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What is 3HP

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Forum topic by agallant posted 579 days ago 1693 views 2 times favorited 46 replies Add to Favorites Watch
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agallant

427 posts in 1485 days


579 days ago

What exactly does 3HP mean? I really doubt my 3HP shop vac motor could replace the motor on my 3HP unisaw. So what exactly is 3HP then?


46 replies so far

View ShaneA's profile

ShaneA

5254 posts in 1197 days


#1 posted 579 days ago

The shop vac is 3 peak hp…whatever that means. Motors should max out in the 1.75hp range with 110 power. The inductions motors should be able to maintain a constant hp output.

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Loren

7234 posts in 2246 days


#2 posted 579 days ago

With induction motors (like on you unisaw) horsepower
is generally a useful and accurate rating of what the
motor can do. With universal (brush type) motors,
it is marketing hyperbole.

-- http://lawoodworking.com

View lab7654's profile

lab7654

250 posts in 845 days


#3 posted 579 days ago

That’s something that bugs me too. Where do the companies get these numbers? I’ve seen shop vacs ranging to 6.5HP…

-- Tristin King -- When in doubt, sand it.

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Dallas

2855 posts in 1086 days


#4 posted 579 days ago

1 HP = 746 watts.
It doesn’t matter if it’s 120V or 240V or 480V. A watt is a watt is a watt.

Watts are derived from this formula: V x A = P (expressed in watts).

When small motor manufacturers post, “3HP”, “5HP”, “6HP”, etc. they are referring to what is called ‘LRA’ or “locked rotor amps” which is the point at which the the armature in the motor actually can no longer turn. They use some sophisticated breakers and software to make sure they are giving an accurate description, (by Law), but it’s not really a true reading.

When you remove the air flow from a vacuum pump like a shop vac, there is actually less stress on the motor.
To put more load on it, you would have to thicken the atmosphere being taken in.

An induction motor is also tested the same way, except they are working with better components and testing for actual LRA by actually putting a physical load on the motor, not a theoretical software induced load.

Good Luck!

-- Improvise.... Adapt...... Overcome!

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Moron

4666 posts in 2492 days


#5 posted 579 days ago

3 HP

=

3 horse power

the original average law of what a horse can do ?

search “you tube” on what 1 horse can wreak havoc on

and imagine 3 of them

beautiful animals

to be respected

versus say a cat power CT

-- "Good artists borrow, great artists steal”…..Picasso

View MJCD's profile

MJCD

452 posts in 970 days


#6 posted 579 days ago

Welcome to Marketing’s wacky world of ‘puffery’ – the legal over-statement of capabilities; as in – that car has the interior space of the Astrodome.

Having said this, the previous posts get you to the facts – a HP is 746 watts; Amps * Volts = Watts: even with this, we’re assuming 100% motor efficiency, and that the motor will still survive at some rated level – router manufacturers have been know to use Bushings rather than Bearings; less than stellar cooper for their armature windings; and all sorts of less-than-forthright manufacturing and marketing terms and conditions.

The only advise is to not trust anything.
MJCD

-- Lead By Example; Make a Difference

View Tedster's profile

Tedster

2267 posts in 810 days


#7 posted 579 days ago

Dallas, thanks for cluing us in… well, me anyway. I favorited this topic just so I can come back and read your formulas a few more times so they’ll sink in.

Moron, I like your formula too… not as scientific but horses are way cool. Who killed the cat?

-- I support the 28th Amendment. http://www.wolf-pac.com/28th

View knotscott's profile

knotscott

5369 posts in 1974 days


#8 posted 579 days ago

”I favorited this topic just so I can come back and read your formulas a few more times so they’ll sink in.”

Ted, as MJCD points out, you need to add a loss factor into that equation in order for it to result in anything close to a realistic HP rating…..most decent motors of the types we use in woodworking operate at only 60-70% efficiency, so multiply the result of Dallas’ formula by a factor of roughly 0.65, and you’ll have something closer to the real world usable HP. The actual efficiency could even be less.

If we assume a nominal 15 amps for a typical 1.5hp induction motor running on 120v. 15 amps x 120v = 1800 watts. Divide that by 746 to get a pure theoretical 2.41hp. Then multiply that times 0.65 for a number approaching the realistic ratiing….1.57hp in this case.

A good common sense rule of thumb….if it plugs into a standard 120v residential outlet, it’s not over 2hp.

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

View Straightbowed's profile

Straightbowed

717 posts in 897 days


#9 posted 579 days ago

who said 2+2 =4 could be 7

-- Stevo, work in tha city woodshop in the country

View runswithscissors's profile

runswithscissors

894 posts in 624 days


#10 posted 578 days ago

Not only has horsepower become an almost meaningless term (as used in marketing), how about “professional” and “industrial”? Do those words have any real meaning nowadays?

View TopamaxSurvivor's profile

TopamaxSurvivor

14589 posts in 2274 days


#11 posted 578 days ago

1 HP = 746 watts in DC motors in a perfect world. For AC motors, 1 hp will be closer to 1400 watts or 11.5 amps. That is about max on your typical 15 amp garage circut at 120 volts.

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View EdwardR's profile

EdwardR

66 posts in 853 days


#12 posted 578 days ago

HP is meaningless ( well almost) lol. The difference is TORQUE. you can have two motors both 3hp the one with what i call empty HP will be weaker. The more powerful 3hp motor with GUTS will also be bigger and heavier and yes more expensive. This can be acheived also with gearing and pully size. Amps = power

A way to explain is take these little bumblebee in a can cars these kids drive with outrages HP in a 4 cylinder. they have to wind the living crap out of it to get it to move and any slight traction loss or bog will kill it.

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TopamaxSurvivor

14589 posts in 2274 days


#13 posted 578 days ago

Hp is meaningless on consumer tools such as table saws and shop vacs. It is still the method of sizing motor circuits in the National Electrical Code. Just taking the first 1 hp motor that popped up on goggle search , notice the full load amps (FLA) are 13.4 on 115 volts o0 6.7 on 230 volts. Forget claimed HP, look at FLA on the motor name plate.

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Tedster's profile

Tedster

2267 posts in 810 days


#14 posted 578 days ago

I had a 3-1/4 HP Porter Cable router some time back and that thing would drive recessed panel bits with no problem. I now have a 3-1/4 HP Craftsman router that no way will it do the same in a single pass.. it takes 2 passes minimum.

-- I support the 28th Amendment. http://www.wolf-pac.com/28th

View knotscott's profile

knotscott

5369 posts in 1974 days


#15 posted 578 days ago

So, to answer your question…..”3hp” is roughly 3 times more BS than 1hp…...;-)

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

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