[Nut-upsdev] Re: CyberPower 685AVR and newhidups

Peter Selinger selinger at mathstat.dal.ca
Mon Oct 31 17:28:18 UTC 2005

Charles Lepple wrote:
> On 10/31/05, Scott Alfter <scott at alfter.us> wrote:
> > ups.power.nominal=552 (close enough to 550 for government work)
> > ups.delay.shutdown=-1 (what you said it should be)
> > ups.test.result=Done and passed
> >
> > Is there a reason why it should return 550 VA?  The specs for this UPS
> > say it should be good for 685 VA.  (390 W is also specified for it,
> > which is what you were getting earlier.)
> Peter, how are you calculating VA?
> VA really isn't going to be much help in the EU where power factor
> correction is required (so VA and watts will be equal). However, we
> only have a variable for "power", and often UPS manufacturers don't
> distinguish between VA and apparent power.

Unfortunately, NUT specifies that the unit of the "power" variable is
VA, not W. My understanding (partly from the USB HID Power Devices
spec) is that W is true power, whereas VA is "peak V" times "peak A".

I have converted W to VA by multiplying by sqrt(2).  
So 390 * 1.4142136 = 552.

Perhaps I should round this number to the closest 5, 10, or 25? 

The manufacturer indeed specifies 390W and also 685VA (see
http://www.cyberpowersystems.com/CP685avr.asp); this does not make any
sense to me. Certainly, we don't get any report from the UPS involving
the number 685. In fact, the UPS claims it is a "BF700", not a
"685AVR" or "BF685"; however, no such product exists on the web.
Probably "BF700" was their original name, and some marketing types
decided at the last minute that "BF685" sounds sexier, but they forgot
to change the name on the chip. 

Since 390W is the lower of the two values, I assume it is probably the
correct one. "Watts" is a well-defined and measurable unit, whereas a
"VA rating" could be something from the manufacturer's dreams. So
probably their "VA rating" is an exaggeration.

In any case, none of these variables have any bearing on the
functionality of NUT; they are just provided for information, along
with the device name, manufacturer, and serial number. 
> > (With the subsequent tests complete and the UPS supplying power to the
> > server again, the load is indicated as 53.0.  This is for a 1.0-GHz
> > Athlon (Thunderbird core) with two hard drives (one 10-krpm SCSI and one
> > 7200-rpm IDE) and a 14" or 15" CRT (not sure which).  I suspect that the
> > load isn't scaled properly.  Runtime is down to 690.)
> 60 W / 12.0 = 5, so 53.0 * 5 = 265 W
> is 265 W too low for that setup?
> (load is usually a percentage of full power)
> --
> - Charles Lepple
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