Motor Load vs HP vs Current
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From: Jamie on 24 Jul 2010 15:52 Bobby Joe wrote: > 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. > > Well, if its a Dayton motor and it's lasted that long, your lucky and it most likely wasn't made in China or Mexico.. Its funny because the one's we have at work have their Caps made in Mexico and the motors in China.. And personally, motors running over loaded like that would make me look at the engineers that designed the system. Makes for a nice camp fire when it decides to sit there and smoke for a while.
From: Paul Keinanen on 24 Jul 2010 16:11 On Sat, 24 Jul 2010 11:16:21 -0700 (PDT), Bobby Joe <bobbyjoe23928(a)gmail.com> wrote: >On Jul 24, 12:15�pm, .p.jm.(a)see_my_sig_for_address.com wrote: >> On Sat, 24 Jul 2010 09:18:14 -0700 (PDT), Bobby Joe >> >> >> >> <bobbyjoe23...(a)gmail.com> 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] So apparently this is 370 W 6 pole asynchronous motor (synchronous speed 1200 RPM at 60 Hz). Assuming 120 V at motor and 12 A consumption, the apparent power is 1440 VA. The slip is also huge, since the motor is running at 60 % of synchronous speed. The losses will most likely be large, since it is quite far from nominal specifications. >> >The problem I was having is any time the AC kicked in I would lose >> >connection to the net and the power would sag. Replacing the motor with a 8 pole design (no load speed about 800 RPM) would at least allow the motor to run closer to the nominal power and hence reducing the losses. >If that pdf is right then > >rpm2 = (hp2/hp1)^(1/3)*rpm1 In wind turbines, the power of the wind is proportional to the third power of wind speed, so assuming the air speed in the duct is proportional to the RPM (no blade stall etc.), that formula makes sense. >which will increase my case about 200 extra rpm to about 950. This is >closer to no load. If the fan rotates at 700 RPM, it will require the same mechanical axial power regardless what the motor nominal power is. What the motor real power depends on the efficiency vs. load curve and in this case, it is not even possible to calculate the real power taken by the motor, since there was a voltage sag and no voltage measurement was taken _at_ the motor, neither was the angle between voltage and current measured. >If I new what the no load current was[or current to >rpm graph] then I could determine if this would be a significant >savings. It would definitely push out more air which would be nice but >I just have to make sure it will take less current. Anyway, if you want to increase the blower speed from 700 RPM to say 1075 RPM, the axial power requirement would be (1075/700)^3 or 3.6 times the current motor output mechanical power. Be prepared that the increase in input power requirement would be similar. If the current motor is driving a simple fan, changing the fan with smaller blades or using blades with lower angle of attack to match the current motor better. Alternatively, use a slower 8 pole motor with the current blower, so that it will reach nearly the nominal speed, thus operating with a reasonable slip and not heating up as badly. If you want to increase the RPM with the current blower, be prepared to use a significantly larger motor and be prepared to deliver the current it wants to consume.
From: Stormin Mormon on 24 Jul 2010 17:47 Since the motor is over amping. Another poster suggested load may be high or low. I'd also want to flush out the berrings, and relubricate. Might be full of dried out oil or grease. -- Christopher A. Young Learn more about Jesus www.lds.org ..
From: Mark on 24 Jul 2010 20:36 On Jul 24, 5:47 pm, "Stormin Mormon" <cayoung61**spambloc...(a)hotmail.com> wrote: > Since the motor is over amping. Another poster suggested load may be > high or low. I'd also want to flush out the berrings, and relubricate. > Might be full of dried out oil or grease. > > -- > Christopher A. Young > Learn more about Jesus > www.lds.org > . or the Voltage at the motor is too LOW, yes LOW.. Mark
From: The Daring Dufas on 24 Jul 2010 23:26
On 7/24/2010 11:18 AM, 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 > It sounds like you have an electrical supply problem and you're chasing butterflies. You mentioned losing connection to the net, I would assume you're referring to your Internet connection and the power to the whole house is sagging. If that's the case, your problem may be in your main electrical panel. It's not unusual for loose connections in main electrical panels to burn up in hot weather when heavy loads from AC systems stress them to the braking point. I would start at the main electrical panel first and inspect ALL of the connections and circuit breakers related to your AC unit. I've traced many AC problems back to the electrical service. TDD |