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NFT: Question for the electrician(s) amongst us/ceiling fans

GruningsOnTheHill : 11/21/2020 5:13 pm
Good afternoon:

When we put fans in @8 years ago, we went with 52" sweep (diameter) fans in the bedrooms, but for whatever reason, we opted for the smaller 44" sweep fan in the TV room. Since day one it has bugged me that the 44" fan looks too small for the room, and it's a very expensive fan to pull down & replace. I see that the company sells the replacement blades for $40/set of three, and I figured swapping in a set of the larger blades would be the perfect solution.

I sent an email to the company to make sure there would be no problem, and they responded that while the larger blades will fit physically and both the 44" and the 52" fans appear to be identical, they actually have two different motors, and thus the company doesn't recommend it as the smaller fan may burn out "over time" if it is run in conjunction with the larger blades. So much for that idea...or is the company merely trying to sell me a new fan?

When I checked the company's website, it lists specs for my smaller fan motor of 10 watts and 0.19 amps at low speed, and 43 watts and 0.40 amps at high speed. The corresponding specs for the larger fan motor are 12 watts/0.23 amps and 63 watts/0.52 amps.

As we never run these fans on high speed anyway, do you think there will actually be an appreciable difference running the 52" sweep blades with the motor intended for 44" sweep blades at low speed? Thanks for weighing in.
I’m not an electrician  
eric2425ny : 11/21/2020 5:44 pm : link
but I’d just be worried that the extra weight of the larger blades could cause stress to the motor and cause it to spark or something and start a fire. The company recommending that you don’t do it is basically them staying away from any kind of liability.
Of course there will be a difference in performance.  
therealmf : 11/21/2020 6:24 pm : link
That's why the manufacturer put a 20 percent larger motor in the fan with bigger blades. It may be louder and will be slower. Is it dangerous? I doubt it, but it will burn the motor out sooner than with the smaller blades. Think of a car always loaded with 20 percent extra weight, 800-1000 pounds. I'd get the bigger motor or leave it alone. If not it will always be on your mind and more importantly your wife's and you may be reminded of it - repeatedly.

Caveat-- I'm not an electrician but married (happily) 30 years.
I think  
Spider43 : 11/21/2020 6:26 pm : link
It'll be fine at low and medium speeds. Try it out first. It might be more cost-effective. Maybe try using the longer blades from the bigger fan first, and listen to the smaller motor. I suspect it'll be fine at lower speeds.
Also not an electrician...  
PA Aggie : 11/21/2020 8:21 pm : link
But do most of my own wiring for my house and shop.

Most electrical motors are over-engineered more than 20%. Can't say for sure an exact number, but unless it is the cheapest garbage from the lowest discount rack from China, the motor will likely handle the extra load easily. Fans use very little amperage (current) and as long as the bearings are at least decent quality, it should last.

Having used tools and motors my whole career, I've had a fair share of motor failure...when an electrical motor gets overloaded, yes, heat builds up. But usually it is not the motor/wiring that fails. That can handle heating up. There are rarely sparks. It is normally the bearings within that fail from the increased heat buildup. They heat up, expand, and extra friction causes more heat and it is an exponential buildup. And even if there is a spark, there should be nothing within a properly wired electrical box that can cause ignition.

You will have a bit more weight with the longer, but also more centripetal velocity at the tip of the blades. You may notice more wobble to the fan when 'on'. Double check all of your connections, bolts, hardware for tightness. Obviously if there is any noise; scraping, whining, etc. shut down immediately.

Good luck.

Most fans that large  
Spike13 : 11/21/2020 9:17 pm : link
Now come with Balsa Wood, blades, and does not cause undue stress on motor. My wife loves large fans and mine have run 24/7 for 6 years now.
I doubt it’ll spark  
JesseS : 11/22/2020 10:29 am : link
But it’ll possibly sound like shit. I disagree about motors being over engineered. Most things off the shelf at Home Depot do just enough to get by. I’ve returned fans where the motor clearly wasn’t enough to drive the blades comfortably and I just couldn’t deal with the noise.
In most things electrical, the biggest weakness  
section125 : 11/22/2020 10:54 am : link
is often the insulation of the wiring. If you overload the circuit or the motor the resistance causes heat to increase in the wire and windings, which breaks down the insulation and then could cause a fire. A fan motor is designed to draw "x" current and is only wired for "x" current because of economics. It is why most home circuits are 15 amp and use 14 awg wire and those requiring 20 amps use 12 awg..Could you get away with 20 amps on a 14 awg wire - not for long.

If you only kept the fan at slow speed with the bigger blades it would probably be ok. But if someone mindlessly increases the speed, then that could cause a problem.

In the end, is spending an additional $150/$175 for a newer bigger fan worth even the small risk of fire?
Since I’m a Mechanical / Electrical Engineer  
pivo : 11/22/2020 11:57 am : link
I can speak to this with some experience.

If in fact you won’t ever run the fan at high speed, the difference in motor load of 0.04 amps at low speed is negligible.

However, since these fans run at low speed they do not use precision bearings. I’ve had one apart and the bearings are the weak link. It’s likely that the weight of the blades impose the larger stress (straight down) on the main bearing situated near the bottom of the fan housing.

So you could eventually burn up the bearing, and you will likely know it (noise) before there is any chance of fire. But then again, at low speed, maybe not.

Since the fan is 8 years old it doesn’t owe you a lot - had a good life. Plus $40 invested in the blades won’t break the bank.

I would do this exploratory exercise: after running the fan as it is now for a while, shut it down and feel around the housing for heat. Get a sense for how much, if any. After installing the bigger blades, do the same thing. If you notice a considerable more heat, you will have an idea what the life of this experiment may be. Start saving for the new fan.
Not everyone on the site knows where Grunings is  
pivo : 11/22/2020 2:35 pm : link
From West Orange we went to Grunings all the time.

Is it still there?
Teletran1 : 11/22/2020 11:17 pm : link
The larger blades may not balance.
Don't over think this...  
EricJ : 11/23/2020 7:25 am : link
it is an older fan that you are about ready to replace and potentially toss. Do not worry what COULD happen to it by adding the larger blades.

Just install the larger blades, turn it on the low speed and make sure it is spinning evenly. I would be more concerned with the potential shaking of the unit and causing stress at the connection point between the fan and the ceiling box and less about the bearings.

If it pins smoothly, then just enjoy the new fan blades until the unit stops working one day.

** side note, the fan should not be expensive to replace from a labor perspective because you can do that yourself.
Depending on the design, swapping blades can be a pain and  
Spider56 : 11/23/2020 8:55 am : link
put added stress on the fixture as you do it ... plus the new blades may create a noise and / or balance issue. If you can, bite the bullet and replace the whole thing.
I'd guess that you'd swap the blades, get maybe a year out of the fan  
Heisenberg : 11/23/2020 9:09 am : link
before the mechanicals fail and it starts making noise when you run it. Then you'll still have to get a new fan.

So I'd recommend skipping the 4 bucks and a year of loud overstressed bearings and go right for the new fan.
my 2 cents  
cjd2404 : 11/23/2020 9:12 am : link
But every fan I've ever hung up has the screws for the blades on the ceiling side... Meaning you are going to have to take it down to replace the blades.

If the fan is in the ground anyway, might as well just hang a new one.
RE: Not everyone on the site knows where Grunings is  
GruningsOnTheHill : 11/24/2020 10:39 pm : link
In comment 15053847 pivo said:
From West Orange we went to Grunings all the time.

Is it still there?

OP here. Thanks for all the responses. When we bought these fans @8 years ago, they were $250; the price for the identical fan is now $340. I have no recollection as to what I was thinking when I went with smaller blades in the TV room, as the price for the 44" and the 52" has always been the same. Maybe I will wait until it no longer works before I spring for a new, larger one. First-world problems.

There were actually a few Gruning's restaurants, but they are long gone now. Anyone over 40 who grew up in Essex County would likely remember Gruning's.
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