Vacuum cleaner horsepower question

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In the formula for figuring motor power-you can't just simply go by what wattage or amperage the motor DRAWS from the line.say if you have a motor that draws 7A from the line-that would be 840W-In real life that motor would be 3/4 to 1 hp if you deduct the losses.for most universal motor-about 10-25%.Some central vac units have two motors-they can be in series for more suction pressure-or parallel for more CFM-air systems of the motors-NOT electrical.electrical they would be parallel.If you have a 15A 120V universal motor-that would be about 2.25Hp average power-for an induction-1.5hp.such as for my XL blender-the motor could delivor 2.25HP average.for most of what I do it would be loaded down to much less than that.Most universal motors are loaded to far less than their ratings.thats good-becuase unversal motors can overheat quickly.no large frame or core to absorb heat like on induction motors.And the armature windings overheat quickly on universal motors-harder to cool- the armature fan may not remove the heat fast enough.
 
You're partially right.......

746 watts per HP is assuming a perfect 100% efficiency. I think we all know that nothing is 100% efficient. The watts/HP conversion is a law of physics. It's a known fact that it takes at least 746 watts (mechanical or electrical) to equal 1 Horsepower.

In a US home, the maximum wattage an appliance should draw on a single 120V outlet is 1500w (although you see hairdryers at 1875w which is literally 15 amps!). At 1500w, the maximum horsepower you can develop (for ANY motor and assuming 100% efficiency) is 2.01 HP.

Mind you a motor is rated at full load. If the motor isn't fully loaded, it will run faster and actually draw less current (due to being more in sync with the AC sine wave). Less current at a given voltage means less wattage being drawn. Less wattage means less horsepower.

It's a rule of science and physics that you simply cannot draw more than 2.01 horsepower MAXIMUM (and assuming you're in a perfect world) from a residential 120V outlet.

Appliances that draw more than 1500w from an outlet are actually in violation of many fire protection laws. The accepted maximum for any circuit is a draw of about 80% of the circuit's capacity by any one appliance.

Assuming a nominal voltage of 120v, that means 1440w as a maximum. That's why the biggest vacuum motors you see in the US are 12.5 amps to comply with fire protection codes.

Resistance appliances are a little different.....as the voltage falls, so does their current draw. That's why they can get away with the 1875w. As the voltage drops in the wiring in the house under load, the voltage falls in the appliance reducing the wattage load. Sort of a self-balancing thing.

Inductive devices like motors however, will draw more current as the voltage falls. They'll still be the same wattage, but it's the current rise that does damage to wiring and blows fuses.

So no.....in the US on a 120V circuit, your blender doesn't produce 2.25 HP. It physically can't produce more than 2.01 HP absolute maximum on a 15 amp plug. Assuming 90% efficiency it can't develop more than 1.8 HP.

If you were lucky enough to have a 20 amp circuit (which appliances rated for a 20A circuit must explicitly have a tag on the plug saying so with large warning letters) then the maximum you can develop (in theory) is 3.21 HP. Assuming 90% efficiency again, the maximum you can actually make is 2.89 HP. That's assuming you have that circuit fully loaded. If the appliance follows rating guidelines and only loads to 80% of the circuit, you can't get more than 2.6 HP out of it absolute maximum at 90% efficiency.

Rules of physics.....

Turn the machine over and read the nameplate. Multiply 120v times amps and it'll give you the wattage. Divide that by 746 and you'll be greeted with the absolute maximum power that machine could possibly produce (if it were 100% efficient). If you want a more realistic answer of it's horsepower rating multiply your theoretical result by .85 or .9. THAT is your actual peak horsepower. NOT what the manufacturer "claims" it to be.
 
I also have a Blendtec "Titan" blender-the manufacturer rates it a 20A 120V-blendtec DOES NOT give a HP rating on this-thats just as well-on universal motors ratings can be slanted-the peak ratings are derived in the motor builders test lab-the motor or engine under test is connected mechanically to a dynamic dynameter-a form of generator that can convertt the motors output to electrical energy-which thru the formula is converted to HP-some dynameters can do the conversion.the dynometer can also "Load" the motor so you can see how much force the motor can produce to overcome the load.-this can give you "Peak"HP-Remmber the motor under test is connected to a supply that can give the power the motor has to have to overcome the load-not a standard 20A or 15A 120V circuit.and yes the motor will probably burn out to give this peak rating.
Anyway on the Blendtec Titan-the machine has a 20A 120V NEMA plug so it can only be plugged into a 20A circuit.And of course remmber most motors ARE NOT loaded to their absolute manufactuers ratings in normal use.the VM blender with the 15A motor would be 1800W.In lab tests of course would be loaded to more than that.like their claim of 4.2Hp-thats 3133.2 watts.that would be the max load that motor could handle.If I tried that with the 15A circuit-of course the breaker or fuse would trip.It should trip if I loaded the motor to 1800W.For motors the codes are slanted.The codes apply more to heating type appliances.I have another 15A 120V motor-its on a Tornado Wet Dry vacuum-they rate the motor as 2.25Hp.Thats 1678.5W.I know that motor isn't loaded to 15A either-I did run another vacuum while the Tornado was going-no tripped breakers.Oh yes-when I worked at the tool supply-repair place someone brought in a block and brick saw that had a 2Hp120V induction motor.It ran off a standard 15A circuit.The motor had both a start cap and a run cap-the motor was blowing fuses when it got up to speed-tried another stat cap-not it-the run cap was bad!-replaced and the machine ran fine-you had to run this on a circuit by itself or the breaker would trip-esp while cutting.Since the motor had a run cap this brought its current down to 15A 120V.Usually for an induction motor-1.5Hp is the largest non corrected motor you can run from a 15A 120V line.these motors are found on contractor and home type table saws.these motors are right at 13A-15A 120V.also 3hp router motors(universal) are made to run from a 120V 15A line.Core drill motors have 20A plugs so they can run only from a 20A circuit.The core drill machine needs two 20A circuits to run-one for the drill motor-the other for the vacuum pump motor to secure the base and the water pump motor to pump water to and from the diamond core drill bit.electricians and plumbers like these for drilling holes in concrete floors for pipes and conduits.Milwaukee Tools and Black and Decker make these machines.
 

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