There is a Craftsman 14a 1hp motor locally for very little. I would like to try to use it to replace the 10a 1hp motor on my Delta 14" bandsaw.
The craftsman would have to be really really inefficient to only product 1hp on 14a. I am thinking they are more conservative than delta on their claimed hp.
Does this seem like a reasonable try, or would I just be wasting money on a really really inefficient motor?
True to a point. Some older motors were very inefficant. If you need a replacement motor it probably will work fine, but don't be surprsed it you see little or no power improvement. If you are replaceing it just for the power gains I would save my money for a motor that you are certain of the power, say a new 1-1/2 HP. Greg
Motor designs and efficiencies haven't changed significantly in the last 90 years, so I would be more willing to believe that the labeling on the Craftsman motor is incorrect. It could be that the motor was originally part of a tool and the label showed the whole tool's power requirements rather than just the motor. Without measuring the current draw of each motor under an equal load and comparing them it will be difficult to know for sure. A 1 horsepower single phase 115 volt induction type motor will normally draw 6.4 amperes at full load, so neither label actually shows the rated current for a typical 1 hp motor.
Are the motors physically the same size? Is the motor label clear (maybe you are mis-reading it)? If it's significantly larger in size than your motor, maybe it's a 2 hp motor. If it is larger, maybe it's worth the gamble to buy it and find out.
Wade Lippman wrote:
Power ratings on electric motors are "variable". As the mechanical load on the motor increases the motor will draw more juice to carry the load. The only thing that prevents the motor from developing near infinite amounts of power is heat. The more juice the motor pulls, the hotter it gets. When it gets hot enough the winding solder joints melt and the electrical insulation cooks. Physically bigger motors have more surface area to dump heat into the air. For continuous duty (say turning a pump) a bigger motor has more power than a smaller one, because the bigger one has more surface area to exchange heat with the air. For intermittant duty (like starting a car engine) we can extract quite a bit more power, because we will turn the motor off before it overheats. The same motor might be able to develop many horsepower for a short period of time, but only a fraction of a horsepower for continuous duty. For instance you can overheat your starter motor by hanging on t he key and grinding away on a cold morning. The maker's marketing dept likes to sell the product by giving it the highest horsepower rating they dare, and they dare more and more as the years go by. Rule of thumb, electric motors of the same size and weight are good for the same amount of horsepower in real service (as opposed to marketing service). Motor current rating is usually concerned with fuse blowing. The motor draws its max current under "infinite" load, i.e. with the rotor locked. Some loads, (for instance table saws) can load the motor enough to stall it. The current rating is the the stall current rating. The 14 amp stall current will twist harder (produce more stall torque) than the 10 amp will. This is acheived by using a lower resistance (thicker wire) winding. Electric motors are better than 90% efficient. 100% efficient motors use 745 electrical watts to produce a mechanical horsepower. 90% efficient motors use 827 watts to produce a horsepower. 827 Watts is
6.89 amps on a 120 volt circuit. So, go with the 14 amp Craftsman if it is a deal. It will run just as cool as the original motor, and perhaps have a little more starting torque (which is a good thing). Or it might simply have a more marketing driven stall current rating. If they are the same size (aprox) then they will produce the same amount of useable mechanical power. The National Electric Manufacturers Association (NEMA) controls the rating of "standalone" motors, and NEMA requires a continuous duty rating for motor power. Tools with built in, cannot-be-sold-by-them-selves, motors like shop vacs and radial arm saws are not NEMA rated and the maker usually gives an optomistic peak power rating.
David Starr
Sears has never been known for being conservative in their claims of motor HP; quite the opposite, in fact.
Make sure you're comparing apples to apples, and not oranges: if the 10A rating on the Delta motor is continuous-duty current, but the 14A rating on the Craftsman motor is (as I suspect) locked-rotor current, you're better off with the Delta.
Your post is accurate as I see it with only a couple of small nits to pick about only" heat limiting power". All it needs is the stipulation that the motor stays in synch with line frequency. Power factor and pole-slippage also limits what one gets to test at the shaft.
Induction motors' biggest problem, aside from weight, is their limited RPM. To get the tip speed on small diameter components to a usable velocity, such as small router bits in edgebanders, for instance, one has to increase the frequency of the supply...IF one wants to deal with induction motors. Induction motors are preferred in those applications, simply because when they're held withing their operating range, the rotation speed is constant.
7 amps for a 1 HP induction motor at 120 volts is a reasonable yardstick.HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.