Best Ferrups Size of Electric Service Requirement

[Steve Thomas]

Does anyone know why the specified electric service capacity for these and
other UPS systems is more than twice the UPS load capacity? There is no way
that operating the battery charger as well as the rated load is going to add
up to any thing like the KVA rating specified for the service needed to
supply the UPS. So why does the manufacturer specify such a large service?

 

[danny burstein]

Does anyone know why the specified electric service capacity for these and
other UPS systems is more than twice the UPS load capacity? There is no way
that operating the battery charger as well as the rated load is going to add
up to any thing like the KVA rating specified for the service needed to
supply the UPS. So why does the manufacturer specify such a large service?

twice as high sounds a bit much, but you do need significant reserve:

a) when you have a continous load on a circuit, you're
supposed to *derate* the ampacity by 20%

So, for example, if you've got a line going out of your
breaker panel rated at 20 amps, you should only pull
a maximum of 16 amps in continuous duty.

and

b) the Ferrups will add a penalty of (WAG) 10% when in
operation. So that 1 kva load is really, to the breaker
box, pulling 1.1 kva.

and finally

c) after the power failure (or, for that matter, a
system test), the UPS will not only draw the power
for the load (plus 10%) but will also draw additional
power to recharge the batteries.

So a doubling sounds a bit high, but the math is easier...

 

[clare @ snyder.on .ca]

Does anyone know why the specified electric service capacity for these and
other UPS systems is more than twice the UPS load capacity? There is no way
that operating the battery charger as well as the rated load is going to add
up to any thing like the KVA rating specified for the service needed to
supply the UPS. So why does the manufacturer specify such a large service?

Because a Ferro is VERY in-efficient.
It makes a lot of heat. It causes significant harmonics.
IIRC it has a non-unity power factor
Inrush current

There are better units than Ferros today - a good dual conversion unit
like a Powerware 9000 series a case in point.

 

[Steve Spence]

power factor and heat.

watts does not always equate to V*A

much electricity is wasted in heat generation.

a APC 3000 is rated at 1600va/1160 watts output with a 20 amp input, but is
rated at 3000 va / 2700 watts output with a 50 amp input. 50 amp input
indicates it might draw a maximum of 6000 va charging a dead battery, 20 amp
indicates a maximum inrush of 2400 va, nowhere near the rated output of the
device.

http://apcmedia.apcc.com/pdf_downloads/tracking.cfm?part_num=996-1060I&country=all

--
Steve Spence
Renewable energy and sustainable living
http://www.green-trust.org
Donate $30 or more to Green Trust, and receive
a copy of Joshua Tickell's "From the Fryer to
the Fuel Tank", the premier documentary of
biodiesel and vegetable oil powered diesels.