Please explain HP

[Dennis Alwon]

Here is the scenario. I went to buy a blower for my furnace and it was a 1/2hp motor. Both places I went to stated that HP didn't matter it was the amperage that they needed to match. :?

I have heard that manufacturers rate HP different ways and that there may be some truth to what they say but I don't get it. Of course, I lost all confidence when one counter guy picked up the old motor in one hand and the new one in the other and did a weigh test. He said that was another means of checking------------:happyno:

Anyway can someone give a basic explanation of this.

 

[charlie b]

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 don't know anything about HVAC system repairs, so I can't answer the question about whether the amp rating is all that matters. I should think, however, that any motor that has the right voltage and the same HP and that would physically fit into the same space should work.

 

[Phil Corso]

Are there any Trivia-Buffs that would like to know how Hp (Value) is different in other parts of the world?

Regards, Phil

 

[charlie b]

Well, I imagine the power that could be generated by a clydesdale might be higher than that of a shetland pony. :lol:

 

[kwired]

When dealing with HVAC you sometimes have blower motors located in the airstream and they are cooled by the airstream. Same motor not located in the airstream will overheat when same load is applied. Often these motors are multispeed motors and the HP rating is max HP at the highest speed. Actual HP used depends on amount of air flow. Amount of air flow will have some effect of motor cooling if in airstream.

I understand this does not exactly answer your question Dennis, but I believe is part of why there is so much confusion in the HVAC industry on sizing of motors. The real issues are too complex for average counter salesperson at a HVAC supply to fully understand. The things they are looking for are usually enough to be able to give you an equivelant replacement. They don't necessarily know if it meets the needs in the first place however.

Add: I think they also want to know information they ask for because the motors are cataloged by that information more so than by horsepower.

 

[Npstewart]

Im pretty familiar with HVAC and not quite sure if you are asking if how the horse power relates to electric, or how it relates to air flow.

If you are replacing the blower in your furnace the horse power would matter up to a certain point. You can solve for kW by multiplying the HP by 0.75. Obviously given kW you can solve for the amps. These is really just a conversion of power though.

Fans/blowers take on many different designs. Typically when I am reviewing a fan I am looking for airflow by using a performance curve. There is airflow plotted on the x axis, and static pressure on the y axis. The higher the pressure the less air flow. HP is used in in airflow equations but these equations are useless because you would need a bunch of information that you don't have in order to use them. The performance curve is good because it is usually test data. Equations can be found below at the link under "blowers/fans".

http://www.iprocessmart.com/techsmart/formulas.htm

Other than that, maybe he was saying only the amps matter because he thought if the amps were too high, the internal wires would be too small, or the drive wouldn't be able to handle it.

 

[rbalex]

If the motor is a recognized component (backward ?UR?) then you are looking for an original replacement and it is the only motor that should be used, horsepower, amp or otherwise; but amps is the original manufacturer?s most likely "short" means of identification. If possible, check with the manufacturer for an authorized dealer.

If the motor is ?general purpose? (not very likely) you need the motor to match the frame size, enclosure type and all applicable nameplate information in 430.7(A). The motor should have no NRTL marks (CSA won?t count in this case); a NEMA mark is possible.

 

[jumper]

IDK, seems to me that amps would only be a concern if radically changing the system, not a good idea; Isn't that why use we 430 tables part XIV for SC/GF according to HP and not nameplate? Two 1/2HP motors may have different amperages, but we size for worst case.

For these small motors, overload thermal protection is usually built in IIRC

Frame, voltage, freq, shaft, rpm, HP, phase type, etc seem to say whether a OEM replacement or generic will work. No?

 

[Dennis Alwon]

Other than that, maybe he was saying only the amps matter because he thought if the amps were too high, the internal wires would be too small, or the drive wouldn't be able to handle it.

Thank you all for your responses-- sorry I have been gone longer than expected.

No I specifically ask if he was talking about the circuit capacity and he said know.

Don- I would prefer the original equipment but it would be a week to get it.

I guess if the rpm & HP is the same for two motors why is the amperage different. Is it just a matter or service factor or is there more to it than that. I saw 1/2HP motors that went from 6 amps up to almost 8 amps. Theses motors are all designed for blowers on furnaces.

 

[rbalex]

Jumper correctly noted that Tables 430.247 through 250 are based on the worst motor any NEMA manufacturer makes in a given category. The table's purpose is to permit any NEMA, 1200 RPM or higher speed motor, be interchangable with motors of the same hp, voltage, phase configuration and frame under 430.6(A)(1). Fundamentally, only overload protection needs to be checked per 430.6(A)(2). The nameplate ampere ratings vary because of efficency and, to some lesser extent, power factor. These motors are not listed nor are they required to be.

Recognized component (backward "UR") motors are part of listed assemblies. More importantly, they are part of specifically tested assemblies. Whether they can be safely replaced or not isn't up to the counter guy.

 

[Dennis Alwon]

Bob are you saying that only a OEM motor may be used???

 

[Dennis Alwon]

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.

 

[iwire]

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

 

[rbalex]

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.

 

[Dennis Alwon]

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.

 

[weressl]

Well, I imagine the power that could be generated by a clydesdale might be higher than that of a shetland pony. :lol:

OK you guys, stop horsing around.:lol:

 

[jumper]

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.

 

[Dennis Alwon]

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. :thumbsup:

 

[Jraef]

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.

 

[Dennis Alwon]

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.