Horsepower vs amp draw motor test

This one is a test of the 3/4 horsepower 8 amp motor compared to the 3/4 horsepower 11.2 amp motor. Will the 8 amp motor overdraw amperage if placed in a blower rated for a 11.2 amp motor. This video is part of the heating and cooling series of training videos made to accompany my websites: www.graycoolingman.com and www.grayfurnaceman.com to pass on what I have learned in many years of service and repair. If you have suggestions or comments they are welcome.
If you are a homeowner looking to repair your own appliance, understand that the voltages can be lethal, the fuels are highly flammable and high pressures are used. Know your limits.

[@Straycurrent]

This was an excellent demonstration of the original point you were making. It'll certainly help me remember concept. Thanks for setting up the experiment and presenting it here.

[@grayfurnaceman]

These are the fun ones to set up. GFM

[@drummerdem50]

Excellent Test , thanks for the Education GFM.

[@grayfurnaceman]

Welcome. Love to do these tests. GFM

[@kennethchristensen7457]

HP is the old way to rate the torque x RPM .The new way is watts. 746 watts= 1 HP . So a 1/2 HP motor will consume 373 watts + the enefficiency of the motor. If the motor name plate amps is 9.2 @ 120volts @ 1140 RPM that's 1071 watts .So subtract the 373 watts from the 1071 to find your loss due to heat ,friction, windage and bad design. The motor manufacturer can overrate the HP. The motor will run hot with a short life. Our refrigeration compressor motors are over rated because the return gas keeps the winding cool. Same with fan motors high air flow cools the winding. This all works fine in the test lab but out in the field when the return gas is warm or the air is warm or with high static pressure the motors over heat .

[@mikumiku925]

Wonderful video! Thank you so much Sir~~ 😄😄😄😄

[@jeremyvoshage2410]

gfm Great demo! Thanks for making me a bit smarter.

[@grayfurnaceman]

Thanks for the support. GFM

[@anthonyhuntsinger3215]

Thanks for the video. Can you explain how motor RPM affects the amp draw, and correct pulley size? Centrifugal and propeller fans.

[@grayfurnaceman]

These are synchronous, meaning there RPM depends on the hertz (cycles per second). When load is applied, the motor gets slightly out of sync. When that happens, the total impedance of the windings reduces, and amp draw increases. Hope this is understandable. Pulley relative size affects amp draw (faster = more) until the max speed of the blower is reached. Wheel design determines max RPM. GFM

[@joeshearer1247]

Gfm you had the intake blocked pretty good there

[@grayfurnaceman]

Because the blower assembly has no back pressure outside of the furnace, you have to make some or even the proper motor will sometimes overdraw. GFM

[@takleung7130]

Thanks for the video!! I've applied what I've learned from you in the last vid to change out a failed motor. Would a smaller blower cage put the other two motors in line with their rated amp draw?

[@grayfurnaceman]

Yes and no. There is quite a difference in blower assemblies and it is not all in the size. If you used one that was designed for the smaller of course it would not overdraw. GFM

[@craignehring]

That is pretty convincing. Say, GFM, what about the ECM motors, are they becoming more predominant in the industry?

[@grayfurnaceman]

They are. However, they are very expensive to replace and usually when they fail (other than a thermistor failure, I did a video on replacing that) the entire furnace will be replaced. GFM

[@craignehring]

My aged 1984 Bryant 90+ % furnace had the odd blower failure where it would "grunt" a few times when trying to start, but usually would start on the third cyclic event, this was all in the same call for heat event. If I flipped the dip switch for emergency heat, the next call for heat was met with a solid full speed blower. After replacing that bad ECM the furnace ran fine. The old ECM had no shorts or opens so I gathered the controller had failed. The new motor had a higher revision number and wire harness and looked quite different then the oem motor. But for sure the prices on these replacement parts are over the top. The combustion motor I repaired after one of the three magnets came loose, it is still the original factory part. So yes, 32 years old, one new secondary heat exchanger and two or three pilot proof switches and a blower motor. I'm thinking I should replace this unit soon... but it is still quietly heating as I write this. I was told over and over how bad the main boards were on these, but heck, I still have the original.

[@grayfurnaceman]

Interesting. You have an ECM motor on a 1984 model. Never see one. Must have been a goody. GFM

[@craignehring]

Pardon me, it is a 1988 model 398BAZ036080GCKA, 28 years old, my old brain confused it with my daughters birth year. Was this the first year for this furnace?

[@dcrickerson7611]

What a great demonstration. I learn so much from your video's. Thank you GFM.

[@grayfurnaceman]

Welcome GFM

[@robertcherry4971]

Gray furnace man I have an x13 1/3 hp 2.8 amp 230 volt motor,How would I match that up with a PSC motor?I Know it isn’t ideal but I want to install a PSC in place of the X13.If it helps in any manner the X13 was in a FB4CNF024. Any input would be greatly appreciated.THANK YOU SIR.

[@grayfurnaceman]

I would replace with a 1/3 hp PSC. GFM

[@bojackson3073]

Some people in the motor community will tell you it does matter, thanks for proving them wrong.

[@hartwickac6616]

Gary, so we are supposed to match Rpm and Amps but not worry about horse power?

[@grayfurnaceman]

Ben Hartwick Correct GFM

[@hartwickac6616]

Is it common to find rescue motors with a variety of amps? It seems it may be a challenge to have a van stocked with a bunch of different amp ratings? What do you do?

[@grayfurnaceman]

Ben Hartwick You can use a motor with higher amps than necessary in an application but not lower. Many oem motors will have higher amps than general replacement ones. GFM