[time-nuts] HP and other equipment failure

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Sun Jun 16 02:50:25 EDT 2013


In the classical (transformer -) [bridge] rectifier - storage capacitor 
configuration, the capacitor charge current is creating short high peaks 
on the current waveform (and therefor truncate the peaks of the voltage 
waveform, the distribution circuit resistance being finite), due to the 
nonlinear load.
The negative effects are much more due to high current harmonics than 
(slightly) capacitive cos fi, and increase the losses in the 
distribution circuits.


On 6/16/2013 12:57 AM, Azelio Boriani wrote:
> Although off-topic here, the PFC (or power factor correction) is a
> switching mode front-end used to correct the cos-phi of the otherwise
> capacitive load that every switching mode power supply is for the
> mains.
>
> On Sat, Jun 15, 2013 at 11:52 PM, J. L. Trantham<jltran at att.net>  wrote:
>> Sorry for the interruption but what is 'PFC'?
>>
>> Thanks.
>>
>> Joe
>>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of Poul-Henning Kamp
>> Sent: Saturday, June 15, 2013 4:09 PM
>> To: Robert Atkinson; Discussion of precise time and frequency measurement
>> Cc: Perry Sandeen
>> Subject: Re: [time-nuts] HP and other equipment failure
>>
>> In message<1371329221.83869.YahooMailNeo at web171902.mail.ir2.yahoo.com>,
>> Robert  Atkinson writes:
>>
>>> While I agree with everything else you say, you CAN have too much
>>> filter capacitance. At least where dc rectifier / filter (smoothing)
>>> circuits are concerned. Increasing C causes increased ripple current
>>> [...]
>>
>> And ripple current can be a major source of power-line frequency noise in
>> all electronics.
>>
>> The main reason why switchmode power-supplies today (can) outperform linear
>> power supplies with respect to noise, is because the legally mandated PFC
>> correction eliminates the bridge-rectifier ripple harmonics.
>>
>> I would not hessitate to use a good quality switchmode to replace the linear
>> supply in a HP5370B.
>>
>> I did some experiments a couple of years ago, with an audio-amplifier:
>> I put a standard PFC corrector chip on the secondary side of the trafo.
>>
>> The overall result was not satisfactory, but the 50 Hz "sneer"
>> we all know and hate was absent, and the "Tzoing!!!!!" power-on mechanical
>> shock from the trafo was also eliminated, as was the consequent dimming of
>> the lights ;-)
>>
>> The main reason not to do this, is that you need some physically gargantuan
>> coils for a 10A+ PFC-switcher.
>>
>>
>> --
>> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
>> phk at FreeBSD.ORG         | TCP/IP since RFC 956
>> FreeBSD committer       | BSD since 4.3-tahoe
>> Never attribute to malice what can adequately be explained by incompetence.
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