"Rich Nute" wrote: > > Hi Doug: > > The issue for me is: What is the safety requirement > that requires cfm (I presume a minimum cfm)?
The issue is a Hazardous Energy ( > 240va). The power output that feeds the board is above the limit. The fan itself is more of an issue of having a baseline with which to allow alternates to be used. If I can prove by way of fan company documenation that the fan is x cfm, then that's the basis for any other fan being used. The NRTLs do only construction review and locked rotor testing. Add to that a plastic housing (that's approved), and then add additional heat to the from the chip in case of fan failure and that does becomes a concern. But the issue with the fan is simply a baseline. > So, I presume the safety requirement is that of > temperature of the PWB. Without the fan, the PWB > temperature would rise above the limit value specified > in the standard. It's possible. > For the purposes of safety, nobody cares whether the > fan is effective at cooling the chip, or even if the > chip gets so hot as to self-destruct. We are only > concerned with the temperature of the PWB. > > Working with these data, I see a number of ways out > of this predicament. > > 1. Control the fan by manufacturer's name and model > number. The cfm is not necessary. We simply > know by test that the cooling provided by this > specific fan is sufficient to keep the PWB from > exceeding the allowable limit. The mfr's p/n is not enough. > 2. Control the fan by electrical ratings and physical > size. The electrical ratings (power) are > proportional to cfm. Good point, but again, it's the cfm as a baseline. Thanks for your input ... Regards, Doug McKean ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [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.rcic.com/ click on "Virtual Conference Hall,"
