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]
*From:*Richard Nute [mailto:[email protected]]
*Sent:* 13 December 2013 20:06
*To:* McBurney, Ian; [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]>
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