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In the first part of this series our discussion turned away from the power of the motors and instead focused on the various types of sewing machine motors and defined the description of each type. This was important because there are so many different types ranging from easy to find to the impossible to replace motors. Most externally mounted motors are going to be relatively easy to find replacements for. Belt drive systems are easier than friction drives simply because there are more of them. Remember a friction drive motor turns the opposite direction of the hand wheel while a belt drive motor turns the same direction as the hand wheel. And gear drive systems follow the same laws of physics as a friction drive, and to my knowledge, they are going to be an OEM motor so replacements can be limited and scarce. In the later years of the all steel vintage sewing machine, manufacturers started adding a cover that enclosed the externally mounted motor and this eventually morphed into the fully enclosed motors and proprietary mounting on the inside of the machine bodies. During this time of metamorphosis these same manufacturers discovered plastic and from this point forward the long-term reliability was traded off for the lighter, quieter, easier to handle, cheaper disposable commodities.
Vintage sewing machine motors are brush type motors which by design can be operated either on AC current or with DC current. These motors allow for variable speeds simply by using a variable resistor to reduce the voltage being applied to the motor. This reduction of voltage through a resistor slows down the motor rpm for slower speeds. The downfall of this is it also cuts the motor power ratio down as well and the resistors will build a lot of heat as it slows the voltage down resulting in a foot pedal for the sewing machine getting hot when slow sewing is required over a longer period of time.
Typical household sewing machines use motors rated in tenths of an amp, with a shaft speed of 3000 rpm; keeping this as simple as possible it is the amount of power the motor is designed to use for the work it is designed to manage. Too much work on the motor and the amps will go above the rating, the shaft speed will slow down at full power and the motor will burn up. The smallest rated sewing machine motor I have personally seen to date is rated at .4 amps. These are found on very basic machines usually only straight stitch. As the functions of the machines increase so does the amount of work the motor needs to do and the motors will reflect this by being rated with higher amp ratings. So the more work means stronger motors needed. The higher the amps, the stronger the motor. The majority of household machines will use motors between .7 and 1.0 amps. Vintage sewing machines that have built-in decorative stitches or use a fashion disc or cam as it is commonly called will typically use motors rated at 1.0 amp up to 1.5 amps with some of the 1.2-1.5 amp motors turning a shaft speed of 5000 rpm. These motors may also utilize a dual rating system in which they show not only amps but also HP (horse power). A 1.2 amp motor at 5000rpm shaft speed will probably be rated at an equivalent of 1/20hp whereas a 1.5 amp motor equates to a 1/15hp.
All this being said not all sewing machine motors will utilize these types of rating systems. Some manufacturers of machines in different countries or motors intended to be shipped worldwide will use a rating system based upon the amount of energy absorbed into the work being performed. Much like a standard light bulb these motors are rated in watts. With the same results as a light bulb, the more light emitted the higher the watt rating, translates to the more work created for the motor to do the higher the wattage must be to do it.
Ok well, I hope I haven’t totally confused everyone yet. Sometimes I think I confuse myself and I know the end of the story. We touched upon the 3 basic motor rating systems and how they each relate to raw power contributed to the strength of the sewing machine. Motors alone do not make the machine strong. So next time we will explain a little about needle speed and gear ratio. Until next time enjoy your machines, and may your grandkids never cut cardboard with your shears.
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