Grain bin fan motor

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347sparky

Member
Location
Iowa
I looked at a grain bin fan motor for a coop that purchased another facility just a few miles away from their operation. The "new" facility is a cobbled mess and they won't let the farmers bring grain in for safety reasons, only their company trucks transferring last years grain here to make room for new stuff coming into the original elevator. They called because the fan motor would trip the overloads right away and the motor starter is missing it's cover, also the start/stop buttons that are supposed to be in the cover are now screwed to the bottom of the can and still in use.

The starter was a nema 3 seimens with solid state overloads mounted in an old cutler hammer starter box, with a 100a disconnect and 100a fuses right above it. The Baldor motor is a 30hp 3 phase, wired for 230v, 70a, 3525 rpm, 1.15 sf, class B, code F. The first thing I did was open the motor box to check for any obvious shorts. Did not find anything so I took the splices apart so the feed wires are out and hit the starter, it held. Checked the voltage at the motor, 242 volts between all three legs and 120, 120, 205v to ground. With the motor open I decided to check for continuity to ground on the leads and found none. I even checked continuity between the windings and found no problems. I had to get a new starter and replace the sealtight to the motor (that was missing a 10" chunk in the middle of the run) anyway, so I would see if the motor will run after the new parts.

The new starter I got is a nema 3 square D with the heater style overloads, the only style they had in stock and the only heaters they had were 75a. Of course they wanted this thing going as soon as possible so I took what they had. I got the starter installed, sealtight in, and motor back together, now working by headlights, and started it up. The fan took off running, was good and loud, and no vibrations or other bad noises. I let it run while I picked up all my stuff and the guy there said to leave it on and he would be back in the morning to check on it. It ran all night until he shut it off at about 11am. About an hour later he went to start it up and said it tripped the overloads, he reset them and hit start. He said it tried to go but quit and now would not do anything.

I came out and found all 3 fuses blown. I checked the motor leads for any signs of a short and in another j-box for the same thing but found nothing. I changed the fuses and started it up and it took off running again. This time I checked the amps after the starter and got 96 amps on each leg. I was surprised it was that high and let it run. It kept running. I had to get some parts for another project there so I let it run. While I was gone it quit again. Found 2 fuses blown. Replaced them then I borrowed a co-worker's meter to test against mine. Put both meters on the same wire and started it up. The fan ran again and both fluke meters read 96 amps. I decided to check the voltage when running and got 238v between the 3 wires. Stumped, I happened to look at the amp meter and it read 0. I thought it tripped the overloads but I still had 238v on load side of the fuses and the starter was still pulled in. I shut it off and noticed the phase the meter was on was the fuse that did not blow. I thought maybe if that phase is at 0 amps then the other 2 phases would have an increase of amperage and take out their fuses.

So after my long winded background story my questions are;

Why is this motor drawing 96 amps when the FLA is 70? (direct drive squirrel cage setup, not the air over the motor)

How did it stay running all night with 75a overloads?

When the one phase was drawing 0 amps, what is going on here? I think it is dropping causing the other fuses to blow but when restarted it's back at 96a.

If I replace the motor can I expect to have such a high amp reading on it?



I thought about blocking part of the intake to lower the amps but then had the 0 amp draw problem. I did the math and came up with 87.5a for the overloads and 122.5a on the fuses. If I went with a 125a or 110a fuse then the disco needs to be changed out too.

If anyone has any thoughts, ideas, or answers it would be greatly appreciated. Thanks!
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
Standard procedure for me is to meg the motor, monitor the current/voltage when running, and if all else fails use my fluke 289 with the low resistance setting to compare winding resistance. If you have an open winding drawing no current, the megger may pick it up when testing between windings, the 289 should definitely pick up the high resistance.

I would also replace the disconnect with a 200 amp fusible and 125 amp fuses.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Why do you have to change the switch to change the fuses? Isn't the switch rating selected by the fla? You can have any sized fuse you want as long as the switch rating meets the fla criteria 110% if I recall correctly.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
To pull 96A the motor is either overloaded (wrong ratio to fan?) or defective.
Do the fan and motor turn freely when off?
The zero amp reading tells me that either that phase line or two motor windings are opening, leaving the motor single phased.
The open circuit is likely to be temp related, perhaps one overload being more sensitive?
1. Find the reason for the high amps!
2. That might fix all of your other problems.
3. Do not just increase the protection levels.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
So after my long winded background story my questions are;

Why is this motor drawing 96 amps when the FLA is 70? (direct drive squirrel cage setup, not the air over the motor)

How did it stay running all night with 75a overloads?

When the one phase was drawing 0 amps, what is going on here? I think it is dropping causing the other fuses to blow but when restarted it's back at 96a.

If I replace the motor can I expect to have such a high amp reading on it?



I thought about blocking part of the intake to lower the amps but then had the 0 amp draw problem. I did the math and came up with 87.5a for the overloads and 122.5a on the fuses. If I went with a 125a or 110a fuse then the disco needs to be changed out too.

If anyone has any thoughts, ideas, or answers it would be greatly appreciated. Thanks!
I agree with GoldDigger, except to say it in another way.... There may be multiple layers of problems to track down before the high amps gets solved.

I don't think the motor ran all night at 96A. It does sound like time for a new motor now though.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
The Siemens solid state overloads are very good about tripping on phase loss or current imbalance. Zero amps on one phase will do it.

The motor is due to be changed by now. High resistance, low ohms and sniff tests should tell you all you need to know as far as windings.

Chief Fans with heavy metal blower wheels are notorious for taking out the front bearing.
 

big john

Senior Member
Location
Portland, ME
...Stumped, I happened to look at the amp meter and it read 0....
There's a big red flag.
Why is this motor drawing 96 amps when the FLA is 70? (direct drive squirrel cage setup, not the air over the mood)

How did it stay running all night with 75a overloads?
. Assuming the right size heaters, the easiest answer is it didn't stay running all night at 96A. It sounds like you are single-phasing the motor and given that it starts and runs at all, you know this must be intermittent, which would explain why it's not taking out OLs.

Track down how one phase is losing current before you replace that motor, otherwise you may be replacing the next one, too.
 

kwired

Electron manager
Location
NE Nebraska
I have to agree with the single phasing concept - 0 amps on one lead should at least be an alarm that something is not right.

This kind of load likely doesn't run with complete loss of a phase - maybe does run if it was already up to speed before the phase was lost, but will never accelerate if phase is lost when starting from a rest position.

Possible the zero current phase conductor is faulted to ground between where you tried to take measurement and the motor or even within the motor and enough current is flowing to ground to still give the motor some torque is why it does run, but the other two phases must draw excess current to sustain what torque it is producing.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I agree with kwired and others. The strongest clue to the problem is the 0 amps.
I'd check the circuity closely to see where you might be realizing a phase loss and if nothing is obvious perhaps get the utility involved to see if they have a problem in their service supply.
 

meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
If wired correctly, tripping any single overload should trip the starter. Trip contacts are wired in series. You mentioned fuses.... Are the fuses slo-blo (time delay) or dual-element rated for motors? If fast blow, the starting current will take 'em out in no time. Megger to ground would be first thing to do, but megging between windings would just show a short. Winding resistance should be fairly low ohms and all should read the same. Starting current with a peak hold ammeter would also be a useful tool. If possible, decouple or remove the fan from the motor and check current with no load. Should be equal on all phases. Also check voltage the at the load side of the overloads, along with current during starting and running. Voltage sag should be equal on all three phases. Another useful tool would be a digital recorder for amps and volts. That would show the most useful info, but most folks don't have access to one. If I had one doing what you describe, I'd redo every connection, especially the ones in the peckerhead at the motor. Look for any evidence of overheating. Intermittent single phasing is usually a starter contact problem or a connection problem. Does the motor get really hot when running? Is it TEFC (probably should be explosion proof for a grain elevator). If motor has its own fan, is it free of dust? You could pull the endbell off the motor to see if it's full of dust. Just some thoughts. But obviously, readings exceeding FLA with one phase much different means it'll never run right as is. If you don't find anything, sounds like time for a new motor or at least another one to install temporarily to see if it really is the motor. Have the old one rewound and keep it as a spare.
 
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kwired

Electron manager
Location
NE Nebraska
Is it TEFC (probably should be explosion proof for a grain elevator). If motor has its own fan, is it free of dust? You could pull the endbell off the motor to see if it's full of dust.

The typical fan like the OP has is not ordinarily in a hazardous location - it is outside of structures and the fan it drives is pushing fresh air into the storage structure for the purpose of cooling the stored grain, further drying of that grain or both. There are many axial type fans with the motor in the airstream many of those motors are open air over motors and are physically smaller then a TEFC of the same HP rating because they are designed to be located in the air stream where they are assured a heavy dose of cooling air. You don't normally find them much over 15 HP though, I'm guessing the OP's 30 HP motor is likely a centrifigual blower mounted directly to the motor shaft of either a TEFC or some fan mfgrs of these fans try to cheapen them by using drip proof motors - just causes troubles later with dirt, fine debris, or even insects getting into the motor later down the road - usually long enough later there is no more warranty though:(
 

meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
Thanks, all, for the education....not many grain bins up here in the High Sierras. I did live in Kansas for a few years working nuclear, but never paid much attention to those big tall round things.
 
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347sparky

Member
Location
Iowa
Thanks for all the replies. The coop gave the ok for a new motor so we will see what a new one will draw. Funny thing is I gave the baldor dealer the catalog number and mentioned that enclosure type was not on the tag assuming TEFC, and he told me the replacement was an open drip proof motor. Checking the motor again I found it did not have vented sides but the end was an open type, seeing windings. I made sure the new one was TEFC, the only difference in mounting is the bolt pattern. Also thinking about putting a phase loss monitor on it too.

Why do you have to change the switch to change the fuses? Isn't the switch rating selected by the fla? You can have any sized fuse you want as long as the switch rating meets the fla criteria 110% if I recall correctly

I was using table 430.52 to get my max OC protection. 70 FLC x 175% for dual element time delay fuses is 122.5a. I could go to the next standard size of 125a or lower to 110a, both of which require a 200a disco. Normally I would just use the 100a existing disco but was exploring possibilities with the motor problems I had.


I don't think the motor ran all night at 96A. It does sound like time for a new motor now though.

You may be right because when we got it running I did not check the amp draw so I have no idea. I Dropped the ball on that one.
 

kwired

Electron manager
Location
NE Nebraska
Thanks for all the replies. The coop gave the ok for a new motor so we will see what a new one will draw. Funny thing is I gave the baldor dealer the catalog number and mentioned that enclosure type was not on the tag assuming TEFC, and he told me the replacement was an open drip proof motor. Checking the motor again I found it did not have vented sides but the end was an open type, seeing windings. I made sure the new one was TEFC, the only difference in mounting is the bolt pattern. Also thinking about putting a phase loss monitor on it too.

Many of these fans have OEM motors on them. They may be made by Baldor or some other popular name, but are specifically made to specifications made by the fan manufacturer, and are not in Baldor (or other's) general catalog.

Often is faster and less cost to replace with a general purpose motor, usually their specifications are more for "cheapening" the manufacturer cost and what you replace it with will be better then the original anyway. Drip proof is not as bad on three phase fan motors but is horrible design on single phase motors as dirt, debris, insects often get inside and inhibit the operation of the starting winding governor, all so the OEM could save a few bucks on purchasing the motor:roll:
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Many of these fans have OEM motors on them. They may be made by Baldor or some other popular name, but are specifically made to specifications made by the fan manufacturer, and are not in Baldor (or other's) general catalog.

Often is faster and less cost to replace with a general purpose motor, usually their specifications are more for "cheapening" the manufacturer cost and what you replace it with will be better then the original anyway. Drip proof is not as bad on three phase fan motors but is horrible design on single phase motors as dirt, debris, insects often get inside and inhibit the operation of the starting winding governor, all so the OEM could save a few bucks on purchasing the motor:roll:
One mud dauber nest = $800 motor + labor
 

347sparky

Member
Location
Iowa
Update

Update

Got the new motor installed. Bumped for rotation then let it run. New motor is drawing 102 amps on each phase. I opened up the box on the motor and took amp readings there, the same thing. Took voltage readings at the motor and getting 240v phase to phase and 120, 120, 210 to ground. I took the cover off of the fan that has an air horn built into it. Restart fan and now it's drawing 72 amps, closer to the 68 FLA on the nameplate. I talked to a motor guru at the motor shop and he told me to totally block off the intake of the motor and see what the amp draw is. He said if it's still high there is and electric problem, if it's below the nameplate FLA it's a mechanical or air flow problem. I did the test and the motor drew 52 amps.

I told the coop about the problem but they can't do anything until the bin is empty. The ducting has to be totally blocked off. Of course no one checked inside the bin before filling it.
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
... I talked to a motor guru at the motor shop and he told me to totally block off the intake of the motor and see what the amp draw is. He said if it's still high there is and electric problem, if it's below the nameplate FLA it's a mechanical or air flow problem. I did the test and the motor drew 52 amps.

I told the coop about the problem but they can't do anything until the bin is empty. The ducting has to be totally blocked off. Of course no one checked inside the bin before filling it.
You are going down the right road, but I think you are going in reverse.

When you block the output of an impeller pump or a bladed or squirrel cage fan the air resistance goes down and the mechanical load on the motor decreases.

When the motor guru said it was an air flow problem, he did not bother to tell you that it means too much air flow.
Either the motor speed, the fan diameter or the blade pitch are wrong for the horsepower of the installed motor.
Either it has been that way forever or the fan was changed or the motor was changed for one of the wrong speed or a deliberate restriction on the air flow was inadvertently removed.

The problem is NOT that the duct is blocked off it is too wide open and the amount of air being moved is causing too high a mechanical load on the motor, above its rated horsepower, and that is causing current higher than the normal FLA.
Until you can get inside the bin, you can run the motor safely by restricting the input to the fan instead of the output. Just block more and more until you get to the motor FLA. That will give them the best sustainable ventilation in the grain bin.

Next you have have an engineer or other expert calculate the motor HP needed based on the specifications of the fan blade and the speed of the motor.
Then you will be able to see whether the air flow can be reduced or whether you have to put in a larger motor.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
The fan and motor came as an engineered unit when purchased and are matched with the bin size, grain, etc.. Something could be wrong with bin but ...(removed this portion of comment after rereading your post for new motor data.)

Go back to the mfg and ensure someone in the past has not changed blower size or rpm of the motor. Give them all the pertaining information on bin size, grain stored.
 
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