Odd power PDU problem

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QN: do I have a bad PDU?

3  servers, each connecting to 2 PDU's via dual power supplies.
Each PDU was showing 6.3 A load. (15 A max.)

When moving all 3 outlets off PDU so it could be physically moved, PDU
B tripped its overload breaker.

The nameplate load of the 3 servers is > 15A, but the combination of 2
x 6.3 (measured Amps) is not.

So, it seems either:
 - PDU B is bad
- the measurements of 6.3 A on each circuit is incorrect
- there is a power draw spike when servers switch from 2 power supplies
to 1.

Does anyone know if the latter case is true?
Or have other theories?

Re: Odd power PDU problem

stevergfrancis@gmail.com wrote:

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There are some pictures here, of what the current consumption of
a computer power supply looks like. They show an oscilloscope
trace for PFC (power factor corrected) and non-PFC supplies. I know
my clamp-on ammeter has a lot of trouble giving a correct readout
on my non-PFC ATX supplies, for a computer in sleep, and it could
be the ammeter on the PDU is not measuring what you think it is.


Power factor is why there is a difference between the "watts" and
"VA" rating of equipment. The first article that came up in a
search for ("power factor", watts, VA) was this.


It could be the PDU display shows "watts", and the breaker is
seeing (2x6.3)/0.7 = 17.8A ?


Re: Odd power PDU problem

Paul wrote:
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There is no such thing as power factor for DC, which is what the
output of a power supply is.  You can talk about it on the input
(mains) circuit.  Power factors involve the phasing, which in turn
requires AC.  Thus, on the DC side, watts = V * A.

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