Jet DC motor gibberish...


I am in the market for a new DC. The local Woodcraft had Delta and Jet 1 and 1.5hp.
The Delta motor were 11a and 15a; about what one might expect.
The Jet were 11a and 11a. Thats right, they were the same. They are also the same diameter, length, and class. Looks to me like they are the same motor.
So how is one 1hp and the other 1.5hp?
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Toller wrote:

11A at 120V is 1320W. 1.5HP is 1120W. That would require 85% efficiency, which is pretty high. I call either BS or typo.
Chris
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I can't give a direct answer regarding the difference/similarity of the two Jet motors. However, as general advice, the CFM and HP ratings provided for most consumer grade DCs are fairly meaningless. Advertised CFM numbers are usually based on completely unrestricted airflow, i.e. with no ducts, filters, etc. Sometimes, they're pure fiction. As a rule of thumb, under realistic working conditions, most consumer DCs deliver no more than 50-60% of their rated flow
HP ratings are something of a non-issue, because a blower is basically a fixed load. It takes a certain amount of HP keep the impeller spinning at a given airflow. Increasing motor HP above this required minimum will not increase performance. So don't sweat the motor specs too much. I agree that the 11A number for the Jet is strange, but this machine has performed comparably to others in tests, with nothing to indicate that the motor is underpowered, so I wouldn't worry.
In any case, I'd pick either of the larger machines, whichever comes with good felt filter bags.
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Toller said:

Creative Marketing.
Greg G.
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Don't you just _love_ conspiracy theories?
Depending on type and application, I would say.
http://www.iprocessmart.com/leeson/leeson_singlephase_article.htm
All induction-run begin with "slip," which is one place to begin.
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George said:

Yes. HP figures for Air Compressors comes to mind...
Greg G.
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Greg G. wrote:

And Shop-Vacs...
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B a r r y said:

OMG - I forgot about those... ;-) LMAO.
Greg G.
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On Fri, 11 Nov 2005 13:28:20 GMT, B a r r y

And cars... Back in 80, we bought a new Chrysler Le Baron... the one we drove was peppy, the one my wife bought was a dog... Salesman said that the difference between the "American" and "Japanese" (Mitso) engines was 4 hp..
Found a report a few months later that said the difference was 5 hp and that the Mitso engine developed peak hp 1,000 rpm lower than the other engine... a LOT of rpm difference, even for a 4-banger.. (I figured that before you could get peak hp from ours, the engine would self destruct)
mac
Please remove splinters before emailing
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mac davis said:

Yeah, it's pretty handy to have a charted printout of the torque curve. And since (torque*RPM)/5252 equates to HP, it is also quite relevant to driveability. As are gear ratios, course maps, etc...
HP figures have become like CPU speeds - or maybe it's the other way around... Advertising Hyperbole. Nevertheless, the basis for almost all hot-rodding attempts, baring more displacement.
I built a rotary engine years ago that developed peak torque at 6200 RPM. It would spin up to 8000RPM. Scary stuff. And it hauled... Wasn't so good off the line... Made a really cool sound as well. Oh, how I wish I still had it - it was a kick.
As for the self-destructing aspect - hey, it sells cars. I think it is Detroit's mantra these days...
I've never been a fan of four bangers, due to the rocking couples and harmonics, and I'm not that fond of V and in-line engines either. My preference is horizontally opposed 6/12 cylinder engines and rotary's. Naturally balanced. I guess I'm a high RPM durability kinda guy. But try finding one these days - for less than 100 big'ens. And fuel costs... ugghh...
And if I touched upon issues you are intimate with, please excuse me and consider it a rhetorical discussion with myself. ;-)
Greg G.
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Greg G. said:
<snip>

Darned, I'm starting to proofread myself now... Should have said...
Nevertheless, shifting the torque peak towards a higher RPM is the basis for almost all hot-rodding attempts, baring more displacement.
NOW the formula... ;-)
Greg G.
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There are many "standards" for measuring HP. There are also many types of motors. The idea is to be smart enough not to be fooled. If the words peak and developed don't key you into thinking, I guess you're one of those folks the inflated numbers are intended to fool.
If you don't care to be manipulated, inform yourself. Good site on motor applications and efficiency was offered.
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George said:

Look, you old fart. You were OK until I said something in another thread about Bush being the dim bulb that he is. And then you got your diapers in a wad and have been answering my posts at every opportunity with smart-ass responses like this. You are not the God Head of enlightenment, and you're not even that freaken smart. So go back to your basement, fire up a log, relax - and quit reading and responding to my posts. Or go feed the gulls around Lake Superior.
I've worked in electronics and mechanical engineering for almost 30 years, and I don't need to read some neophyte level web site to know you are an angry, lonely old troll with nothing better to do. I come here for entertaining conversation, not trolls. But just FYI, I have an _inkling_ about hysteresis, stall, efficiency, slip, AC phase, ohms law and many other terms you looked up on the net only yesterday.
I have never done this before, and hope to never do it again (but I feel there's another one coming up) - Welcome to my killfile.
<PLONK>
Greg G.
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Joe Brophy said:

Briefly (and sloppily...),
HP and Watts are direct measurements of work force. But with a motor that converts electrical force into mechanical force, there are other factors to consider. Motor design and efficiency come to mind. Heat generation, losses from friction (=heat) and other conversions skew that one to one relationship.
The problem with "Creative Marketing" comes from manufacturer's attempts to push for higher and higher advertised HP ratings because they see it as a primary sales and marketing 'talking point' to an uninformed public. Same as the IHF/RMS/Peak power output ratings which were bandied about in the early days of audio. So they came up with stall HP ratings, which are totally meaningless, and are based upon the stalled rotor current draw of a motor - typically it's peak current consumption mode. From this they extrapolate the HP ratings you see on numerous appliances. Particularly things that appeal to the Tim Allen in all of us. More Power.
These methods of measuring HP ignore usability, real world power output, and logic in general.
FWIW,
Greg G.
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I finally found my ampmeter... My Penn State 1.5hp 8a (240v) DC measures 3.3a. I can get it up to 3.8a by taking the bag off. I was blaming the single bag for it's less than stellar performance, but it is actually lies about the motor. Oh well, live and learn.
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"My Penn State 1.5hp 8a (240v) DC measures 3.3a. I can get it up to 3.8a by taking the bag off. I was blaming the single bag for it's less than stellar performance, but it is actually lies about the motor."
You seem to be assuming that an 8A motor should always draw 8A. Not so. Motor current draw depends on load: a motor will draw it's rated current only when it's under full load. In a DC, the load is the airflow, which is limited by the impeller size and blower design. I think you have a PSI DC-3, which has a 9" impeller. That, and the 4" inlet/outlets, are the limiting factors, not the motor specs.
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have been close to 8a without it. And an 11a (120v) Jet. It drew 9.5 with the bags on; presumably 10+ without them. It also has a 9" impeller (it is small, I think it is 9") and a 4" inlet. So, the Tufo did what it claimed, and the Jet did nearly so. The PS might be somewhat reduced by the small impeller and inlet, but not by the 60% I actually measured. There was only a 25% hit by going from no bag or hose to completely blocked! Besides, the 8a PS motor is half the size of the 8a Tufo motor (or my 8a table saw motor for that matter); it might even be smaller than the Jet DC650 motor. No way to explain that except that PennState is simply making up numbers.
Bear in mind that PennState claims their DCs are half as loud as anyone elses, which certainly isn't true with my DC-3. It claims 62db, but is significantly louder than my 68db generator.
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