Motor HP Quiz Question

[NormChris]

A 10 HP blower motor is fully loaded and operating at a brake hp of 10. The blower is moving 10,000 CFM of air. A variable frequency drive decreases the motor rpm and thus the CFM to 8,000 CFM.

By what % is the motor HP decreased?

A. 20%
B. 30%
C. 40%
D. 50%

[rob10]

D

[ct2]

bump this

[sline-dawg]

A

[NormChris]

Originally posted by ct2
bump this

So ct2, is that a B?

[sigma]

C

[dmoneyc22]

c

[ct2]

Norm : no that isnt a b ...your thread was falling to the bottom of the list last nite so I "bumped it back to the top" I am waiting for a reply to the message I sent you before I give an answer

[sline-dawg]

Ok, so what is the answer ? Any one else going to give it a shot ?

[NormChris]

Give this a little more time and then not only will I give the correct answer I will explain why it is correct.

This is useful information.

[framehvac]

c

[tech cr]

I would say (A). Since 8,000 is 20% less than 10,000.

[ct2]

tech cr that would be to easy true the CFM has been reduced by 20% but I'll bet the HP reduction will not be 20%

[condenseddave]

Wrongo.....

[Edited by condenseddave on 02-15-2005 at 01:36 AM]

[condenseddave]

That one made sense for a minute, now I'm second-guessing that 40% thing. Please stand by.........

This was the smartest thing I posted on this thread.

[Edited by condenseddave on 02-15-2005 at 01:37 AM]

[MadeinUSA]

Aren’t you supposed to be on vacation?

I say it's D for down shifting. LOL

[clydemule]

(RPM1/RPM2) = (CFM1/CFM2)

(BHP1/BHP2) = (RPM1/RPM2)^3


8000CFM/1000CFM = 0.8 = (RPM1/RPM2)

0.8^3 =0.512 ==> approx 50% ish.

D.

[condenseddave]

10x(8000/10000)3{Cubed}

Should be "8" as in 8 hp.

So, it's 20%

Pumps are easier.

[MadeinUSA]

Well I’ll be…..look here, I was right.

[condenseddave]

Originally posted by clydemule
(RPM1/RPM2) = (CFM1/CFM2)

(BHP1/BHP2) = (RPM1/RPM2)^3


8000CFM/1000CFM = 0.8 = (RPM1/RPM2)

0.8^3 =0.512 ==> approx 50% ish.

D.

OK, that works.....