WELLSIANA - I suggest you study the EAWR and the small print of your insurance policy before doing work which you have to ask about on a DIY forum....
emergency stops
- Thread starter WELLSIANA
- Start date
Sponsored Links
Indiscriminate application of eddy current braking could result in arbours etc. unscrewing with the inertia of the wheel, potentially releasing a rapidly spinning grinding wheel to bounce around the shop a few times.
I have heard of a similar accident when the reversing switch for a 3-phase lathe motor was accidentally switched past 'stop' and into 'reverse', unscrewing a large, heavy and rapidly spinning 4-jaw chuck from the threaded headstock mandrel.
I have heard of a similar accident when the reversing switch for a 3-phase lathe motor was accidentally switched past 'stop' and into 'reverse', unscrewing a large, heavy and rapidly spinning 4-jaw chuck from the threaded headstock mandrel.
We fit two types of DC brakes - production and safety.
Production brakes will stop a motor under control, say 5-8s and are called upon with every stopping action - stop buttons, e/stop buttons etc. Great for woodworking machines though we've also fitted them to buffers which can sometimes take well over a minute to slow down.
Safety brakes will attempt to stop a motor as quickly as possible and are only called upon when a safety device has been activated - e/stop, telescopic probe, safedge etc. They require a reset before the motor can be re-started.
I've never been asked to fit either to a bench or pedestal grinder though.
Production brakes will stop a motor under control, say 5-8s and are called upon with every stopping action - stop buttons, e/stop buttons etc. Great for woodworking machines though we've also fitted them to buffers which can sometimes take well over a minute to slow down.
Safety brakes will attempt to stop a motor as quickly as possible and are only called upon when a safety device has been activated - e/stop, telescopic probe, safedge etc. They require a reset before the motor can be re-started.
I've never been asked to fit either to a bench or pedestal grinder though.
Production brakes can also be set to stop instantly, such as an elevation table on a production line, and cut the supply to the motor whilst holding the table in the elevated position. When the motor is re-energised the brake is released allowing the table to descend under control of the motor.
Safety brakes often use the phase reversal method which brings the motor to an almost instantaneous stop and then cuts the supply to the motor. As you say, these then have to be reset before continuing. One important thing to remember is never to rely on the brake holding the motor still while you work on a machine, always use additional methods such as chocks/props etc.
As the OP seems quite unsure how to tackle this problem I would suggest he declines to do the work.
Safety brakes often use the phase reversal method which brings the motor to an almost instantaneous stop and then cuts the supply to the motor. As you say, these then have to be reset before continuing. One important thing to remember is never to rely on the brake holding the motor still while you work on a machine, always use additional methods such as chocks/props etc.
As the OP seems quite unsure how to tackle this problem I would suggest he declines to do the work.
Sponsored Links
The brakes we use are DC injection, not phase reversal.
For example, a safety brake would be fitted to a radial arm drill. On activation of the emergency device, the AC supply would be removed and DC would be injected across one winding of the motor. On this occasion the result would be an almost instantaneous stop of the motor. As the resistance of the winding is a constant we can adjust the DC voltage which results in a current rise or fall to give us more control over the stopping of the motor.
For example, a safety brake would be fitted to a radial arm drill. On activation of the emergency device, the AC supply would be removed and DC would be injected across one winding of the motor. On this occasion the result would be an almost instantaneous stop of the motor. As the resistance of the winding is a constant we can adjust the DC voltage which results in a current rise or fall to give us more control over the stopping of the motor.
Just an industrial/commercial/domestic electrician.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
