hi,
I was trying to run my table fun on an UPS (660 VA, with full load time
10 mins). My table fan has a rating of 80VA. On searching on net for
calculation I came up with the following figu

time of run = 660/80 * 1.5 * 10 = 123.75 mins

The figure 1.5, to be applied if ( UPS rating / FAN rating ) = 660/80
(this case) is grtr than 3 else multiplying factor = 1.3, This was
from one of the pages, can someone reason out this.

I am not from an electrical background I was able to come up with this
figure after some googling.

but I find my UPS supporting my fan on an average of 1/2 hr. Can
someone verify this and tell me wat am I missing .

"hurry" wrote in message
oups.com...
hi,
I was trying to run my table fun on an UPS (660 VA, with full load time
10 mins). My table fan has a rating of 80VA. On searching on net for
calculation I came up with the following figu

time of run = 660/80 * 1.5 * 10 = 123.75 mins

The figure 1.5, to be applied if ( UPS rating / FAN rating ) = 660/80
(this case) is grtr than 3 else multiplying factor = 1.3, This was
from one of the pages, can someone reason out this.

I am not from an electrical background I was able to come up with this
figure after some googling.

but I find my UPS supporting my fan on an average of 1/2 hr. Can
someone verify this and tell me wat am I missing .


Some batteries discharge at differant rates depending on the load. Usually
the smaller the load the longer the discharge curve. That is if you draw
the full 660 VA the battery will last 10 minuits or a factor of 1. If you
only use say 66 va the supply should last 100 minuits, but it may last 1.5
times longer than this because the current load is much less than its
maximum ratings.

Even without the multiplying factor it should run 660/80 x 10 or 82.5
minuits.

The batteries may be old and weak.

"hurry" wrote in message
oups.com...
hi,
I was trying to run my table fun on an UPS (660 VA, with full load time
10 mins). My table fan has a rating of 80VA. On searching on net for
calculation I came up with the following figu

time of run = 660/80 * 1.5 * 10 = 123.75 mins

The figure 1.5, to be applied if ( UPS rating / FAN rating ) = 660/80
(this case) is grtr than 3 else multiplying factor = 1.3, This was
from one of the pages, can someone reason out this.

I am not from an electrical background I was able to come up with this
figure after some googling.

but I find my UPS supporting my fan on an average of 1/2 hr. Can
someone verify this and tell me wat am I missing .

How old is the UPS (battery age)? Where is the 660 VA for 10 minutes listed?
Some of these are a little on the optomistic side. 660 VA for 10 minutes
would need somewhere around the capacity of two 7 amp hour, 12 volt
batteries. (7ah * 12volts * 2= ~168 watt hours) * 6 (the 10 minute run
time) = 1008 watts for 10 minutes. This is reasonable considering conversion
inefficencies, and heat generation in the batteries due to fast discharge. I
picked 7 ah batteries for the calcs because that's what's common for that
size UPS. The runtime should be longer for smaller loads because of the
battery discharge rate. As in, it might do 100 wats for much longer than an
hour.

"hurry" hath wroth:

I was trying to run my table fun on an UPS (660 VA, with full load time
10 mins).

Make and model of UPS please? Many UPS manufactories lie as to their
runtime. The usual problem is that they can't seem to agree on
exactly when to declare the runtime over. Is it when the battery
alarm declares that the battery needs a charge? Or is it when the UPS
quits altogether? Does one shutoff the load when the battery is
discharged to 70% of capacity (to not destroy the battery by
discharging to zero), or do they just run the battery into the ground.
Hard to tell what the 10 minutes really means as each vendor seems to
have their own definition and tests.

There are also some oddities. Note that the runtime at half load is
far more than twice the runtime at full load. For example, see:
| http://www.apcc.com/products/runtime...m?upsfamily=17
| http://www.apcc.com/products/runtime...dedruntime.cfm
for some APC UPS's. At full load (300w), the BK-500 will go for 2
minutes. At half load (150w), the BK-500 will go for 14 minutes. I'm
not sure I could supply a suitable physics explanation of why
batteries deliver less power near full load. You cannot use a linear
calculation to calculate UPS runtime.

My table fan has a rating of 80VA.
On searching on net for
calculation I came up with the following figu
time of run = 660/80 * 1.5 * 10 = 123.75 mins
The figure 1.5, to be applied if ( UPS rating / FAN rating ) = 660/80
(this case) is grtr than 3 else multiplying factor = 1.3, This was
from one of the pages, can someone reason out this.

A fan is a motor which is an inductive load. The UPS runtime
measurements were probably tested with a purely resistive load. Unlike
the AC power meter, which works on a power factor corrected billing,
the typical UPS has no power factor correction on the load. It works
on volts times amps with the worst case numbers. No power factor
correction. My guess(tm) is that the 1.5 is someones attempt at PF
correction or perhaps preserving the battery at some level above where
the UPS just craps out. Hard to tell.

I am not from an electrical background I was able to come up with this
figure after some googling.

but I find my UPS supporting my fan on an average of 1/2 hr. Can
someone verify this and tell me wat am I missing .

Sounds like old batteries. Runtime drops as the batteries get old.
Try the same test with an incandescent light bulb of known wattage.

You might wanna invest in one of these:
| http://www.the-gadgeteer.com/review/...monitor_review
They're not exactly a precision instrument, but are useful in making
basic electrical measurements (including power factor).

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Thnk you. had a good insight .

bye,
hurry.


Jeff Liebermann wrote:
"hurry" hath wroth:

I was trying to run my table fun on an UPS (660 VA, with full load time
10 mins).

Make and model of UPS please? Many UPS manufactories lie as to their
runtime. The usual problem is that they can't seem to agree on
exactly when to declare the runtime over. Is it when the battery
alarm declares that the battery needs a charge? Or is it when the UPS
quits altogether? Does one shutoff the load when the battery is
discharged to 70% of capacity (to not destroy the battery by
discharging to zero), or do they just run the battery into the ground.
Hard to tell what the 10 minutes really means as each vendor seems to
have their own definition and tests.

There are also some oddities. Note that the runtime at half load is
far more than twice the runtime at full load. For example, see:
| http://www.apcc.com/products/runtime...m?upsfamily=17
| http://www.apcc.com/products/runtime...dedruntime.cfm
for some APC UPS's. At full load (300w), the BK-500 will go for 2
minutes. At half load (150w), the BK-500 will go for 14 minutes. I'm
not sure I could supply a suitable physics explanation of why
batteries deliver less power near full load. You cannot use a linear
calculation to calculate UPS runtime.

My table fan has a rating of 80VA.
On searching on net for
calculation I came up with the following figu
time of run = 660/80 * 1.5 * 10 = 123.75 mins
The figure 1.5, to be applied if ( UPS rating / FAN rating ) = 660/80
(this case) is grtr than 3 else multiplying factor = 1.3, This was
from one of the pages, can someone reason out this.

A fan is a motor which is an inductive load. The UPS runtime
measurements were probably tested with a purely resistive load. Unlike
the AC power meter, which works on a power factor corrected billing,
the typical UPS has no power factor correction on the load. It works
on volts times amps with the worst case numbers. No power factor
correction. My guess(tm) is that the 1.5 is someones attempt at PF
correction or perhaps preserving the battery at some level above where
the UPS just craps out. Hard to tell.

I am not from an electrical background I was able to come up with this
figure after some googling.

but I find my UPS supporting my fan on an average of 1/2 hr. Can
someone verify this and tell me wat am I missing .

Sounds like old batteries. Runtime drops as the batteries get old.
Try the same test with an incandescent light bulb of known wattage.

You might wanna invest in one of these:
| http://www.the-gadgeteer.com/review/...monitor_review
They're not exactly a precision instrument, but are useful in making
basic electrical measurements (including power factor).

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558