ptonsparky
Tom
- Occupation
- EC - retired
Two weeks ago: 30 hp motor failed. 10-15 yrs old. Replaced. My help informed customer centrifugal fan was vibrating badly. Yea, they knew.
6 days ago: Fan came apart.
2 days ago: Fan was replaced by customer.
6 hrs later: 30 hp motor failed. Smoke was let out.
I told customer to not touch a thing so I could see exactly what went wrong. How can my help screw up a simple change out? Motor was wired correctly. Branch circuit to motor megged out at 11G. 50 to 60 yr old starter was rated @ 25hp. Nice. One load lug was discolored from overheating at sometime but not lately. Conductors all good shape. Overload contact was still closed (heaters had obviously been hot more than once) so I removed a solder pot to cause it to open. Nope. Removed all three, still closed. Dissected entire overload block and found it had been reset so many times the internal parts had broken. I mumbled something about my help not checking the amp draw on the new motor and was informed by customer that he had indeed checked. What the? Rebuilt overload block with scavenged parts from smaller unit. Put everything back together and started up new motor. 64 amps. Nameplate FLA 32. Took belts off to fan, about 12 amps. Told customer we had to slow the fan up because we are moving to much air. He says "Yea this fan moves a lot more air!" ???? Asked what the CFM was for the new fan and if they had any paper work for it. Blank look. Then the details come together and my faith in my help is restored. The customer had a local machine shop duplicate the old fan, only they didn?t quite make it the same. Exposed blade is about 3" more than the old.
This customer has made for one fantastic year.
I can figure the CFM for a fan if I know what it should be at a certain rpm. In this case I am not so worried about the CFM as the motor amps. I know that we were almost double in amps, what size sheave should I use to get it down to FLA? We dropped this motor sheave from 9.75 to 6 and are now @ 22 amps. 7" would be closer but just wondering how to get closer than a guess. Sheaves are 60 miles away.
6 days ago: Fan came apart.
2 days ago: Fan was replaced by customer.
6 hrs later: 30 hp motor failed. Smoke was let out.
I told customer to not touch a thing so I could see exactly what went wrong. How can my help screw up a simple change out? Motor was wired correctly. Branch circuit to motor megged out at 11G. 50 to 60 yr old starter was rated @ 25hp. Nice. One load lug was discolored from overheating at sometime but not lately. Conductors all good shape. Overload contact was still closed (heaters had obviously been hot more than once) so I removed a solder pot to cause it to open. Nope. Removed all three, still closed. Dissected entire overload block and found it had been reset so many times the internal parts had broken. I mumbled something about my help not checking the amp draw on the new motor and was informed by customer that he had indeed checked. What the? Rebuilt overload block with scavenged parts from smaller unit. Put everything back together and started up new motor. 64 amps. Nameplate FLA 32. Took belts off to fan, about 12 amps. Told customer we had to slow the fan up because we are moving to much air. He says "Yea this fan moves a lot more air!" ???? Asked what the CFM was for the new fan and if they had any paper work for it. Blank look. Then the details come together and my faith in my help is restored. The customer had a local machine shop duplicate the old fan, only they didn?t quite make it the same. Exposed blade is about 3" more than the old.
This customer has made for one fantastic year.
I can figure the CFM for a fan if I know what it should be at a certain rpm. In this case I am not so worried about the CFM as the motor amps. I know that we were almost double in amps, what size sheave should I use to get it down to FLA? We dropped this motor sheave from 9.75 to 6 and are now @ 22 amps. 7" would be closer but just wondering how to get closer than a guess. Sheaves are 60 miles away.
