# What is the HP of my motor?



## yukon_rose (May 13, 2020)

I have an old Repulsion-Induction motor with no nameplate. Well it actually has a nameplate but it is so destroyed that I might as well not have it.

However, I was able to read the name of the manufacturer: Century Electric Motor Co.

I've determined the voltage as 120VAC by experiment.

The motor needs new bearings but is otherwise just dirty. The brushes are in very good shape.

I  want to know the approximate horse power of the motor. Can I measure the rotor (and possibly count the number of windings) to tell what the HP is?

Gary


----------



## RJSakowski (May 13, 2020)

yukon_rose said:


> I have an old Repulsion-Induction motor with no nameplate. Well it actually has a nameplate but it is so destroyed that I might as well not have it.
> 
> However, I was able to read the name of the manufacturer: Century Electric Motor Co.
> 
> ...



If you have access to a clamp on a.c. ammeter, you can make a fairly good guess.  Measure the current draw under load and the  applied voltage..  Multiplying the two will give you power in watts.  Dividing the watts by 750 will give you the input horsepower.  Output horsepower will be approximately 80% of that number.  A rough estimate but better than nothing.


----------



## WCraig (May 13, 2020)

The size of the motor shaft is often another clue.  A 1/2" shaft is usually less than 1/2 horsepower.  A 1-1/8" shaft is in the 3 HP range.

Craig


----------



## Bi11Hudson (May 13, 2020)

I have a couple of old Craftsman motors that are 1/2 HP with a 1/2 inch shaft. A 5/8 shaft would likely be a 3/4 HP. 3/4 inch shaft would be 1.0 HP. These are not hard and fast shaft sizes by any means. But for small motors would provide a reference point.

I haven't seen a repulsion/induction motor since the 70s when I was on a ship. An old ship~~~ The estimates above may not apply that well. The motor could well be a "special" application. But it does give a starting point.

Without a prony brake, setting the load would be difficult at best. Load it up until it runs *warm*, not hot after five minutes.
.


----------



## WCraig (May 13, 2020)

The Vintage Machinery website has some photos of Century motors, from 1/2 to 7.5 HP.  Maybe you can find something close.  They also have a series of Publication Reprints that might help.



			Century Electric Co. - Photo Index  | VintageMachinery.org
		


Craig


----------

