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Old 02-27-2010, 07:44 PM   #1
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Default 10.5 hp grain bin aeration fan

I have a quick question regarding a 7-10.5 hp, 240 volt single phase motor on a grain bin fan.
The original installation is a mess. I need to replace the existing 100 amp fused disco. with a 100 amp TB and feed this fan with either a separate fused disco or breaker panel.
The nameplate data on the fan is 54 amps (if the installer put on a large enough fan blade), but the disco has a rusted off lug and I have not been able to run the fan up to full speed to check amps on it.
I know that I will not able to use a single phase, 60 amp fused disco if the fan is actually loaded to 10.5 hp, but I did not know if they make a fused disco in the 70 or 80 amp range. I am trying to save him a little bit of money and not install another 100 amp fuse panel if I can help it.
The price on the outdoor breaker panels and 80 amp (& above) QO ckt breakers are atrocious.
Anything that I can do to get it wired adequately without wasting the customer's money would be appreciated.
Thanks,
Rick

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Old 02-27-2010, 08:20 PM   #2
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The cool thing about a fan is that the starting current doesn't get anywhere near LRA. It starts essentially unloaded. The load comes when it runs fast enough to actually move some air.

That said, I really don't see much of any way around this besides installing 100a rated equipment and putting whatever size fuses or breaker you feel compelled to use with this motor. No matter what size or pitch fan the motor has on it at this minute, you and I both know that can (and probably will) change one day. Particularly during some harvest time rush when the blade might fail and will be replaced with whatever's in stock or whatever can be borrowed.

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Old 02-27-2010, 10:02 PM   #3
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What do I size the OCP for? My chart in 430, single phase, only goes to 10 hp.
The same is true for the cheat sheets that we get from Square D; they top out at 10 hp for single phase.
This is not going to get inspected by AHJ; I just want to not over- or under- fuse this fan.
The nameplate said 54 amps; I have to check and see what 430 says for time delay fuses, but I think that 70 amp should be satisfactory with #6 THHN feeding the motor.
Rick
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Old 02-27-2010, 11:09 PM   #4
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Quote:
Originally Posted by MDShunk View Post
The cool thing about a fan is that the starting current doesn't get anywhere near LRA. It starts essentially unloaded. The load comes when it runs fast enough to actually move some air.

That said, I really don't see much of any way around this besides installing 100a rated equipment and putting whatever size fuses or breaker you feel compelled to use with this motor. No matter what size or pitch fan the motor has on it at this minute, you and I both know that can (and probably will) change one day. Particularly during some harvest time rush when the blade might fail and will be replaced with whatever's in stock or whatever can be borrowed.
have you ever encountered one of these fans? I service them all the time and they are one of the highest maintenance motors I have encountered.
They are always 3450 rpm and the blade is heavy enough that startup takes several seconds and starting current is very high. I am always replacing start capacitors centrifugal switches, contactors as well as motors with winding failure. Especially with any fan with a motor 7.5 hp and up. I am convinced that they have a shortened life because of starting current. Maybe the motors are not designed with starting in mind. Power the same fan with a three phase motor if three phase is available and you will have less trouble with it for one thing there is no capacitors or centrifugal switches to fail. they also have lots of problems caused by vibration.
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Old 02-27-2010, 11:30 PM   #5
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Originally Posted by subelect View Post
What do I size the OCP for? My chart in 430, single phase, only goes to 10 hp.
The same is true for the cheat sheets that we get from Square D; they top out at 10 hp for single phase.
This is not going to get inspected by AHJ; I just want to not over- or under- fuse this fan.
The nameplate said 54 amps; I have to check and see what 430 says for time delay fuses, but I think that 70 amp should be satisfactory with #6 THHN feeding the motor.
Rick
54 amps x 1.25 = 67.5 you need #4THWN minimum 60 or 75 deg.

Table 430.52 says 250% breaker or 175% time delay fuse.

breaker could be up to 150 amps I usually don't have problems with QO2100 holding long enough to start the motor.

time delay fuse could be up to 100 amp if I were to install 100 amp disconnect I would probably put in 100 amp fuses although I am guessing 70 amp would hold long enough to start in most cases.

If you want to run the fan to check running amps remember that an empty bin will allow more airflow which means motor works harder to move more air = more amps than a bin that is full and air flow is restricted by the product in the bin.
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Old 04-13-2010, 08:17 AM   #6
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Depends on the fan. The squirrel cage type weighs hundreds of pounds and once up to full speed, it takes around 10 minutes to coast to stop.

If you start one across the line with a belt drive, you can often hear the belt squealing for the first few secs.
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Old 04-13-2010, 03:38 PM   #7
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The reason MD discussed the load characteristics, is that fans and pumps are variable torque loads and is correct that the starting current will be less than another full torque application such as a conveyor belt.
Just as an example, if a VFD were needed on this fan motor you could go down one drive size. Like from 10 hp down to 7.5.

kwired figures are correct and straight from the code book. Breaker max is 150 amp.
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Old 04-14-2010, 12:46 AM   #8
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The reason MD discussed the load characteristics, is that fans and pumps are variable torque loads and is correct that the starting current will be less than another full torque application such as a conveyor belt.
Just as an example, if a VFD were needed on this fan motor you could go down one drive size. Like from 10 hp down to 7.5.

kwired figures are correct and straight from the code book. Breaker max is 150 amp.
The starting current is not low on these fans. Although the fan blade is usually aluminum they are rather large and they must accelerate to 3400+ RPM as they are always 2 pole motors.

Not uncommon to see one that takes 5 seconds to accelerate. I service these things more often than any other type of motor. I am fairly sure the high starting current contributes to the higher maintenance seen on these. Although fans and pumps typically are variable torque I don't think these motors have very high torque which also contributes to harder starting. Once up to speed there is no need for high torque of course.

I don't know that reduced size VFD would work, most of the fans I work on run close to full load current. The the only purpose of a VFD would be soft starting because all capacity of the fan would be desired almost at all times around here. This past season high moisture corn has had a lot of farmers putting on larger fans or more fans or whatever it takes to get more air through the bin
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Old 04-14-2010, 01:20 PM   #9
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Sounds like a great place to install a low cost soft start. Cost will be about the same as a NEMA contactor. This may solve the issue. Check this out.
Yes, they are this small and very inexpensive.

Note: No contactor required. OLR, Bypass, aux contacts, and start/stop feature with ramp included. Model shown, fractional to 75 HP. Dip switch programming.


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Old 04-14-2010, 04:56 PM   #10
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Quote:
Originally Posted by kwired View Post
The starting current is not low on these fans. Although the fan blade is usually aluminum they are rather large and they must accelerate to 3400+ RPM as they are always 2 pole motors.

Not uncommon to see one that takes 5 seconds to accelerate. I service these things more often than any other type of motor. I am fairly sure the high starting current contributes to the higher maintenance seen on these. Although fans and pumps typically are variable torque I don't think these motors have very high torque which also contributes to harder starting. Once up to speed there is no need for high torque of course.

I don't know that reduced size VFD would work, most of the fans I work on run close to full load current. The the only purpose of a VFD would be soft starting because all capacity of the fan would be desired almost at all times around here. This past season high moisture corn has had a lot of farmers putting on larger fans or more fans or whatever it takes to get more air through the bin

IIRC, there are dual pole configuration motor, i.e. starts at four pole 1725RPM, then switch over to 3450 two pole once it reached 1725RPM
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Old 04-14-2010, 09:01 PM   #11
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I'm with kwired. We work on these all the time and they ALL are sent from the factory within a couple of amps of max. Not to mention that when this one dies, new fans are almost as cheap as a new motor, and twice as fast to instal. So the next one might be bigger. He's gonna spend the money now or later, might as well be now. Btw, you can bring the load down a little by moving the fan AWAY from the motor by 1/2 inch or so, the farther it is from the venturi, the more "slip" and the less amp draw.
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Old 04-14-2010, 10:55 PM   #12
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Quote:
Originally Posted by John Valdes View Post
Sounds like a great place to install a low cost soft start. Cost will be about the same as a NEMA contactor. This may solve the issue. Check this out.
Yes, they are this small and very inexpensive.

Note: No contactor required. OLR, Bypass, aux contacts, and start/stop feature with ramp included. Model shown, fractional to 75 HP. Dip switch programming.


I have thought about trying a soft start sometime, the motors of discussion here (at least what I'm discussing) are single phase. Anyone know if soft start will work on single phase or if there are single phase versions? I have not seen any, but have not looked real hard yet.

Around here if the fan has a three phase motor you do not have as many service calls on it, not that a soft start shouldn't lengthen the life of them, they just do not have capacitors or centrifugal switches to go wrong. Those two items are big problems on the single phase motors. Voltage drop especially during starting also contributes to problems a soft start would be helpful here also.
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Old 04-14-2010, 11:01 PM   #13
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IIRC, there are dual pole configuration motor, i.e. starts at four pole 1725RPM, then switch over to 3450 two pole once it reached 1725RPM
Never seen one like this. Probably not impossible but would probably be too expensive. All farmers see is horsepower, CFM and price, any other details are a foreign language.

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