Stalling would like be required by the agency anyway since a typical failure is a jam or bearing failure that would lock the rotor.
Gary From: Richard Nute [mailto:[email protected]] Sent: Monday, December 16, 2013 11:03 AM To: [email protected] Subject: Re: [PSES] Cooling fan safety query Hello Ian: In my opinion, if you stalled the fan for all testing, there would be no reason to require the CFM rating. Stalling the fan would be the better course of action as this would require the fan motor to dissipate some power as well as the series resistor, thus causing more heat -- but not much -- in the equipment. Best wishes for the holiday season, Richard Nute Product Safety Consultant Bend, Oregon, U.S.A. On 12/16/2013 1:30 AM, McBurney, Ian wrote: Hello Rich; Can I suggest to the safety testing agency to disconnect or stall the fan rotor for all testing? Would this then mean the CFM rating for the cooling fan would not be required? Regards; Ian McBurney Design & Compliance Engineer. Allen & Heath Ltd. Kernick Industrial Estate, Penryn, Cornwall. TR10 9LU. UK T: 01326 372070 E: [email protected]<mailto:[email protected]> From: Richard Nute [mailto:[email protected]] Sent: 13 December 2013 20:06 To: McBurney, Ian; [email protected]<mailto:[email protected]> Subject: Re: [PSES] Cooling fan safety query Hello Ian: The first question is whether or not the fan is necessary to meet the temperature requirements of the standard. If yes, then the fan and its alternates must be tested to prove that the end-product meets the temperature requirements. A UL-certified fan should reduce the testing requirements. The fact that you put a resistor in series with the motor does not affect this requirement. However, in stalled rotor condition, the resistor must not exceed its power rating. The CFM rating of the fan is not applicable with a resistor in series with the fan. So, if meeting temperature requirements with the fan, it would be necessary to meet temperature requirements with each different fan (because the CFM cannot be predicted with a resistor in series). Model numbers of tested fans would be required, although I don't know why the CFM rating of each fan would be required since compliance with the temperature requirements would not be dependent on the CFM rating. If no, then the fan can be removed (or disconnected) and the end-product should meet all the applicable safety requirements, including the temperature requirements. Under this condition, the fan is just another functional component. Ask the cert house to perform all testing without the fan. However, the fans should meet the stalled rotor requirements and, if applicable, the plastic flame rating requirements. These should be a part of the UL certification. Also, the series resistor must be rated for the power dissipation in the stalled rotor condition. This may require testing each alternate fan; if so, each different fan must be identified. With best wishes for the holiday season, Rich On 12/13/2013 2:02 AM, McBurney, Ian wrote: This is a question for the safety testing engineers. We have products that contain 12V/24V DC cooling fans that cool either the PSU or processing circuits. The fan speeds are reduced with basically a series resistor to reduce audio noise. The safety testing agency demands to know the exact model number and CFM of each fan even though the products continue to function during the stalled rotor test. Obviously there is temperature rise within the product. My question is why does the agency list the exact model number and CFM rating of the fan even though it doesn't run at full speed and the product continues to function with a stalled rotor. We have to use alternative fans due to supply issues and this incurs considerable test agency costs as the agency won't accept a manufacturers range of fans without testing each one. All fans used are UL listed and the products are tested to IEC/UL 60065. Your comments would be appreciated. Many thanks in advance. Ian McBurney Design & Compliance Engineer. Allen & Heath Ltd. Kernick Industrial Estate, Penryn, Cornwall. TR10 9LU. UK T: 01326 372070 E: [email protected]<mailto:[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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