Re: is the calculation right ?????
- From: "hurry" <hurrynarain@xxxxxxxxx>
- Date: 7 May 2006 23:04:53 -0700
Thnk you. had a good insight .
bye,
hurry.
Jeff Liebermann wrote:
"hurry" <hurrynarain@xxxxxxxxx> 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_for_extendedruntime.cfm?upsfamily=17
| http://www.apcc.com/products/runtime_for_extendedruntime.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 figure:
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/kill_a_watt_electric_usage_monitor_review
They're not exactly a precision instrument, but are useful in making
basic electrical measurements (including power factor).
--
Jeff Liebermann jeffl@xxxxxxxxxxxxxxxxxxxxxx
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
.
- References:
- is the calculation right ?????
- From: hurry
- Re: is the calculation right ?????
- From: Jeff Liebermann
- is the calculation right ?????
- Prev by Date: Re: ITT Tech
- Next by Date: Re: Help needed w/battery charger circuit
- Previous by thread: Re: is the calculation right ?????
- Next by thread: samsung ct-3352v
- Index(es):
Relevant Pages
|
Loading
