UPS battery

#1

I am considering to get a APC 1KVA UPS (custom fitted with a good charger) for around 7800. I plan to use a 100AmpHr EXIDE car battery with it to power 2 fans, 2 to 3 tube lights, PC with CRT and TV.

Any ideas about how much backup time will it give? and are the ratings of local EXIDE car batteries somewhat precise or the same as is the case with desi stuff :-)?

#2

1KVA is not enough for your listed equipment. In this capacity, you can either run the PC with CRT OR the TV but not both.

1 Fan = 100 watts approx

1 tubelight = 40 watts

CRT/TV = check labels on these as rating depends on CRT tube size

Sum it all up and you will get total rating in watts. For APC UPS, 1KVA is approximately equal to 850 watts (taking power factor of 85% due to near sine wave output)

For Desi UPS, power factor is about 60% due to sqaure wave output. So 1KVA of Desi UPS means 600 watts of power.

Hope you get the idea. By the way, APC website has a calculator for checking UPS sizing. Maybe that will help as well.

To estimate backup time, check factory provided battery rating. Backup time will be 10 minutes with that battery on full load (1KVA). Let's say the factory provided battery is 50Ah..so 100Ah battery will give:

* approx 20 minutes of backup time for 1KVA load

* approx 40 minutes of backup time for 500VA (half of 1KVA) load

... and so on

Cheers

#3

yar what hapens if the load on ups increases than specified

and what iz kva y dont they use watt as unit?

How many kvas are real equal to wats

these things realy confuse me

#4

I just checked the power consumption with clampmeter at the main power meter. It was 2.5 amps with 4 tube lights 2 fans and tv and PC running.

Power (wattage) = Current (amps) x Voltage

2.5 (amps) x 220 (volts) = 550 watts

I have also heard the values kuya said but aren't the measured 550 watts value low considering the load that i just mentioned for the test

Correct me if i am wrong

#5

i dont want to hijack this thread, but just needed to know about the other type of UPS that are available with wet batteries, are they good? which is better the dry one's or the wet ones. i think i have got a bargain on one with a wet battery

#6

[quote=", post:, topic:"]

I just checked the power consumption with clampmeter at the main power meter. It was 2.5 amps with 4 tube lights 2 fans and tv and PC running.

Power (wattage) = Current (amps) x Voltage

2.5 (amps) x 220 (volts) = 550 watts

I have also heard the values kuya said but aren’t the measured 550 watts value low considering the load that i just mentioned for the test

Correct me if i am wrong

[/quote]

550 watts, for 4 tubes and 2 fans seems ok. I have a 1 KVA (650 watts) UPS with 128Ah FB battery, and wht I exactly tested was 200 watts ran for 3.5 hours. the max recommended wattage for 1 KVA is not more than 500 watts.

ShoukaT, when load increases the UPS has a breaker which turn the UPS output off. but u have to avoid this practice as much as u can, because ur UPS life reduces as the breaker is basically a heat sensor on the capacitor, if capacitor heats up to a certain level, the breaker trips off.

#7

[quote=", post:, topic:"]

i dont want to hijack this thread, but just needed to know about the other type of UPS that are available with wet batteries, are they good? which is better the dry one’s or the wet ones. i think i have got a bargain on one with a wet battery
[/quote]

if u avoid desi made ups, then all r good with wet battries. I am not sure if high capacity dry cell battries are available easily in pakistan. u can go for excide or FB which r good. anyway wet battries are selling in black these days, so hurry.

#8

#9

Battery type does not make much difference as far as the UPS operation is concerned. It does make difference though in costs and maintenance requirements.

Sealed/Dry Batteries are maintenance free, typically 4-5 years life but cost more.

Wet batteries need topping up with distilled water, typically 2 years life but cost less.

For cost comparison, 40Ah wet battery is around 3500 in Karachi whereas same rating Sealed Battery (good brand like power sonic) will costs around 8500.

#10

Remember, most devices, including light bulbs and tubes, require more amperes "when starting" than when simply running. Not sure if this applies to PC's though.

#11

[quote=", post:, topic:"]

yar what hapens if the load on ups increases than specified

and what iz kva y dont they use watt as unit?

How many kvas are real equal to wats

these things realy confuse me

[/quote]

#12

[quote=", post:, topic:"]

Not sure if this applies to PC’s though.
[/quote]

it applies at least to the monitor

#13

@Shoukat: To convert from KVA to KW, you need to consider the power factor. As stated earlier, for Desi UPS, power factor is about 60% due to square wave output whereas it may be as high as 80% for computer grade UPS which has near-sinewave output.

1000VA or 1KVA rated Desi UPS will provide around 600 Watts of power.

1000VA or 1KVA rated Computer Grade UPS will provide around 850 Watts of power.

UPS ratings are always listed in KVA. Its industry standard.

#14

kuya, 1KVA Computer Grade UPS will be advertised by the Company as having 850 Watts of Power? Or it will be advertised as 600 Watts of Power but can actually take up loads up to 850 Watts? Because I have seen APC's 1KVA models ranging from 600Watts to 700 Watts, with different prices of course.

What exactly causes the different of Watts for the same 1Kva? Batteries or something else?

#15

^ Charging rates/current maybe?

#16

Nope...nothing to do with battery or charging current etc. Its the power factor. Seems like a definition is in order:

The power factor of an AC electric power system is defined as the ratio of the real power to the apparent power, and is a number between 0 and 1 (frequently expressed as a percentage, e.g. 0.5 pf = 50% pf).

Real power is the capacity of the circuit for performing work in a particular time. (This is what we measure in watts)

Apparent power is the product of the current and voltage of the circuit. (This is the VA or Volts x Amperes)

Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power can be greater than the real power. Low-power-factor loads increase losses in a power distribution system and result in increased energy costs.

Typical examples of non-linear loads are fans and flourescent lights with ballast.

Now in case of UPS's (and Generators), the better the design/type of UPS, the higher the power factor. In plain english, the higher grade UPS will be able to provide "real" power almost as much as its rated "apparent" power....that is....the ratio of real power to apparent power (power factor) nearest to 1.

So you need to take note of rated Watts when purchasing UPS/Generators. Don't decide on the VA or KVA rating alone as it does not indicate "real" power the UPS/Genset can provide.