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Thread: Please explain HP

  1. #11
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    Bob are you saying that only a OEM motor may be used???

  2. #12
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    Quote Originally Posted by charlie b View Post
    I have heard that a manufacturer can market a motor that is capable of, for example, 3 HP, and using different nameplate labels sell it as either a 3 HP, or a 2HP, or a 1HP. The HP rating might be a nominal value, or a maximum value, or some other value. The only thing we can count on as being the manufacturer's message to us is that if we need a motor of XXX HP, this one would do the job.
    I was thinking just the opposite where the manufacturer of a motor states they are 1/2 hp and they aren't. I remember someone on the forum talking about shop vacs and how they do something "devious"- IMO, to state that the vac motor is 10 HP when in fact it is much less.

  3. #13
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    Quote Originally Posted by Dennis Alwon View Post
    Bob are you saying that only a OEM motor may be used???
    I believe that is exactly what Bob A. is saying.

    Kind of a bummer, I know if it was my own unit I would not wait a week

  4. #14
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    Quote Originally Posted by Dennis Alwon View Post
    Bob are you saying that only a OEM motor may be used???
    Yes, if you want to know you're using the right motor. Warranty and "listing" are probably no longer issues, but unless you're qualified to analyse the entire assembly, the OEM motor is your best bet. A non-OEM motor may be safe, but not as effective; it may be as effective, but not as safe especially if the efficency is lower or the amperage higher than the original. You had a tested assembly; with a non-OEM motor, it's a bit of a crap-shoot.
    "Bob"
    Robert B. Alexander, P.E.
    "I know that you believe you understand what you think the NEC says, but I am not sure you realize that what you read is not what it means." (Corollary to Charlie's Rule)

  5. #15
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    Well the crap shoot is done. We sweated for 2 days and didn't want to wait another week. I just found out from a friend that I probably could have gotten one in Raleigh that same day. I didn't think it was that important -- oh well it was only $75.00- seems to work fine.

    Thanks again for all the help. I am glad to know I wasn't wrong thinking these guys were off the wall with this ampacity stuff. He says he sizes it that way for 30 years. Dang.

  6. #16
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    Quote Originally Posted by charlie b View Post
    Well, I imagine the power that could be generated by a clydesdale might be higher than that of a shetland pony.
    OK you guys, stop horsing around.

  7. #17
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    Quote Originally Posted by Dennis Alwon View Post
    Well the crap shoot is done. We sweated for 2 days and didn't want to wait another week. I just found out from a friend that I probably could have gotten one in Raleigh that same day. I didn't think it was that important -- oh well it was only $75.00- seems to work fine.

    Thanks again for all the help. I am glad to know I wasn't wrong thinking these guys were off the wall with this ampacity stuff. He says he sizes it that way for 30 years. Dang.
    Dennis, I have literally swapped a few hundred blower/AHU/FCU with non OEM replacements and had very few problems. As long as frame, RPM, shaft, rotation, etc are okay-I would not sweat it-pun intended.

    Sizing a motor according to weight or amperage, as those clerks did, is just wrong and weird.
    "Electricity is really just organized lightning." George Carlin


    Derék

  8. #18
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    Quote Originally Posted by jumper View Post
    Dennis, I have literally swapped a few hundred blower/AHU/FCU with non OEM replacements and had very few problems. As long as frame, RPM, shaft, rotation, etc are okay-I would not sweat it-pun intended.

    Sizing a motor according to weight or amperage, as those clerks did, is just wrong and weird.
    Yeah, I knew the weight thing was ridiculous and just had to contain my laughter. I figured the motor wouldn't be an issue but two supply companies said the same thing about amps it had me scratching my head thinking there was something I wasn't seeing.

  9. #19
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    The residential HVAC world has been taking notes from the rest of the consumer electrical appliance world. In the consumer electrical appliance world, there is a "marketing HP" vs a real HP, and it works like this:

    Mechanical HP = Torque (lb.-ft) x RPM / 5250. That is the official definition. Forget that, it means next to nothing to marketing people except as a tool to get them to where they want to go.

    Electrical HP = 746W

    The "marketing" angle is that when you increase the slip of a motor by loading it, even OVER loading it, you are essentially increasing the HP, even if it is temporary. So let's say you have a motor that is rated for 1.5kW. Electrically, we would call that a 2HP motor (2HP = 1492W). But, if you temporarily overload that motor to the Break Down Torque (BDT) point of 220% of Full Load Torque (FLT), then the mechanical HP formula can be back-fed to say that you have 2.2X the rated torque, thus 2.2X the rated mechanical Power or 3.3kW. Now to be fair, they will also adjust for the fact that the RPM will need to drop to be able to put the motor into BDT, but then they also will say that the PF increases as well, so those issues are a wash (not really, but that's not important to them). So they take that 1.5kW motor and say in their marketing that it develops 4.4HP (3300/746). Now mind you, if the motor stays in BDT for any appreciable length of time, it will overload. It is after all really a 2HP motor. But that's not what they are after, they want you to believe that the motor is larger than it really is.

    But if you read the ELECTRICAL rating of Watts or kW, they cannot lie about that because that is what the motor will CONSUME safely at full load according to UL or whoever tested and listed the product. So in essence your guy is sort of right in that if the kW rating changes, the FLA changes, so reading the amps is an indirect way of seeing what is REALLY going on if the nameplate does not show Watts or kW. This has unfortunately become more common, because in other parts of the world, they don't use HP for motors, they use kW. But it's not ELECTRICAL kW, it's MECHANICAL kW, so it can feed right into the hands of these marketing people. That's probably why he said to look at the FLA, because you cannot lie about that.
    Last edited by Jraef; 06-12-12 at 09:36 PM.
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  10. #20
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    Quote Originally Posted by Jraef View Post
    The residential HVAC world has been taking notes from the rest of the consumer electrical appliance world. In the consumer electrical appliance world, there is a "marketing HP" vs a real HP, and it works like this:

    Mechanical HP = Torque (lb.-ft) x RPM / 5250. That is the official definition. Forget that, it means next to nothing to marketing people except as a tool to get them to where they want to go.

    Electrical HP = 746W

    The "marketing" angle is that when you increase the slip of a motor by loading it, even OVER loading it, you are essentially increasing the HP, even if it is temporary. So let's say you have a motor that is rated for 1.5kW. Electrically, we would call that a 2HP motor (2HP = 1492W). But, if you temporarily overload that motor to the Break Down Torque (BDT) point of 220% of Full Load Torque (FLT), then the mechanical HP formula can be back-fed to say that you have 2.2X the rated torque, thus 2.2X the rated mechanical Power or 3.3kW. Now to be fair, they will also adjust for the fact that the RPM will need to drop to be able to put the motor into BDT, but then they also will say that the PF increases as well, so those issues are a wash (not really, but that's not important to them). So they take that 1.5kW motor and say in their marketing that it develops 4.4HP (3300/746). Now mind you, if the motor stays in BDT for any appreciable length of time, it will overload. It is after all really a 2HP motor. But that's not what they are after, they want you to believe that the motor is larger than it really is.

    But if you read the ELECTRICAL rating of Watts or kW, they cannot lie about that because that is what the motor will CONSUME safely at full load according to UL or whoever tested and listed the product. So in essence your guy is sort of right in that if the kW rating changes, the FLA changes, so reading the amps is an indirect way of seeing what is REALLY going on if the nameplate does not show Watts or kW. This has unfortunately become more common, because in other parts of the world, they don't use HP for motors, they use kW. But it's not ELECTRICAL kW, it's MECHANICAL kW, so it can feed right into the hands of these marketing people. That's probably why he said to look at the FLA, because you cannot lie about that.
    Thank you. I knew someone on here has stated this before - or something similar- It was probably you. This makes some sense now.

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