Amps and HP on a table saw??

I am looking at moderately priced 1.5hp table saws. Jet's is 18a and
Delta's is 15a.
What does this mean? Is Delta's more efficient. Is Jet's more powerful?
Would you expect one to be more dependable than the other? Or is one of
them exaggerating something?
Assume I don't know anything, and explain it all.
Thanks.
Reply to
John
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The difference may be that the delta motor has a higher power factor, which is probably insignificant for something used as little as most table saws are.
Reply to
Bob Peterson
It is usually just marketing hype. You may be able to use these numbers as a broad selection criteria but it is certainly not a precise mesurement of power. My Sears saw brags about 2HP and runs quite reliably on a 15a circuit. NEC 340.148 says a 2HP motor pulls 24a. Somebody is lying.
Reply to
Gfretwell
I will not Assume, you don't know anything. The 18a and 15a means the ampere that the motor draws, between these two, 3 amps don't make a bit of difference. Let's face it, both Jet and Delta are both made in some foreign country like China. Buy the cheaper one and you'll get the same performance as the other. This is the world we live in, buy cheap.
Reply to
Maintech
In the case of a table saw "performance" really has more to do with the ease of setup and quality of the cut than raw power. In that respect "buy cheap" may not be the best choice.
Reply to
Gfretwell
It's not necessarily marketing hype and, no, somebody is *not* lying.
Firstly, the 15A and 18A are likely "Rated Motor Currents" (or average Full Load Currents) and will vary a bit depending upon the way the motor has been designed. You might think that 3 Amps is no big deal, but is enough to affect breaker trip settings in a graded protection scheme (in a factory setting, for instance).
Secondly, 15 Amp circuit breakers will not instantly trip at 15 Amps. To prevent nuisance tripping on motor startup, depending on the Curve Type (usually 'C' or 'D'), this might be up to 6x for a brief second or two (ie. 90 Amps!) before it will actually trip.
Thirdly, I don't know where you get 24A from for a 2HP motor - locked rotor current maybe? My book says the rated motor current for an NEC 2HP squirrel-cage motor is 13.6A at 115VAC..
Cameron:-)
PS: I might be crap at electronics, but I do know something. Now, where did I leave my coffee?.... ;-)
Reply to
Cameron Dorrough
Not really.
Keep in mind that the current drawn is dependent on the HP being OUTPUT by the motor and not its idle current. A fully loaded 2 HP motor must draw at least 2x746 Watts (because a HP is defined as the mechanical equivalent of 746 Watts), or when run on 115V will draw a minimum of 12.97 Amps (making the unrealistic assumption that the motor is 100% efficient).
If we assume that the 2 HP motor is only 50% efficient, it will corresspondingly draw 25.94 Amps. Note that this is only slightly higher than the NEC 3.40.148 value, suggesting that something like 55% average motor/power train energy efficiency.
Measuring the true mechanical power output of a power saw is almost impossible to perform by the average power tool user not equipped with either a a Prony Brake or other form of dynamometer.
Given the above, it goes without saying that for a specified HP output, the product pulling the LEAST current is the higher quality. Beware when you sell marking hype that attempts to confuse current draw with the HP of a product, be it a table saw or a vacuum cleaner.
Harry C.
Reply to
Harry Conover
Yep, you're right.. but the OP didn't state that the unit was single-phase!
If that's the case the FLC will be *much* higher than either 15 or 18 Amps. So, what's he looking at then? A model number??
Cameron:-)
Reply to
Cameron Dorrough
I guess that's why it is so easy to lie. ;-)
I figure my "2 HP" saw was measured at the millisecond after I hit a knot in a hickory log I was cutting into BBQ chunks.
Reply to
Gfretwell
I have a made in Taiwan Delta copy with a 2HP motor. For a few years, I had no problems on a 15A circuit. Then I started ripping some bigger lumber and the breaker started popping.
Fortunately, the motor was a dual voltage and runs just fine off a 20A 240V circuit.
Reply to
Paul Hovnanian P.E.
Since 2 HP is by definition 1,492 Watts, your NEC citation would reqire the motor and power train to be 95% efficient. This is totally unrealistic since not even transformers operate at that level of efficiency. I don't have my copy of the NEC here at home, but I'd be almost willing to bet that the 13.6 Amps you cite is for a 1 HP motor.
Just run the numbers for yourself.
24 Amp is a much more realistic estimate for your average 2 HP motor operating under a full 2 HP load with 50-60% efficiency (motor and power train).
Harry C.
Reply to
Harry Conover
Sorry, Harry. As pointed out by Gfretwell, I was looking at the three-phase table. That was the only one that made sense given the "15a" or "18a" from the original post.
No arguments from me. I guess that's why we use 3-phase over here - even for table saws in backyard workshops. Hey, is this an *American* newsgroup or what?? ;-)
Cameron:-)
Reply to
Cameron Dorrough
Yup. And how about the "3 hp" compressor that requires a 15 or 20 amp circuit, per manufacturers instructions, or a "5 hp" compressor that runs on a 120 volt circuit, if what I've read on this newsgroup from time to time is true?
Reply to
ehsjr
Amen to that! The useful life of the tool is another consideration, and I've never found cheap power tools to be a bargain at any price. Hand tools too for that matter.
Harry C.
Reply to
Harry Conover
First of all everyone, the OP states, "... a moderately priced *1.5hp* [emphasis added]..."
Why are you all looking at 2 hp??
1.5*746 = 1149 watts.
The *
motor* rating of 1.5 hp means it probably draws about 1270 watts (90% efficient motor). Where did you ever get the idea that electric motors are so inefficient. And the drive drain efficiency (if it's a V-belt) is probably also in the high 80's to 90%. Not that drive train efficiency is what is listed. You can be sure they are quoting the motor rating, and no further.
1270 watts @120V that is 10.6 A
Guessing a pf of 0.85, that would be 12.5A.
But as you say, the motor will seldom develop that particular amount of hp. When running idle, it will develop only a small fraction of 1.5 hp. And if you 'jam' the wood in hard enough, it will develop *
more* than 1.5 hp (for a time at least).
daestrom
Reply to
daestrom
Will your utility deliver 3ph power to a standard household? Looks as if you are in Australia. John
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Reply to
jriegle
Correct on both counts. Since every major city and town has 3-phase running down the street, as long as you pay the bills they will connect you.
We have 2-phase to our house (stove/hot water) and the boss has 3-phase to his garage..
The side effect of all of this is that if they lose a phase for any reason, in the newer suburbs you get every third house blacked out.. :-)
Cameron:-)
Reply to
Cameron Dorrough

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