Motor starter opening every afternoon around the same time

[hillbilly1]

Maybe an over temp switch (fire stat) in the control circuit somewhere? Usually those have to be manually reset. Or maybe a pressure differential switch to shutdown on a clogged filter? Probably something they are not telling you.

 

[zbang]

f the overload is tripping, I would look to see if the dust collector is getting full & plugged up, which might increase the motor load.

As I understand things and assuming a centrifugal blower, it'll actually lower the motor current as it's not able to move as much air.

 

[Krusscher]

As I understand things and assuming a centrifugal blower, it'll actually lower the motor current as it's not able to move as much air.

This is true, when the fan stops moving air it just free spins which is opposite of what you would think.

 

[drcampbell]

... An employee was pushing the Test button on an overload relay in a crane starter when he wanted a break. It would take the crane maintenance people 10+ minutes to get there, a half hour to troubleshoot making sure the motor was OK, then they would reset and test that everything was fine until the next day. In total it was usually 45-60 minutes every day. ...

I hope they implemented a creative administrative solution, such as retroactively punching him out for the day and billing him for the maintenance people's time each time he did that.

 

[ptonsparky]

...punching him out for the day.,.


O, you meant on the time clock. For a second there...

 

[JimInPB]

As I understand things and assuming a centrifugal blower, it'll actually lower the motor current as it's not able to move as much air.

As I understand it, increased back pressure physically loads the motor & increases slip, which increases current. The next time I'm around that type of equipment, I'll hang a meter on it & see what actually happens.

 

[Krusscher]

As I understand it, increased back pressure physically loads the motor & increases slip, which increases current. The next time I'm around that type of equipment, I'll hang a meter on it & see what actually happens.

AT my last job they had 200 hp blowers for their baghouses. They put a adjustable damper after the fan so they could squeeze the output down and lower the current draw on the motor.

 

[zbang]

As I understand it, increased back pressure physically loads the motor & increases slip,

Doesn't work like that. When the blower isn't moving air, it has less load so less power consumed.

 

[drcampbell]

As I understand it, increased back pressure physically loads the motor & increases slip, which increases current. The next time I'm around that type of equipment, I'll hang a meter on it & see what actually happens.

Actually, the opposite happens.

The mechanical power needed to drive a fan is a function of both the mass flowrate and the pressure differential, but the mass flowrate is the more significant of the two. Increasing the pressure differential a little usually results in decreasing the mass flowrate a lot, and reducing the total power requirement.

But don't hesitate to give it a try and report your results.

This is much more evident if demonstrated on a household vacuum cleaner with a brushed universal motor, whose speed changes a lot more with a load change. Blocking the hose causes the motor speed to increase significantly and audibly.

 

[JimInPB]

Well, the consensus seems to be firmly against my expectation. That will make it all the more interesting for me to do a real life test. It seems likely that I will be filling a hole in my knowledge base.

 

[ptonsparky]

Well, the consensus seems to be firmly against my expectation. That will make it all the more interesting for me to do a real life test. It seems likely that I will be filling a hole in my knowledge base.

Your typical home furnace has a centrifugal fan. Turn the fan to On vs Auto. Then open and close the blower access door while watching your amp meter.

The blower on my zoned HT pump is on a variable speed of some sort. IDK if it's AC or DC. That may screw with your amp readings if it uses pressure feedback.

Axial flow fans work as you think.

 

[JimInPB]

Your typical home furnace has a centrifugal fan. Turn the fan to On vs Auto. Then open and close the blower access door while watching your amp meter.

The blower on my zoned HT pump is on a variable speed of some sort. IDK if it's AC or DC. That may screw with your amp readings if it uses pressure feedback.

Axial flow fans work as you think.

Thank you. That clears up my misunderstanding.

 

[Jraef]

...punching him out for the day.,.


O, you meant on the time clock. For a second there...

Yeah, my kind went there too…

I don’t know what happened to him. I was not a Boeing employee, we were on contract.

 

[kwired]

Actually, the opposite happens.

The mechanical power needed to drive a fan is a function of both the mass flowrate and the pressure differential, but the mass flowrate is the more significant of the two. Increasing the pressure differential a little usually results in decreasing the mass flowrate a lot, and reducing the total power requirement.

But don't hesitate to give it a try and report your results.

This is much more evident if demonstrated on a household vacuum cleaner with a brushed universal motor, whose speed changes a lot more with a load change. Blocking the hose causes the motor speed to increase significantly and audibly.

Which some may confuse as it is working harder if it is louder, not the case. Less air flow means it is easier for it to turn faster because the blower is less loaded.

To OP: centrifugal pumps are the same way. Positive displacement pumps however will be loaded by restriction particularly on the higher pressure side.

 

[GeorgeB]

To OP: centrifugal pumps are the same way. Positive displacement pumps however will be loaded by restriction particularly on the higher pressure side.

Think long and hard before restricting the inlet of a positive displacement pump. Cavitation will commonly occur unless the inlet is pressurized. Cavitation usually causes damage.

 

[drcampbell]

Think long and hard before restricting the inlet of a positive displacement pump. Cavitation will commonly occur unless the inlet is pressurized. Cavitation usually causes damage.

Or any other pump, for the same reason. That's why the NPSH (net-positive suction head) specification exists and why it's important.

 

[kwired]

Or any other pump, for the same reason. That's why the NPSH (net-positive suction head) specification exists and why it's important.

probably good advice, the work load is still decreased with centrifugal pumps regardless of how/where you restrict flow.

 

[mtnelect]

Around 2PM every afternoon, customer’s dust collector motor starter opens. I would attribute that to how hot it is in this warehouse (around 100 F degrees) and exposing a defective component. I’m not really a motor guy, but would assume its a bad solenoid as i replaced the coil and it didn’t help. The solenoid is boiling hot in the afternoons.

Any tips on other items to check? Could the heat be causing issues with the start switch?

I don't know if this would apply to your problem. But we have a Maintenance Contract on a produce warehouse. The conveyer selection tables have a sheet metal rectangular air return hood over the tables. On the roof is a 208-volt 1 horsepower 3 Phase axial fan. Recently, the return air flow became low. We found that a fire damper closed, because of a defective link, and restricted the return air flow.

 

[kwired]

I don't know if this would apply to your problem. But we have a Maintenance Contract on a produce warehouse. The conveyer selection tables have a sheet metal rectangular air return hood over the tables. On the roof is a 208-volt 1 horsepower 3 Phase axial fan. Recently, the return air flow became low. We found that a fire damper closed, because of a defective link, and restricted the return air flow.

That likely would increase load on the axial type fan. You are also likely to notice performance issues with whatever it is intended to do as well.

 

[mtnelect]

That likely would increase load on the axial type fan. You are also likely to notice performance issues with whatever it is intended to do as well.

This produce warehouse receives products (Limes, Coconuts, chilis) etc. Then they unpack the receivables and select the best product to be repackaged to the supermarkets. Also, I found interesting, they score the coconuts, so it makes it easier to open.