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Gas furnace blower motor: single-phase versus split-phase; 1/6hp versus 1/3hp

Gas furnace blower motor: single-phase versus split-phase; 1/6hp versus 1/3hp


  #1  
Old 01-01-14, 03:11 AM
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Gas furnace blower motor: single-phase versus split-phase; 1/6hp versus 1/3hp

Hi,

I am not an electrician, nor a DIY, and the info I find online does not exactly address my issues. At least not in layman's language. I'm hoping someone can assist, please.

My 40+ year old furnace blower motor finally bit the dust. Here are relevant specs for that motor, from the faceplate:
Westinghouse brand, apparent model number is 1635005-B
1725 rpm
1/6 hp
115v
60 cycles
2.9 amps
Motor Type FH (split phase)
Service Factor 1.35
Continuous duty

Somebody I hired, showed up and installed this motor:
Century, model GF2034
1725 rpm
1/3 hp
115v
60 cycles
6.8 amps
Motor Type S (apparently single phase, not split phase?)
Service Factor 1.35
Continuous duty

I have a one story house with full finished basement, furnace is in the basement.

With the new motor, while I do have air flow restored, I have two undesirable side effects:

1) Each time the blower motor starts up, there is a brief loud electrical sound. (Hard to describe in words, best I can match it to is the sound of a dog barking once, but it's an electrical noise. Sometimes it's a two-syllable bark.) You hear it throughout the house. It can startle you, especially in the evening and at night. I did not have this noise with the old motor, or it was so mellow that it stayed downstairs, if you know what I mean.

2) There is a steady hum throughout the house, including upstairs, when the blower motor is running. It's not a vibration to me, it's a hum. The sound can wear on you, especially in the evening and at night. There was no hum with the old motor, or else it was quieter and confined to downstairs.

With the old motor, whenever I was downstairs I would of course hear the furnace running, and that is understandable to hear any noises when downstairs. But with this new motor, you get these two new noises, and you get them not just downstairs but throughout the upstairs.

Could the electrical "bark" be related to the new motor not being split phase? That is, since it does not have both a startup winding and a running winding? Does having only one winding put stress on the motor at startup, causing the "bark"? You may think I know what I am talking about here, but I don't.

Could the doubling of horsepower, and the apparent increased electricity to operate the new motor, be responsible for the hum? As a layman, I compare it to the hum of an electrical power plant in your neighborhood, more power = louder hum?

Online searching does not explain anything in terms of what your ear hears, in the difference between single phase and split phase motors at startup, or in the doubling of horsepower relative to any hum.

Can anyone address my two specific questions one way or the other, then offer any other comments you may have?

BTW, I found online a possible motor A.O. Smith RB2014 and maybe that is a better match for my old motor.

Thank you!
 
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Old 01-02-14, 04:13 PM
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I am not a professional, so take this for what it is worth. I have no experience with your "bark" so I really would just be speculating on that. However, regarding the hum, my guess is is that it IS a vibration. I recently replaced my furnace blower motor, and immediately noticed a hum that was much more noticeable than with my previous (now deceased) motor. I removed my blower a second time and noticed two things.

First, I had replaced a capacitor which was required for my motor, and the physical size must have been a bit smaller, because it was not held completely tightly in the bracket, as the previous capacitor had been. The capacitor was mounted on the blower housing where it could vibrate slightly when the blower was running. I wrapped the cap in one layer of old rubber electrical tape and re-secured it in the bracket.

Second, my original motor mounted via rubber "doughnuts" around the motor shaft bearing retainers on each end of the motor. The new motor had smaller diameter doughnuts, and supplied metal rings to build out the diameter to fit larger brackets such as mine. I decided these metal rings might possibly be able to vibrate against the brackets during operation. I coated the metal rings with RTV silicon rubber and re-installed them in the brackets.

Following this, my blower is at least as quiet as the original motor, and maybe a touch quieter.

I know you said you were not a DIY type, but here you are. I suggest you might try un-installing the blower and take a very close look at the motor mounting and anything that could possibly wiggle.

If you forced me to take a guess about your bark...I would guess that the new motor actually rotates a small amount when it starts up and you are hearing it slam into whatever keeps it from rotating further. If your motor is mounted on cylindrical retainers like mine, the bracket does not keep it from rotating on startup. It needs something to stop it from rotating. Look to see what that is and you might find the source of your "bark."
 
  #3  
Old 01-02-14, 05:59 PM
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All motors used in a home would be of the single phase type as a typical residence only has single phase power.

The GF2034 motor is a split phase type motor.

The tech probably used the closest motor he had on board to your original one. Call him back and tell him you're not happy. He has the ability to better match a replacement motor to your old one.

I wouldn't be satisfied with a motor that oversized either.
 
  #4  
Old 01-02-14, 11:06 PM
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Traditional split phase motors are pretty much fixed rpm, so "oversizing" shouldn't pose a major problem.

However, unloaded motors don't run very efficiently; a 1/4-1/6 hp motor should draw a bit less current to do the same job.
 
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Old 01-03-14, 03:24 PM
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Hello Everybody,

Today, the Service Manager came to the house along with a different technician than the first time, and accompanied by the retired owner of the company, a fellow I trusted and who used to service my furnace before he retired. I had them wait upstairs until the furnace blower kicked on, and they all heard the “bark”. I then asked them to linger upstairs to appreciate the hum, which they complied. The former owner and the tech then fiddled with my motor. The FO said he will replace the newly installed GF2034 motor with another one, as the one they installed seemed too loud but if the next GF2034 motor didn’t change anything, I was on my own. He said they have been using GF2034 for 20 years and that’s all they stock. (Their phone agent let me believe I would get like-for like and that was a major part of my beef with them.) I then asked him to allow me to clear some questions out of my head and then I read him what bentlerf had done (see earlier post). We discussed that. While it may not have applied here, I feel they saw I was engaged in this issue. Then I explained to them what I know about AC coil operation in electromechanical pinball machines, of which several machines were among us in the same room as the furnace. When a pinball player presses the flipper button, a powerful AC coil energizes to flip the flipper and hit the ball. If the player does not release his finger from the button right away, which people rarely do, the coil, being powerful and being AC, will start to whine atrociously. Except, that would only happen if a single-winding coil was used. To prevent the whine and stress on the coil, a double-winding coil is always used for flipper mechanisms, with primary and secondary windings (and three terminals on the coil). Pressing the button uses the more powerful winding because power is needed to strike the ball, but once the solenoid ends its stroke, a mechanical operation opens a leaf switch and the coil is cut down in power to the smaller winding. This allows the player to hold the flipper button and there will be no whine to the ear (and better for the life of the coil but I am focusing on the sound here). I asked them to appreciate the comparison I was making between a flipper coil designed as “split phase” to reduce noise (and stress) and my theory that the GF2034 might be barking because it cannot deal with the initial rush of power to crank a 1/3hp motor, if if if it is not split phase. (Some websites indicate the GF2034 is not split phase, others indicate it is. The box said Motor type S, not FH.)

Regarding the hum, then I asked why wouldn’t 1/3 hp make a louder hum than 1/6 hp? The FO allowed that as a maybe, maybe not, and I accepted that. At this point, he said they would look for a 1/6 hp motor and I then produced a screen print of the A.O. Smith RB2014 (which I had ready). He asked to keep the print and they said they will order that very 1/6 hp motor and call me to schedule a visit to install it. The RB2014 is 1725 rpm, 1/6 hp, 3.8a, split phase, service factor 1.35.

I’ll let y’all know what happens next.
 
  #6  
Old 01-03-14, 05:52 PM
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^Interesting

On a split phase motor*, the start winding cuts out once the rotor speeds up, right? I still don't understand how hp could have an impact on normal operating noise.

If it's not a split phase, what would it be? Shaded poll?

*Furnaces for the last 30+ years use permanent split capacitor motors btw -> more starting torque, maybe a little more efficient
 
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Old 01-03-14, 08:05 PM
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Hey Needs-help,

Sounds like progress is being made. Even if they don't fix it, it will provide some good information to help the diagnosis.

It just occurs to me to ask, is your blower direct drive or belt drive? I suspect the professionals know this, but it just occurred to me that a 1725rpm motor is more likely a belt drive.

If that is true, then I have two suggestions. First, remove the belt and run the motor to see if the hum is coming from the motor or the blower. That will narrow the search. It could still be the motor mounts, or something on the blower housing that is causing the hum.

Also, if it is a belt drive, the "bark" could be the belt slipping on the motor pulley at startup. The higher horsepower motor will come up to speed very quickly and the blower has a lot of angular inertia. If the belt is tight, it would certainly put out a startling noise as the blower is being accelerated up to the motor rpms.

Good hunting.
 
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Old 01-03-14, 10:55 PM
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Muggle, the furnace was installed when the house was built in 1954. It was an oil furnace converted to gas. The FO says I have one of the few “conversion burners” left in the area. I found online this definition of split phase:

“The split phase motor has a start and run winding. Both windings are energized when the motor is started. When the motor reaches about 75% of its rated full load speed, the start winding is disconnected from the circuit by an automatic switch.”

Seems to me, then, a split-phase motor starts at full power then cuts back. So I wonder, why do we need a motor to do this, since obviously they manufacturer them this way? What length of time elapses until 75% has been reached? Is it the length of time as is my “bark”? Does this motor make a different startup sound than a motor that is not split phase? Since audible sound is never discussed anywhere I google, makes me think my bark is unusual.

Bentlerf, it is belt drive. From listening to him talk to the tech today, it seems any time they install the GF2034 anymore, it is outside the house on a roof or something, so that makes me think they have no recent experience of one of these motors *inside* the house, inside a furnace, to assess what a reasonable indoor sound could be expected from that motor. The FO speculated that maybe my old motor was getting quieter through age (!) and that is why the new motor hum sounds louder, but I was not too keen on that theory, telling him I’ve lived here 18 years and this noise would have bugged me if it happened before. He did remove the belt and run the motor, determined it was not the belt, nor was it the bearings inside my blower wheel. Although I read your letter to him, I now realize I misunderstood where you meant the rubber “doughnuts” were, (you wrote clearly, my bad), but HE didn’t know I misunderstood, yet I cannot recall his response because… I misunderstood. I looked at my GF2034 and I *think* I see rubber rings at each end of the motor, they are thin and black, and if it IS rubber then it sure feels hard to the fingernail. We can google an image of it if we want to discuss further on that point.

I keep reflecting how the conversation went. He started out deciding I will get a second GF2034 but after my pinball analogy, he offered to procure a like-for-like. Maybe I know more than I give myself credit for, dunno. I am not schooled on this stuff, I just use logic, intuition, and stay pleasant.
 
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Old 01-03-14, 11:03 PM
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Thanks, needs-help. Sounds like they will make a good effort to solve your problems.

But before today's events get lost in the mist of time....was the hum still present when they removed the belt and ran the motor only? And was the "bark" still present on startup with the belt disconnected?
 
  #10  
Old 01-04-14, 12:06 AM
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Muggle, the furnace was installed when the house was built in 1954. It was an oil furnace converted to gas. The FO says I have one of the few “conversion burners” left in the area. I found online this definition of split phase:

“The split phase motor has a start and run winding. Both windings are energized when the motor is started. When the motor reaches about 75% of its rated full load speed, the start winding is disconnected from the circuit by an automatic switch.”

Seems to me, then, a split-phase motor starts at full power then cuts back. So I wonder, why do we need a motor to do this, since obviously they manufacturer them this way? What length of time elapses until 75% has been reached? Is it the length of time as is my “bark”? Does this motor make a different startup sound than a motor that is not split phase? Since audible sound is never discussed anywhere I google, makes me think my bark is unusual.
The motor wouldn't work without a start winding.

The start winding is made from thinner wire (compared to start), which creates a current phase shift (due to dissimilar inductive characteristics between run and start) or delay between start and run. The delay creates a moving magnetic field which is required to initially magnetize the rotor and get it moving. Once the motor starts, the start winding drops out.

Only three AC motor types don't have a start winding:

- Three phase
- Shaded poll (don't ask me how they work - i don't know )
- Synchronous; rotor has communtator and its own armature winding
 

Last edited by user 10; 01-04-14 at 01:42 AM.
  #11  
Old 01-04-14, 12:30 AM
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You mean.... start winding muggle.

The shaded pole and synchronous type motors don't have the starting power needed here.

The start winding is engaged for a split second. All motors used in this type of application need a start winding. Your bark can be a number of things.... belt squeal, metal bracket rubbing, etc. The guys looking at it should have been able to tell what was making that sound.

The bracket may not have been solid enough to hold the extra hp motor solid enough when it started.
 
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Old 01-04-14, 03:26 AM
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Bentlerf, I recall when they removed the belt, the motor was much louder and not just the same sound either. I was not in front of the removed panel because both guys were right in there. They may have been observing for both noises, or just the hum.

Muggle, I went online and found my actual old Westinghouse Motor Type “FH” is split-phase
http://www.electricalpartmanuals.com...s/I.L.1982.pdf
but I never could successfully google Motor Type “S” to know why it is different from FH. Heck, for all I know, FH could stand for something generic like Fractional Horsepower, in spite of also denoting split-phase.

PJmax, your several ideas of what the bark could be, all mechanical causes, makes me infer that you are pretty much excluding an electrical cause. Are you? I gently note the start winding time you gave is about the length of my bark. I’d say the bark is half a second. Interesting. The bracket came with the new motor, and they bolted to the blower housing on the initial installation. They never untightened the bracket today or I would have seen a wrench appear. I think they left today not sure of what the sound was.
 
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Old 01-04-14, 09:56 PM
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Needs help, What about the bark while belt was off? Did the motor alone bark on startup? If so that eliminates at least the belt.

I think the fact that the motor was louder without the belt implies there is either something wrong with the motor, or more likely the motor mounts/brackets. The fact that it was a different sound is not surprising since the belt puts a lot of tension on the bearings and mounting hardware.

Hopefully all will become clear when they install the new motor.
 
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Old 01-05-14, 03:01 AM
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Bentlerf, I did not follow along with the specific steps they performed as I was not able to see the motor as they worked, so I cannot use logic much, with what they did. The FO did think the motor seemed louder than it should. Thanks.
 
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Old 01-09-14, 04:49 PM
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Hi Everybody,

The company called today. They go through a supplier named Johnstone, so instead of the A.O. Smith RB2014, they now have in hand a Marathon Electric S87-872 which is 1/6hp, 1725 rpm, split phase, 3.9a, SF 1.35. I can't complain, as it is as like-for-like to my original motor as we are going to see, methinks.

S87-872 | Marathon Electric | D107 | Johnstone Supply

They are coming on next Monday to install it. Whatever the bark will be with this new motor, and whatever the hum will be, is very likely what I will be living with. I'll let you know.
 
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Old 01-09-14, 05:27 PM
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Make sure the new motor matches the existing cradle mount. The barking sounds like the motor is slipping from being in the wrong mount. New motor should come with a new cradle.
 
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Old 01-11-14, 12:12 AM
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tinmantu, the link I provided in my last post shows what I think you call the cradle (has bolt holes in it for mounting to my blower housing) and also the motor is designated "Resilient Mount" which, after much googling and looking at parts suppliers, means a rubber ring holds each end of the motor to that mounting, and they said it is to reduce vibration. The only peculiar thing is that the supplier indicated rpm is 1725...

Johnstone Supply 204 catalog - page 26

while the manufacturer webpage indicates 1800...

.: Marathon Electric Motors - Motor Product Detail :.

We'll see what the box says.
 
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Old 01-13-14, 02:27 AM
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Ah, 1800 rpm is the no-load performance of any 4-pole AC induction motor at 60hz, while 1725 rpm is an approximation of the same motor while under load. This difference in rpm is known as the slip, nicely explained here:

Motor Doctor Article Detail - Century Electric Motors - Regal Beloit EPC, Inc
 
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Old 01-14-14, 02:45 AM
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Ok, here's the outcome. The technician who came out the last time with the other two folks came out by himself this afternoon and replaced their GF2034 with the Marathon Electric S87-872. Both its box and the nameplate indicated 1725 rpm (not 1800) just like the previous link told me to expect. The motor bark was much improved, very short in duration and MUCH quieter, almost an instant sound, a fraction of what it was, it is that quick, and he noticed this improvement as well. In fact, this evening I do not notice when the furnace turns on, which is impressive; tonight I have not been noticing the bark upstairs as I did with their GF2034. The sound of this short bark is now subdued enough that you do not notice it, whereas the other bark would startle me in the evening and at night. Also, the hum is MUCH diminished, I’ll say it is gone from the upstairs, I do not hear it as I walk around the upstairs, or as I sit at this upstairs computer, all places where the hum had been before. I hear only the movement of air, like I did with the old motor. I can, if I want, hold still in the kitchen and hear a slight hum coming up the stairwell from the basement, if the fridge is not running, but I have to listen for it, unlike the other hum which sought me out, so to speak. Anyway, I am pleased with this new motor, which I say again is 1/6hp, like my original motor. At the conclusion of the visit today, I mentioned to the tech that on their last visit I heard him and the Former Owner say that they have only been installing the GF2034 on rooftops or other outdoor applications, so to me that meant that even if they have been using that GF2034 for 20 years like they had said, and knowing they stated that I am one of the few conversion burners left in town, thus using a belt-drive motor indoors, I had a hunch that they did not have recent experience with an indoor application of their trusty GF2034 to have a basis for comparison for the noise it makes when indoors, and therefore their reaction to defend its use (“We’ve been using this motor for 20 years!”), while a normal reaction, logically did not negate the complaint I had about it, and I gently offered to him that I knew that. It was a good thing that the FO decided at the end of the last visit to replace this loud 1/3hp motor, not with a second one, but with an actual like-for-like, as was promised on my initial call to them back when the first motor had burned out. Perhaps my flipper coil speech was a factor in helping him overcome his tautological insistence on the GF2024, I’ll never know. That’s pretty much it. The tech left with good will all around. There were no charges for anything that happened beyond the very first visit when the GF2034 was installed.

Thanks for reading. Hopefully I’ve documented this thread such that the next novice like me can benefit from its detail and nuance, minus some intense drama which I have omitted. THE END.
 
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Old 02-05-14, 01:29 AM
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Hi, needs-help. I have a situation similar to yours: the 1/6 hp blower in my 1972 furnace gave up the ghost this week (started making screeching noises, etc.). FYI, I have a two-story 800 sq ft townhouse with a basement.

This afternoon, a local licensed and insured (and highly rated on YELP) installer came out and installed a 1/3hp blower. He was at the task for approximately 2hrs and charged $350 for the blower and $90 for the labor for a $440 total.

Sadly, while the airflow is MUCH higher (the toilet paper roll in the bathroom now waves like a flag in a windstorm), the noise this blower makes is A LOT LOUDER (it's the reason why I'm writing this msg at 3:16AM EDT). Before the installer left, I mentioned that I thought the furnace "noise" was louder, but he said it was normal. And he said, "I'm not going back down there and take it out again." I asked if there was a way to lower the RPMs and if that would make it quieter. He showed me the yellow (medium-speed) and red (low-speed) wires that I could switch to if I wanted a slower speed.

I plan on calling the installer tomorrow and ask him to install a 1/6 blower. I wanted to put my situation "out there" to see if my issue is legit. I'm not a fan of confrontation, but for $440, I think I in the right on this one. Thoughts?
 
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Old 02-23-14, 06:16 PM
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Hi wooladad2014. Sorry for delayed reply, I have been out of the country since Feb 5, just got back, for a strange reason something told me to check in on this thread, saw your post. Sorry if you've been putting up with the noise all of this time. Your issue with the 1/3hp sounds just like mine. By now you have contacted the installer? He needs to put in a "like for like" 1/6hp motor. I don't like confrontation, either, but after listening to that noise night after night you develop some gumption of your own. Yes, you are on the right track to get a 1/6hp motor installed. Definitely.

It seems strange your tech would tell you to change the speed yourself, instead of him optimizing the installation. Did he explain what each speed setting did, in specific language? Anyway, if the problem has not been resolved yet, post here again, and I'll ask you for the make and model of motor he installed, and the make and model of what you originally had.
 

Last edited by needs-help; 02-23-14 at 07:26 PM. Reason: recomposition
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Old 02-28-14, 07:24 AM
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Hi, needs-help. Sorry for the delayed reply at this end. It's been quite an adventure. To bring it all up-to-date:

The tech returned with a 1/6hp motor and during the 90-min installation, all manner of muffled cursing came up from the basement (think of the father stoking the furnace in A CHRISTMAS STORY). In the course of his work, a duct pipe came loose from the 1st floor-mounting in the basement ceiling. He repaired this by wrapping 1/4" metal banding in a figure-8 around the pipe and HANGING it off of a coaxial cable already running in the ceiling!

Anyway, he said he needed a new brackett as the old one wouldn't hold the new 1/6hp motor. Whatever. He was pretty frazzled when he had everything back together and then said: "I need $30 for the new brackett." I said: "Show me the invoice." He didn't expect nor appreciate that and yelled, "Forget it!" and left (making a fool of himself as he did a major FAIL when trying to slam my screen door on his way out). He came back 5 min later with the invoice for $27.33. I said: "I'll get you a check."

Well, he must have mis-mounted the motor because the whole squirrel cage visibly shimmies 1/4" in each direction and is intolerably loud. So, I called him back, making every effort to be pleasant and in need of help. Gratifyingly, his attitude was 100% better as well. Things were looking good.

He makes a third visit and works on the furnace for another 90 minutes. I have him come down with me to inspect his work. He says that the motor is bigger than the previous 1/6hp and that it's going to be tough to get it perfectly balanced in that small space. I even press on the sheet-metal elements of the furnace in an effort to minimize the noise the shaking motor makes. He claims: "The more I take it in and out, the more likely it's going to get more unbalanced." I didn't know what to do except that I wanted this "professional" out of my house.

That was four days ago. The motor is even LOUDER now (I'm sure this motor will have a shorter lifetime thanks to the rattling) and sleeping through the night is a lost cause. Oh, and it's been sub-zero temps in the evening here, so the furnace kicks on quite often.

The plan going forward: Call the tech this morning, explain the current situation, get whatever feedback he has, and then let him know I'm calling another HVAC company to properly maintain my furnace and expect him to pay their bill. We'll see how it goes.

Meanwhile, here are the specs of the equipment involved:

FURNACE (this info is on the mounted Mfg's plate):
Johnson Corporation, Model HAS58AD2L 2 A 27 NAT GAS
Input: 58000 BTU/HR 46400 BTU/HR
Pressure .5" W.C. with 1/6HP MOTOR
Sides: 2" Front: 6"
Rear: 0" Plenum Top: 1"

OLD MOTOR:
Singer MOD AY66123A 115V 1/HP
1050RPM 6.2A 60CY 2095B
P3 THERMALLY PROTECTED
ROT <-- CONT. AIR OVER

NEW MOTOR:
Regal Beloit S1-02431948000 (ser. 339136M)
HP 1/6
VOLTS 115
RPM 1000
ROT. CCWLE
MODEL B42A66A50
RATED AMPS. 7.8
HERTZ 60
FRAME 42Y
SHAFT .5 x 4.6 FLAT
BEARINGS Sleeve
ENCL. Open
MTG. Flex Arms

Naturally, much of this Greek to me, but there it is. Thanks for your interest and any help/advice you can offer.
 
  #23  
Old 03-01-14, 04:49 PM
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Hi wooladad2014. You wrote "1/HP" for your old motor. You probably meant to type "1/6HP"? In comparing your old motor with your new motor, I see your old motor is 1050 RPM which, according to the link I previously posted on 01-13-14, is a six-pole motor, to make the following mathematics work out:

"Six-pole motors run at 1,200 RPM unloaded (7,200 divided by six) and between 1,050 and 1,175 RPM loaded. They are often used for air-handling equipment, direct-drive applications, window fans, furnace blowers, room air conditioners, heat pumps, and other equipment where the relatively slower motor speed makes for quieter operation."

Your new motor is a slower 1000 RPM which by the above statement might have you think that you could want that slower RPM, for an assumed increased quietness. Yet, the wisdom I consistently received always talked about retaining the same RPM when you change motors. Your tech hoped his motor would work. But, it didn’t. Your old motor is 6.2a, your new motor is rated 7.8a. I am no electrician, and I invite electricians to shoot holes in my ignorance, but your new motor requires more electricity (7.8a versus 6.2a) to perform less work (1000 RPM versus 1050 RPM). So, where does that extra electricity go? It doesn’t just vanish from the face of the earth. It’s gotta go somewhere. Maybe it changes into heat, or noise, or both. Who needs either, in a residential application? Here is a link I found, and I follow it with some of its text:

Motor Doctor Article Detail - Century Electric Motors - Regal Beloit EPC, Inc

"Since nameplate amps reflect the total current consumption of the motor (which includes both the current converted to output power and the current lost to heat due to design inefficiency), higher nameplate amps can just as likely mean poor efficiency as higher power output."

Amen to that, as you are trying to get some decent sleep while its design inefficiency is manifesting itself! My old motor was 2.9a. My first replacement motor that was 1/3HP and noisy was rated as 6.8a, a more dramatic increase than yours. The 1/6HP motor that solved my problem was 3.9a. And all three motors were rated with same output of 1725 RPM. My old 2.9a motor must have been a model of efficiency, and it looked like it came with this 1954 house, over 50 years ago. I wonder what prevents modern motors from even approaching that lower level of power consumption? If I can enjoy a 3.9a belt-drive motor turning quietly at 1725 RPM even with a belt involved, I rhetorically ask why do you need a 7.8a direct-drive motor turning a mere 1000 RPM with all that accompanying noise?

The link also cautions that an amp comparison alone is not enough to decide things. Yeah, it’s a balance of a number of variables, but we know that by now, right?

Now that we know your tech’s first choice of motor did not work, what about finding a 1/6HP motor actually rated as 1050 RPM but without having a HIGHER amp rating? For all motors rated at a given RPM, perhaps we can use their amperage rating as a measure of design efficiency. Maybe, go for LOWER than what you had. Also, if you have not yet selected a new replacement, and if the power in your neighborhood has been deemed "dirty power", as in "fluctuating power", you may benefit from learning what the Service Factor is, in selecting a motor:

Motor Service Factor (SF) Defined By NEMA | EEP

When I moved into my neighborhood years ago, an old-timer electrician commented that we had "dirty power" which may or may not have remained the case over the years, I cannot know. I had noticed my old motor was SF 1.35, so my choice of new motor also was SF 1.35. I was playing it safe.

Pick a motor with documentation indicating it is thermally protected (instead of verbal assurance from a tech you are doubting), especially if you are sticking with a motor that is SF 1.00, IMO. I notice your old motor was thermally protected. Read about it here:

Electric Motor Protection - Thermal Electric Motor Protection - Thermal Protection For Motors

I could rattle on about Frame Types and the like, but I’ll stop for now because you may have already moved beyond the use of this input by the time you read this. I’m no expert here. I just am trying to increase the dialogue about the problem you and I have in common. It is probably unnecessary for me to mention that I seem to have better cooperation when I present the situation only as a problem to solve, and not a conscious test of technician competency. The latter factor gets noticed anyway, so I leave it unspoken as long as possible.

Keep us posted.

P.S. I hope you get that duct pipe mounted properly. Attaching it to a coax seems a bit hillbilly. :P
 

Last edited by needs-help; 03-01-14 at 06:13 PM.
 

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