Computer on UPS


#1

Total load of my PC is 600W. Can someone tell me how do I ensure that the UPS I get does not make my PC restart when the light goes. Also, will the UPS trip when the battery is low? Because low battery = low voltage = computer damage.

I already have a UPS in mind, its 1KV but I just dont know if it will restart my PC and whether it will automatically shut down when the battery is low.


#2

Make sure you buy a UPS and not a Inverter+Charger. I would recommend APC Smart UPS 1000.

APC will give you audible warnings when battery is getting low.

Computers have Switch Mode Power Supply (SMPS) which does not get damaged by low voltage. However UPS should not lower its o/p voltage when battery gets low. It will instead stop the inverter at low battery.

For reliable operation of computer on UPS, look for the UPS which has transfer time of <5ms

Check the specs of your (in mind) UPS before buying.


#3

check the link

http://www.digitech-ups.pk/index_files/Page491.htm


#4

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#5

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#6

[quote=", post:4, topic:14472"]

UPS with modified sine wave current is also not so good for computer.

[/quote]

Not correct - For computer power supply, it really does not make any difference whether input is a square, sine or modified sine wave. This is becasue of the fact that AC input is converted to DC (at very first stage) and then the rest of circuit starts working with this DC voltage.


#7

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#8

[quote=", post:7, topic:14472"]

But when my PC runs on UPS, I hear motor cycle engine like noise coming from the speakers. In speakers, AC is also converted into DC. On my LCD monitor display, sometimes, blur lines appear when it is on UPS. So, why this happen? Modified sine wave current is the reason. I checked the frequency of Homage UPS current via digital multimeter, and it was showing 1.8 kHz value when UPS was providing current from backup batteries, and 50 Hz when it was on WAPDA. Any idea!

[/quote]

Well, your audio system must have a power supply (may be internal or external adapter). If this power supply is based on conventional transformer, then there will be HUM sound in the speakers if input mains in not sinze wave.

Your LCD monitor, though has a switched mode power supply, might mis-behave if

(1) this power supply has power factor correction

(2) if some part of incoming AC is tapped to derive a 50Hz signal ( or a time base for some circuits inside).

As regards the frequency shown on digital multimeter, 1.8KHz is a wrong figure and the reason is that low cost digital meters are calibrated / designed to measure frequency of sine wave only (this saves money on internal hardware of multimeter). A true RMS meter will show correct reading.

Have you noticed that APC (a well respected name in computer UPS) and many others make modified sine wave UPS for computers and millions of units are sold every year.


#9

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#10

[quote=", post:9, topic:14472"]

Low cost multimeter! I think, I have the expensive one. What I have read about APC, they make UPS with ‘‘stepped sinewave’’ current. Infact, UPS with ‘‘modified sinewave current’’ can be used but it shortens the life span of electronic devices, and this is my personal experience. My old PC and a DVD player used to run on UPS but couldn’t last long.

[/quote]

Ok, for the information of all, I will check the output waveform or APC and Mercury Radiant 1000 and will post the results.

Even if your meter is expensive and capable to measure any kind of waveform, I still can not believe 1.8KHz, but as I said, I will continue this discussion once I have seen those waveforms.

To my knowledge (till date) stepped sine and modified sine wave are both same terminology and refer to same thing.


#11

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#12

[quote=", post:11, topic:14472"]

Pure sine wave current UPS’ are available?? Any brand?

[/quote]

yup i think APC … i am using this one… http://www.apc.com/resource/include/techspec_index.cfm?base_sku=sua1500i

with external batteries and i am loving it…


#13

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#14

Really disappointed from Ahmed Talal, if he is not sure about any things, why write first and after sometimes delete everything (at least 6 times in this thread alone) making it difficult for others to follow complete story. Purpose of editing is to improve post and not delete everything. Do not know why administrators of forum promote such members as platinum member.

Just want to share my personal experience about UPS for computer.

It is simple UPS like we are using for other purpose like fans, tube lights etc. Only difference is that the main card is different and is capable of better voltage control. It is 500 Watt UPS with AGS 120AMP battery. Price of normal UPS is Rs 7000 and this one with better card is Rs7500 in Lahore. With my 23inch LCD and computer (built-in VGA, no special card) it is providing backup of more than 100 minutes. Do not play games or any heavy load work. It is only one month that I am using it and so far there is no restart problem except one time and that can be some other problem as well. My computer as whole takes 170 watts on average

There is one strange issue which I did not know before it. Normal UPS provide more than 300 volts (without any load), but under load provide almost 220 volts. Keeping this decrease in voltage, it asked UPS technician to design my UPS for 240 volts (without any load) so that under load it will provide 220 volts approx. But to my surprise, computer load does not make any real difference in voltage except a decrease of 2 or 5 volts even after one hour of UPS backup. But when I disconnect computer and power on a bulb (60 watts), voltage drops to 220 volts.

So better to check this voltage drop when one goes for simple local UPS for computer use.


#15

[quote=“urbanplanner, post:14, topic:14472”]

Really disappointed from Ahmed Talal, if he is not sure about any things, why write first and after sometimes delete everything (at least 6 times in this thread alone) making it difficult for others to follow complete story. Purpose of editing is to improve post and not delete everything. Do not know why administrators of forum promote such members as platinum member.

[/quote]

exactly :slight_smile: or he is just increasing his posts? hehe