[quote=“nvd650, post:13, topic:16417”]

Again you are giving strange statements? there is nothing like 1000 will only run on 2 batteries, you can run it on 4 batteries and even on one battery… basically it is volts that is calculated for number of batteries, is it 12 volt, 24 or 48 volts?

1000 watt UPS running on 12 volt will drain battery in lesser time as compared to 48 volt running on 4 batteries (assuming that capacity of one battery is 200 amph and of 4 batteries it is also 200 amph- 50 amph for each battery)

[/quote]

First, let me say you do seem quite knowledgeable on local UPS scene and I have learnt quite a lot from your posts here.

You are bang on the money when you say that a 1000 watts UPS can have 1 battery or 4 batteries.

However I couldn’t stop my self when I read that a UPS with single battery will drain faster than a UPS with 4 batteries. Key point here is that single 12 volt battery is 200 Ah and 48 volt are 4 times 12 volt batteries with capacity being 50Ah as well.

To elaborate, UPS is just a voltage conversion device. It takes energy and converts into another form of energy like every single ‘machine’ out there and spends a small amount of energy during doing that conversion.

So energy output = energy input - energy consumed during the process.

Lets assume a load of 660 Volts-amps (VA and watts are not same and I pretty sure you know the relation amongst them, so not going into that discussion), also assuming a UPS efficiency of 85% (just a figure, it can vary hugely from UPS to UPS but doesn’t really matter in our discussion).

Hence input power required by the UPS will be = 660 VA / 0.85 = 776 VA

So the batteries will have to provide 776 VA in all. It doesn’t matter if we have a single 12V - 200Ah battery or 4 batteries with 12V and 50Ah.

Calculations:

Battery currents

For 12 V = 776VA / 12 V = 64.66 Amps

since our battery is 200Ah, it will drain completely in (200Ah / 64.66A ) 3.09 hours. (Theoretical value ofcourse, the UPS will go on to low battery mode long before that )

For 48 V = 776 / 48 V = 16.16 Amps

Battery is 50Ah, it will drain in (50Ah / 16.16 A) 3.09 hours also.

The point to note is when you put four batteries in parallel connection, you can add-up the current to 200Amps, but the voltage remains the same i.e. 12 Volts.

If you put the batteries in series connection (which is our setup) you can only add-up the voltage to 48, but the ampere-hour rating will remain that of one battery i.e. 50Ah in our case.

This is assuming that the UPS has same efficiency at 12 V battery input and 48 V battery input.

Untill here it was pure physics; my opinion is that 48V batteries will last longer because it will draw lower current (64 amps vs 16 amps) and hence lower heat dissipation and other losses. However the gain may be very small and negligible.

Bottom line is: the two setups will always give you same battery drain time.

Cheers,

Joji