Strange Voltage Drop, over amperage on motor

Status
Not open for further replies.

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Is the current the same at the motor as it is at the overload? If so, the wiring between them is probably not the issue.

If the current is the same at both ends of the wires, my guess is that your load needs more HP than the motor can produce and that is why it is tripping on over current.

A bearing going bad can cause additional friction that requires additional HP to overcome. could be on the motor or the fan itself.

Sometimes you can get mechanical binding of other types as well. I once ran into a situation where a guy had run a screw into the side of something a motor was trying to turn, requiring additional HP.

Sometimes people will take apart a pulley system and put it back together wrong so that it either has the wrong ratio or is binding in some way.

A motor that is misaligned with the load can take additional HP as well.
 
Last edited:
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
vane_axial_cutout.gif
This, or similar, is what he is dealing with.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
I was able to mimic the same voltage drop on the other fan, but not the same amperage conditions. But only once.
Baldor UCLE1015
I don't think blocking the air flow is going to solve the problem.

Both fans are supplied by the same feeder, no? Why is only one of them acting up?

I still think if you want a temp feed you wouldn't need anything bigger than #2CU or 1/0AL. Heck, even some #2AL would be fine just to see if you have a problem underground.
 

gk351

Senior Member
Location
IL
I don't think blocking the air flow is going to solve the problem.

Both fans are supplied by the same feeder, no? Why is only one of them acting up?

I still think if you want a temp feed you wouldn't need anything bigger than #2CU or 1/0AL. Heck, even some #2AL would be fine just to see if you have a problem underground.

I dont believe the other motor is experiencing the same amperage problems. I have decided to get some 1/0-1/0-1/0 and lay it on the ground and see if this alliviates the problem! Hopefully it does. Im running out of options, plus Id like to recycle that 4/0 CU after I pull in 250 ALU on the redo! (dont think bad of me lol)
 

gk351

Senior Member
Location
IL
Yes, you are going to see drops on starting. The motor has to provide enough torque to start, plus the torque to get fan moving. Without dampers on the inlet, it will have the highest torque requirement. If you had a speed versus torque curve to look at it would help explain.

Your voltage drop on starting is only about 5%, that's really not bad; or are you say you have a continuous voltage drop of 5% when its running? If that's on starting, how long does it take to recover to near nominal?

Keep in mind your motor is most likely rated for 230V not 240V, so it should be running just fine, unless it is undersized for the fan.

The voltage drop isnt on startup, its continuous until you shut the fan off. Thats running the 1 troublesome fan, add the other fan but I dont lose but 1 more volt. The Voltage drop is weird to me because the meter is fed with 250kcmil CU goes through a SQD feed through panel to 4/0 CU conductors 250' to the bin. I shouldnt see these kinds of drops.
 

kwired

Electron manager
Location
NE Nebraska
Just tested a 1ph 230v. Amps increase as flow is blocked. 7.2 to 8 amps. Not totally closed off but restricted at outlet by cardboard.
I may have to check that out myself. I know a centrifugal fan will draw less if you restrict the airflow, and does not matter if at the inlet or the outlet, the fact is that the volume of air moved is what puts load on the motor, I kind of always assumed those axial fans were similar in that the volume loads the motor, but I could be wrong.

Ok I'm going to try to respond to all comments. I have tried the blocking the inlet trick. Yes amperage goes down to around 65-67 amps. This is a vain axial fan direct drive, stock fan blade. It has a sister fan on a another bin right beside it. Before POCO changed xfmr I had voltage at 244. When u start this fan, I've saw drops as low as 231-233. I haven't checked the volts since the change out due to weather. I was able to mimic the same voltage drop on the other fan, but not the same amperage conditions. But only once. I'm on the verge of buying a megger or fluke 1505/1520. I'm still not sure using a megger to test is gonna get me anywhere. I guess I could go buy 300' of 40/40/20 URD and quickly be able to determine if I do have a bad UG cable.

Fan specs, GSI group 28" vane axial fan, 1 ph
Baldor UCLE1015
Trust me, I can just about install the Baldor UCL1015 blindfolded, those are all over the place in these parts.

My biggest problem with them is the centrifugal governor likes to hang up and usually in the run position keeping the start capacitor from being put in the circuit at startup. Usually the thing will try to accelerate with just the run capacitor - and this may take out the run capacitor if tried too many times - which could be what you have going on, you said you are losing run capacitors. But most of the time it never gets to full speed before kicking out motor overload device, The fans they put these motors on have such a heavy propeller and because it is a high speed motor and is pushing 12-15 hp out of what is otherwise about a 10 hp winding it takes time to accelerate even with a stout supply and reasonable voltage drop, but I have seen many that run for years in horrible voltage drop situations, the biggest hurdle is starting them, once up to speed the voltage drop usually improves. But at same time that voltage drop is not a whole lot different than using reduced voltage starting as far as the motor is concerned.

The biggest problem I have with using an open air over motor in this application is that it allows enough moisture and dirt to enter the motor and the centrifugal governor hangs up because of rust on the close fitting shaft. I don't know how many times I have been called and fixed that problem, and the next harvest season I may be called back to do it again.

A megger is a handy tool, but generally with these motors if there is a ground fault, the motor doesn't work, and the megger just helps you say it has a ground fault. If you have a high resistance fault, your motor needs replaced or rewound anyway, and the high resistance fault generally wouldn't last for long before you have a fairly obvious ground fault. I have never run into a crop aeration fan motor that was on its way out and causing trouble, they either are toast or need a capacitor or governor switch type of trouble, or have trouble with the control or the supply, anything else electrical within the motor is always replace/rewind time, sometimes they need bearings and nothing else.

Is the current the same at the motor as it is at the overload? If so, the wiring between them is probably not the issue.

If the current is the same at both ends of the wires, my guess is that your load needs more HP than the motor can produce and that is why it is tripping on over current.

A bearing going bad can cause additional friction that requires additional HP to overcome. could be on the motor or the fan itself.

Sometimes you can get mechanical binding of other types as well. I once ran into a situation where a guy had run a screw into the side of something a motor was trying to turn, requiring additional HP.

Sometimes people will take apart a pulley system and put it back together wrong so that it either has the wrong ratio or is binding in some way.

A motor that is misaligned with the load can take additional HP as well.
Like I said I can just about replace that motor blindfolded. There is no pulleys or gearboxes, it is a direct drive fan with the motor located in the airstream so it is also an air over cooled design motor, he said he did send the motor in to a shop, hopefully they would have replaced a bearing if one was bad, and any binding because of misalignment usually means no rotation at all and locked rotor current. Very simple machine, motor with propeller mounted directly on shaft and placed inside a tubular housing that is just slightly larger in diameter than the propeller, usually a 3450 RPM motor.

Both fans are supplied by the same feeder, no? Why is only one of them acting up?

We don't know that they both have the same load (amount of air being moved) even if they are the same identical machines.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
We don't know that they both have the same load (amount of air being moved) even if they are the same identical machines.
But we do know that the voltage is in operable range, the problem motor has been checked out and found ok, and even it it wasn't actually ok it has been replaced with a new motor and the new motor still draws too many amps. To me that rules out the motor, at least for now.

We all can agree that moving less air equals less work, but my opinion is when you get to the point of drawing fifteen or twenty amps more than FLA and killing caps you have a bigger problem than just reducing the air flow can solve.

The fact that there are two fans that seem to be coming off the same feeder makes me wonder why only one is having a problem. It's either the feed or the branch circuit. The other fan is the one armed man at this point.
 

kwired

Electron manager
Location
NE Nebraska
But we do know that the voltage is in operable range, the problem motor has been checked out and found ok, and even it it wasn't actually ok it has been replaced with a new motor and the new motor still draws too many amps. To me that rules out the motor, at least for now.

We all can agree that moving less air equals less work, but my opinion is when you get to the point of drawing fifteen or twenty amps more than FLA and killing caps you have a bigger problem than just reducing the air flow can solve.

The fact that there are two fans that seem to be coming off the same feeder makes me wonder why only one is having a problem. It's either the feed or the branch circuit. The other fan is the one armed man at this point.
Most all of that information is what prompted me to check out how much load is indeed being put on the motor. His underground conductor is not bad. With the kind of load he has that would become much more obvious if it were bad weak connections would not handle the starting current and would burn themselves completely open. Even if he had a weak connection adding voltage drop, his measured voltage is not all that low. Yes many would like to see it higher, but I have seen much worse that runs for long time with no trouble on the same kind of equipment. There are many of that size and type around here that are only supplied by a 100 amp service, (only one bin supplied and that fan is the heaviest load, plus when the fan is running hardly anything else ever is running) with the POCO only supplying it with a 25 KVA transformer, maybe just as much length of conductor as he has but it is only #2 overhead aluminum for the greater portion of the distance. All those in that situation have horrible voltage drop when starting, usually voltage recovers to a reasonable level once the motor is up to speed though, but like I said before it is kind of no different than using reduced voltage starting methods as far as the motor is concerned.
 

gk351

Senior Member
Location
IL
Actually the POCO xfmr has been upgraded to 50 kva from 37.5. The service pole where the meter is I about 10' from the xfmr pole. I have parallel 1/0 triplex feeding this meter pole. Other than that, this service feeds the bin under ground through 4:0 CU.

The bin and electrical was installed in 2006 and has always worked fine in previous years. This bin stores corn only. Te moisture content was about 18% when it was put in the bin.

The only thing I can think if is, either I have a bad underground wire, or I have about 4' plug in the bin. Farmer was supposed to core it, but has yet to do so. I'm going to get done 1/0 triplex today and see if this changes anything.


Sent from my iPhone using Tapatalk
 

gk351

Senior Member
Location
IL
Went back today. I ran 1/0 UG Triplex on the ground, and no changes. Amperage is around 74 amps. Kinda jumpy about 2-3 amps. Voltage is 244, drops to 217 on starting, and steadies at 239 while running. I did find some bolt on lug that were slightly loose, but no changes. I had the wire reel I used to bring the triplex on, so I put that on the front of the fan, effectively blocking 90-95 percent of it. This dropped my amperage to 62.5, and steadied it. But you shouldn't have to do this, the fan should have unrestricted flow. I'm going to call GSI group and see if I can get some suggestions. The bin is 36' diameter, 8.5 rings tall.


Sent from my iPhone using Tapatalk
 

kwired

Electron manager
Location
NE Nebraska
Went back today. I ran 1/0 UG Triplex on the ground, and no changes. Amperage is around 74 amps. Kinda jumpy about 2-3 amps. Voltage is 244, drops to 217 on starting, and steadies at 239 while running. I did find some bolt on lug that were slightly loose, but no changes. I had the wire reel I used to bring the triplex on, so I put that on the front of the fan, effectively blocking 90-95 percent of it. This dropped my amperage to 62.5, and steadied it. But you shouldn't have to do this, the fan should have unrestricted flow. I'm going to call GSI group and see if I can get some suggestions. The bin is 36' diameter, 8.5 rings tall.


Sent from my iPhone using Tapatalk

And you have had same trouble with more than one motor correct? If you have not had different motors you may have one that is not going to last much longer, maybe a short from turn to turn or something not so obvious or easy to detect. I think bearing problems has been brought up already, but I don't know that you confirmed the bearings are ok.

I don't have a problem with your voltages, and have seen much worse that run with little troubles.
 

gk351

Senior Member
Location
IL
I've had only this trouble with one motor. Yet today I checked amperes on motor #2, and it was @70a. First time I've seen that.

The first motor I've changed caps, and after no changes, I took to a motor shop. They changed a rear bearing, and that was it. Said motor checked ok, but said he wouldn't be able to know run winding conditions. Re-installed motor, same amperage72-75. Ok, BOUGHT BRAND NEW MOTOR, Same problems, no changes. That's when I started digging a little deeper. Customer is going to core bin tomorrow, I'm thinking it's crusted midway through bin. He'll find out quickly if it is, and I'm going to call GSI for some answers


Sent from my iPhone using Tapatalk
 

kwired

Electron manager
Location
NE Nebraska
I've had only this trouble with one motor. Yet today I checked amperes on motor #2, and it was @70a. First time I've seen that.

The first motor I've changed caps, and after no changes, I took to a motor shop. They changed a rear bearing, and that was it. Said motor checked ok, but said he wouldn't be able to know run winding conditions. Re-installed motor, same amperage72-75. Ok, BOUGHT BRAND NEW MOTOR, Same problems, no changes. That's when I started digging a little deeper. Customer is going to core bin tomorrow, I'm thinking it's crusted midway through bin. He'll find out quickly if it is, and I'm going to call GSI for some answers


Sent from my iPhone using Tapatalk

You could pull fan away from the transition and see how the load responds with no restriction.
 

gk351

Senior Member
Location
IL
You could pull fan away from the transition and see how the load responds with no restriction.

Interesting approach! I might consider that, but it's too cold for me to not call GSI and wasting more time. Trying to give the customer the benefit of the doubt here. But ill laugh if the bin is plugged, I told him I thought it might be back before Christmas, and I've been dealing with this since after thanksgiving. Frustrated!


Sent from my iPhone using Tapatalk
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
I've had only this trouble with one motor. Yet today I checked amperes on motor #2, and it was @70a. First time I've seen that.

The first motor I've changed caps, and after no changes, I took to a motor shop. They changed a rear bearing, and that was it. Said motor checked ok, but said he wouldn't be able to know run winding conditions.
What kind of motor shop only changes one bearing?
Re-installed motor, same amperage72-75. Ok, BOUGHT BRAND NEW MOTOR, Same problems, no changes. That's when I started digging a little deeper. Customer is going to core bin tomorrow, I'm thinking it's crusted midway through bin. He'll find out quickly if it is, and I'm going to call GSI for some answers.
If you have zero air flow over the motor that would be a problem.
 
Status
Not open for further replies.
Top