On Aug 4, 9:11*pm, The Daring Dufas
wrote:
DerbyDad03 wrote:
On Aug 3, 11:07 am, bud-- wrote:
Doug Miller wrote:
In article , Aaron Fude wrote:
When translating amps to hp for a 120V appliance, is the formula essentially
120*amps/745.699872
That would give a 15amp ryobi table saw a rating of 2.41hp which is
ridiculously high, no? Is my formula not right, or is 2.41hp not
ridiculous or is there something else I'm missing?
You're missing two things:
1) The amperage rating on any electric motor represents the locked-rotor
current, i.e. the current it draws when the rotor is unable to move. This is
*much* higher than the current the motor draws when it's in operation, and is
in no way representative of the motor's actual power output.
Nope. The nameplate will have the running amps at rated HP. Overload
protection of may motors is based on the nameplate current rating.
(Many motors also have a "service factor" greater than one which means
the motor can be operated at higher current (and HP) at a little shorter
life.)

Motors typically have a code letter for locked rotor amps. Locked rotor
amps is about 6x the running amps. Unlikely the running amps for a table
saw is 2.5A. (An even 15A is probably not a motor current rating.)

The "lie" in motor HP *may* be the max HP you can get from the motor
before stall (which which would be a lie), which you might very
occasionally use. Wouldn't think *that would make sense for a shop vac.

2) You're also assuming 100% efficiency, which will never be the case.. There
will always be some losses due to friction in the bearings, etc.
Quite right.

--
bud--

The "lie" in motor HP *may* be the max HP you can get from the
motor before stall (which which would be a lie), which you might very
occasionally use. Wouldn't think *that would make sense for a shop
vac. "

The way I heard it years ago is that the max-claimed HP of a shop-vac,
etc. was actually achievable. It was the based on the max amperage the
unit would draw if you jammed a screwdriver in the impeller. Just
before the motor fried, you will have achieved maximum HP.

AC compressors are rated in RLA Run Load Amps and LRA Locked Rotor Amps.
Of course when you're putting the freon in a system, you can watch the
current draw increase as the compressor does more work. My favorite
question to use to tax the mind of a neophyte is "Will the blower draw
more or less current if the inlet is blocked off?"

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