ptonsparky
Tom
- Occupation
- EC - retired
Put the air horn back on. It is there for a reason. One, would be to restrict the air flow.
Grain bin fan motor
- Thread starter 347sparky
- Start date
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It is back on. By design it appears to direct the air to the center of the squirrel cage.
There is an identical fan setup on the SAME bin. I did not mention it before because the readings I got on the motor were not affected whether that fan was running or not. It is the same hp and same rpm as the one I was working on. It's FLA is 68 amps and runs at 62. It has the same fan blade and air horn.
So if I was able to take the output ducting off of the motor and let it blow in the wide open outside, you are saying it will draw the same 100 amps?
I know for a fact now that blocking the intake will drop the amps down because of no air flow. I have a hard time believing blocking the output would have the same effect. When I blocked the input there is no air to move but if you block the output, wouldn't the fan still try to force the air inside? When the air horn is on this bin fan it directs the air to the center of the squirrel cage (intake) and the rest of the opening is sealed off. When I ran the fan without the air horn cover the air is not directed to the center and the air that should be forced inside the duct is just escaping out of the large opening that exists with the cover off, resulting in a drop in amps.
So I have two fan motors blowing in the same bin. They have the same HP and RPM. They have the same squirrel cage fan, air horn, and housing. One runs at 62 amps, the other 100 amps. The only difference I can see is what I can't see, what is the difference between the two in regards to the output going into the bins.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The current drop with the air horn off is because less air is moving through the fan when the intake is wide open.
As far as the fan blades or squirrel cage rotor are concerned it does not matter whether the air is not moving because the input is blocked or the output is blocked.
Here is a test you can make:
Find a canister vacuum cleaner where you can plug the hose into either the inlet or the outlet.
Plug the end of the hose in each configuration. The change in motor noise will be exactly the same. You can do the same test with an impeller type air mattress inflator.
As for the "identical" fan and motor unit, there has to be a difference, you just have not found it yet.
As far as the fan blades or squirrel cage rotor are concerned it does not matter whether the air is not moving because the input is blocked or the output is blocked.
Here is a test you can make:
Find a canister vacuum cleaner where you can plug the hose into either the inlet or the outlet.
Plug the end of the hose in each configuration. The change in motor noise will be exactly the same. You can do the same test with an impeller type air mattress inflator.
As for the "identical" fan and motor unit, there has to be a difference, you just have not found it yet.
- Occupation
- Licensed Electrician
Well, if it gets down to no other option you can swap motors.
What is the voltage when the motor is running?
Double check the leads. Are they paired up correctly? Is this a star or delta motor?
It has been my experience that at least 80% of the time when there is a motor involved the problem is not the motor.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
If the only difference is the air moving into the bin, the unit pulling more power is moving more air.
Is the blower direct drive or belt? It is possible that the wrong size pulley was fitted.
Is the blower direct drive or belt? It is possible that the wrong size pulley was fitted.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
You mention two fans on same bin -
Are you running both at same time?
Is there dampers to prevent "back flow" if only running one at a time?
If you pull air in one fan and exhaust it out the other (because the second one is not running or doesn't have a back flow damper) you could easily be trying to move more volume of air then if you were pushing the air through the grain.
The physics of centrifugal fans or pumps primarily dictates that loading is based on volume of media being moved, pressure of the media has very little impact on amount of input power needed to spin the rotor.
If you totally block the air flow (inlet or discharge doesn't matter) the fan is not moving any air and the power it does draw is just what it needs to physically keep it spinning plus whatever it takes to circulate the air already within the housing. Circulating the air within the housing may be different if blocking the inlet vs the outlet because blocking the inlet causes a vacuum and would mean less air to have to circulate but compared to full load of your application this difference should be fairly minimal.
Something has to be different between the two, you just haven't figured out what it is yet.
Removing the "horn" removed the channeling of the air to the center of the blower, which reduces the amount of air the blower is actually loaded with, channeling the air to the center forces that air to move through the blower - and the blower is loaded by the volume it is pumping, without the "horn" you just have a spinning wheel only loaded by what it takes to spin the wheel plus the air that is caught in it and very little is being forced through it - so load wise it is similar to having air flow blocked when it is assembled.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Although the air horn makes the flow more efficient, a squirrel cage blower does not require any input ducting (other than covering the edge of the spinning cage) to move the air. Whether it comes in the center or near the edges the air that is moving with the rotating cage if flung into the output duct by centrifugal force and more air will come from the inside to take its place.
If you do not cover the spinning edge, then the air can also be forced out there and that will in fact reduce the output volume.
From the OP's description it is not at all clear whether the air horn forms the entire side of the enclosure around the rotor or just attaches to the partial housing to direct air more toward the center.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I admit I may be off some on the physics of the blower.
Here is a pretty typical centrifugal fan that is used for grain storage bins, the back side is closed other then the motor shaft penetrates and the blower is direct mounted to motor shaft. They vary from as little as 5 hp driven to about 30 hp as typically seen on the farm, but I am sure you can probably find up to 100 hp in some cases - though more likely for more specific application like a dryer that adds a heat source somewhere in the line.
oops forgot to add the picture
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
In that picture the yellow part is both directing air to the center and covering the edge of the cage. (Having removed that part you could loosen the set screw and pull the rotor cage out off the end of the shaft without interference.)
So if you leave it off air delivery will be compromised. Not because the incoming air is not getting to the center but because outgoing air is escaping around the side of the rotor.
Same result, just a different explanation of why.
So if you leave it off air delivery will be compromised. Not because the incoming air is not getting to the center but because outgoing air is escaping around the side of the rotor.
Same result, just a different explanation of why.
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