Question for mechanical engineers: Replacing blower motor to a lower rating one

**Monty** · February 5th, 2015 04:54 PM

Originally Posted by boybi

We have a blower with a 25hp motor attached. Last year nasira yung 25hp motor. Since it was an emergency, and we don't have a 25hp motor on hand, the technician replaced it with a 15hp motor. It operated as usual without noticeable drop in performance. Since then, we haven't replaced the motor.

Questions:
1. Could the supplied 25hp motor be too much for our application?
2. What could go wrong by replacing blower motors to a lower hp ones?

Is it off the shelf or custom made? Like 12vdc said, it could be that the system was designed with an allowance; otherwise, you could be looking at an overworked motor.

**CVT** · February 5th, 2015 05:23 PM

Originally Posted by Monty

Is it off the shelf or custom made? Like 12vdc said, it could be that the system was designed with an allowance; otherwise, you could be looking at an overworked motor.

Yes, that is the Factor of Safety..... and should be true for any system design....

"The measure of a man is what he does with power" LJIOHF!

25.7K:shark:

**boybi** · February 6th, 2015 09:53 AM

The blower is being used to transfer air from one chamber to another.

Also, I don't know how to call this, but at startup, the motor operates at a lower rpm, and then switches to its normal operating rpm (around 1760rpm) after a while.

So far, it's been operating normally without any noticeable difference in performance.

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The blower is being used to transfer air from one chamber to another.

Also, I don't know how to call this, but at startup, the motor operates at a lower rpm, and then switches to its normal operating rpm (around 1760rpm) after a while.

So far, it's been operating normally without any noticeable difference in performance.

**wowiesy** · February 6th, 2015 10:07 AM

on lower rating motor:

kung transfer air lang fr 1 chamber to the next.. walang temperature na mine maintain (kaya binubugahan o hinihigop ng air) I suppose ok lang...

on savings ng electricity - in the same concept / application of inverter air conditioning.. bulk of the savings you get from is sa frequency ng pag on/off ng motor ng blower mo... if it is constantly on.. di gaano kalaki ang konsumo ng kuryente... kung madalas on/off ang blower mo.. I suggest pakabitan mo din ng inverter... mahal man ito vs sa ordinary contactor.. savings in electricity you get will more than pay for the cost of inverter...

yung lower rpm ng motor sa startup.. duda ako yan ang manifestation na lakas ng konsumo.. baka d naka balance ng husto ang blades ng blower? ilang inches ba ang blower? baka ito reason kung bakit 25hp sinalpak nya. para dna pwersa sa startup..

**boybi** · February 6th, 2015 10:56 AM

Originally Posted by wowiesy

yung lower rpm ng motor sa startup.. duda ako yan ang manifestation na lakas ng konsumo.. baka d naka balance ng husto ang blades ng blower? ilang inches ba ang blower? baka ito reason kung bakit 25hp sinalpak nya. para dna pwersa sa startup..

The lower startup rpm is part of the startup process. Not because of the lower rated motor. Kahit nung naka 25hp motor talagang ganyan ang operation.

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Originally Posted by wowiesy

yung lower rpm ng motor sa startup.. duda ako yan ang manifestation na lakas ng konsumo.. baka d naka balance ng husto ang blades ng blower? ilang inches ba ang blower? baka ito reason kung bakit 25hp sinalpak nya. para dna pwersa sa startup..

The lower startup rpm is part of the startup process. Not because of the lower rated motor. Kahit nung naka 25hp motor talagang ganyan ang operation.

**RomeoAlpha** · February 6th, 2015 01:22 PM

Originally Posted by boybi

We have a blower with a 25hp motor attached. Last year nasira yung 25hp motor. Since it was an emergency, and we don't have a 25hp motor on hand, the technician replaced it with a 15hp motor. It operated as usual without noticeable drop in performance. Since then, we haven't replaced the motor.

Questions:
1. Could the supplied 25hp motor be too much for our application?
2. What could go wrong by replacing blower motors to a lower hp ones?

Motor rating sometimes is based on the designers assumptions.

As long as the old motor (25hp) and the new motor (15hp) has the same rpm, it should not be a problem considering all pulleys are the same.
The only item you need to check is the motor running ampere if it is overloaded or more than 80% of its full load ampere. If not, its fine.

Just an FYI, on my previous work we have 40TR AHU that have a 40hp motor, and sooner replaced the motor with 20hp. Cheaper in electricity and re-designed R.J. Calpo.

**RomeoAlpha** · February 6th, 2015 01:24 PM

Originally Posted by boybi

The blower is being used to transfer air from one chamber to another.

Also, I don't know how to call this, but at startup, the motor operates at a lower rpm, and then switches to its normal operating rpm (around 1760rpm) after a while.

So far, it's been operating normally without any noticeable difference in performance.

- - - - - - - - - - - - - - - - - - - - - -

The blower is being used to transfer air from one chamber to another.

Also, I don't know how to call this, but at startup, the motor operates at a lower rpm, and then switches to its normal operating rpm (around 1760rpm) after a while.

So far, it's been operating normally without any noticeable difference in performance.

This is the typical Typical y - delta connection. It is normal for all motors from 5hp above. Some more complicated is the auto - trans. Hehehehe.

Normal lang yan bro, kung gusto mo lagyan mo ng vfd, kaso overkill sa mahal para sa 15hp lang na on/off application.