I'm looking to purchase a woodowrking bandsaw and in their catalog (King Industrial), they rate their bandsaws by the amps tha motor takes and they don't show the HP. So to compare it to other brands, I tried the following :
If I remember well Watts = Voltage x Intensity So 120V x 7.5A = 900W. To convert it to HP = Watts x 0,00134. So a 7.5A gives 1.2 HP and a 10A gives 1.6 HP. I'm sure I missing something here like the efficiency of the motor (cos phi I think?), I would doubt very much that they gives so much HP for a small bandsaw like that. So with a cos phi factor of about 60%, a 7.5 Amps gives the 3/4HP motor which is usually what we find in that kind of equipement. ANd the 10 amps would be a 1 HP motor. Is my reasonning ok ? Any electrician in the croud ?
in article TmwId.64407$ snipped-for-privacy@weber.videotron.net, Junkyard Engineer at snipped-for-privacy@engineer.com wrote on 1/22/05 9:50 AM:
That sounds about right.
In addition to the power factor correction, a single phase induction motor behaves like two motors in one. The first, the one that gives useful power, runs a bit slower than if it were synchronous. The second is being run backwards at close to synchronous speed. This is another hit on efficiency.
You are close... type of motor though is a big issue, brush type, split phase capacitor start...or the ultra cheap versions with no capacitors used as in many of the chinese drill presses.... those lack even workable levels of torque.
They list amps because they are using chinese motors mostly and those are not rated in HP often but just running amps...and if you are not careful are cheap low torque motors with sleeve bearings...some of the brush types (high torque) with PLASTIC brush holders for the hand tool motors.... the brush holders *melt in about half an hours run time... in some but not all cases... I had that with a 12 dollar 3/8" drill. Junk. but it drilled 12 dollars worth of holes none the less when I needed multiple drills laying around the job site.
My dewalt 3/8" drill cost 80 dollars 15 years ago, it still runs strong, twice the torque of the chinese drill/// and has drilled a million dollars worth of holes. Its so old now the rubber cord got hard and cracked I have to put a new cord on it.
My craftsman 3/8 drill got sunk with a clients house boat into salt water for a week.... I dried it out on the dock... it still works great...it is 15 or 20 years old.... though the chuck needed a little loosening up. The chinese tools were toast. Bearings shot. etc.
For tools you are going to use a lot ... buy good ones...if you use a tool rarely and need it for logistics issues only..say one pipe thread on site...or on the truck just in case you need the capability....then a cheap tool is the way to go in some but not all cases.
----------- You are assuming that the motor is at unity pf- it isn't. Consideriing an efficiency of 75% and a power factor the same, and estimating full load pf about the same (0.8) then
1HP requires about 1KW input and the corresponding KVA is approximately
1/0.8 =1.25 KVA For single phase 120V, this will be about 10-11A For the example below the efficiency and pf have not been factored in. Note the HP rating is an output rating, not an input and for AC motors, Power factor is involved in the corresponding current. The calculator is fine but it doesn't agree with FLA tables that I have.
I'm so tired of all those chinese stuff reminds me of the 60-70's when everything was made in Japan.
But you know what, I'm not so sure that we have to blame Chinese companies. It would certainly be those F*** marketing gurus here that think that we would be pissed off to pay 50$ more for a decent motor on an equipment. I would guess that it's a woman who is marketing director that do not care about men's stuff.
"Phil Scott" a écrit dans le message de news: 1ezId.4695$ snipped-for-privacy@newssvr14.news.prodigy.com...
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