UPS Calculation

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Frikkenator

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Hi guys,

I've seen some guys on here are quite clued up on UPS related matters so I'm hoping someone can help.

We've got a total load of only 200W that we need to keep running for 4 hours.

Currently I'm looking at the following, and I need to know whether it will work or if there are better/cheaper options:

*If the links don't work just copy and paste into a new window, dunno wtf they're not working otherwise.

1x 1000VA UPS (Link)
2x Battery Packs (Link)

Thanks!
 
I've actually started looking into this as well today, and from what I have learnt, it seems that an Inverter would work better (a UPS only lasts about 15 minutes). I found this article, which might help explain inverters:
Choosing the Right Inverter

The difference between an inverter and a UPS is that the inverter feeds power to your devices directly from the mains when there's power and only switches to battery when the power goes down (so there's a lag where your devices might turn off). The UPS feeds all power into the battery first (so there's no lag when the power goes off).

However, I'm also looking forward to the experts helping us out here! :)
 
That thing won't even power your devices for 15 minutes. You need something with much more reserve capacity...or a generator...or both.

edit: apologies, I see now its 200w and not 2000w! :D

To answer your question, theoretically you should be god to go
 
Last edited:
200W for 4 hours is 800 Watt Hours
Then if you are running off 12v you divide the Wh by the voltage to get the amp hours you will drain from a 12v battery:
800/12 = 67 Amp Hours
Batteries should not be fully drained so you need twice that amount for a deep cycle battery aka at least a 134Ah battery.

Your load is constant so you need an inverter that has more than a 200W ability(remember some appliances have a higher startup draw so add some fat in here)

In short you are looking for a system with at least a 134Ah 12v(67Ah if its 24v) battery and a 400W inverter.


EDIT:
I see your link has 48v battery packs with 36Ah total:
864VAhx2/48v= 36Ah@48v

So if we take your 800Wh need and devide it by 48v:
800/48=16.6Ah
We then double the amount so not to draw more than 50% of capacity and get 33.3Ah

So yes the parts you linked to should be perfectly fine.

By the way the site has charts so I didnt need to do math :) :


Curve Part Number(s)
A SURT1000RMXLI
B SURT1000RMXLI + (1) SURT48RMXLBP
C SURT1000RMXLI + (2)SURT48RMXLBP
D SURT1000RMXLI + (3)SURT48RMXLBP
E SURT1000RMXLI + (4)SURT48RMXLBP

Untitled.png
 
Last edited:
Relooking at this, those expansion battery packs are overkill for what you're intended use is :wtf:
 
Beachless said:
200W for 4 hours is 800 Watt Hours
Then if you are running off 12v you divide the Wh by the voltage to get the amp hours you will drain from a 12v battery:
800/12 = 67 Amp Hours
Batteries should not be fully drained so you need twice that amount for a deep cycle battery aka at least a 134Ah battery.

Your load is constant so you need an inverter that has more than a 200W ability(remember some appliances have a higher startup draw so add some fat in here)

In short you are looking for a system with at least a 134Ah 12v(67Ah if its 24v) battery and a 400W inverter.


EDIT:
I see your link has 48v battery packs with 36Ah total:
864VAhx2/48v= 36Ah@48v

So if we take your 800Wh need and devide it by 48v:
800/48=16.6Ah
We then double the amount so not to draw more than 50% of capacity and get 33.3Ah

So yes the parts you linked to should be perfectly fine.

By the way the site has charts so I didnt need to do math :) :


Curve Part Number(s)
A SURT1000RMXLI
B SURT1000RMXLI + (1) SURT48RMXLBP
C SURT1000RMXLI + (2)SURT48RMXLBP
D SURT1000RMXLI + (3)SURT48RMXLBP
E SURT1000RMXLI + (4)SURT48RMXLBP
Click to expand...

Thanks for the great explanation, now I also know how these calculations work :D
 
bekdik said:
Go to this site, click on Home, Office and you will get options as to how you want to calc
Click to expand...

Yea I did that, they recommended a 5000VA with one extended run battery which costs in total more than double this setup. And it uses a fraction of the capacity so your efficiency drops drastically. Overall the recommendation made no sense.
 
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Frikkenator said:
Those are actually quite awesome and really well priced, thanks! Unfortunately though we have some serious space constraints which will prevent us from using something like that :(
Click to expand...

You could go with this but they are pricey:

http://www.victronenergy.com/inverters-chargers/multiplus-12v-24v-48v-800va-3kva/

I have one of these (1200VA) with a deep cycle 102Ah 12V battery and it lasts me for around 4-6 hours depending on what I plug into it. They are kickass units with good support.
 
Last edited:
CriticalConsumer said:
The can be rack mount...just not standard rack mount shelf heights.
Click to expand...

Just had a look at the datasheet and they are actually tiny! The batteries less so, but still usable. Do you use those, and what region are we talking about when you say pricey?

I'll stick to the UPS for our current requirements but that there is somewhere else we can use those.
 
Frikkenator said:
Just had a look at the datasheet and they are actually tiny! The batteries less so, but still usable. Do you use those, and what region are we talking about when you say pricey?

I'll stick to the UPS for our current requirements but that there is somewhere else we can use those.
Click to expand...

You are looking @ around R21k retail pricing with 1x 100Ah battery for the 1200VA. I use one as my primary source of power when Eksdom decide to have blackouts. You can connect the units in parallel and also attach solar panels to them...

I do supplement them with APC units for other sensitive equipment that need less power.
 
Last edited:
CriticalConsumer said:
You are looking @ around R21k retail pricing with 1x 100Ah battery for the 1200VA. I use one as my primary source of power when Eksdom decide to have blackouts. You can connect the units in parallel and also attach solar panels to them...

I do supplement them with APC units for other sensitive equipment that need less power.
Click to expand...

That's not bad! We specifically need the on-line UPS in this case, but I can see a use for this in the future. Who did you buy from?
 
wvantzand said:
I've actually started looking into this as well today, and from what I have learnt, it seems that an Inverter would work better (a UPS only lasts about 15 minutes). I found this article, which might help explain inverters:
Choosing the Right Inverter

The difference between an inverter and a UPS is that the inverter feeds power to your devices directly from the mains when there's power and only switches to battery when the power goes down (so there's a lag where your devices might turn off). The UPS feeds all power into the battery first (so there's no lag when the power goes off).

However, I'm also looking forward to the experts helping us out here! :)
Click to expand...

Only the expensive OnLine UPS's do this, the Line-Interactive ones (One's most people use) feed mains and switch to battery before your computer notices.
Whilst Line-Interactive UPS's start pricing in the mid to upper hundreds depending on capacity and brand your OnLine's will start in the multiple thousands of rand price bracket.
 
In general, is an inverter cheaper than a UPS? (For a similar wattage and up-time)
Edit: I'm also not sure that I understand the whole set-up... Is a UPS usually inclusive of a battery, or can you switch out batteries? Are batteries the biggest expense when looking at a UPS or inverter?
 
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