014
8,116
2,008
You didn't find any motor speed control circuits using Google?
I assume you are trying to control its speed not just switch it on and off, though you do not make that clear.
Motor AC or DC? Voltage? Universal, induction, etc?

Jul 18, 2013
18,805
5,857
Control can be anything from a simple contactor (on/off) to speed control, which as stated is motor dependent.
What type are you interested in?
Max.

4. ### Alec_t Expert

Sep 17, 2013
10,227
2,497
Welcome to AAC.
Weren't you given some background material to study before being given this assignment? A 5HP motor is a dangerous beast to handle if you've no experience, so you should at least read up about the type of motor you have.

5. ### Tellwisdom Thread Starter New Member

Jan 1, 2017
23
0
thank you for the response,

What i am looking at here is a three phase AC motor,i have found some motor speed control circuits but i am not sure if it would control a motor of such capacity,that`s why i am here to be sure i don`t do the wrong thing

6. ### Tellwisdom Thread Starter New Member

Jan 1, 2017
23
0
Dear sir,
i am interested in controlling a three phase AC Motor of that capacity....i mean 5HP

Last edited: Jan 3, 2017
7. ### Tellwisdom Thread Starter New Member

Jan 1, 2017
23
0
Dear sir,

i was not given any material,i would have read up or have something to upload here...the lecturer just came and said " design a circuit to control a 5HP Motor: a three phase AC motor" and submit in the next class.that`s all.

Jul 18, 2013
18,805
5,857
If speed control then you need a VFD, these can run off of 240v 1 ph service if 3ph is not available.
If just to control the switch on/off then a contactor and a start/stop P.B. station is needed.
See schematics.
Telemecanique wiring diagrams
The only thing now it is considered bad practice to place the O/L seen wired to the right of the contactor coil, it should now be on the L.H. side of the coil.
Max.

9. ### Tellwisdom Thread Starter New Member

Jan 1, 2017
23
0
sir,
thank you for the swift response,in the PDF,i am seeing different circuit drawings.

would it be best to go here:Type S AC Magnetic Starters .............. to enable me get what i want..
i am completely new to Electrical Engineering.
best regards

Jul 18, 2013
18,805
5,857
You want the basic elementary diagram on page 5, it does not have the complete control P.B. etc as shown on fig2 P6, you just marry to two diagrams for a basic 3ph control station.
M in fig 2 is the coil of the contactor.
Max.

11. ### Tellwisdom Thread Starter New Member

Jan 1, 2017
23
0
thank you,
please see the attachment ,do i need the auto transformer in the circuit?,

is it possible to simplify the circuit for me from the attached?,i want to start with a simple circuit first to enable me understand this complicated one

• ###### motor circuit.png
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Jul 18, 2013
18,805
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The combo I gave you in #10 is the basic simple circuit, the control transformer in the one you show is optional, for any motor circuit above 230v it is usually included for the control circuit.
You just need to add suitable fusing to the basic schematic, the majority in your png is not required, if this is home work, try drawing one up and post it for review.
The policy here with homework is to help not supply the complete solution. It is the best way to learn.
Max.

13. ### Tellwisdom Thread Starter New Member

Jan 1, 2017
23
0
alright sir,
i will study it up and post a reply of my understanding.

thanks for the help...i really appreciate

Jul 18, 2013
18,805
5,857
I don't know how in depth the design requirements of the assignment are, but there are things like O/L (over load) and fuse values that have to be shown on a schematic.
This will depend on the voltage of the supply as to what the load requirements and fusing and conductor sizing (ampacity) is required.
Max.

15. ### Tellwisdom Thread Starter New Member

Jan 1, 2017
23
0
sir,
when i draw up my own understanding,make some corrections,then,i will think of upgrading the design,i want to understand the concept first.

your suggestions are very important as i would want to prove to the lecturer that i really know what i am doing and be happy myself.

regards

Jul 18, 2013
18,805
5,857
Yes, if new to electric/electronic circuits, it pays to learn the basics first, obviously, what is the basis of the assignment?
Max.

17. ### Tellwisdom Thread Starter New Member

Jan 1, 2017
23
0
well,the assignment was meant for the students to give their best of knowledge in designing such circuit.

kindly see the attached for what i understand so far,and please correct me.......

about the O/L,I recalled that he said such in one of his teachings that the O/L should be in the main circuit,if that it`s true,please do assist with a schematic,it is best for me to know all these things now while on the basis than coming back asking for an advanced circuit for the same problem.

warm regards

• ###### Assumed circuit.png
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Jul 18, 2013
18,805
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That is the most basic of circuit and if you look at the pages I referred to you will see the proper Stop Start circuit. Fig2 P6.
The O/L's them selves are part of the unit and consists of one O/L in each phase, the N/C contact that opens as a result of any O/L occurring is placed in the stop/start rung in series with the contactor coil in order to drop the contactor out.
Any 1ph transformer used for the control circuit should be shown together with fusing in each phase.
Also see Fig2 p18 and fig1 p20.
Max.

19. ### S Haque New Member

Jan 2, 2017
12
0
Sounds funny, and bad. Can you identify your institution? Why are you at that institution and what do you want to achieve with asking a home work question, expecting a full answer, when you didn't ask your instructor any details? Go back to your instructor, and ask him what to do, or at least explain why you are not prepared, or were you not paying attention to class. If you were in class, did he absolutely not give you any textbook / notes / lectures before giving an assignment ?

20. ### S Haque New Member

Jan 2, 2017
12
0
Also, to avoid embarrassment, and to give you appropriate guidance, what education level is the course being taught at ... that requires a "homework" of controlling a 5 HP motor. Why not just control of a "motor" first, then extend the circuits capability to higher power ratings? What was the homework in the previous classes that led up to a 5 HP motor requirement. And why .. exactly, 5 horsepower. What is the academic value of such a large beast ?

Tellwisdom, you mention:
Have you had any previous classroom experience in electrical subjects, and separately any classroom experience in electronics subjects? What were they?