Replies

1. 
   saschafer | Apr 28, 2009 03:59pm | #1

   I think the lesson here is, "Don't listen to salesmen."

   Induction motors, the kind you find on large stationary equipment, including all but the smallest of benchtop table saws, are rated using a pretty straightforward set of rules, and the numbers are pretty reliable. That doesn't mean that all 1-1/2 HP motors are created equal, of course. One may have better bearings, or heavier windings that don't heat up as much under load (heat is the primary enemy of a motor). But if it says 1-1/2 HP on it, it can probably deliver 1-1/2 HP to its load. You should be able to find a nameplate on the motor, and it will tell you the volt/amp rating of the motor. At 120 V, a 1-1/2 HP motor should consume 16-18 A at full load. (At 240 V, the current is halved.)

   Universal motors, the kind you find on routers, lunchbox planers, and most smaller, portable equipment (the kind that scream like a banshee) don't follow any similar rating rules, and so it's pretty much caveat emptor. A "3-1/4 HP" router can probably deliver 3-1/4 HP for a second or so, before it stalls out or burns up.

   -Steve

    

1. 
   4runner | Apr 28, 2009 05:16pm | #2

   Good job, maybe you should be the salesman.

   4Runner

1. 
   flairwoodworks | Apr 28, 2009 09:08pm | #3

   But would you still listen to him?Chris @ http://www.flairwoodwork.spaces.live.com and now http://www.flairwoodworks.com)

    - Success is not the key to happiness.  Happiness is the key to success.  If you love what you are doing, you will be successful. - Albert Schweitzer

2. 
   Taigert | Apr 30, 2009 08:16am | #7

   4Runner,

   There's an equasion (sp) to figure HP on electic motors. I think it is watts divide by amps = HP, it been a long time since I looked at it. I'm sure you can look it up, or one of the other guys can give you the correct one, if I have it mixed up. It's late and the mind is getting fuzzzy.

   But rule #1, verify whatever the salesman tells you.

   Taigert

1. 
   4runner | Apr 30, 2009 04:51pm | #8

   I knew there had to be a full proof way.

   Thanks.

   4Rnnr

2. 
   082250 | Apr 30, 2009 05:52pm | #9

   I believe watts divided by amps equals volts

1. 
   Ray | Apr 30, 2009 09:51pm | #10

   Volts*Amps*motor efficiency / 746 = HP

2. 
   Taigert | May 01, 2009 07:24am | #11

   It was late & I knew someone would bail me out

   Thanks guys,

   Taigert

2. 
   jointerman | Apr 30, 2009 06:56am | #6

   Good information on induction motors. Also, don't forget to look at features like run capacitors. The start capacitor gives the push to get the coils rotating on the motor. Run capacitors provide that extra oomph cause they stay on and remain as part of the circuit of the motor. They give that extra torque to keep the motor rotating when needed. So a saw with a run capacitor will be happier with thicker wood.Of course, you could just go with 3-phase power and not worry about the capacitors!

2. 
   roc | Apr 29, 2009 05:36am | #4

   >Don't listen to salesmen

   That is very sound advice in my experience.

   Steve,

   Don't you just love the shop vacs with " 3 hp" or " 5 hp " plastered on the side ? !

   Not going to see a true 3 or 5 hp using 120 volts

   roc

   Give me six hours to chop down a tree and I will spend the first four sharpening the axe. Abraham Lincoln ( 54° shaves )

   
   

   ---

   Edited 4/28/2009 10:37 pm by roc

1. 
   4runner | Apr 29, 2009 02:30pm | #5

   Thank you, thank you, thank you. I almost like all the words, wit and wisdom I gather from these messages as much as the insight from the answers.

   4Rnnr