Comparing Sewing Machine Motors in Simple Terms

Let’s try and answer these questions in a simple manner, but with some explanations to help it all make sense, and we’ll start with some of the basic terms.  Or, if your having a little insomnia, reading this should cure it in no time.  

• AC- Alternating current
• DC – direct current
• Universal motor- runs on either AC or DC
• Amps- the amount of power drawn by the motor.

Universal motors have been used quite successfully on domestic sewing machines for the last centrtuy or so. These motors are durable, compact, provide good torque (pushing power) at start-up and are well suited to this application.

They are not used on machines that are operated continually as one would find in a factory setting, and for good reason, Their design is better suited to the start and stop sewing as you will find most home sewists doing.  I routinely encounter universal motors on sewing machines that are 50, 60, 70 years old or more, that operate superbly with just a little “tune-up”. 

It’s inaccurate to refer to these motors as “AC” motors as they are quite different in design than motors that operate exclusively on AC (alternating current).  The universal motor can use standard household,  AC supplies while having have some characteristics more common in DC motors, specifically high starting torque and  a compact design. 

As you may already know, universal type electric motors are used in railway applications because of their ability to produce high starting torque. 

The speed controllers for universal motors are actually a simple, variable switch. Not too different from the dimmer switch on your dining room wall. The resistors in the controllers that manage the flow of electrical power to the motor can be wire wound, carbon pile or basic electronic devises.

Yes, you can use an electronic controller on a traditional (inc. vintage) sewing machine. The electronic controller will NOT increase the power of the motor in any way. It simply regulates the amount of electrical power reaching the motor.

Most Sew-Classic machines can be upgraded to an electronic controller. If you have a habit of doing extended, continual, slow speed sewing, you may find the mechanical resistor type controllers (carbon pile or wire wound) get warmer than you like. Under these conditions, the plastic, electronic controllers are a good option.

In the 1970’s electronic controlled DC motors began appearing in domestic sewing machines. The main advantage for this type of motor is that it can be precisely controlled (starting, stopping and speed) via more complex electronic controls or computers.

The reason these motors are used on so many modern machines isn’t a matter of power, It’s a bit like buying a model A Ford. You can have any color you want, as long as it’s black!

The DC motors are the only option when using advanced electronics or computer controls. These DC motors run cooler by design and have the ability to accept precise computer and electronic controls. You know the little motors inside your PC? They’re all DC motors too, and for the same reasons.

Put simply, this makes a DC motor the only option for sewing machines with advanced electronics or computerized controls.

These machines also have a series of DC stepper motors moving various parts of the machine as directed by the computer. This, rather than a mechanical cam stack, is what gives them the ability to make hundreds of decorative stitches.

From a physics standpoint, there is more to the equation of piercing power at the needle on a home sewing machine than just the motor.

Heck, just remember Granny’s old treadle?? No motor at all, yet granny could sew just about anything on that machine. Was brute, granny power really the secret? Was it because she ate her spinach and Wheaties everyday? Well…. physics played a role. The hand wheel on Grandma’s treadle was a large diameter, heavy hunk of spinning mass. 

Add to that the even larger, cast iron fly wheel at the base. These heavy, spinning, rotating masses along with all the heavy metal rotating masses within the machine supply a great deal of kinetic energy to the system.

So, the faster the machine goes, the more kinetic energy that is created and the more piercing power you will have on these older, all metal, vintage machines.  Image two balls rolling down the street.

One is an air filled, rubber play ball, and the other is a heavy, 4 foot wide cast iron ball. Which will be more likely to push you over if you stand in the way? That’s kinetic energy.

On newer machines, you don’t have these heavy rotating masses as part of the equation, so there really isn’t the increase in piercing power as the machine speeds up. The marketing gurus for the sewing machine companies translate this factoid into “full piercing power at any speed”.

Not only does a machine’s mechanical design provide power, but it’s condition as well contributes to the mix. Any friction within the system steals away power. So, a machine that is clean, properly oiled and lubricated , and in correct adjustment will always perform better.

So, should you get a machine with a DC motor or an universal motor?? It’s really not the primary choice that you will be making. It will be a side effect of the type of machine that you choose.

For more information about comparing a new machine to a quality vintage machine, check out this article : Choosing a Sewing Machine – New, Used or Vintage?

OK, amps… Is more amps always more power at the needle?? Well…sometimes. There are several factors at play here. A vintage straight stitch machine will generally require less amperage to produce the same piercing power by virtue of have fewer friction points within the machine.

Also, the quality and condition of the motor is an important factor to consider as well. The gear ratio between the motor pulley and the hand wheel will affect both speed and piercing power as well.

Unfortunately, there is no gauge that we can set directly on any machine and easily measure piercing power. I rely upon actual application (sewing with the machine) to gauge the piecing power at the needle. Decide on the type of material you’d want to sew, test it out first. 

Be certain that the machine is in top mechanical order and that the proper needle type and size is being used. Generally speaking, you want to use the smallest diameter needle size as possible that will not bend or break with the type of material you are sewing. 

Original Author, Jenny – Sew Classic Shop