Jump to content

Designing a UPS system


Forkinhades

Recommended Posts

How to design a simple UPS system

1. Calculating your power need

For this example I am going to use

1 Modem/Router 20W

2 Desktop Computer 250W

3 Monitor 50W

4 Networked Attached Storage 15W

5 Fan 50W

So the total power required is 385W

2. Calculating required inverter's capacity

Now that you know how much power is required, it's easy to get the VA rating of inverter. In ideal condition, the VA rating would have been same as the power need i.e. 385VA. But in practical conditions, the power factor of Inverter is less than 1 hence power supplied by 385VA Inverter won't be 385W but lesser than that. Assuming power factor of Inverter to be 0.7, following are the details of calculation -

Required VA of Inverter X 0.7 = 385

Therefore Required VA of Inverter = 385/0.7 = 550

3. Calculating battery capacity

Till now, you will have clear understanding of the Inverter capacity required for your need. But the next question is that how much back up will the inverter provide and for how many hours you can run all of your equipment. This is where battery capacity comes into picture. It's the battery which determines the back-up hours. The higher capacity battery you have, the more back-up hours you'll get. So let’s get into the calculation fast.

Required power (in Wattage) X Required back-up hours (in Hours) = Inverter Voltage (in Voltage) X Battery Capacity (in Ampere Hours)

Let's look for an Inverter which can give back-up of up to 1 hour, so for our case -

385W X 1Hours = 12V X Battery Capacity

Therefore Battery Capacity = (385 X 1)/12 = 32 Ampere Hours

So we need a battery of 32AH capacity. So that should be more or less sufficient for your need.

For my equipment I just want my computer to shut down, along with my NAS to save my hard drives and data, so I just really want my battery to last for 10 mins, whilst hard drives spins down, and computer turns off. So I can divide the 32AH by 6 (60/6=10mins)= 5.33AH

I actually bought a Leonics 650va UPS for this which has a 7AH Battery, and under test it actually lasted for 45mins, before critical beeps occurred from the unit. The graphical display had 4 bars, and 1 bar was left, so possibly had an hour of runtime.

So my next assignment is to swap out the battery, and replace with 32AH which hopefully will give me about 4.5 hours of runtime.

Link to comment
Share on other sites

There's a couple of pieces of the puzzle I think need to be added to this..

Seeing as most UPS's are using Lead Acid batteries, one must also take into consideration the battery "Depth of Discharge" (DoD) - which has a direct effect on battery life:

slalifecycle.png

As you can see, if you discharge a lead acid battery 100%, after just 200 cycles you've lost between 20-40% of it's capacity, and after 200-300 cycles, it's toast. Some cheaper/lower end batteries will become unserviceable after just 40 or 50 100% discharges though.

Most commercial UPS systems will only go to 50% DoD in order to provide decent battery life - if you've ever done the math on a commercial UPS and wondered why the runtimes the manufacturer publishes are so low, now you know why wink.png

Off grid solar systems, where battery lifespan is paramount usually target only 20% DoD - i.e. they install 5 times the battery capacity they would need if discharging 100%, and then multiply that again by the number of autonomy days required to make the system last throughout stormy seasons when the solar energy harvested is low (typically 1.5x to 3x).

One other thing you need to also consider if simply adding a bigger battery to and existing UPS is the fact that the battery charger in the UPS has a fixed maximum charge current, so that bigger battery will take longer to recharge (assuming you discharged it for a longer period). While this might not seem too much of an issue, it is if the battery is so big that it can't always be fully recharged between cycles - constantly under-charging a lead acid battery will result in heavy sulphation of the plates, and very quickly reduce it's life.

Link to comment
Share on other sites

  • 1 month later...

Are you wanting to be more frugal, with the devices, or is that what your working with?

Besides that 50W on cooling,that is excessive.

Also this sticky fails to address the fault condition expectations, and such factors as online, double online, voltage drop protections, filtering.

What you are talking about is dead simple.

Furthermore a power factor of .7 is quite poor, if you were in a double online unit, even a fully stacked. 3.5kVA to 10Kva would make you afraid to open your electrical bill I am sure anywhere in the world with such losses.

The topics of shutdown signals, just need the PC to be graceful, NASs u can probably just die on ac out depending on what it's doing / sophisticated it is.

Sent from my iPad using Tapatalk HD

Link to comment
Share on other sites

  • 3 weeks later...

I cannot take any credit for this...
however it should be a sticky.
I first saw this here...
http://icrontic.com/article/super_ups
16 May, 2007
This link is still good, I checked.

Then here
http://www.thaivisa.com/forum/topic/517870-ups-battery-question/
wherein Crossy mentioned this..
http://www.thaivisa.com/forum/topic/490635-help-me-wire-my-house/

Pics [Crossey]...
post-39337-0-10792400-1409917641_thumb.j

post-39337-0-95317400-1409917672_thumb.j

post-39337-0-73410200-1409917729_thumb.j

post-39337-0-94022100-1409917763_thumb.j
note: I can not tell if the are 4 or 6 batteries,
likely running at 24v, using regular auto-batteries.
Crossey stated [then] the inverter came from Zeer rangsit.
He did not mention it's cost, nor the batteries used.

PIC [Naam}
post-39337-0-99542000-1409917797_thumb.j
Naam mentioned the inverter came from Europe.
Did not mention it's cost.
Obvious he is using big batteries from 16-wheeler's.
A pair in series for 24v.

and [astral]
post-39337-0-96978800-1409917827_thumb.j

Crosseys unit did go thru abuse during the big flood,
and recently died, having to be replaced.
He mentioned that towared the end of his excellent post...
http://www.thaivisa.com/forum/topic/671221-build-a-low-cost-semi-automatic-generator-transfer-switch/

I need to mention the batteries.
Note that all the above is using flooded wet cells.
-Not SLA (sealed lead acid)
-Not those 'maintaince free"
-Not AGM (absorbed glass matt)
-Not Deep cycle marine batteries.
Note:
here (LOS) the AGM is very expensive
also the marine deep cycle,
both hard to find.

Batteries in Thailand are Crap.
Not built on a 'standard' we are use to,
[Europe or USA] where they easily last +5 years, and endure winters.
See these threads...
http://www.thaivisa.com/forum/topic/404855-car-battery-lifespan/
http://www.thaivisa.com/forum/Brand-Auto-truck-Battery-t215776.html

In any regard
one should have some tools for battery maintenance,
such as
- a multimeter (at least)
- a battery hygrometer
- and perhaps a secondary charging unit
see this...
http://www.thaivisa.com/forum/topic/404855-car-battery-lifespan/
and
http://www.ctek.com/gb/en/chargers/12v
there are several models...
They are available here in LOS.

Link to comment
Share on other sites

Hi crossy,

yep my bad, I do know the difference,

just posting this took 2 hours,

I really had issues with TV, and should have linked that,

and should have spell checked more closely.

And thank you for that recent excellent 'generator' thread,

and the 'disconnect switch' thread.

CAN YOU please take over the thread, and make it a stickey.

You have so much more to offer...

Link to comment
Share on other sites

  • 2 weeks later...

Crossy,

Can you please tell us about your Inverter UPS.

Where did you buy it, TPE or Amorn.

Cost?

How effecient is it?

Can it really do 2000 watt?

Does it need fan cooling?

What do you suggest for batteries?

- 4 as in your setup or 2 as in Naam's?

Well, you get the guist of it.

Thanks for your imput!!!

And thanks for merging this!

Link to comment
Share on other sites

OK, firstly I cannot recommend the unit shown in my images!

It has a number of issues (biggest is slow changeover on power fail) and is currently only powering lighting. It also has (very) noisy cooling fans which run constantly even when it's only charging the batteries.

They also seem rather delicate when it comes to power surges, we lost at least two under warranty (fixed FOC), none since adding a quality surge arrestor.

That said, I tested it to 1500W on resistive loads (kettles), worked fine. Not so wonderful on electronic lighting (LED and CFL) at only 200W the inrush current tripped the beast and it failed to start correctly. It's currently driven by a single 12V pickup truck battery (same as my Ranger) and will run all night driving the bedroom fan (on the lighting circuit) so we don't need to run the genset at night.

Our current arrangement has each piece of technology on its own cheapo UPS (Refurbished, 850 VA, 1000 Baht from Zeer) which keeps stuff alive whilst the genset starts (30 seconds delay).

Link to comment
Share on other sites

Many thanks for the reply Crossy.

So in essence, it's a cheap Chinese POS.

Please tell us it's name so we can avoid it.

There must be better inverter units to be had.

Perhaps from the USA or Europe.

In as much I really like the auto-start genny...

and the auto disconnect switch...

I just don't have the tools since the flood.

Wish I could get Naam into this thread, I don't know how...

I seem to recall his unit was from Europe, perhaps Germany?

Naam please help us.

Link to comment
Share on other sites

Many thanks for the reply Crossy.

So in essence, it's a cheap Chinese POS.

Please tell us it's name so we can avoid it.

There must be better inverter units to be had.

Perhaps from the USA or Europe.

In as much I really like the auto-start genny...

and the auto disconnect switch...

I just don't have the tools since the flood.

Wish I could get Naam into this thread, I don't know how...

I seem to recall his unit was from Europe, perhaps Germany?

Naam please help us.

i bought my units in India, they are Chinese products but i am very happy with the performance. two of the (meanwhile 4 units) are in service since 6 years. two other units which broke down could be locally repaired for a few hundred Baht each.

in between (for testing purposes) i imported some units from Europa (Chinese products too) which lack two required main functions, namely integrated battery charger and automatic switch from public grid to batteries and vice versa.

note: not all Chinese products are crap!

Link to comment
Share on other sites

I cannot take any credit for this...

however it should be a sticky.

I first saw this here...

http://icrontic.com/article/super_ups

16 May, 2007

This link is still good, I checked.

PIC [Naam}

attachicon.gif05-naam-ups-inverter-setup.jpg

Naam mentioned the inverter came from Europe.

Did not mention it's cost.

Obvious he is using big batteries from 16-wheeler's.

A pair in series for 24v.

that's unit #2, an "Indo-Chinese" inverter, operational since 6 years, connected in series to 2 truck batteries each 160Ah. switching time <20ms (my PC doesn't even blink when there is a brown-out or complete failure of the phase). the unit serves my study and my TV-room.

unit #3 serves my wife's TV-room as well as her study.

most important is unit #1, function to power 2 water pumps (house watet supply).

recently i installed unit #4 which powers a microwave.

Link to comment
Share on other sites

Thank you gentlemen for the reply...

Naam, yes I am fully aware the Chinese can build good stuff.

that said, you know a good deal of it is POS.

I'm trying to get to the 'good stuff'.

And yet neither of you has said the 'name' of what you bought.

It possibly does not matter, as the units are re-branded.

Possibly all mfg from one place in "Schezwan China".

But we can at least try to determine what is a decent unit.

I need a minimum of 2 units.

Perhaps 3.

So do I just google-foo for days...

then just trust a 'wing-and-a-prayer' and see how it turns out?

Thanks, but I desire imput from member whom I trust.

That being you guy's.

Thanks again...

Link to comment
Share on other sites

HT, both myself and Naam have published images of the offending articles, both have 'Names' clearly visible.

But as you rightly observe so much 'badge engineering' goes on it's difficult to impossible to determine if a unit is any good (even one that looks the same may be different internally).

The GXQ unit that I have is apparently made by Huatian Electronic in Guangdong, China but who really knows?

Link to comment
Share on other sites

Moving along, I wonder if the lack of robustness in my inverters is related to their transformerless design which exposes the (no doubt marginally specified) output devices directly to the house wiring and any transients which may appear thereon (from nearby strikes). Some interesting stuff here http://www.elp.com/articles/powergrid_international/print/volume-17/issue-1/features/what-you-need-to-know-about-solar-design.html

Up until now I hadn't considered that maybe these inverters may need a surge suppressor on the OUTPUT to stop nasties getting in that way.

The simpler, small units that I've been using to supply the technology all have (heavy) iron cored transformers and seem much more robust when it comes to surviving surges and other nasties that come along via the mains supply.

EDIT Handy with the soldering iron? Make your own http://danyk.cz/menic230_6_en.html

Warning! Despite the fact that these circuits are 12V powered, the HV reservoir capacitor is quite capable of killing you! Take great care.

Link to comment
Share on other sites

Handy with the soldering iron? Make your own http://danyk.cz/menic230_6_en.html

a project which i am very eager to start. but because there's a backlog of other projects to finalise it is scheduled to start on February 30th, 2015 (right after breakfast).

Like so many things one could build, if you price your time at the going rate it's far cheaper to go and buy one.

Link to comment
Share on other sites

how to

Naam, yes I am fully aware the Chinese can build good stuff.

that said, you know a good deal of it is POS.

perhaps i am one of the few rare lucky persons who uses Chinese electronic and electric products since a quarter century without big hassles. i am also a paranoid who does not mind spending a fistful million Baht for a car which i drive for an hour or two once a week crazy.gif

but when i choose a pump and i have the choice between a European/American brand costing 10,000 Baht and a Chinese brand costing 3.800 Baht then i become a pragmatic and select the Chinese one wink.png

note: the last batch of Chinese made inverters (nominal capacity 2000VA) i imported from India cost me approximately 6,500 Baht a piece. the older batch still in use were nearly double the price because my "purchase manager" in India was an idiot who enjoyed wasting my money. both models are of course not pure but modified sine wave. do i have to mention that i bought half a dozen of the newer models, installed two and keep the others for potential rainy days?

Link to comment
Share on other sites

  • 3 months later...
  • 4 weeks later...
  • 1 year later...

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.




×
×
  • Create New...