Short Answer: No. Motor braking has no adverse effect on a machine or motor when used properly and in the right application.
If you want the longer and more technical answer, please continue reading or just give us a call.
Why it’s always good to ask
You’re probably reading this because you’ve identified motor braking as a great solution to this problem but you are asking yourself if there are any complicating factors you should be aware of. For most shop applications, motor braking is a safe and effective way to mitigate coasting tool hazards but, like any technology, you want to make sure it’s a good fit for your application. The following excerpts are pulled from conversations with our Founder, Scott Swaaley, a licensed electrical engineer and the inventor of the MAKESafe motor brake.
Table of contents
How does motor braking work?
Interviewer: You said in your demo that you are using a standard unmodified grinder yet it stopped in less than a second. How does that work?
Scott: Right – this is just a normal off-the-shelf grinder. All we’ve done is plug our product into the power cord so the braking you saw is all done electrically, through the power cord, using the machine’s own motor. The technique is called DC Injection and it’s been around for decades but it’s applications were historically restricted to large industrial machines. Our innovation is that we made it really, really small, we made it plug-and-play and easy to use, and we had the whole thing listed as a UL508 Industrial Motor Control.
Interviewer: But how does it work? Does it reverse polarity or something?
Scott: Well let me give a bit of background. When an AC induction motor is supplied with alternating current (the same kind of power you have in a normal wall socket), the current creates a rotating magnetic field that causes the rotor and shaft to rotate. This is how most industrial motors work. However, if that same motor is instead supplied with direct current (the kind of power you’d find in a battery), the current creates a stationary magnetic field that causes the rotor and shaft to resist rotation until the rotor stops completely. Thanks to Tesla (the man, not the car company), these everyday industrial motors are electromagnets that chase whatever magnetic field you create. If you create a rotating field, the rotor (the spinning electromagnet) chases it, making a motor rotate. If you make a stationary field, the rotor tries to be stationary, causing it to stop. In other words, all we’re doing is changing the type of field that gets created. And, of course, we’re doing it in a very compact and easy-to-use way.
Does motor braking hurt the motor?
Interviewer: Does this hurt the motor or shorten its life or anything?
Scott: From the motor’s perspective, the braking process looks very similar to the starting process. I like to think about it in terms of energy. When a motor is started, electrical energy is converted into mechanical energy by applying a turning force to the motor. This energy brings the motor from a kinetic energy of zero (at rest) to a kinetic energy of not zero, let’s say 100 joules to make things easy. When in braking mode, the motor does the same thing in reverse, converting electrical energy into mechanical energy by applying a turning force to the motor, only this time it’s in the opposite direction so the energy starts at the 100 joules (spinning) and is reduced to zero (at rest).
Interviewer: So no effect whatsoever on the motor?
Scott: Correct, unless you consider extreme cases. Energy conversion isn’t perfect so whenever you start (or brake) a motor, some of that energy is converted to heat instead of mechanical energy. In an extreme case, if you were to start and stop your motor over and over again without giving it time to run or rest, it could potentially get too hot. But it’s important to consider how extreme this case is for most operations. Motors have a standard limit of how hot they can get before the life of the motor is significantly impacted. Most industrial motors have a NEMA Class F rating (and often higher). This means that the maximum internal operating temperature for the motor is 155°C (311°F). And that isn’t even a failure temperature – it just the temperature at which the motor’s life will begin to be significantly impacted. To give that some perspective, if a motor was at that maximum temperature the outside of the motor would be around 125°C (257°F). So if you ever touch a motor and think “hrm, that’s warm”, it’s probably at about 40°C, less than a third of what the motor is rated to operate at.
Interviewer: So in layman’s terms ….?
Scott: If it’s a machine tool that’s getting used intermittently in a typical shop environment like 95% of our customers, then you have absolutely nothing to worry about. If you’re working in a production line setting where a machine is turned on and off quickly and repeatedly over extended durations, or if you’re already running a motor at or near it’s operating limit, then give us a call and we’ll help you determine if this technology makes sense for your application or not. And I also want to mention that motors are already installed with external or internal thermal overloads which protect them from high temperatures so protection from these conditions is already inherent in nearly every motor installation, even vintage ones!
Does motor braking hurt the machine?
Interviewer: So far we’ve just been talking about the motor. What about the machine it’s connected to – does braking have an impact?
Scott: Early in our UL508 listing process, a regulator asked me “But how do you prevent someone from plugging a toaster into it?” I’ll admit up front, I can’t guarantee that your toaster would still work or be safer to use (though I’m pretty sure it would). My point is that there is an infinite amount of machine types in the world, and I’ve seen some incredible (and less incredible) DIY machines in shops across the country, so we of course can’t guarantee every possible variation but I can tell you then we’ve worked very hard to validate our product through conservative design and in-field testing on every reasonably conceivable machine type, drivetrain variation, and machine vintage. We’re also the only motor control that can claim to have a full UL508 Listing (not just recognition) which is the gold standard for evaluation from an OSHA-regulated test lab. That being said, in an overabundance of caution, there are a few things to be aware of when evaluating, installing, and calibrating our product. They’re covered in detail in our user manual (and they’re mostly common sense) but to summarize, we give all of our customers the following advice.
Scott: First – when setting the aggressiveness of your braking, don’t brake the machine any faster than it starts. This is an easy way to ensure that the machine parts are not exposed to higher than normal stress levels. Second – if you’re machine has a reverse threaded spindle, use locking fasteners and ensure proper guarding is in place. And third – if you’re not sure about anything in the manual or your machine has an existing control system you need to integrate with, give us a call, we’d be happy to help.
Interviewer: One last thing – could braking make a grinder wheel explode?
Scott: Oh gosh no. A grinding wheel will experience the same forces during braking as it does during startup so it won’t know the difference. Grinding wheel explosions are caused by fractured wheels (see OSHA’s ring test), using a wheel on improper materials (like aluminum), exceeding their speed rating, or physically damaging them.
An All-In-One Solution
The MAKESafe Power Tool Brake is a plug-and-play braking solution that also includes anti-restart and emergency stop. All you have to do is plug it in, perform a calibration that takes less than five minutes, and you’ve added multiple machine safeguards to your machine. See the product demonstration video and specifications for more information.