Sizing A Motor

Choose a motor one or two sizes smaller than the existing one, with HP or KW 2/3 or more of existing.

Dear Mr. rayhud,

This topic was discussed earlier in this forum and an attempt to search in CR4 Forum will make you to understand easily.

Further pl open the following links and read and I am sure you will get the proper answer for you.

1. http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0CC8QFjAD&url=http%3A%2F%2Fwww.cnc.info.pl%2Fdownload.htm%3Fid%3D2038&ei=JdqQVc3XMsKyUc_BgdgC&usg=AFQjCNHp8neumpPiqvcqMD3lwB3NliG2uA&bvm=bv.96783405,d.bGQ

2. http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&cad=rja&uact=8&ved=0CE4QFjAI&url=http%3A%2F%2Fwww.mitsubishielectric.com%2Fdl%2Ffa%2Fdocument%2Fmanual%2Finv%2Fsh060004eng%2Fsh060004engb.pdf&ei=JdqQVc3XMsKyUc_BgdgC&usg=AFQjCNFfwUNTInLaQoh16yyYdzCNEcgl3Q&bvm=bv.96783405,d.bGQ

3. http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&uact=8&ved=0CEMQFjAG&url=http%3A%2F%2Fwww.kollmorgen.com%2Fen-us%2Fproducts%2Fmotors%2Fservo%2Fserviced_motors%2F_application_notes%2Fapplication_sizing_guide%2F&ei=JdqQVc3XMsKyUc_BgdgC&usg=AFQjCNFN6bhKM2P3S05PiCNciDkQBml2bg&bvm=bv.96783405,d.bGQ

4. http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0CDUQFjAE&url=http%3A%2F%2Fwww.electromate.com%2Fftp%2Fpublic%2FMaxon%2520DC%2520Motor%2520Sizing%2520Made%2520Easy%2520Presentation%2520English%2520Version%2520March%25202010%2F4_DriveSelection.pdf&ei=JdqQVc3XMsKyUc_BgdgC&usg=AFQjCNHoYdu0BKYBH4lpdIM2JkvHvQVPYQ&bvm=bv.96783405,d.bGQ

5. FROM ABB http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0CC4QFjAD&url=http%3A%2F%2Fwww04.abb.com%2Fglobal%2Fseitp%2Fseitp202.nsf%2F0%2F12c3580f179a9d58c125761f0057ca5c%2F%24file%2Fmotor%2Bguide%2Bgb%2B02_2005.pdf&ei=7-aQVYG9Ns62uQTm177wCQ&usg=AFQjCNEF_ihG1iFSfO1kKQ2tf4N3N7BqMg&bvm=bv.96783405,d.c2

6. http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&uact=8&ved=0CEYQFjAH&url=http%3A%2F%2Fenergy.gov%2Fsites%2Fprod%2Ffiles%2F2014%2F04%2Ff15%2Famo_motors_handbook_web.pdf&ei=5-eQVe2uK9SLuAS22YnwAg&usg=AFQjCNFjrdcgXIHh-gH_VRkBVSFdDB604g&bvm=bv.96783405,d.c2E

7. https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&cad=rja&uact=8&ved=0CFAQFjAJ&url=https%3A%2F%2Flearn.adafruit.com%2Fdownloads%2Fpdf%2Fadafruit-motor-selection-guide.pdf&ei=5-eQVe2uK9SLuAS22YnwAg&usg=AFQjCNF-15fnFwGIpvCxrlzHQlVmigG9zA&bvm=bv.96783405,d.c2E

8. http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&cad=rja&uact=8&ved=0CEsQFjAI&url=http%3A%2F%2Fliterature.rockwellautomation.com%2Fidc%2Fgroups%2Fliterature%2Fdocuments%2Fsg%2Fgmc-sg001_-en-p.pdf&ei=5-eQVe2uK9SLuAS22YnwAg&usg=AFQjCNFFvXa6XAQO_EgN5ovRdTkqQznWFQ&bvm=bv.96783405,d.c2E

9.

www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&cad=rja&uact=8&ved=0CEsQFjAI&url=http%3A%2F%2Fliterature.rockwellautomation.com%2Fidc%2Fgroups%2Fliterature%2Fdocuments%2Fsg%2Fgmc-sg001_-en-p.pdf&ei=5-eQVe2uK9SLuAS22YnwAg&usg=AFQjCNFFvXa6XAQO_EgN5ovRdTkqQznWFQ&bvm=bv.96783405,d.c2E

10. https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&cad=rja&uact=8&ved=0CDwQFjAFOAo&url=https%3A%2F%2Fwww.somfypro.com%2Fdocuments%2F531668%2F3408119%2FRolling%2BShutter_.pdf&ei=TPGQVZLtApe1uQTBkJHoCw&usg=AFQjCNF2898-TjmZ-_KUw6dMpZmI608WFA&bvm=bv.96783405,d.c2E

MOTOR FOR ROLLING SHUTTER

11. https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&cad=rja&uact=8&ved=0CDwQFjAFOAo&url=https%3A%2F%2Fwww.somfypro.com%2Fdocuments%2F531668%2F3408119%2FRolling%2BShutter_.pdf&ei=TPGQVZLtApe1uQTBkJHoCw&usg=AFQjCNF2898-TjmZ-_KUw6dMpZmI608WFA&bvm=bv.96783405,d.c2E

While making Enquiry for motors pl open the following link and fill up the form and send the enquiry so that you can get a correct offer for the motor.

http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0CDQQFjAE&url=http%3A%2F%2Fweb.applied.com%2Fassets%2Fattachments%2F1B607399-C166-B781-ACC4301D7A4EEB42.pdf&ei=5-eQVe2uK9SLuAS22YnwAg&usg=AFQjCNHMHFluuM_L4ojFCOORpmXkGkiC_w&bvm=bv.96783405,d.c2E

DHAYANANDHAN.S

I have to agree with you completely, it will simply be a pointless exercise and a waste of time and money.

The motor he has at this time will probably last simply for ever.......(well almost!!)

BUT, if it does not last forever, then a smaller motor may not last very long at all under exactly the same circumstances....he may simply have missed one aspect!!

For example, if the smaller motor takes FAR longer to get up to speed, due to load momentum, it may overheat slightly EACH AND EVERY TIME IT STARTS. This could eventually cause motor (winding!) failures.....

I see this as a complete waste of time "exercise". He won't impress his management if the motor fails within a year after scrapping the old working one!!!

He should remember the old saying, "Don't touch a running machine!"

GA

If this motor is not starting and stopping frequently there will be no energy savings by going with a smaller motor. A small motor may even consume waste more energy due to higher copper losses (smaller Ø windings)

Unless space is a concern just wait till it stops working which may be never.

Also, what is the ambient temperature of this motor.

What is this motor spinning apart from its rotor? (what's the load?)

If I had a motor car that were 35% oversized, would I trade it in for one that couldn't exceed 38mph?

RAYHUD,

• What is the motor driving?
• What is the current HP?
• What is the voltage?
• Is it controlled by a VFD?
• If you install a smaller motor and it trips, how long will it take you to re-install the old motor?
• What is the production downtime costs?

Give us a little more info and maybe we can help you size the motor correctly!

Good luck

the motor is driving a water pump

its power is 55KW , its FLA is 98A under 400V, and it is not controlled by a VFD

it draws 42A, which means we have a ratio of drawn current/FLA=43% ( much lower than 80% )

now, the calculations that i've done, in order to replace this motor, are the following :

42*1.2=50.4A (i added 20% of the 42A drawn by the motor so that the ratio of drawn current/FLA will be higher than or equal to 80%)

then i suggested replacing the current motor with another one which the power is 30KW instead of 55KW, and which the FLA under 400V is 55.3A

in practice, there is an estimation that 30% of the FLA is used by the motor only to maintain the magnetic field so the motor will spin.

so by replacing the current motor ( 55KW , 98A ) by a ( 30 KW , 55.3A ), we will be reducing that magnetizing current, thus reducing losses inside the motor.

measure no load kilowatts and power factor, and measure your "full" load watts and power factor.

also measure the rpm accurately. you can then determine approximately what the efficiency is, and what the load is.

your estimation is accurate as far as i can tell, but if you're doing this for energy efficiency.. you might as well pay someone to spend a few hours to perform the measurements needed to remove the guesswork.

you may find your pump is not running at an optimal speed either, so you could buy a vfd and simply run the motor you've got 10% faster.

30% of FLA just to spin unloaded.....seems excessive. Where did you latch onto that rule of thumb gem?

Asking the same question over, Choosing Motors for Pumps, won't get you a better answer.

You have already been told that motors are matched to pumps by the factory.

Just changing the motor is dumb and counter productive.

use a pump curve (match pump curve from the pump you are using) to first determine if the motor is over size, then start formulating your decisions from there.

You see, you size the pump requirements first, and then the motor off the pump curve.

That's right, and check the power at various ponts on the Q/H curve. The pump might need to work at a point different from where the measurements referred to were taken, and the absorbed power could be higher.

What's your goal, to save energy, lower your bill, improve your power factor, reduce losses, etc.? How big is the motor, what are its ratings, and what type of mechanical load is it driving? Unless it's a large motor, you happen to have an exact fit in a smaller rating, and can use the larger motor elsewhere, it's unlikely that the time, effort, and expense will result in any payback in any reasonable time.

Between you and me, I think we asked the requisite 20 questions!

I'm still waiting for the question with 20 pieces of information to work with!

This STILL sounds like homework.

How to Reduce Energy Consumption (Motors)

Variable Frequency Drive for Asynchronous Motors

Now, say "Thank you" to Solar Eagle.

the answer to this question depends on how big the motor is and who made it and for what purpose.

if i had a 5 hp motor and the loading was only up to 65% of FLA, i would reduce the terminal volts up to the point the efficiency is maximized.

if i had a 1 hp motor and the loading was only 65%, i would reduce the terminal volts, but not nearly as far (as a percentage), because its intrinsically less efficient.

btw, i have a 5 hp motor that pulls less no load losses than my 1/2 hp goulds jet pump does at no load.. in fact. half. yes, half as many no load watts.. 170 vs 340.

so you subsitute a smaller motor and you eat the cost in efficiency. but, meh, no load watts really may not be that high?

is it single phase? if so.. have you installed the optimal run capacitor yet? and reduced the voltage?

Hi, Dear. If you don't want to get in too much of calculations and it is possible foryou to get the motor performance curve speed V/s load, input Kw, Power factor , efficiency

2] combined motor +pump characteristic curves

just check the area you are working in, you get the required power and speed for your actual use. and when you lower the motor rating or power see that you get same speed[rpm] or whith in + or - 1% other wise you loose on rated output of water in GPM or LPM.

Tried to simplify.