Motor Load vs HP vs Current
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From: Bobby Joe on 24 Jul 2010 12:18 If I have a motor that is being overloaded ~2x it's rated will doubling the HP improve this? I have a 1/2HP Direct drive 1P, 120V, 1075RPM blower motor that is drawing 12A while it is rated at 6.5A Full load, 9A max and only spinning at about 700RPM. [No load it draws 3A] The problem I was having is any time the AC kicked in I would lose connection to the net and the power would sag. I went to the attic and measured the AC and found it was drawing 2x the rated current at full load. I thought the motor was bad so I got an identical replacement but almost exactly the same measured specs and same problem. I figured I could replace it with a 3/4 or 1HP motor and get better results but I'm not sure how much. I want to save power and possibly increase the rpm's, The main thing I would like to know is how HP, current, and load are related. If I double the HP I should effectively be doubling the max load and probably the current at max load? Basically, if I have an x HP motor using a certain load and I move to y HP motor then what can I expect the RPM's and current to be? [simple estimates are ok. I understand that it depends on a lot of factors but there should be general principles involved] As I said, I would like to be able to determine if a 1HP is effectively going to allow me to increase the RPM's and reduce the current[since the motor shouldn't be overloaded]. Motor used, http://www.grainger.com/Grainger/AO-SMITH-Direct-Drive-Blower-Motor-4KA36?Pid=search Possible replacements, http://www.grainger.com/Grainger/DAYTON-Direct-Drive-Blower-Motor-4M183?Pid=search http://www.grainger.com/Grainger/DAYTON-Direct-Drive-Blower-Motor-3LU91?Pid=search BTW, what is the difference between a Y and YZ frame? Thanks for the help, Bob
From: Jamie on 24 Jul 2010 13:03 Bobby Joe wrote: > If I have a motor that is being overloaded ~2x it's rated will > doubling the HP improve this? > > I have a 1/2HP Direct drive 1P, 120V, 1075RPM blower motor that is > drawing 12A while it is rated at 6.5A Full load, 9A max and only > spinning at about 700RPM. [No load it draws 3A] > > The problem I was having is any time the AC kicked in I would lose > connection to the net and the power would sag. I went to the attic and > measured the AC and found it was drawing 2x the rated current at full > load. I thought the motor was bad so I got an identical replacement > but almost exactly the same measured specs and same problem. > > I figured I could replace it with a 3/4 or 1HP motor and get better > results but I'm not sure how much. I want to save power and possibly > increase the rpm's, > > The main thing I would like to know is how HP, current, and load are > related. If I double the HP I should effectively be doubling the max > load and probably the current at max load? Basically, if I have an x > HP motor using a certain load and I move to y HP motor then what can I > expect the RPM's and current to be? [simple estimates are ok. I > understand that it depends on a lot of factors but there should be > general principles involved] > > As I said, I would like to be able to determine if a 1HP is > effectively going to allow me to increase the RPM's and reduce the > current[since the motor shouldn't be overloaded]. > > > Motor used, > > http://www.grainger.com/Grainger/AO-SMITH-Direct-Drive-Blower-Motor-4KA36?Pid=search > > Possible replacements, > http://www.grainger.com/Grainger/DAYTON-Direct-Drive-Blower-Motor-4M183?Pid=search > http://www.grainger.com/Grainger/DAYTON-Direct-Drive-Blower-Motor-3LU91?Pid=search > > BTW, what is the difference between a Y and YZ frame? > > Thanks for the help, > Bob > Did you replace or test the Capacitor ? Those motors like cooking the caps that come with them.. Made in Mexico! also, the bearings are crappy! Make sure you are not voltage sagging at the leads. Also, have you pull the motor out in the open with blades on and tested the load? You could have a restricted vent some where. That does not sound normal..
From: Tim Wescott on 24 Jul 2010 13:28 On 07/24/2010 09:18 AM, Bobby Joe wrote: > If I have a motor that is being overloaded ~2x it's rated will > doubling the HP improve this? Not necessarily, particularly since you don't know what the torque is at the shaft of the motor, just that the motor is running slowly. > I have a 1/2HP Direct drive 1P, 120V, 1075RPM blower motor that is > drawing 12A while it is rated at 6.5A Full load, 9A max and only > spinning at about 700RPM. [No load it draws 3A] (a), there's no guarantee that doubling the horsepower of the motor will spin the blower at the right speed. (b), if the blower and motor are in good shape, is properly installed, and all the duct work is designed correctly, then you shouldn't have a problem. Fix the blower and motor, correct the installation, and fix the duct work. (b1), if your car had frozen rear brakes and always went slower than before, would you want to just put a bigger motor in it? > The problem I was having is any time the AC kicked in I would lose > connection to the net and the power would sag. I went to the attic and > measured the AC and found it was drawing 2x the rated current at full > load. I thought the motor was bad so I got an identical replacement > but almost exactly the same measured specs and same problem. > > I figured I could replace it with a 3/4 or 1HP motor and get better > results but I'm not sure how much. I want to save power and possibly > increase the rpm's, See my "car with frozen brakes" analogy. More power out means more power in -- if you actually manage to stick a motor on there that can turn the blower without making the motor unhappy, it'll still need enough current to do the job. > The main thing I would like to know is how HP, current, and load are > related. If I double the HP I should effectively be doubling the max > load and probably the current at max load? Basically, if I have an x > HP motor using a certain load and I move to y HP motor then what can I > expect the RPM's and current to be? [simple estimates are ok. I > understand that it depends on a lot of factors but there should be > general principles involved] But it isn't all that simple... _If_ the motor isn't being bogged down, and if turning the shaft at rated speed took 1/2 HP, then your 1/2 HP motor could turn the shaft at it's rated speed. Going to a 2 HP motor with the same rated speed would only consume slightly more current, because motors are pretty efficient, and the underlying physics makes sure that they don't pull more current than they need to generate the torque they're delivering. If it takes 2HP to turn that shaft at rated speed, then the 1/2HP motor simply won't cut it. The 2HP motor will, and should take roughly four times as much current (at the same voltage) to do the job as the 1/2HP motor would to deliver it's 1/2HP. Within limits, a motor's power in will be equal to the motor's power out, plus enough power to make up the motor's losses. If the motor shaft is loaded enough that it starts turning at much less than rated speed then the power requirements go up, both for the shaft (obviously) and the motor losses. Even if efficiency doesn't go down, the motor gets hot -- and at some point, the efficiency starts to go down. > As I said, I would like to be able to determine if a 1HP is > effectively going to allow me to increase the RPM's and reduce the > current[since the motor shouldn't be overloaded]. > > > Motor used, > > http://www.grainger.com/Grainger/AO-SMITH-Direct-Drive-Blower-Motor-4KA36?Pid=search > > Possible replacements, > http://www.grainger.com/Grainger/DAYTON-Direct-Drive-Blower-Motor-4M183?Pid=search > http://www.grainger.com/Grainger/DAYTON-Direct-Drive-Blower-Motor-3LU91?Pid=search > > BTW, what is the difference between a Y and YZ frame? Fix your blower and ductwork. You'll be happier. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
From: Tim Wescott on 24 Jul 2010 13:29 On 07/24/2010 10:03 AM, Jamie wrote: > Bobby Joe wrote: > >> If I have a motor that is being overloaded ~2x it's rated will >> doubling the HP improve this? >> >> I have a 1/2HP Direct drive 1P, 120V, 1075RPM blower motor that is >> drawing 12A while it is rated at 6.5A Full load, 9A max and only >> spinning at about 700RPM. [No load it draws 3A] >> >> The problem I was having is any time the AC kicked in I would lose >> connection to the net and the power would sag. I went to the attic and >> measured the AC and found it was drawing 2x the rated current at full >> load. I thought the motor was bad so I got an identical replacement >> but almost exactly the same measured specs and same problem. >> >> I figured I could replace it with a 3/4 or 1HP motor and get better >> results but I'm not sure how much. I want to save power and possibly >> increase the rpm's, >> >> The main thing I would like to know is how HP, current, and load are >> related. If I double the HP I should effectively be doubling the max >> load and probably the current at max load? Basically, if I have an x >> HP motor using a certain load and I move to y HP motor then what can I >> expect the RPM's and current to be? [simple estimates are ok. I >> understand that it depends on a lot of factors but there should be >> general principles involved] >> >> As I said, I would like to be able to determine if a 1HP is >> effectively going to allow me to increase the RPM's and reduce the >> current[since the motor shouldn't be overloaded]. >> >> >> Motor used, >> >> http://www.grainger.com/Grainger/AO-SMITH-Direct-Drive-Blower-Motor-4KA36?Pid=search >> >> >> Possible replacements, >> http://www.grainger.com/Grainger/DAYTON-Direct-Drive-Blower-Motor-4M183?Pid=search >> >> http://www.grainger.com/Grainger/DAYTON-Direct-Drive-Blower-Motor-3LU91?Pid=search >> >> >> BTW, what is the difference between a Y and YZ frame? >> >> Thanks for the help, >> Bob >> > Did you replace or test the Capacitor ? Those motors like cooking the > caps that come with them.. Made in Mexico! also, the bearings are > crappy! Make sure you are not voltage sagging at the leads. > > Also, have you pull the motor out in the open with blades on and tested > the load? You could have a restricted vent some where. That does not > sound normal.. Some blowers load the motor more heavily when the duct work isn't restricted -- have you ever noticed how your vacuum cleaner speeds up when the intake is clogged? I don't think this is a problem with the motor, assuming that it is the correct motor for the blower. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
From: Bobby Joe on 24 Jul 2010 14:18
On Jul 24, 12:03 pm, Jamie <jamie_ka1lpa_not_valid_after_ka1l...(a)charter.net> wrote: > Bobby Joe wrote: > > If I have a motor that is being overloaded ~2x it's rated will > > doubling the HP improve this? > > > I have a 1/2HP Direct drive 1P, 120V, 1075RPM blower motor that is > > drawing 12A while it is rated at 6.5A Full load, 9A max and only > > spinning at about 700RPM. [No load it draws 3A] > > > The problem I was having is any time the AC kicked in I would lose > > connection to the net and the power would sag. I went to the attic and > > measured the AC and found it was drawing 2x the rated current at full > > load. I thought the motor was bad so I got an identical replacement > > but almost exactly the same measured specs and same problem. > > > I figured I could replace it with a 3/4 or 1HP motor and get better > > results but I'm not sure how much. I want to save power and possibly > > increase the rpm's, > > > The main thing I would like to know is how HP, current, and load are > > related. If I double the HP I should effectively be doubling the max > > load and probably the current at max load? Basically, if I have an x > > HP motor using a certain load and I move to y HP motor then what can I > > expect the RPM's and current to be? [simple estimates are ok. I > > understand that it depends on a lot of factors but there should be > > general principles involved] > > > As I said, I would like to be able to determine if a 1HP is > > effectively going to allow me to increase the RPM's and reduce the > > current[since the motor shouldn't be overloaded]. > > > Motor used, > > >http://www.grainger.com/Grainger/AO-SMITH-Direct-Drive-Blower-Motor-4... > > > Possible replacements, > >http://www.grainger.com/Grainger/DAYTON-Direct-Drive-Blower-Motor-4M1... > >http://www.grainger.com/Grainger/DAYTON-Direct-Drive-Blower-Motor-3LU... > > > BTW, what is the difference between a Y and YZ frame? > > > Thanks for the help, > > Bob > > Did you replace or test the Capacitor ? Those motors like cooking the > caps that come with them.. Made in Mexico! also, the bearings are > crappy! Make sure you are not voltage sagging at the leads. > > Also, have you pull the motor out in the open with blades on and > tested the load? You could have a restricted vent some where. That does > not sound normal.. Of course. The capacitor was good. Everything is fine except the motor. I took the blower out of the duct so none of that is an issue. It is simply an overloaded motor. This was probably done intentionally to cut costs. From what I have read most motors are underrated anyways. This motor has been drawing 12A for about 10 years and hasn't burned up yet so it's max current is a bit conservative. The real question I had was not about what I have done but about the relationships between HP, rpm, and current. It seem Paul was the only one that got that. |