UPS for heavy load 42 Computers

I need to run my office 42 computers... the office is located in rural madurai and there often power cut... I have generator but the power will shut for 20 mins and come back after that 1 Hr again power cut like this it is going and coming.. so generator is good for using in this place... so I need to use ups that gives backup for atleast 3Hrs... for other appliances i will use generator but for PC alon I need UPS so what ups can I use... I went to vendor he gave me estimate for 7.5KVA... is this enough for 42 computers...??? if so means I have an idea to buy 8 1KVA ups so that any trouble in one ups can't affect other work... pleas geuide me.... I may go wrong....:-(

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and my PC is dual core, 250Gb HDD, 2Gb RAM, Intel Board, 15.6" LCD display, KEy board and mouse,

7.5 KW/42 ~150 watts each, seems about right, why don't you google your computers to find out what the actual wattage is? Out of interest, if you switch all the computers off then switch them all on at the same time, there will be a big surge in power, make sure that any UPS system you use can cope with this or make some other arrangement, i.e. switch the PCs one after another. Make sure that the "1 KW UPS" can actually support 1 KW for the specified time period. What you should be doing is to use the UPSs to hold up the PCs while your own generator starts. This means that the batteries in the UPSs can be very much smaller (5 mins against 3 hrs = ~3% of the size!!)
Frank

chuckey said:

What you should be doing is to use the UPSs to hold up the PCs while your own generator starts. This means that the batteries in the UPSs can be very much smaller (5 mins against 3 hrs = ~3% of the size!!)

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I agree but that approach may mean extra wiring; one set for the PCs only [connected to the UPS], and other set of wiring for the printers, scanners, etc.

This is what I would do;

Cluster say 5 to 10 PCs to one UPS, each UPS to have a delayed [and settable] power off [to avoid over-loading the generator, and the initial voltage spike]. Equipment like printers, scanners, etc not on the UPS circuit.

The UPS power [AH] is tricky, as you need to have enough to last until the generator kicks in and settling time, and in your case, enough reserve power to handle the next power outage - the batteries need time to re-charge. Better too much, than too little!

Don't forget to include the switches, hubs, server etc.

In my opinion use a single UPS . If you use 8 UPS it lost lot of current as losses .and a lot of places.
Calculate the full Load with the help of an electrical experts and take decision.

Thanks for the advice... I need backup for atleast 30Mins because running generator for 30Mins is more cost than batteries... The power fluctuation is often so that i need backup for atleast 30mins to one hour...

chuckey said:

7.5 KW/42 ~150 watts each, seems about right, why don't you google your computers to find out what the actual wattage is? Out of interest, if you switch all the computers off then switch them all on at the same time, there will be a big surge in power, make sure that any UPS system you use can cope with this or make some other arrangement, i.e. switch the PCs one after another. Make sure that the "1 KW UPS" can actually support 1 KW for the specified time period. What you should be doing is to use the UPSs to hold up the PCs while your own generator starts. This means that the batteries in the UPSs can be very much smaller (5 mins against 3 hrs = ~3% of the size!!)
Frank

Click to expand...

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Yes so I can do as like this....

kam1787 said:

I agree but that approach may mean extra wiring; one set for the PCs only [connected to the UPS], and other set of wiring for the printers, scanners, etc.

This is what I would do;

Cluster

say 5 to 10 PCs to one UPS, each UPS to have a delayed [and settable] power off [to avoid over-loading the generator, and the initial voltage spike]. Equipment like printers, scanners, etc not on the UPS circuit.

The UPS power [AH] is tricky, as you need to have enough to last until the generator kicks in and settling time, and in your case, enough reserve power to handle the next power outage - the batteries need time to re-charge. Better too much, than too little!

Don't forget to include the switches, hubs, server etc.

Click to expand...

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What I thought is if there are number of small units servicing and repairing won't affect the whole system and also a problem in single unit will not impact on others...

thannara123 said:

In my opinion use a single UPS . If you use 8 UPS it lost lot of current as losses .and a lot of places.
Calculate the full Load with the help of an electrical experts and take decision.

Click to expand...

kanni1303 said:

What I thought is if there are number of small units servicing and repairing won't affect the whole system and also a problem in single unit will not impact on others...

Click to expand...

Quite so - as well if one UPS fails, the rest keep going. With one central unit if it fails you have nothing, Plus space considerations, plus vendor support, plus wiring.

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kanni1303 said:

Thanks for the advice... I need backup for atleast 30Mins because running generator for 30Mins is more cost than batteries... The power fluctuation is often so that i need backup for atleast 30mins to one hour...

Click to expand...

30 minutes is a long time - bigger AH batteries - you might need to add batteries to the UPS for greater AH.

I would not rely too much on what the vendors state - in my experience they tend to over-state. Check the reviews, or do your own testing.

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there is a good discussion here for AH http://cr4.globalspec.com/thread/32655/How-to-calculate-the-required-AH-for-ups