Re: How do redundant power supplies in servers work?

On 9/11/11 6:47 PM, Chris Adams wrote:
> Once upon a time, Seth Mattinen <sethm-z7IltzP/[email protected]> said:
>> Yeah, any UPS that outputs a stepped approximation sine wave (rather
>> than a pure sine wave) will probably not play nice. Always go for the
>> pure sine wave models for important stuff. Of course, convincing a
>> client not to cheap out on the UPS is a different story.
> 
> A switching power supply (as found in all computer power supplies)
> really doesn't care.  There's a reason most modern supplies can run on
> any common power (50/60 Hz, 120/208/240 V).

PFC power supplies may care about waveform changes, however. Voltage and
frequency are always well within the acceptable range but when the
waveform goes from a nice sine wave to a jagged stepped thing can make
it drop out for a moment. (I suppose it could also depend on exactly how
stepped the approximated wave is, and I'd expect the cheapest of the
cheap UPS doesn't get more than basic attention in that respect.)

But this is only based on experience and an entry level Fluke scopemeter
so YMMV.


> Also, the referenced blog is wrong AFAIK; APC SmartUPS models are not
> online UPSes.  They do have a "pure sine wave", although APC doesn't
> give a total harmonic distortion, just the "pure sine wave" (marketing
> speak) line (or at least this was all true the last time I looked).
> 
> The only real take-away from that blog is that BackUPS are apparently
> crappy UPSes.

I do have a bunch of Back-UPS Pro series units on various things
(usually a single workstation) and I haven't had any switchover issues
with them. For the big stuff I've been using Eaton PowerWare three phase
units since about 2 years ago, prior to that Smart-UPS RT. At home I
have a non-pro that powers a table lamp.

For curiosity's sake I think I'll unrack a DL385 G7 tomorrow and put it
on a Back-UPS Pro and see what happens when it goes to battery.

~Seth
-- 
Eat sushi frequently. - Avi
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