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Home > Archive > Electrical Engineering > May 2006 > PDU tripping unexpectedly...
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PDU tripping unexpectedly...
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| stevergfrancis@gmail.com 2006-05-30, 3:21 pm |
| QN: do I have a bad PDU?
Symptoms:
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?
Thanks
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| Dale Farmer 2006-05-31, 1:21 am |
| stevergfrancis@gmail.com wrote:
> QN: do I have a bad PDU?
>
> Symptoms:
> 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?
> Thanks
>
with a dual power supply computer, when both supplies are running,
they usually are designed to share the load equally. So when you pull
the plug on power supply A, now power supply B is supporting the entire
load. So basically you doubled the load on the PDU when you shut off
the first one. ( handwaving power factor, derating and so on)
This is also an indication of a deeper problem in your data center.
If one of your PDUs goes down the other one is going to go down from the
overload. So your much more expensive dual power supply computers are
not actually protecting you from a PDU failure.
I suggest you get an experienced data center infrastructure person to
come in and do an assessment on the place, to identify other not so
obvious problems that are lurking for murphy to dump on you.
--Dale
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| stevergfrancis@gmail.com 2006-05-31, 2:21 pm |
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Dale Farmer wrote:
> stevergfrancis@gmail.com wrote:
> with a dual power supply computer, when both supplies are running,
> they usually are designed to share the load equally. So when you pull
> the plug on power supply A, now power supply B is supporting the entire
> load. So basically you doubled the load on the PDU when you shut off
> the first one. ( handwaving power factor, derating and so on)
> This is also an indication of a deeper problem in your data center.
> If one of your PDUs goes down the other one is going to go down from the
> overload. So your much more expensive dual power supply computers are
> not actually protecting you from a PDU failure.
Well, I know I doubled the load, but 2 x the shown 6.3 Amps per circuit
should still leave one circuit running at 12.6 A, which is less than
their limit of 15A.
So why the trip?
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