calculation for UPS

[robe]

THe standby UPS like APC Smart UPS are offline type of UPS and consume little power when not on battery mode. That means power consumed is mainly used by battery charger. Only the online type of UPS have losses of 2% to 8% due to double conversion circuitry. The smaller online UPS are APC Symmetra, MGE Comet or Liebert GXT, Powerware, etc.

You can parallel the small UPS but you need relays to cut in one after the other as the UPS might get damaged by the reversed voltage applied to its output. Only bigger 3 phase UPS can be paralled using a synchronising kit to ensure that the all outputs are in phases.

I will be replacing the batteries of my APC SU1000 prior to using it in my tank (I have 4 of them)....

[ervine]

just a simple question... where do we go to buy UPSs? Or shop around for them? Sim Lim?

[Rocky99]

Bro,

They are. Power backup units like the one Marineman is using come with a built-in 12V charger, and an inverter that converts DC to AC, and then is amplified back up to 220/240V, with our local frequency of 50Hz. This is the main reason why they're pretty expensive - it's not as easy as what most people think.

And with models like this, you can connect multiple 12V car batteries in parallel, thus increasing the Ah rating, and thus the power-up period during a blackout. Of cos, the more batteries you have, the longer it will take all of them to charge up.

i see.... thanks.....complicated stuff but interesting...

[surfedelic]

My company have alot UPS sort of chuck one side but they are 120 V type as it was meant for a mexico plant which just tore down .. and there are like 20 of them at least .... I think it is the SMART 1400 model ... but the problem is the input/output are all in 110/120 V - I am just wondering if it ok if I buy a stepdown transformer to connect from the mains to the UPS and then buy another step up transformer to connect to my pump ... do you guy think it will work ?

I just need to power up my pump for the circulation that's all.

[Marineman]

My company have alot UPS sort of chuck one side but they are 120 V type as it was meant for a mexico plant which just tore down .. and there are like 20 of them at least .... I think it is the SMART 1400 model ... but the problem is the input/output are all in 110/120 V - I am just wondering if it ok if I buy a stepdown transformer to connect from the mains to the UPS and then buy another step up transformer to connect to my pump ... do you guy think it will work ?

I just need to power up my pump for the circulation that's all.

When you buy a transformer, make sure it about 6 times higher in output, for example I bought a US 80 W pump runs on 110/120 V. I have busted a few transformers until DIY shop was able to check and work out the calculations for me. This is how they calculate, when pump is starting, it needs more power (3 times) and conversion from 110/120 to 220/240 is 2 times, there the right size transformer to run a 80Watts pump would be 80*3*2= 480 watts transformer. I bought one 800W transformer and it finally works!

[robe]

Why you need to use a bigger transformer for pumps ?

It is due to motor's low power factor which can be a slow as 0.6. This causes the transformer to overheat as the transformer is actually being overloaded.

If an electric motor pump is rated at 50 watts but its power factor may be 0.7. In this case you divide the rated power 50w by 0.7 which will give you the rating in VA (apparrent power). The 50w rating translates to 71.4 VA. That means the pump is drawing an apparent power of 71.4 VA.

Your transformer minimum power rating should then be 71.4 VA but transformers are recommended to be loaded continuously up to 70% to 80% of its rating. The transformer capacity in order to run your pump is now 71.4 VA divided by 80%. The minimum transformer capacity required to run your pump is now 89.2 VA. This is the capacity required to run the pump continuously

For start-up inrush current. It's about 2 to 3 times the rated fill load current. 50 watts /110V x 3 = 1.36 A. The inrush current will last a few hundred milliseconds but can be longer if your pump is stuck. Your transformer winding should be able to withstand the inrush current for a second or two without giving way. If you want to play safe the transformer rating have to be increase further to 3 times the minimum rating required or 89 x 3 = 267 VA. You can use a 250 VA rating.

Sadly most cheap transformers are overrated and some uses the same or slightly higher size wires for their windings. By right the primary and secondary for 220/110V should have the lower voltage output winding sized to carry at least twice the current of the primary winding.