Power rating confusion

[Bryan Rocker]

Ok I have been on this forum for quite some time and I do understand the difference between 110 and 220 power ratings. However, I just purchased a Jet DC-1200 for $100, a real good deal. It has a 2 HP @220V. The motor is big and pulls 15 amps. I looked at my Delta X5 3HP and it only pulls 12 amps. How is that a lower amp motor is rated higher than the higher amp motor? Am I missing something here?

While I am on the subject of my DC, it is rated at 1200 CFM, a comparable grizzly which also has a 12" impeller is rated at 1750 CFM both of them have a single 6" opening. Would it be possible to remove the 6" opening and enlarge it to 7"? Would the motor be able to handle it?

Bryan

[Jim Becker]

Could be a different efficiency rating, etc., that makes for the difference in the motor rating...

Your DC is "rated" at 1200 CFM for marketing purposes, but will never see that in the light of day. That's typically a "free air" rating, which means no duct work and no filters. Rule of thumb is about half of that with optimized 6" duct work. Less if you use 4" duct or hose...you can't fit more than about 350 CFM or so in a 4" duct.

[Dan Friedrichs]

The HP rating of a DC is usually also highly influenced by marketing. Don't rely too heavily on it...

[Bryan Rocker]

Understood, luckily for me it will only be me and SWMBO in the shop. She has a nice scroll saw which will not be used that much, my main load will be my table saw, I am confident it can support both of those at the same time with no issues.

I am looking at modifying the layout of the motor/bag set up to something closer to the delta one where the exit from the motor is straight into the bag and adding a cyclone as well.

Thanks for the inputs.

Bryan

[Jeff Bratt]

Ok I have been on this forum for quite some time and I do understand the difference between 110 and 220 power ratings. However, I just purchased a Jet DC-1200 for $100, a real good deal. It has a 2 HP @220V. The motor is big and pulls 15 amps. I looked at my Delta X5 3HP and it only pulls 12 amps. How is that a lower amp motor is rated higher than the higher amp motor? Am I missing something here?

The Jet website specs that motor at 8 amps/230V. Perhaps the 15 amps comes from a 120V motor, or is a misprint. HP ratings on induction motor nameplates are generally pretty accurate - not to be confused with "HP ratings" on shop vacs and routers - which are pure marketing fiction.


While I am on the subject of my DC, it is rated at 1200 CFM, a comparable grizzly which also has a 12" impeller is rated at 1750 CFM both of them have a single 6" opening. Would it be possible to remove the 6" opening and enlarge it to 7"? Would the motor be able to handle it?Bryan

The CFM ratings quoted are not indicative of real-world performance. Also, the manufacturer's specs are misleading - both list XXX CFM and about 11 in. static pressure. Maybe the fans can move some air against 11 in. of pressure, but it will be more like 100-200 CFM. You need to see the "fan curve" for an impeller, then calculate the static pressure of your ductwork to estimate the actual CFM of a system.

Start by assuming half the specified CFM for these units once you actuallly hook them up to ductwork. Also note that a 30 micron filter bag is not a very good filter. You might want to see Bill Pentz's web site for his views on dust collection systems.

[Chip Lindley]

I've never compared CFM ratings as some obsess over here in the forums. I found an older 3hp Oneida commercial system at auction and scarfed it up post haste (with miles of ducting, gates and flex hose) for Only $1100!! *Gloat* Not sure of the CFM, but it would suck up a hammer if I'm not careful. It's all the DC I will ever need for a one man shop. (wish I had a 5hp tho!!) *grin*

Hype abounds in marketing (and inefficient cheap motors.) There is no such thing as a 115v 6hp shop vac!! Sears was the first to start this hype by the mid 70s, and every other consumer oriented tool manufacturer soon followed. As for hp/amp ratings, I compare the import motors to tried-n-true commercial brands and act accordingly. Even these differ in comparison.

Machines I use as a reference (per motor nameplate):

Rockwell RC33 planer (Rockwell/Leeson 230v/2hp/12a)
Powermatic 66 TS (Baldor 230v/3hp/13a)
Unisaw (Leeson retrofit 230v/3hp/16a)
Oneida DC (Leeson 230v/3hp/13a)

Quite a difference in amp draw for the same hp rating. I am sure my old 2hp planer would be touted as 3HP today. But as long as my machines do the work they are required to, I won't obsess!

[Bill Brady]

I would check the motor nameplate for the correct current, sometimes manufactures rate current and horsepower of their devices differently. The motor efficiency rating will not change the printed current, it will allow you to overload the motor if it is rated at a 115% or something different. The other thing that will make a difference is the motor speed, 1140 or 1725 or 3450.