Hi Richard:
> Can anyone comment how you may have handled motor protection > issues related to brushless dc motors? I'm particularly concerned how the > regulatory concerns, such as UL & CSA requirements for motor protection, > have been addressed. Any and all advice is appreciated. We can discuss this from a safety point of view, not necessarily from a standards point of view. First, for the purposes of safety, I am not aware of any distinction between brushless motors and brush motors. The basic issue with motors is they tend to over- heat under various conditions. The safety issue is to control the overheating such that there is no fire from the end-product. The first requirement is that, under rated load, the motor insulations don't exceed their ratings. This implies the motor insulation should last for the motor lifetime without failure. The next requirements are related to fire when the motor is subjected to (1) running overload, and (2) locked rotor. While these conditions could result in motor (insulation) failure, the motor should not itself catch fire, nor should it cause adjacent materials to catch fire. Any number of safeguards are available to prevent extensive overheating that might result in the motor insulation catching fire. Most motor safeguards involve disconnecting power from the motor. Some of these are thermal sensors, fuse, power source impedance, latch-off power supply, movement sensors, etc. We tend to use a latch-off power supply. So, we test at the max current just before latch-off. Our motors are permanent magnet motors that are encased in steel, which is a good heat-sink. We often get a partial winding short-circuit during the test, and we get some temperatures in the 250 C range, but not high enough to cause ignition of the cheesecloth or charring of the pine wood (UL's standard mounting for small motor testing). We sometimes get arcing when the windings short, and these can be exciting, but not usually result in a test failure. If the brushless motors use a control circuit, then you need to consider faults in the control circuit and whether or not these would result in motor overheating. Best regards, Rich This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
