[time-nuts] HP5370 power supply measurements

Chuck Harris cfharris at erols.com
Fri Jul 15 10:06:44 EDT 2016

It is important to remember that the fans specified in
most of this equipment are sized so that the instrument
can operate safely, in a rack full of equipment, at the
maximum temperature rating for the instrument.

If you plan to run at a comfortable room temperature,
you can usually get by with a much smaller fan.

It might be nice to leave a label somewhere that says
what you did, so the next owner won't be unpleasantly
surprised by it failing in his desert tent.

-Chuck Harris

Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
> On 13 Jul 2016 08:31, "Charles Steinmetz" <csteinmetz at yandex.com> wrote:
>> An external fan blowing on the heatsink keeps my 5370s nice and cool, for
> about $10 each.
> So more noise.
>> *if the counters were operated 24/7/365*.  I sometimes take data for a
> few months straight, but very, very far from 24/7/365 on average.  So for
> me, break-even would be more like 50 years.
> I don't suppose Poul's main motivation is to reduce his electric bill.
>> Speaking of fan noise -- you can't really get away with replacing the
> internal fan with one that moves less air, so it is hard to find a
> replacement that generates significantly less noise.  If you find one,
> please share the make and model -- all 5370 owners would love to know.
>> Best regards,
>> Charles
> Surely one of the main  advantages of the SMPS route is the higher
> efficiently means less cooling air is required.  That means less noise.
> I often here of people replacing fans with quiter ones, but I suspect that
> all they really do is reduce the airflow. I believe that most of the noise
> one hears is the movement of the air.  From what I have read, sleve bearing
> fans make a bit less noise than ball bearings fans.  However,  although the
> MTBF of both types is similar at 20 degree C, the MTBF of sleve bearing
> fans decreases quite a bit with only a modest increase in temperature.
> Dave.
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