Differences in electric motors

[SolarAndWood]

I have a few electric motors I have collected over the past few years. The motor I use on my splitter is stamped as 5hp, 3400 RPM, single phase 220 and 15 amps. It came off a rotted compressor that was probably 20 years old or so. I have another motor that weighs many times more than this one. It is a Westinghouse that is stamped 1.5hp, 3450 RPM, single phase 220 and 15 amps. I think it came off an old piece of industrial equipment. Is it as simple to deduce from this that the older motor produces 1/3 the power with the same current or is there more to it than that?

 

[Mcbride]

I personally find those old motors are far more powerful than their rating compared to the newer ones.
I replaced an electric motor in my shop about 5 years ago.
The new one rated at 7.5 hp cannot do the work of the one it replaces rated at just 5 hp.

Just my experience, but i am far from an electric motor know it all.

 

[jimbom]

Something doesn't add up for me. Check out this web site. http://www.engineeringtoolbox.com/elctrical-motor-full-load-current-d_1499.html

The information in NEC Table 430.248 seems to match the information shown on the above web site.

 

[SolarAndWood]

Maybe you add the current on both legs of the 220 for that table? I have the splitter on a pair of 20 amp breakers and it has only tripped a handful of times.

 

[SolarAndWood]

The new one rated at 7.5 hp cannot do the work of the one it replaces rated at just 5 hp.

Just my experience, but i am far from an electric motor know it all.

I wonder the same thing. I don't see how it is possible that the old one is less than a third as efficient as the newer old one.

 

[bogydave]

This may help

http://www.engineeringtoolbox.com/electrical-motor-horsepower-d_653.html

http://www.engineeringtoolbox.com/electrical-motor-hp-amps-d_1455.html

% Efficiency is a variable.
Typically, current (amps) & voltage being the same, HP should be very close to the same.
My guess is the 2 motors, you describe, are close to the same HP.

Some older ones may be rated at the pulley calculated with the specific equipment mechanics factored in which
gave real usable HP at the work end,
now, I believe, most all motor data plates rate specs at the motor shaft.

But it comes back to the math in the above link for HP rating. (Watts/746--- Watts = Volts x Amps)
Your motors calculate to be 4.4 HP with no % efficiency loss calculated (which will mean, less HP, around 3.75 real HP)
220V x 15 Amps / 746 x .85 (*high side efficiency of 85%) = roughly 3.75 HP

Check your house voltage, it may be single phase 208 & not 220, (some motors are rated for 230V, 240V which skews the HP you will get
plugged into your 220V outlet & causes the motor to heat up more--less efficient)
"Load" vs "No load", start current, torque & duty are also variables to be considered.

Best Answer: Try it, if it works, great. If it overheats (smokes, gets too hot to touch) after 15 minutes or trips circuit breakers, it won't work.
*****Just have it electrically grounded well! Plug into a well grounded outlet. Make sure ground (green wire) is connected to the motor frame.
Run a ground wire from the motor the frame to the splitter frame. Mounting a elec motor on wood can cause an electrical shock !! if not well grounded.
Don't count on mounting bolts for electrical ground.*****

I've found that the older motors were built heavier duty, but have less electrical insulation(a shocking issue), so a ground wire to the case is a MUST.
Many old motors will not work on a GFI circuit for this reason.

 

[SolarAndWood]

My boss told me that electric motors have been all over the place over the years. Early cast ones were more efficient than the later ones with the cheap sheet metal but the windings in neither compare to what we have today. He thought that the difference in windings could very well be the difference in hp and thus efficiency given they use the same current. I have a little splitter with a single stage pump that I am going to put the old motor on and see how it does. With as few hours as go on a splitter in a year, the difference in efficiency probably doesn't matter as long as it can adequately power the pump.

 

[JustWood]

From scraping them out i know that the older ones have 2-3 times the copper in them and Lincoln motors are mostly aluminum.