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December 11, 2017

Induction vs. Universal Motors in Table Saws

Table Saw Induction MotorIf you have only ever used portable power tools like routers, circular saws and drills you have probably never given any thought to the two main types of motor that power electric woodworking tools – induction motors and universal motors.

It is also highly likely that you are not even aware that all your portable power tools use universal motors or even that there are other types of electric motor out there. All of that changes when you decide to look at larger shop-based woodworking tools, and the first time most woodworkers do that is when they think about buying a Table Saw.

What you will find is that there is a large difference in performance and price between the two, and, as with all power tool decisions, the starting point should be to ask yourself a number of questions regarding your planned usage:

  • HOW much do you want to pay
  • WHAT type of work are you likely to want to do
  • HOW often will you use it
  • HOW easy is it to set up

In order to help you make those decisions we will look at a number of differences between induction and universal motors. Please bear in mind that the aim of this article is to help you make your decision, and it is not intended to be an in-depth technical paper! If you want to get technical you can check out the Wikipedia article on electric motors

Size and Weight
Induction motors are typically larger and heavier than universal motors, making them the best choice for stationary woodworking machines like high end cabinet saws that benefit from the extra weight helping to keep them stable and reduce vibration.

The flip side is that their size and weight make them impractical for handheld or portable tools, which is why you will find all your handheld and portable power tools use universal motors.

Cost
Induction motors are more expensive and are therefore used in larger, top of the range woodworking machines such as cabinet saws.

Universal motors are less expensive and are used in smaller, less expensive power tools such as routers and circular saws. That doesn’t mean tools using universal motors are “cheap” – it’s just that a top of the range router isn’t in the same class as a top of the range cabinet saw.

Speed
Induction motors typically have a slower max speed, compared to universal motors. The higher speed of a universal motor means that you can get more power out of a small motor.

Torque at Start Up
Induction motors have less torque at start up – they’re like being in top gear – once they’re up and running you can run them all day long if you want, but they don’t particularly like to be stopped and started frequently. Induction motors are designed for continuous duty at full load.

Universal motors typically have great torque at start up that gets them working and up to maximum power quickly, so they’re good for short repetitive operations like drilling lots of holes, but they’re not designed to be run all day long which can cause them to overheat.

Longevity
Induction motors are long-lived and can easily last the whole of your woodworking life.

Universal motors don’t last as long as induction motors – this type of motor has a commutator with brushes, which will eventually wear out, and it’s not unusual for universal motors to burn out when subjected to continuous operation.

Noise
Induction motors are much quieter than universal motors.

Universal motors are noisy and it’s not a pleasant noise either. Until you understand the difference between induction and universal motors it seems counter-intuitive that large woodworking machinery is quieter than small handheld tools.

Standardization
Induction motors have been standardized by NEMA, which means that it’s possible to easily replace the motor in your machine with another motor made by a different electric motor manufacturer.

Universal motors are not standardized – once a universal motor packs in, that’s it! Modern universal motors are not replaceable or repairable – you have to replace the whole tool.

Energy Efficiency
Induction motors are highly efficient motors that require less amperage per horse power.

The Universal motor is an electrically inefficient design that draws high amperage for a  given horse power, and in some cases can generate enough heat to cause the motor to burn out when subjected to continuous operation.

Summary
Universal motors have been around for a long time, in small appliances and tools such as vacuum cleaners, circular saws and hand drills. The universal motor is compact, cheap to produce, and due to it’s high speed (10,000 rpm or higher is normal) can provide a lot of HP in a small package. They can easily be designed to run on AC or DC current. That’s why they are so popular.

Most tools that you own and other household appliances will have a universal motor, and it’s not until you start to look at tools where there is actually a choice between universal and induction motors (table saws being the first time for most woodworkers) that you need to think about the pros and cons of each.

As we said before, your usage will make a lot of the decision for you – if you want a portable table saw that you can take to the job-site, then your decision is made for you as you’re only looking at benchtop table saws and they all use universal motors.